Viability Assessment in Southwark

A financial viability assessment is a structured piece of financial evidence that tests whether a development can afford to meet the planning policy requirements placed on it. In residential development the requirement that matters most is affordable housing: Southwark's policy asks for a substantial proportion of the homes to be affordable, and where a developer says the scheme cannot deliver that proportion and still be worth building, the viability assessment is the document that has to demonstrate it — with figures, assumptions and evidence a planning authority and its own advisers can test.

At its core, an FVA is a residual land value appraisal. It starts from the gross development value (GDV) of the finished scheme — the total the completed homes and any commercial floorspace would sell or let for — and deducts all the costs of delivering it: construction, professional fees, finance, the Community Infrastructure Levy, Section 106 contributions, marketing, and a competitive return (profit) to the developer for taking the risk. Whatever is left is the residual value — in effect, the most the land can be worth once the scheme has borne all its costs. That residual value is then compared with a benchmark land value: the value the land can reasonably be expected to command. If the residual exceeds the benchmark, there is surplus that could fund more affordable housing; if it falls short, the developer argues the policy requirement cannot be met in full.

It is essential to understand that viability is a test of the scheme, not of the developer's or landowner's aspirations. The national guidance is emphatic that the price actually paid for a site cannot be used to argue that policy requirements are unaffordable — otherwise a developer could overpay for land and then plead poverty to escape affordable housing, an obvious circularity the reforms were designed to close. The benchmark is set by the land's existing use value plus a reasonable premium, not by whatever was paid or hoped for. This single principle is the beating heart of modern viability and the reason so many assessments are contested.

An FVA is therefore a specialist financial and valuation exercise, usually prepared by a development surveyor or viability consultant, not by the architect. But it is inseparable from the design, because every one of its inputs flows from the scheme on the drawings: the mix and number of homes drives the GDV; the form, structure and specification drive the build cost; the density and layout drive the CIL; and the affordable-housing offer is itself a design decision. Crown's role is to design the scheme so the viability case is honest and strong, to give you a realistic view of where the numbers land before you commission a full assessment, and to coordinate the architecture with the viability evidence so the two tell the same story.

Viability assessment is relevant to anyone bringing forward residential development in Southwark that triggers the affordable-housing policy and where the full requirement is genuinely in doubt. The most common is the developer or landowner promoting a scheme of ten or more homes — the threshold at which the full on-site affordable-housing requirement bites hardest — who has run the numbers and found that, once build costs, CIL, Section 106 and a competitive profit are accounted for, the scheme cannot deliver 35% affordable housing and still be worth building. For them the FVA is the mechanism for justifying a lower provision, and the quality of the evidence determines whether the council accepts it.

A second group are smaller developers and homeowners bringing forward schemes below ten homes. It is a common misconception that small schemes are exempt from affordable housing in Southwark — they are not. The borough applies an affordable-housing expectation to schemes that create even a single new home, generally as a financial contribution in lieu of on-site provision for the smallest schemes, and viability can be relevant to those contributions too. Understanding whether your small scheme attracts a contribution, and how it is calculated, is part of the early advice we give.

A third group are those appraising a site before purchase. This is where viability advice earns its keep most clearly. A site's value depends on what can be built on it and what that development must contribute, and paying a price that assumes little or no affordable housing — when policy requires 35% — is the classic way to end up with a scheme that cannot proceed. We help appraise sites realistically, on the policy-compliant assumption, so that money is not committed to land whose price only works if the affordable-housing requirement can be dodged.

Finally, there are those responding to the council's own scrutiny — where an application has stalled because the viability case has been challenged, an independent reviewer has disputed the figures, or the council is pressing for more affordable housing than the applicant offered. In every case the aim is the same: a residential scheme that gains permission and can actually be delivered, with an affordable-housing position that is honest, evidenced and acceptable to Southwark. We work with developers, landowners, self-builders and their surveyors and solicitors to get there, and the first thing we give every one of them is a candid view of whether viability is really the issue — because very often the better answer is to redesign the scheme so it does not need to plead viability at all.

Southwark is the oldest part of south London and one of the most historically layered boroughs in the capital. It grew up at the southern end of London Bridge — the only crossing of the Thames into the City for centuries — and its very name comes from the Old English for the defensive works of the men of Surrey. It was the Roman and medieval gateway to London from the south, the disreputable liberty outside the City's jurisdiction where theatres, inns and markets flourished, and the setting for a remarkable amount of English cultural history. Borough Market has traded on or near its present site for the best part of a thousand years and remains one of London's great food markets; the George Inn on Borough High Street is the last galleried coaching inn in London; and Chaucer's pilgrims set off for Canterbury from the Tabard Inn in Southwark.

Bankside, the riverside strip facing the City, was the entertainment district of Shakespeare's London. The original Globe Theatre stood here from 1599, and Shakespeare's Globe — the modern reconstruction near the original site — sits today alongside Tate Modern in the former Bankside Power Station, the Millennium Bridge, and a string of cultural institutions that have made the north of the borough one of London's most visited places. Further out, Southwark reaches through Bermondsey and its converted riverside warehouses, the great regeneration district around Elephant and Castle, the Victorian and Georgian streets of Walworth, Camberwell and Peckham, and the leafier, more suburban character of Dulwich, with Dulwich College (founded 1619) and the Dulwich Picture Gallery (England's first purpose-built public art gallery, opened 1811).

