New builds and the Future Homes Standard

Part L of the Building Regulations changed on 24 March 2026, and takes effect on 24 March 2027. A new requirement L3 says that when a building containing dwellings is erected, a system for on-site renewable electricity generation must be installed, sized to produce a reasonable output and designed so the electricity is available to the people living there.

In practice that means solar panels, because on a house nothing else comes close.

Three things about it are worth getting straight, because the coverage generally does not.

The 40% figure is not a coverage rule. It describes a notional array — panels at 0.22 kWp/m² over an area equal to 40% of the ground floor area, facing south-east to south-west, at 45 degrees, unshaded — and the requirement is to match that array’s annual output. A roof that faces the wrong way needs more panels to comply, not fewer.

Flats get much less. For a building containing dwellings, ground floor area is the gross internal area divided by the number of storeys, so the taller the block, the smaller the target per home.

It is not a UK rule. Wales requires its own version three weeks earlier, Scotland requires nothing of the kind, and Northern Ireland has proposed rather than enacted — see how the devolved standards differ.

Plenty of new homes will still have none. Transitional arrangements protect work applied for before 24 March 2027 and commenced before 24 March 2028. Homes completing well after the standard starts may lawfully have no solar at all, and two plots on one estate can differ.