Part L 2026: Future Homes Standard Explained
Part L 2026 and the Future Homes Standard: what to design for now
Approved Document L 2026 has been published and takes effect for most building work in England on 24 March 2027, requiring new homes to cut carbon emissions by around 75% against 2013 standards.
Schemes entering design now could still be under construction when the requirements bite. Decisions on heating, fabric and roof layout determine whether a project complies smoothly or needs an expensive redesign, and on phased sites, protection applies building by building, not site-wide.
What is Part L 2026?
Part L of the Building Regulations covers energy use and greenhouse gas emissions from buildings. The 2026 edition of Approved Document L forms part of the wider Future Homes and Buildings Standards, intended to combine low-carbon heating with high energy efficiency so new buildings do not need major retrofit as the grid decarbonises.
| Date | What happens |
| 24 March 2026 | Approved Document L 2026 published |
| 24 March 2027 | Takes effect for most building work |
| 24 September 2027 | Takes effect for higher-risk building work |
| 24 March 2028 | Transitional protection ends – work must have commenced |
What are the Part L 2026 transitional arrangements?
The transitional arrangements matter most on phased developments.
For a non-higher-risk building to remain under the previous Part L requirements, the relevant building notice, initial notice or full-plans application must be submitted before 24 March 2027, and work must then commence on that individual building before 24 March 2028.
Protection applies building by building, not site-wide. This is how Part L transitions have always worked: where an application covers several buildings, only those on which work has commenced can use the provisions.
On a 100-home scheme where documents are submitted before March 2027 but only 40 homes start before March 2028, those 40 may retain protection while the other 60 could need to meet Part L 2026.
One site may therefore contain two different specifications, affecting house types, procurement, cost plans and buyer information. Teams working on residential development should map the transition at plot level, rather than assume that starting work somewhere protects everything.
What changes under the Future Homes Standard?
Compliance is assessed across the whole design – fabric, heating, hot water, controls and renewable generation. Three areas shape most residential schemes.
Low-carbon heating becomes the default
The standard is built around low-carbon heating, and heat pumps will be the most common route, though the regulations do not require one in every home. The notional dwelling used to set compliance targets assumes a heat-pump specification, and changes to the gas carbon and primary energy factors make fossil-fuel heating extremely difficult to comply with. Gas, oil and LPG boilers are not banned by name, but they will not get a scheme through.
Heat pumps also have to be designed into the building. Performance depends on accurate heat-loss calculations, suitable emitters, lower flow temperatures, controls, storage and positioning – making early coordination between the architect and building services engineering team essential.
Solar PV becomes a requirement
Requirement L3, introduced by the March 2026 amendments, makes on-site renewable electricity generation a functional requirement wherever a dwelling, or a building containing dwellings, is erected.
For houses, Approved Document L sets a benchmark of panels covering an area equal to 40% of the ground-floor area, at an assumed efficiency of 0.22 kWp per square metre. A three-bedroom house with 50 square metres of ground floor therefore needs at least 20 square metres of panels, around 4.4 kWp. Flats are assessed on a lesser figure, floor area divided by 4.5.
Where the full area is not achievable because of roof geometry, orientation or shading, a reasonably practicable area can be substituted, but the reasoning must be evidenced and the carbon target met another way. Exemptions apply to buildings over 18 metres, higher-risk buildings, and sites where 720 kWh a year cannot be achieved. Panels need not sit on the building: ground-mounted arrays count, and batteries are optional.
Solar cannot wait for the roof design to be finished. Dormers, vents, plant and shading all reduce available area, so energy and architectural strategies need developing together.
What are the fabric and airtightness requirements?
Low-carbon technology does not remove the need for an efficient envelope. New dwellings must meet targets for primary energy, emissions and fabric energy efficiency, with limiting values set for individual elements.
Airtightness is where the numbers get confused. The limiting air permeability remains 8 m³/(h·m²) at 50 Pa, but that is a backstop, not a design target. The figure to work to is the notional dwelling benchmark, tightened from 5 to 4 m³/(h·m²). Designing to the backstop will not produce a compliant dwelling, and the guidance is explicit that some elements may need to perform well beyond the limiting standards for a dwelling to hit its overall target.