The modern London Borough of Southwark was formed in 1965 from the former metropolitan boroughs of Southwark, Bermondsey and Camberwell. It is a borough of extremes: some of the most valuable riverside development land in Britain sits within a mile or two of some of the most deprived wards in the country, and the tension between them runs straight through the borough's planning. Southwark contains dozens of conservation areas — Bankside, Borough, Bermondsey, the Dulwich villages, Camberwell and many more — a great number of listed buildings, and areas of intense development pressure where the value uplift from consent is enormous. That combination of high land values, acute housing need and cultural sensitivity is exactly why viability is such a live and contested issue here.

For a viability assessment, this context is not background colour — it is the substance of the argument. High and sometimes volatile sales values in the north of the borough, very different values in the south, historic and conservation constraints that raise build costs, and a council under intense pressure to deliver genuinely affordable homes for its own residents all feed directly into the numbers and the negotiation. A viability case in riverside Bankside behaves quite differently from one in Peckham or on the edge of Dulwich, and understanding the local market and the local politics is as important as understanding the arithmetic.

No borough's attitude to viability has been shaped more directly by its own history than Southwark's, and the story centres on the Heygate estate at Elephant and Castle. The Heygate, a large 1970s council estate, was demolished and redeveloped as a major regeneration scheme — now known as Elephant Park — delivered by Lend Lease (Lendlease). The scheme became a national cause célèbre because of how viability was used to reduce the amount of affordable housing it delivered, and because of the years-long battle to make the viability evidence public.

Southwark's policy required 35% affordable housing. The developer's confidential financial viability assessment argued that the scheme could not afford anything like that, and the affordable provision approved for the masterplan fell far below policy. Local campaigners — the Elephant Amenity Network, campaigning through the 35% Campaign (35percent.org) — pressed for the viability assessment to be released so residents could see the basis on which their estate's affordable housing had been cut. The council and its development partner resisted disclosure for years, and it took a lengthy battle through the information-rights tribunal system, culminating in a multi-day hearing, before a decision notice directed that the Heygate viability assessment be released (minus some financial-modelling figures) in 2015.

When the numbers came out they crystallised a national argument: that confidential, adversarial viability appraisals were being used to justify systematically stripping affordable housing out of major schemes, in a borough with desperate housing need, on a former council estate whose original social tenants were dispersed. The Heygate story, and similar disputes across London, were a significant part of the political pressure that led directly to the 2018-19 reforms of the NPPF and PPG — the introduction of the standardised approach, the EUV+ benchmark, and above all the requirement that viability assessments be made publicly available. In a very real sense, the modern national rules on viability transparency were written with Southwark in mind.

The legacy is a council, and a community, that scrutinise viability with unusual rigour and treat any attempt to reduce affordable housing on viability grounds with justified suspicion. Southwark expects viability assessments to be robust, standardised and public; it retains its own independent reviewers to test them; it builds review mechanisms into its permissions to claw back any later uplift; and its officers and members are acutely alert to the tactics of the past. For anyone bringing forward a scheme here, the lesson is unambiguous: a viability case has to be genuinely honest and properly evidenced, because it will be tested by people who have seen the alternative and are determined not to repeat it.

The starting point in national policy is that viability should be resolved at the plan-making stage, not at the application stage. When Southwark adopted its Local Plan it tested the viability of its policies — including the 35% affordable-housing requirement — across typical development types, so that a policy-compliant scheme is presumed to be viable. The practical consequence, set out in the PPG, is that where a proposal complies with all the relevant policies, including affordable housing, a viability assessment at the application stage should not normally be necessary. Deliver the policy and you do not need to argue viability at all.

A viability assessment at the application stage is therefore the exception, needed only where a scheme cannot meet the full policy requirements and the applicant wishes to argue that this is because of genuine, site-specific viability constraints. Those constraints have to be real and particular to the site — abnormal ground conditions, extraordinary remediation or heritage costs, a genuinely constrained value area, or similar — not simply a land price that assumed the requirement could be avoided. The burden is on the applicant to justify, with transparent evidence, why the departure from policy is necessary, and the weight the council gives that evidence is a matter for its judgement.

In Southwark specifically, the affordable-housing requirement is set by Policy P1 of the Southwark Plan 2022, and it is that requirement a viability assessment is measured against. The policy offers a fast-track route for schemes that provide affordable housing at or above a defined threshold with a policy-compliant tenure mix and no public grant, which do not need to submit a full viability assessment for scrutiny; and a viability-tested route for schemes providing less, which must submit a full assessment and accept review mechanisms. Which route a scheme falls into is one of the first strategic decisions on a Southwark residential project, and it has significant cost and programme consequences.

The honest question we help you answer at the outset is therefore not 'how do we write a viability assessment' but 'do we need one at all, and is it in our interest to need one'. A scheme designed to deliver the policy affordable housing avoids the cost, delay, scrutiny, review mechanisms and reputational friction of the viability-tested route entirely. Where the numbers genuinely will not allow that, an FVA is the right tool — but it should be a considered choice made with eyes open, not a default assumption that affordable housing can be negotiated away.

