Deliverable and developable sites in housing supply

Deliverable developable sites are the two categories national policy uses to sort a council's housing land supply, and the difference between them decides whether a site counts towards the five year requirement or only towards years six to fifteen. Deliverable means a realistic prospect that housing will be delivered within five years. Developable means a reasonable prospect that the site will be available and could be viable at the point envisaged, which is a considerably softer test applied over a longer horizon.

Most housing supply arguments at appeal are arguments about which category a handful of large sites belong in.

The definitions in national policy

Both definitions sit in the glossary to the National Planning Policy Framework rather than in the body of it, which is why they are quoted in full so often and read so rarely.

A deliverable site should be available now, offer a suitable location for development now, and be achievable with a realistic prospect that housing will be delivered on the site within five years. A developable site should be in a suitable location for housing development with a reasonable prospect that it will be available and could be viable for housing at the point envisaged.

The Framework was re-issued in August 2026 with policy-coded chapters, so check the current glossary wording before quoting it in evidence. The substance of the two tests has been stable across editions, but the surrounding numbering has not.

The practical distinction is time and certainty. Deliverable is a five year judgement with evidence attached. Developable is a longer term planning judgement about a site's prospects.

Evidence needed to show a site is deliverable

The glossary splits deliverable sites into two groups, and the evidential burden differs sharply between them.

Sites that do not involve major development and have planning permission, and all sites with detailed planning permission, are treated as deliverable until the permission expires, unless there is clear evidence that homes will not be delivered within five years. The presumption runs in favour of inclusion.

Sites with outline permission for major development, allocations in a development plan, grants of permission in principle, and sites identified on a brownfield register are different. Those count only where there is clear evidence that housing completions will begin on site within five years. Here the presumption runs the other way, and the council has to produce something.

What counts as clear evidence in practice is a question of substance rather than form. A letter from a housebuilder confirming a start date, a reserved matters application submitted, a signed section 106 agreement, discharged pre-commencement conditions, infrastructure contracts let, marketing evidence, or a current sales programme. What does not count is a statement in a five year supply paper asserting that a site will come forward because the council expects it to.

Sites with outline permission and allocations

This is where most of the contested capacity sits, because the large sites that carry a council's supply are usually allocations or outline consents.

A strategic allocation of 800 homes with no planning application, no landowner agreement in place and a spine road that has not been designed is not deliverable, however confident the trajectory looks. An outline permission granted four years ago, where reserved matters have not been submitted and the section 106 remains unsigned, needs evidence of an imminent start rather than an assurance.

Look at the components. Who controls the land, and is there more than one owner. Are the pre-commencement conditions discharged. Is there an access agreement with the highway authority under section 278. Where does the foul drainage go, and has the undertaker confirmed capacity. Is there a housebuilder on board or is the site being promoted for sale.

Each of those is a question the council's own evidence base should answer, and where it does not, the gap is the argument.

The clear evidence test in practice

Courts have been clear that deliverable is not a test of certainty. The Court of Appeal in St Modwen Developments confirmed that the question is whether there is a realistic prospect of delivery within five years, not whether delivery is guaranteed.

That cuts both ways. An appellant arguing that every allocation should be excluded because delivery is not certain will lose. A council including a site with no evidence beyond optimism will also lose. The exercise is a judgement on evidence, which is why the quality of the evidence base matters more than the rhetoric around it.

Build the analysis site by site in a table, with the category each site falls into, the evidence relied on, the number of completions claimed in each of the five years, and your position on each. Inspectors work through these methodically and reward a schedule that lets them do so.

Lapse rates and non-implementation

Not every permission is implemented, and a supply position that assumes otherwise overstates itself.

Councils apply a lapse rate, sometimes called a non-implementation allowance, to reflect permissions that expire unbuilt. The rate should be derived from the authority's own monitoring rather than from a figure borrowed elsewhere, and the base date and the source data should both be stated.

Watch for double counting too. A site can appear as a commitment and again as an allocation, and on large sites a phase can appear in both the five year supply and the longer term trajectory.

Build-out rates are the related issue. A single outlet rarely delivers the numbers a trajectory sometimes assumes, and where a large site is claimed to deliver at a high annual rate, the evidence should show how many outlets will be operating.

Challenging a supply position

If the council cannot demonstrate a five year supply, the policies most important for determining the application are treated as out of date and the tilted balance in national policy applies. That changes the decision, which is why these arguments are fought hard.

The requirement side matters as much as the supply side, and the starting point is the calculation of local housing need. Our note on the standard method for calculating local housing need covers that, and the treatment of unplanned sites is dealt with in our piece on how windfall allowances are justified.

Using the definitions in an appeal

Be specific and be fair. An appellant who attacks every site loses credibility, and an inspector will notice that the same submission challenges a site with a signed contract and one with nothing.

Pick the sites that matter. On most appeals the outcome turns on three or four large sites, and a focused challenge to those, with evidence, does more than a spreadsheet objecting to forty.

Then do the arithmetic both ways. Show the supply position on the council's figures and on yours, and identify the point at which the supply falls below five years, because that is the finding the inspector has to make.

Where the site's own prospects are in question, a Planning Statement should set out the deliverability evidence for the appeal site itself, and where viability is raised, a Viability Assessment prepared to the recognised professional standard will be expected rather than an assertion. Settlement policy interacts with all of this, and our note on settlement boundaries in local plans explains how those constrain where supply can come from.

PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.

This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it.