How is Part L 2026 compliance calculated?
SAP 10.3 is initially the sole approved methodology for new homes. The Home Energy Model was expected to launch alongside the Future Homes Standard but was delayed pending further assurance work; it should follow later and eventually replace SAP.
SAP is not a final calculation to run once the design is fixed. Early modelling tests fabric, glazing, heating, hot water and renewable generation together before changes get expensive. The as-built calculation uses the final specification and measured air-permeability result, so product substitutions can affect compliance even where the design passed.
What will Part L 2026 add to build costs?
The government’s Impact Assessment puts the additional build cost at roughly £4,350 per dwelling on a weighted average at 2025 prices, covering solar PV, an air source heat pump, enhanced insulation, mechanical ventilation and improved windows and doors. That average hides real variation: a three-bedroom semi sits nearer £3,800, larger detached homes up to £6,200.
For schemes being appraised now, this belongs in the budget alongside the Building Safety Levy rather than absorbed later. Both land inside the same eighteen-month window, and both are easier to manage through early cost planning than late redesign.
What about higher-risk buildings?
Higher-risk building work follows a separate route. The Part L changes take effect for it on 24 September 2027, and to retain the previous standard a valid building control approval application must have reached the Building Safety Regulator before that date and must not later be rejected or lapse.
The energy strategy should therefore be coordinated with the Gateway 2 programme, since late changes to the façade, services or renewables carry wider building safety consequences. The solar PV requirement does not apply to higher-risk buildings, so the carbon target must be met another way.
What should project teams do now?
Any scheme reaching construction during or after 2027 should be reviewed against the new requirements:
- Confirm the building type and intended building control submission date.
- Map commencement dates building by building, not site-wide.
- Model in SAP 10.3 early, not once the design is fixed.
- Protect space for heat pumps, hot-water storage and panels.
- Coordinate fabric, airtightness and ventilation together.
- Reflect the likely specification in procurement, cost plans and programme.
The main risk is reaching technical design with assumptions that no longer work together.
Preparing for Part L 2026
Part L 2026 changes the default approach to heating, efficiency and renewable generation across new development in England, reaching commercial and mixed-use schemes as well as housing.
Bailey Partnership brings architecture, building services engineering, sustainability and project delivery together to treat this as one coordinated design problem, across residential and commercial schemes alike.
Part L 2026 FAQs
When does Part L 2026 come into force?
It takes effect for most building work in England on 24 March 2027, and for higher-risk building work on 24 September 2027.
What is the Part L 2026 transition deadline?
For most non-higher-risk buildings, documents must be submitted before 24 March 2027 and work must commence on that individual building before 24 March 2028.
Are gas boilers banned under Part L 2026?
Not by name. But changes to the carbon and primary energy factors, plus a notional dwelling built around a heat pump, make fossil-fuel heating extremely difficult to comply with.
How much solar PV does Part L 2026 require?
For houses, panels covering an area equal to 40% of the ground-floor area, at an assumed 0.22 kWp per square metre. Flats use a lesser figure, and a reasonably practicable area can be substituted where roof geometry prevents it.
How much will the Future Homes Standard add per home?
Around £4,350 per dwelling on a weighted average, per the government’s Impact Assessment, roughly £3,800 for a three-bedroom semi, up to £6,200 for larger detached homes.
Does Part L 2026 apply to flats?
Yes, though the solar PV benchmark differs, floor area divided by 4.5 rather than the 40% applied to houses. Buildings over 18 metres and higher-risk buildings are exempt from the PV requirement.
Talk to us about your programme
If you have schemes reaching construction around 2027, the transition is decided plot by plot, and the submission and commencement dates are still in your control. We can review your programme and energy strategy, identify which buildings retain protection, and set out what the rest will need.
Contact Bailey Partnership to discuss Part L 2026 on your project.