The requirement a viability assessment is tested against in Southwark is Policy P1 of the Southwark Plan 2022 (the borough's development plan, adopted in 2022). Policy P1 requires development that creates new homes to provide affordable housing, with a minimum of 35% affordable housing on schemes of ten or more homes, subject to viability. That 35% figure is the benchmark: it is what the council starts from, what its own viability testing at plan-making assumed, and what any application offering less has to justify through a viability assessment.

Policy P1 provides two routes, mirroring the approach in the Mayor of London's guidance. The first is a fast-track route: a scheme that provides at least 40% affordable housing, without public grant, with a policy-compliant tenure mix, is not required to submit a full viability assessment for scrutiny and benefits from a faster, more certain determination. The second is a viability-tested route: a scheme providing less than that threshold must submit a full financial viability assessment, which the council scrutinises (with independent review), and must accept both an early-stage and a late-stage review mechanism. The fast-track route trades a slightly higher affordable-housing offer for speed, certainty and the avoidance of viability scrutiny — a trade that is often worth making.

Tenure matters as much as the headline percentage. Southwark's policy prioritises social rented housing — the most genuinely affordable tenure and the one for which need in the borough is greatest — alongside intermediate housing, and it expects a policy-compliant split between them (with a substantial proportion as social rent). Affordable-housing requirements are measured in habitable rooms rather than simply units, which prevents the requirement being satisfied by lots of small affordable flats against large market homes. The council's affordable-housing approach is set out in more detail in its Affordable Housing SPD, which was refreshed and re-adopted in 2025 to replace the long-standing 2008 document.

It is also important that smaller schemes are not exempt. Southwark applies an affordable-housing expectation to development creating even a small number of homes, generally as a financial contribution in lieu of on-site provision for schemes below the on-site threshold. So a viability assessment can be relevant across the size range — from a large regeneration scheme arguing it cannot reach 35% on site, to a modest scheme where the in-lieu contribution is in issue. We identify exactly which limb of Policy P1 applies to your scheme, and design the affordable-housing offer around it, because getting the route right at the start shapes everything that follows.

Financial viability in the English planning system is governed by the National Planning Policy Framework and, in far more detail, by the Planning Practice Guidance section on viability. Both were substantially reformed in 2018 and 2019 in direct response to the way viability had been used — Heygate and its like — to reduce affordable housing. The reforms had three central aims: to move viability testing to the plan-making stage so that policy-compliant schemes are presumed viable; to standardise the key inputs so that assessments could no longer be manipulated through convenient assumptions; and to make viability assessments transparent by requiring them to be publicly available.

The NPPF now provides that where up-to-date policies have set out the contributions expected from development — including affordable housing — planning applications that comply with them should be assumed to be viable, and that it is up to the applicant to demonstrate whether particular circumstances justify the need for a viability assessment at the application stage. It also provides that all viability assessments should reflect the recommended approach in the PPG, including its standardised inputs, and should be made publicly available. This is the policy hook Southwark relies on when it insists that any viability evidence follow the national method and be disclosed.

The PPG viability guidance is where the detail lives. It defines how each input is to be assessed — gross development value, costs, benchmark land value on the EUV+ basis, and developer return — and sets out the principles that prevent circularity and manipulation: that the price paid for land is not a relevant justification for reducing policy contributions; that benchmark land value must be based on existing use value plus a premium, excluding hope value; and that assessments should be simple, standardised, proportionate and transparent. It also introduces the review-mechanism concept and the expectation of a non-technical executive summary that anyone can understand.

For an applicant in Southwark this framework is both a constraint and, properly understood, a discipline. It means a viability assessment cannot lean on the inputs that used to make schemes look unviable; it must use the standardised approach, show its working, and stand up to public and independent scrutiny. Prepared honestly, that actually makes for a stronger case — an assessment that plainly follows the national method and discloses its figures is far more persuasive to a Southwark officer than one that looks like special pleading. We design schemes and coordinate their viability evidence to work with this framework rather than against it.

The first of the four standardised inputs is gross development value — the total income the completed scheme is expected to generate. For a residential scheme this is principally the aggregate sales value of the market homes, plus the (much lower) value attributed to the affordable homes, plus any income from commercial or other floorspace and any ground rents or other revenue. GDV is the top of the appraisal, and small changes in it have a large effect on the residual, so it is heavily scrutinised.

The PPG requires GDV to be evidenced from actual, achieved values — completed sales of genuinely comparable new-build homes in the relevant market — rather than from optimistic projections. In Southwark this is where the borough's extreme internal variation shows: values on the Bankside and Bermondsey riverside, or in a prime Elephant and Castle tower, are worlds apart from values in parts of Peckham, Walworth or the south of the borough. A credible GDV has to be built from the right comparables for the specific location and product, and Southwark's reviewers will test the comparables closely. Overstated affordable values, or market values assumed from the wrong end of the borough, are quickly exposed.

The mix and design of the scheme drive the GDV directly, which is why the architecture and the viability are inseparable. The number of homes, the balance of unit sizes, the proportion of dual-aspect and outlook, the amount of private amenity space, the quality of the specification and the efficiency of the plan all feed into what the homes will sell or let for. A well-designed scheme with a mix matched to the local market achieves a higher, more defensible GDV than a poorly planned one — and a higher GDV, other things equal, means the scheme can carry more affordable housing.

