Phasing affordable delivery across a large site
The percentage is agreed in a morning. The phasing schedule takes six weeks, and it is the part that decides whether the scheme can actually be built out in the order the developer intends.
On a site of several hundred homes built over a decade, the affordable housing percentage is the easy part of the negotiation. Phased affordable housing delivery is the hard part, because it decides when market homes can be occupied, what happens if a phase stalls, and whether the scheme still works when a different developer owns half the land.
The mechanism is a set of occupation triggers in the section 106 agreement. Everything else is detail around them.
Why phasing has to be written into the agreement
A planning permission grants development. It does not sequence it. Left to itself, a developer will build the highest value parcels first, and the affordable homes, which are typically on the less commercial parts of the site, arrive late or not at all.
Authorities know this, and the trigger mechanism is their answer. It is also, properly drafted, in the developer's interest, because it gives certainty about what has to be delivered and when, which is what a funder wants to see.
The alternative, a condition requiring delivery in accordance with an approved phasing plan, is weaker and harder to enforce. Obligations are the right instrument here.
There is a second reason to take the drafting seriously. On a long build the people who negotiated the agreement will have moved on, and the document has to be operated by a site manager and a monitoring officer reading it cold. Clauses that need the negotiation history to make sense do not survive that.
Trigger points tied to market occupations
The standard form ties occupation of market homes to progress on affordable homes in the same phase.
A workable structure has three layers. A cap on market occupations in a phase before the affordable homes in that phase are at practical completion. A second cap before they have been transferred to the registered provider. And a site-wide backstop so that no more than a stated proportion of market homes across the whole development can be occupied before a stated proportion of the affordable homes across the whole development are complete.
Choose the measurable events. Practical completion, certified by a named party. Transfer of title. Issue of a building control completion certificate. Avoid triggers that depend on something outside the developer's control, such as the registered provider taking possession, unless the agreement also deals with what happens when the provider does not.
Then check the mechanism against a realistic build programme. A trigger that stops market occupations at 50 per cent of a phase, in a phase where the affordable homes are in the last block to be built, will stop the site.
Run the test with the programme in front of you and a pen. Take each phase, mark the month the affordable homes reach practical completion, and mark the month the trigger bites on market sales. If the second comes before the first anywhere, the drafting needs changing or the build sequence does.
Pepper potting and its practical limits
Policy usually asks for affordable homes to be distributed across the site rather than concentrated. Design guidance supports it, and it produces better places.
The limits are practical. Registered providers manage stock, and they need clusters large enough to be worth servicing, with sensible arrangements for shared spaces, parking and refuse. Single units scattered one to a street create management costs that get reflected in the price the provider will pay, which feeds back into viability.
The usual landing point is clusters of a modest size distributed across each phase, with the arrangement shown on the phasing plan. Agree it with the intended provider before it goes into the agreement, not after.
Say what has been agreed and why in the Affordable Housing Statement, because an officer reading a distribution that looks concentrated will otherwise assume nobody tried.
Delivery in each phase against the overall percentage
Phases rarely divide evenly. A phase of 43 homes at a 35 per cent requirement gives a fractional number, and a phase that is all apartments may suit a different tenure mix from one that is all houses.
Two devices handle this. A schedule in the agreement setting the number and tenure of affordable homes phase by phase, agreed at the outset and amendable by written agreement. And a reconciliation clause requiring that, on completion of the final phase, the total delivered equals or exceeds the overall requirement.
Write the arithmetic into the agreement rather than leaving it to be calculated later. Disputes about rounding are common and they are tedious.
Consequences of a phase not coming forward
This is the clause both sides skip and both sides later need.
Set out what happens if a phase has not started by a long stop date, if a phase has started but is not completed, and if the site is sold in parcels. The mechanisms available include a financial contribution in lieu calculated on a stated basis, an obligation on the remaining phases to make up the shortfall, and a restriction on further market occupations across the site until the position is corrected.
A long stop date is worth agreeing even where it feels remote. Without one, an authority faced with a half-built site has nothing to enforce against except the trigger caps, which bite only if someone wants to occupy more market homes.
Reconciliation at the end of the development
The final reconciliation should be simple to operate: a statement from the developer setting out units built by tenure and by phase, a period for the authority to respond, and a mechanism for making good any shortfall.
Keep the records as you go. On a ten year build with two changes of ownership, the reconciliation depends on records nobody will be able to reconstruct if they were not kept contemporaneously.
The practical version of this is a single spreadsheet, updated on each completion, showing plot number, phase, tenure, completion date and transferee. It takes minutes a month and it answers every monitoring question the authority will ever ask.
Where contributions are deferred or indexed, the same discipline applies to the calculation as in deferred contributions and indexation.
Drafting that survives a change of developer
Assume the land will be sold, because on a site of this scale it will be.
- Define phases on an annexed plan with parcel boundaries, not by description.
- Make the obligations severable by parcel so a purchaser takes only the obligations attaching to what they bought.
- Include a mortgagee exclusion clause in terms a funder will accept, without letting it swallow the obligation.
- Provide for release of a plot on completion of a dwelling and sale to an individual purchaser.
- Keep the notice provisions simple, with service by email to a named officer.
- Annex the agreed phase schedule so a later reader does not need the negotiation history.
Where the affordable quantum itself is in dispute, the appraisal has to carry the argument, and the transparency expectations set out in viability at appeal apply. PlanScope can produce an AI-assisted draft Viability Assessment structured to the standard headings, with inputs marked as to be confirmed until you supply them. Councils expect a suitably qualified author for that work, and professional review before submission is strongly advised.
This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. Enter your postcode on PlanScope to see which reports your site needs.
PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.
Frequently asked questions
What is a typical occupation trigger?
A cap on the number or percentage of market homes in a phase that may be occupied before the affordable homes in that phase reach a defined stage, usually practical completion or transfer to the registered provider. The cap is often expressed as a proportion of the phase, with a further cap on the phase as a whole. The exact figures are negotiated rather than standard.
Should triggers be set per phase or across the site?
Per phase, with a site-wide backstop. Triggers set only across the whole site allow a developer to build market housing across several phases before delivering any affordable homes, which no authority will accept on a long build programme. Triggers set only per phase can stall a scheme where one phase is delayed for reasons unconnected with housing delivery.
What happens if a phase does not come forward?
The agreement should say. The usual answer is that the obligation attaches to phases as they are brought forward, with a reconciliation at the end so the overall proportion is met, plus a long stop date. Without that, a developer who stops after three of six phases may have delivered the market homes and a smaller share of the affordable ones.
Can the affordable tenure mix change between phases?
It can, if the agreement allows it, and some flexibility is sensible over a ten year build. Authorities usually accept variation within defined limits, with written approval required beyond them. What they will not accept is an unlimited discretion, so propose a band rather than an open door.
Do the obligations bind a future owner?
Yes. A planning obligation entered into under section 106 of the Town and Country Planning Act 1990 is enforceable against the person entering into it and against anyone deriving title from them, subject to the terms of the agreement. That is why the drafting has to be readable by a purchaser's solicitor five years later without the negotiation history.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.