Last week we wrote about the national section 106 templates aimed at 10–49 unit sites. This is the other end of the same telescope. The National Planning Policy Framework published on 17 August 2026 creates, for the first time, a distinct planning category for the very largest housing schemes — and the policies that govern it are almost entirely about phasing.
For anyone doing SAP work on a strategic site, that is not a planning-nerd detail. It is the thing that decides which edition of Part L each phase is built to.
What counts as a strategic site
The Framework’s plan-making policy, HO4: Land for strategic site development, describes them by type rather than by a bare number:
“The development plan should, where appropriate, identify suitable locations for strategic sites for housing-led development (such as new settlements, new urban quarters or significant extensions to existing settlements).”
The Planning Portal, summarising the government’s position on publication, reports that strategic sites will typically be those with capacity for 1,500 homes or more, though the figure can vary with the mix of uses on the site. Treat that as the government’s working scale rather than a hard threshold in the policy text.
HO4 then sets three tests for the locations chosen. They should be capable of being supported by the necessary infrastructure and facilities at appropriate points in the development’s delivery; capable of supporting a sustainable community with access to services and employment “without expecting an unrealistic level of self-containment”; and they should
“Address strategic environmental opportunities and safeguards, including those set out in Local Nature Recovery Strategies.”
Local plans are then expected to identify specific sites with their infrastructure and site-specific requirements, set design expectations through masterplans and design codes, make “a realistic assessment of the likely rates of delivery”, and identify routes to rapid implementation such as joint ventures, land assembly or locally led development corporations.
HO13 is where it gets practical
The decision-making counterpart is HO13: Build out of residential and strategic sites. Paragraph 1 sets the general expectation that land with permission is developed without unnecessary delay, and paragraph 2 invites councils to consider conditions requiring development to begin sooner than the statutory default.
Paragraphs 3 and 4 apply specifically to strategic sites. Paragraph 3 says the consenting framework should:
“a. Set out the parameters and requirements for the design, infrastructure and other features of the development (including the quantity and type of affordable housing to be provided), with the level of initial and subsequent detail tailored to the proposed scale and phasing of the development; and
b. Be flexible enough to respond positively to changing circumstances as phases are brought forward, including changes to housing need, infrastructure requirements, viability and design.”
Paragraph 4 adds that where an emerging plan — “however advanced” — proposes to allocate strategic sites, development proposals should not be inconsistent with the proposed scale, location and phasing of those sites.
So: parameters set early, detail scaled to phasing, and an explicit instruction that the consent should flex as phases come forward.
Why this matters for Part L
Here is the bit that lands on assessors’ desks.
A strategic site is, by definition, a scheme that will still be building out in ten years. The Future Homes Standard transitional arrangements are not that generous. As we’ve written before, protection under The Building Regulations etc. (Amendment) (England) Regulations 2026 (SI 2026/335) requires two things: a building notice, initial notice or full-plans application before 24 March 2027, and the work on that individual building commenced before 24 March 2028 — with “commenced” meaning a completed sub-structure including ground floor structure, plot by plot.
On a 1,500-home site, that is a small fraction of the programme. Phases one and possibly two might be protected. Everything after that is being built to ADL 2026 — heat pumps, on-site generation under requirement L3, and the tighter fabric that goes with them.
HO13(3)(b) is helpful here, in a backhanded way. A consenting framework that is required to “respond positively to changing circumstances as phases are brought forward, including changes to… infrastructure requirements, viability and design” is one that ought to be able to absorb a change of Part L edition mid-build-out without a full section 73 fight. But that only works if the parameters set at outline are drafted to allow it.
The trap is a parameter plan or design code written to the fabric and services of the current regulations. Fixed roof pitches and orientations that don’t work for the PV array L3 now expects. Plot-wide glazing ratios set against a 2021 overheating assessment. External wall build-ups locked into a design code at a thickness that won’t take the insulation ADL 2026 needs. Heat network capacity sized on the assumption every plot has a gas boiler. None of those are hard to fix at masterplan stage. All of them are expensive to fix at phase four.
The other long-programme problems
Two more that phasing makes worse rather than better.
Nutrient budgets. In a protected catchment, the nutrient budget for a strategic site is calculated on the whole scheme, but the mitigation is usually delivered and paid for in tranches. If the budget was struck on an occupancy assumption or a wastewater treatment consent that changes between phase one and phase five, the arithmetic moves. The new NPPF chapter on clean energy and water pushes catchment capacity into plan-making, which should mean fewer surprises — but only on plans prepared after August 2026.
Drainage. HO4(1)(a) asks that infrastructure be capable of support “at appropriate points in the development’s delivery”. Surface water is the classic case where phase-by-phase attenuation designed in isolation adds up to a strategy that doesn’t work at full build-out, and where the national SuDS standards now expect a scheme-wide answer.
What we’d suggest doing
Map your transitional cliff-edge against your phasing plan, on paper, now. Which plots realistically get a full-plans application in before 24 March 2027 and a completed sub-structure before 24 March 2028? Everything to the right of that line is an ADL 2026 scheme. If nobody has drawn that line, the design code is being written blind.
Write the design code so it survives a regulation change. Ask for parameter ranges rather than fixed values on the things Part L touches — wall thickness, roof form and orientation, plant space, glazing ratio. HO13(3)(b) gives you the policy hook to argue for it.
Get the fabric strategy tested against ADL 2026 before the code is fixed, not after. A notional-building run on a representative house type from each phase is a day’s work and will tell you whether the code you’re about to adopt is buildable under the standard that most of the site will actually be built to.
Thermal bridging is the cheapest margin you have. On a scheme with repeated house types across ten phases, bespoke PSI values are calculated once and used thousands of times. Default y-values on a 1,500-home site are, in aggregate, a very expensive convenience.
ΨMonkey calculates bespoke PSI values for your junctions to BS EN ISO 10211, following BR 497 and BRE IP 1/06 conventions, in your browser — so your SAP model reflects the junctions in your design code rather than the worst case the software assumes.
If you’re masterplanning a site that will still be building out well past the Future Homes Standard transitional dates and you’d like the Part L strategy stress-tested before the design code is signed off, get in touch — that conversation is much cheaper at outline than at phase four.
Sources: National Planning Policy Framework, August 2026 (PDF), GOV.UK — chapter 6, policies HO4 and HO13 · National Planning Policy Framework guidance page, MHCLG, 17 August 2026 · Government publishes latest NPPF with new strategic sites policy, Planning Portal Blog, 19 August 2026 · The Building Regulations etc. (Amendment) (England) Regulations 2026 (SI 2026/335), legislation.gov.uk