It is worth stressing that the affordable homes are valued at their affordable value in the GDV — the capitalised value of the social or intermediate rents, or the discounted sale price — which is far below market value. Increasing the affordable proportion therefore lowers the GDV, which is precisely the tension viability tries to resolve: how much affordable housing the market element can subsidise while the whole still delivers a competitive return over the benchmark land value. Getting the GDV right, and designed to be as strong as the market genuinely supports, is the foundation of an honest viability case.

The second standardised input is the total cost of delivering the scheme, and the third — closely related — is the developer's return. Costs include construction (build cost per square metre, driven by the form, structure, specification and site constraints); professional and design fees; site-specific abnormals such as demolition, remediation, ground works and infrastructure; finance costs; sales and marketing; the Community Infrastructure Levy; Section 106 contributions; and contingencies. In Southwark, heritage and conservation constraints, difficult brownfield ground, tall-building complexity and the cost of high London construction standards can all push costs up, and where those are genuine and site-specific they are legitimate parts of the appraisal.

The discipline the PPG imposes is that costs must be reasonable and evidenced, not inflated to depress the residual. Build costs should reflect recognised cost data for the type and quality of development; abnormals should be demonstrated, not assumed; and the appraisal should not double-count or pad the contingency. Southwark's independent reviewers scrutinise the cost side as hard as the value side, because overstated costs are the mirror image of understated values as a way to make a scheme look unviable.

The developer's return — profit — is treated as a cost of development in the appraisal, because a developer will not proceed without a competitive return for the risk taken. The PPG's standardised approach places market-housing return in the region of 15% to 20% of gross development value (with 20% a common working assumption for private residential, and government having consulted on narrowing this), and a lower return on the affordable housing — often around 6% of GDV — because it carries much less sales risk (an affordable provider is usually a committed purchaser). Using a blended, standardised profit figure prevents the return being flexed to engineer a result, and Southwark expects the standardised approach to be followed.

Because so many of these costs flow from the design, the architecture again shapes the viability. An efficient, buildable scheme with a sensible structural strategy, a specification matched to its market, and site constraints properly understood carries lower, more defensible costs than an over-engineered or poorly coordinated one. Crown designs schemes to be genuinely buildable and cost-efficient, and works with the viability surveyor so the cost inputs reflect the real scheme rather than worst-case assumptions — which, on the cost side, strengthens the case for more affordable housing, not less.

The fourth and most contested input is the benchmark land value (BLV) — the yardstick the residual value is compared against to decide whether the scheme can afford more affordable housing. The 2018-19 reforms rewrote how BLV is set, and understanding the change is the key to understanding modern viability. The BLV is now based on the 'existing use value plus a premium' approach — EUV+ — which supersedes the old 'competitive return to a willing landowner' and the practice of justifying land value by reference to comparable prices paid.

EUV+ works in two parts. First, the existing use value: the value of the land in its current lawful use (for example, as the industrial, retail or existing residential use it presently has), excluding any hope value from the prospect of the new development. Second, a premium: a reasonable additional sum on top of EUV that provides a competitive incentive for the landowner to release the land — the '+'. The premium must be reasonable and evidenced, and it is here that much of the negotiation happens, because a high premium raises the BLV and reduces the apparent surplus available for affordable housing.

The single most important principle is that the price actually paid for the site is not a valid benchmark. If a developer pays a price that only works on the assumption of little affordable housing, that overpayment cannot then be used to argue the affordable housing is unaffordable — that circularity is exactly what the reforms closed. The BLV is set by EUV+, disciplined against market evidence of comparable transactions only in a way that is itself consistent with policy, and hope value is excluded. In a high-value borough like Southwark, where the uplift from consent can be enormous, this principle is doing a great deal of work, and it is why sites should be appraised and bought on the policy-compliant basis in the first place.

The practical lesson for anyone acquiring a site in Southwark is stark: the affordable-housing requirement must be priced into the land at acquisition. A viability assessment cannot rescue a scheme where too much was paid for the land, because the excess land price is not a legitimate cost. We advise on site appraisal on the correct, policy-compliant EUV+ basis before purchase precisely so that the viability of the eventual scheme is not fatally compromised on day one by an overpayment that policy will not recognise.

Perhaps the most consequential of the 2018-19 reforms — and the one most directly born of Southwark's own history — is transparency. The NPPF and PPG now require that viability assessments be made publicly available. Gone are the days when a confidential appraisal could be used to cut affordable housing behind closed doors: the assessment, its inputs and its conclusions are, as a matter of national policy, to be open to public scrutiny, so that residents and campaigners can see and challenge the basis on which a scheme's affordable-housing offer is set.

The PPG allows assessments to be kept confidential only in exceptional circumstances, and any redactions have to be justified to the satisfaction of the decision-maker — the presumption is firmly towards disclosure. To make the evidence accessible, the guidance expects a non-technical executive summary, written so that a member of the public can understand the assessment's key figures and conclusions without wading through the full financial modelling. In Southwark, a borough with an organised and knowledgeable community of housing campaigners (the 35% Campaign being the best known), you should assume that a viability assessment will be read, understood and challenged in public.

