Approved Documents L and F were published on 24 March 2026. The amended regulations take effect on 24 March 2027, followed by a transitional period closing on 24 March 2028.
Building Regulations apply per house regardless of who the project is for. The exemptions that self-builders receive elsewhere have no bearing on building control. A replacement house on the site of a demolished one is a new dwelling and falls within the scope of the FHS.
Much of the published articles on the standard address volume housebuilding. The implications on a large individual house are different and should be considered now.
How is compliance measured?
Compliance is demonstrated against a standard building of the same size and shape as the proposed building, which assumes a heat pump, solar PV, improved fabric and mechanical ventilation. The target is a carbon reduction of at least 75% against the 2013 Part L baseline.
Calculations currently use SAP 10.3, with the Home Energy Model expected during 2027. The newer method is understood to be less accepting of designs that offset weak fabric with additional PV capacity, which matters for any design intending to compensate for a heavily glazed elevation with a larger array of PV.
Generation is now a legal requirement, and it conflicts with roof design.
New dwellings must include on-site renewable electricity generation, positioned on the building or within the curtilage.
The approach assumes PV panels covering an area equivalent to 40% of the ground floor area, at 0.22 kWp per square metre, oriented between south-east and south-west at 45 degrees without significant shading. Where those assumptions cannot be met, output should be maximised by other means. Exemptions apply for buildings taller than 18m, and where shading or roof geometry prevent a annual output of at least 720 kWh.
This is the requirement most likely to confilict with a design. The array is sized against ground floor area, so a large single-storey or horizontal house carries a substantial obligation while offering comparatively little south-facing roof space. Flat roofs, zinc and lead finishes, complex geometry and north-light strategies all reduce the available area. Panels within the curtilage can work where the roof cannot fit the array, though that moves the problem into landscaping!
A second difficulty arises sites in conservation areas or listed buildings. Generation is a legal requirement under the Building Regulations, while a local authority may try to push back. This should be resolved during the planning process, since discovering it at building control leaves few options.
Heating, and what it needs in plan
Gas boilers aren’t banned. Instead, the carbon target sits at a level that gas, oil and direct electric heating cannot reach. Air source heat pumps will serve most houses, while ground source and shared loop systems suit larger plots where boreholes can be coordinated with groundworks.
Electrical capacity and grid connection deserves attention early. A heat pump, PV array, cooling, potential pool equipment and vehicle charging together produce a load profile that requires a three-phase supply, and network operator lead times can be several months.
Airtightness, ventilation and acoustics
The notional airtightness figure tightens to 3 m³/(h·m²) at 50 Pa, against a Part L 2021 notional value of 5 and an unchanged backstop of 8. Reaching that level needs a continuous air barrier drawn and coordinated with service penetrations from the outset, and it makes mechanical ventilation, such as MVHR, the default.
MVHR requires dedicated duct routes to every room and wet room. In houses with deep plans, double-height spaces and exposed structure, those routes are difficult to manage. Acoustic transfer between rooms sharing a duct run is a further concern in a house where the client expects quiet. Both issues cost little to resolve during spatial planning and a great deal to resolve later.
Overheating is the big issue to manage
Part O is unchanged, but it has a new framing with the new standard. A better insulated and more airtight house retains unwanted gain more readily, so the overheating assessment becomes harder to manager at the same time as the fabric improves. On projects with lots of glazing, this is usually the requirement that decides the design.
Mechanical cooling does not remove the Part O obligation. The simplified method restricts glazing areas and sets a minimum free area for purge ventilation, which few large houses will satisfy. Dynamic thermal modelling under TM59 allows cooling to be taken into account, though the analysis must then be produced and defended, and it should be commissioned before the glazing schedule is fixed.
Capacity in a domestic wet system is limited. A chilled underfloor circuit delivers roughly 15 to 25 W/m² before condensation risk sets the lower limit on flow temperature, whereas solar gain through a large south-facing opening can exceed 100 W/m² of floor area. Shading, glazing specification and orientation remain the primary controls. Where fan coil units are used to reach higher capacity, the chilled pipework requires vapour-sealed insulation and the units require condensate drainage, both of which affect ceiling voids and joinery.
Transitional arrangements
Work can continue under the current standard where a building notice, initial notice or full plans application is submitted before 24 March 2027 and construction commences on the dwelling before 24 March 2028.
Protection attaches to individual buildings, which suits a single house. The practical difficulty is length of build. A plot acquired this year, taken through planning and design development, then built in stages, might not reach start inside the window. Any client currently at feasibility should be advised which standard their house is likely to be built to.
Points to address early
- Confirm with the client whether the project falls inside the transitional window before the design is developed.
- Size the array against ground floor area at concept stage, and test the roof form and landscape against it before elevations are settled.
- Raise the generation requirement during pre-application discussions on any sensitive site.
- Allocate plant space, riser positions and electrical supply capacity during spatial planning.
- Commission the overheating assessment before the glazing schedule is finalised, and develop a cooling strategy which is cost and output effective.
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