This transparency requirement changes how a viability case should be prepared. An assessment that is plainly standardised, well-evidenced and open — one that follows the national method, discloses its comparables and assumptions, and reads as an honest appraisal rather than an advocacy document — is far more likely to survive both public scrutiny and the council's independent review. Conversely, an assessment that looks engineered will attract exactly the kind of forensic challenge that Southwark's community and officers are practised at mounting, and can derail an application entirely.

For applicants who find transparency uncomfortable, the honest answer is usually that the discomfort is a signal. If a viability case can only work when its figures are hidden, it is probably not a case that should be made. The far better position — and the one we help clients reach — is a scheme designed to deliver its policy affordable housing so that no viability assessment, and no public argument about it, is needed at all; or, where an assessment genuinely is required, one so evidently honest that disclosure holds no fear.

Where a scheme is permitted on the viability-tested route with less than the full affordable housing, Southwark does not simply lock in the reduced figure. It secures review mechanisms in the Section 106 agreement that revisit the scheme's viability at defined points, so that if the economics improve — as they often do between permission and completion — the additional value is captured as more or more affordable housing. These reviews are a central feature of the Southwark approach and a direct product of the lessons of the past.

An early-stage review is typically triggered if the development has not made substantial progress within an agreed period after permission (commonly a couple of years). Its purpose is to prevent an applicant securing a low affordable-housing figure and then sitting on the permission until values rise, banking the uplift privately. A late-stage review is carried out towards the end of the scheme, once actual costs and values are largely known, to test whether the completed development performed better than the appraisal assumed; where it did, a share of the surplus is directed to additional affordable-housing provision or a payment in lieu.

A crucial feature of Southwark's review mechanisms — reflecting the Mayor's guidance the borough follows — is that they are one-way: they can increase the affordable-housing contribution where viability improves, but they cannot reduce it below the level secured at permission. The developer keeps the downside risk it is being paid a profit to bear; the community shares in the upside. This asymmetry is deliberate and is a point of frequent negotiation, but it is settled policy in Southwark and applicants should plan for it rather than expect to negotiate it away.

The practical implication is that a viability-tested permission in Southwark is not a final settlement but the start of an ongoing relationship, with obligations that run for years and reviews that require further appraisal work at defined milestones. This is a real cost and commitment, and it is another reason the fast-track route — a policy-compliant offer that avoids the assessment and the reviews altogether — is so often the better commercial choice. We factor the review mechanisms into the appraisal of the two routes so the decision is made on the full picture, not just the headline affordable-housing percentage.

Southwark does not take a viability assessment at face value. Where a scheme relies on viability to justify less than policy affordable housing, the council instructs its own independent viability reviewer — a specialist surveyor — to scrutinise the applicant's assessment, test every input, and advise the council on whether the conclusions are justified. This independent review is the mechanism by which the council satisfies itself, and demonstrates to its members and community, that a reduced affordable-housing figure is genuinely necessary and not the product of favourable assumptions.

The cost of that independent review is met by the applicant, not the council — it is a standard condition of running the viability-tested route that the developer funds the council's scrutiny of its own case. This is a real and sometimes substantial cost, and it is one more item that has to be budgeted for at the outset and weighed against the fast-track alternative. It also means the applicant's assessment needs to be robust enough to withstand a hostile, expert reading, because the reviewer's job is to probe every soft assumption.

The review typically becomes a negotiation between the applicant's surveyor and the council's reviewer over the contested inputs — the comparables underpinning GDV, the build costs and abnormals, the profit assumption, and above all the benchmark land value and the premium. Where the two sides converge, the affordable-housing offer settles at a level both can defend; where they do not, the disagreement is a matter for the council's planning judgement, and ultimately for the committee, with the reviewer's advice carrying significant weight. A well-prepared, standardised, transparent assessment shortens this process; a weak one prolongs it and can sink the application.

Crown's contribution to this process is on the design and coordination side: we make sure the scheme on the drawings is efficient, buildable and matched to its market so that the GDV and cost inputs the surveyor relies on are as strong and defensible as the scheme genuinely allows, and we keep the architecture and the viability evidence consistent so the reviewer is not handed easy points of attack. We work alongside your viability surveyor and solicitor rather than replacing them, so the whole package — design, financial evidence and legal agreement — tells one coherent, honest story.

A viability assessment does not deal with affordable housing in isolation; it has to account for all the policy costs a scheme must bear, and in Southwark the two big ones alongside affordable housing are the Community Infrastructure Levy (CIL) and Section 106 obligations. Both are inputs on the cost side of the appraisal, and both interact with the affordable-housing outcome, because money spent on one is money not available for another.

CIL is a fixed, non-negotiable charge per square metre of net new floorspace, levied to fund infrastructure. In Southwark a development is liable for both the borough's own CIL and the Mayor of London's CIL (MCIL2), and the charge is calculated mechanically from the floorspace regardless of viability — CIL is not reduced because a scheme is marginal. Because CIL is a fixed cost, it reduces the residual available for affordable housing, and the appraisal has to carry it in full. Certain affordable housing benefits from CIL relief, but the market element is fully charged, and the CIL liability should be calculated early because it is a significant, unavoidable number.

Section 106 obligations, by contrast, are scheme-specific and secured by legal agreement: affordable housing itself, but also contributions to matters made necessary by the development, and the review mechanisms discussed above. Unlike CIL, the scope of Section 106 obligations can be affected by viability — where a scheme genuinely cannot bear everything, the negotiation is over how the limited surplus is allocated between affordable housing and other contributions. Southwark's clear priority, reflecting acute local need, is affordable housing, and the council will resist allowing other contributions to erode the affordable-housing offer.

The interaction matters for the design and the strategy. Because CIL is fixed and driven by floorspace, and affordable housing and Section 106 draw on the residual, an efficient scheme that maximises defensible value for its floorspace and controls its costs leaves more in the pot for affordable housing. We design with the whole cost stack in mind — CIL, Section 106 and affordable housing together — and calculate the likely CIL for your specific scheme so it is a known figure in the appraisal from the start, not a late surprise.

It is tempting to think of viability as a purely financial exercise handed to a surveyor, but almost every input in a viability assessment is set by the design of the scheme — which is why the architecture and the appraisal have to be developed together. The number and mix of homes, their sizes and quality, the efficiency of the plan, the structural and construction strategy, the treatment of difficult ground and heritage, and the affordable-housing offer itself are all design decisions, and each one moves the numbers.

On the value side, a scheme designed to the local market — the right mix of unit sizes, good outlook and daylight, generous and well-planned amenity, an efficient net-to-gross ratio, and a specification matched to the values it needs to achieve — produces a higher and more defensible GDV than a scheme that is poorly configured for its location. On the cost side, a buildable, well-coordinated design with a sensible structure and realistic abnormals carries lower, more credible costs than an over-engineered or under-designed one. A higher defensible value and a lower defensible cost both increase the residual — and a larger residual means more affordable housing the scheme can genuinely carry.

The affordable housing is itself a design problem. Its tenure mix, the size and quality of the affordable homes, how they are integrated (Southwark expects genuine integration, not poor-door segregation), and how they are distributed through the scheme all affect both the policy compliance and the value. A scheme designed so that a policy-compliant affordable offer sits comfortably within a viable whole is a scheme that can take the fast-track route and avoid the entire viability apparatus — which is very often the best outcome commercially and reputationally.

This is where Crown adds value that a viability surveyor alone cannot. We design the scheme so that the honest numbers are as strong as the site allows, so that the affordable-housing offer is genuinely deliverable within a viable whole, and so that the design and the financial evidence are consistent and mutually reinforcing. The earlier this integration happens, the better the outcome — testing the design against the viability picture at feasibility routinely changes the scheme for the better before a single formal appraisal is commissioned.

A residential application where viability is in issue has to tell the council a complete and consistent story: what the site is now, what will be built, what it is worth, what it costs, what it can afford to contribute, and why. Crown prepares the design side of that package and coordinates it with the financial and legal evidence, so the application is coherent and the viability case is properly supported by the drawings rather than contradicted by them.

The drawing and design package normally includes an accurate measured and topographical survey of the site; existing and proposed site plans and floor plans, elevations and sections; the housing schedule setting out the number, size and tenure of every home with areas annotated against the London space standards; the affordable-housing plan showing tenure, mix and integration; and the design and access statement making the case for the scheme's quality and its response to local character. These are the documents from which the surveyor draws the GDV and cost inputs, so their accuracy and consistency directly affect the strength of the appraisal.

Alongside our work sits the viability evidence itself — the financial viability assessment prepared by the development surveyor, with its standardised inputs, its EUV+ benchmark, its residual appraisal, and its non-technical executive summary for public disclosure — and the legal documents that secure the outcome, chiefly the Section 106 agreement with the affordable-housing obligations and the early and late-stage review mechanisms. Where the scheme takes the fast-track route, the emphasis shifts to demonstrating the policy-compliant affordable offer clearly enough that no full assessment is required.

The essential discipline across all of it is consistency. The housing schedule must match the GDV, the design and specification must match the assumed build cost, the affordable-housing plan must match the Section 106 obligations, and the whole must be internally coherent and capable of surviving independent review and public scrutiny. A coordinated, self-consistent package is materially more likely to be accepted — and much harder for a reviewer or a campaigner to pick apart — than a set of drawings and a financial appraisal that tell different stories.

Understanding why viability arguments fail in Southwark is the best way to avoid the failure, and the reasons are consistent. The most common and most fatal is overpaying for the land and then trying to use the price to justify less affordable housing. The national guidance forbids exactly this: the price paid is not a valid benchmark, and the benchmark land value must be set by EUV+, so an appraisal built on an inflated land value is built on sand. A great many Southwark viability disputes come down to this single point.

The second recurring error is optimistic or wrongly-evidenced inputs — GDV supported by the wrong comparables (or values borrowed from a higher-value part of the borough), build costs or abnormals inflated beyond what the evidence supports, or a profit assumption pushed above the standardised range. Southwark's independent reviewers are expert at finding these, and each one that is corrected reduces the case for less affordable housing. An assessment that looks like advocacy rather than valuation invites forensic challenge and loses credibility as a whole.

A third failure is treating viability as a way to negotiate affordable housing down rather than as a genuine test — approaching a high-need borough with a strong campaigning community and an unhappy institutional memory of Heygate as though it will quietly accept a reduced offer. It will not. Officers scrutinise, reviewers probe, campaigners publicise, and members care deeply about affordable housing. A weak or aggressive viability case in Southwark is more likely to stall or sink an application than to secure a concession.

The fourth, and most avoidable, mistake is needing a viability assessment at all when the scheme could have been designed to deliver the policy affordable housing. Every pound spent arguing viability — the surveyor's fees, the council's independent review that the applicant funds, the delay, the review-mechanism obligations, the reputational friction — is a cost that a policy-compliant, fast-track scheme avoids entirely. Our approach is to test this first: to see whether an honest, well-designed scheme can deliver the policy affordable housing, and only to reach for a viability assessment where the numbers genuinely require it.

The cost of dealing with viability on a Southwark scheme has several parts, and we set them out clearly at the start. Our design fee covers the feasibility, the scheme design, the drawings and the housing and affordable-housing schedules, and the coordination of the design with the viability and legal evidence; we scope it to your specific scheme and quote a clear fee before work begins. Separate from our fee is the financial viability assessment itself, prepared by a development surveyor or viability consultant, whose cost depends on the scale and complexity of the scheme.

The viability-tested route carries costs the fast-track route avoids. Chief among them is the applicant's obligation to fund the council's independent viability review — a real and sometimes substantial sum. There are also the statutory costs common to any application: the planning application fee (higher for major residential schemes), any pre-application advice fee, and the eventual CIL liability (Southwark's CIL plus the Mayoral CIL) on the net new floorspace. And the review mechanisms secured in the Section 106 agreement mean further appraisal work at defined milestones for years after permission.

On timescales, feasibility and the design package take a few weeks to a few months depending on the scheme's scale and the surveys required; the viability assessment is prepared alongside the design; and on the viability-tested route the independent review and negotiation add time — often significant time — before the affordable-housing position settles. Major residential applications in Southwark do not run to the eight-week minor-application target; they take substantially longer, and a contested viability case, potentially going to committee, longer still. The fast-track route is materially quicker precisely because it avoids the assessment and the review.

It is worth being clear where money is really lost. It is lost on land bought at a price that only works without affordable housing, which no viability assessment can rescue; on assessments prepared as advocacy that fail independent review and stall the scheme; and on choosing the viability-tested route, with all its cost and delay, when a slightly more generous, policy-compliant offer would have unlocked the far quicker and cheaper fast-track route. Getting the strategy right at the outset — and designing a scheme that can carry its obligations — is comfortably the most cost-effective way to develop in Southwark.

The process starts with feasibility, and on a scheme where viability might be in issue this stage is decisive. We survey the site, establish the applicable Policy P1 requirement, and run an early appraisal of the scheme against the 35% affordable-housing benchmark — testing, with our viability colleagues, whether a policy-compliant or fast-track offer is achievable, or whether the numbers genuinely fall short. This is where we tell you honestly which route you are on and whether viability is really your issue, before you commit to a full application.

Because major residential schemes and viability cases are complex and contested, Southwark's pre-application advice service is almost always worthwhile. A pre-application dialogue lets us establish the council's expectations on affordable housing, tenure and design, test the viability position early, and develop the scheme in a direction the council will support — which on a viability-tested scheme is far better than presenting a reduced offer cold. We advise on and manage pre-application engagement where it adds value, which on schemes of any scale in Southwark it usually does.

The full planning application is then submitted with the drawings, the design and access statement, the housing and affordable-housing schedules and — where the route requires it — the financial viability assessment with its public executive summary. Southwark validates and consults, instructs its independent viability reviewer where viability is relied upon, and the review and negotiation over the affordable-housing offer run in parallel with the planning assessment. Neighbour and community representations are common in Southwark, particularly on affordable housing, and the viability evidence is scrutinised in public. We manage the design side of the application through determination, respond to the case officer and reviewer, and keep the design and financial evidence consistent as the offer settles.

Once the affordable-housing position is agreed, it is secured in the Section 106 agreement — including the early and late-stage review mechanisms — and permission is granted with its conditions. We then prepare the detailed design and building-regulations information, discharge the pre-commencement conditions, and support the appraisal work required at the review milestones. Because the design and the viability evidence were coordinated from the start, the transition from consent to delivery is smooth and the ongoing Section 106 obligations are understood and planned for rather than a surprise.

To make the process concrete, consider a common Southwark scenario: a developer has an option on a former light-industrial site in the wider Old Kent Road area, one of London's largest regeneration opportunity areas, and wants to build a residential scheme of around forty homes. The immediate question is not the design but the affordable housing: Policy P1 asks for 35%, and whether the scheme can deliver that — or reach the 40% fast-track — depends entirely on the numbers, which depend on the design.

At feasibility, we and the viability surveyor test the fundamentals together. The existing industrial use sets a modest existing use value, and EUV+ gives the benchmark land value the developer's option price has to be sense-checked against — if the option was struck on the assumption of little affordable housing, the whole scheme is compromised before it starts, and we say so plainly. We test achievable sales values from genuine comparables in this part of the borough (not the higher riverside values), estimate build costs including the brownfield abnormals, and model the residual against the 35% and 40% offers to see which the scheme can honestly carry.

Suppose the appraisal shows the scheme can comfortably carry 35% but not 40%. The strategic choice then becomes clear: take the viability-tested route with a 35% offer, submitting a full public assessment, funding the council's independent review and accepting early and late-stage review mechanisms; or refine the scheme — a better mix, a more efficient plan, a specification and tenure arrangement that lift the defensible value or trim cost — to reach the 40% fast-track and avoid the entire viability apparatus. Often a modest design improvement bridges the gap, and the certainty and speed of the fast-track make it the better commercial choice even at a slightly higher affordable percentage.

Suppose instead the numbers genuinely fall short even of 35% because of exceptional site costs. Then the FVA is the right tool, and it is prepared properly: standardised inputs, EUV+ benchmark, honest comparables, a public executive summary, and evidence of the genuine abnormals that constrain the scheme. It goes in knowing it will be independently reviewed and publicly read, so it is built to survive both. The affordable-housing offer settles through negotiation with the reviewer, is secured in the Section 106 with review mechanisms, and the permission proceeds on an honest footing.

Either way, the difference between a scheme that resolves its viability cleanly and one that stalls is the same: the numbers were tested honestly at the outset, the land price was sense-checked against EUV+ before commitment, the design was used to make the affordable offer deliverable rather than to argue it away, and the evidence was prepared to withstand the scrutiny Southwark is certain to apply. That is what turns a contested viability question into a consented, deliverable scheme.

Southwark contains some of London's largest and most closely watched regeneration areas, and viability plays out at a different scale in them. The Old Kent Road Opportunity Area, with a planned capacity of tens of thousands of new homes over the coming decades (linked to the proposed Bakerloo line extension), the continuing transformation of Elephant and Castle, and the long-running Aylesbury estate redevelopment are all places where affordable housing, viability and community expectation collide on a large canvas. On the Aylesbury, for example, the council's stated ambition over the lifetime of the project is for around half the new homes to be affordable, with a large majority of those at social rent — a scale of ambition that reflects both the estate's history and the borough's priorities.

On large and phased schemes the viability picture is more complex and more dynamic. Values and costs shift over a delivery period measured in years or decades; phasing affects when affordable housing is delivered and when reviews bite; grant funding from the Mayor or Homes England can change what is deliverable; and the interaction of viability with masterplanning, infrastructure and the community is intense. The review mechanisms matter more on these schemes precisely because the gap between the appraisal at permission and the reality at completion is widest, and Southwark's insistence on capturing later uplift for affordable housing is at its strongest.

These schemes also carry the heaviest weight of Southwark's institutional memory. The Heygate experience means that viability on a large estate-regeneration or opportunity-area scheme is scrutinised with particular care, publicised by an engaged community, and expected to deliver genuinely affordable homes — especially social rent — for the borough's residents. A large scheme that appears to use viability to minimise social rent, or to disperse existing communities, faces resistance that is political as much as technical.

Crown works at the residential scale that most of the borough's development actually comprises — individual sites, infill, small and mid-sized schemes and the residential components of larger regeneration — and coordinates the design with the viability and affordable-housing strategy on each. Whether the scheme is a handful of homes or a phase of a larger masterplan, the disciplines are the same: honest numbers, EUV+ land value, a design that makes the affordable offer deliverable, and evidence prepared for the scrutiny Southwark will apply.

Crown Architecture designs residential schemes across Southwark and the surrounding boroughs, and we approach viability the right way round: by designing schemes that can carry their policy obligations, so that the affordable-housing requirement is delivered and a viability argument is avoided wherever the site honestly allows. Where a viability assessment genuinely is needed, we coordinate the architecture with the financial and legal evidence so the case is honest, consistent and defensible — because in Southwark, more than almost anywhere, that is what works.

We know the Southwark framework specifically: Policy P1 and its 35% requirement, the 40% fast-track route and the viability-tested route, the tenure priority for social rent measured in habitable rooms, the refreshed Affordable Housing SPD, and the borough's uncompromising insistence on standardised, public, independently-reviewed viability evidence with early and late-stage review mechanisms. We understand why Southwark is as rigorous as it is — the Heygate and Elephant Park history that shaped the national transparency rules — and we prepare schemes that work with that rigour rather than against it.

Just as importantly, we are straightforward to work with. We tell you early and candidly whether your scheme really needs a viability assessment or whether a policy-compliant, fast-track offer is within reach; we sense-check the land price against EUV+ before you commit; we quote a clear fee; and we design a scheme whose honest numbers are as strong as the site allows, so the affordable offer is genuinely deliverable. We work alongside your viability surveyor and solicitor as one team, keeping the design, the financial evidence and the Section 106 consistent.

We also stay with the project. We manage the design side of the application through Southwark's determination — responding to the case officer, the independent reviewer and community representations, and keeping the scheme coherent as the affordable-housing position settles — and once permission is granted we carry it through to the detailed design and building-regulations information, discharge the conditions, and support the appraisal work the review mechanisms require. The aim is a single, accountable design partner from the first appraisal to a consented, deliverable, genuinely affordable-inclusive scheme.

If you are bringing forward a residential scheme in Southwark — whether you are appraising a site to buy, wrestling with the affordable-housing requirement, or facing a challenge to a viability case — send us the site and what you have in mind, and we will tell you honestly where the numbers land, which Policy P1 route fits, and how to get a viable, consentable scheme through.