Underfloor heating, Part L and the Future Homes Standard

Part L of the Building Regulations covers energy efficiency. For underfloor heating it sets the design flow temperature, the controls, the floor insulation and how the heating is sized and commissioned. This guide sets out what the rules say now, what changes on 24 March 2027, and what that means for your floor.

Everything here applies to England. Wales and Scotland have their own building regulations, so check with your local building control body there. Paragraph numbers refer to Approved Document L, Volume 1: Dwellings.

When does the new Part L come into force?

The 2026 edition of Approved Document L takes effect on 24 March 2027 for building work in England. The government published it on 24 March 2026, alongside the regulations that bring in the Future Homes and Buildings Standards. Higher-risk buildings, such as tall blocks of flats, follow on 24 September 2027.

The transitional rule is the one to plan around. If a building notice, initial notice or full plans application goes in before 24 March 2027, and the work is commenced before 24 March 2028, the changes don't apply to that work. "Commenced" has a defined meaning in the regulations, so ask your building control body if you are close to either date.

What is the Future Homes Standard?

The Future Homes Standard is the government's standard for new homes in England, built so they won't need retrofitting to be zero carbon in use. It is delivered through the 2026 editions of Approved Documents L and F and changes to the regulations.

• Heat pumps as the reference. The notional dwelling, the benchmark a new home's design is measured against, is based on a heat pump. The government says boilers are unlikely to be present in new buildings under the new carbon limits for heating fuel.
• Renewable electricity. A new requirement, L3, means new dwellings need an on-site renewable electricity system, subject to limits.
• Heat pump installation. New guidance covers commissioning, following the heat pump maker's instructions and using competent person schemes for heat pumps.
• Information for owners. A new regulation, 40C, requires information for homeowners in a suitable format, including a Home User Guide.

For underfloor heating this is good news. A heat pump works best at low flow temperatures, and a well designed floor gives the room its heat at low water temperatures. Our guide to underfloor heating with a heat pump covers the design side.

What does Part L say about underfloor heating flow temperature?

Under the 2021 edition, when a wet heating system is newly installed or fully replaced, all of it should be sized to run at a maximum flow temperature of 55°C or lower (paragraph 5.10). Underfloor heating counts as a wet heating system. If 55°C is not feasible, the system should be designed for the lowest temperature that still meets the home's heating needs.

Paragraph 5.10 does not cover an existing system where only the boiler or heat pump is replaced. In that case the control rules apply instead. The guidance points to BRE's Design of Low-temperature Domestic Heating Systems (FB 59) for further design help.

Most screed floors already run well below 55°C, so meeting this is rarely difficult with underfloor heating. A floor designed at 35 to 45°C also leaves room for a heat pump to run efficiently.

What does the 2026 edition change for underfloor heating?

The 2026 edition keeps a dedicated section on underfloor heating systems and changes how floor coverings are treated. In its consultation response, the government says the wording on floor coverings used with underfloor heating now requires the overall design to take account of the thermal resistance of the floor covering, rather than setting a fixed U-value, and refers to third party guidance.

In practice, your design should state the floor finish and its thermal resistance, and the heat output and flow temperature should be worked out with that covering in place. A thick carpet chosen after the design was done can push the floor outside what was approved. Our guide to UFH floor coverings explains tog values.

Other changes that affect UFH jobs:

• Sizing. Space heating should be sized using a heat loss calculation to BS EN 12831-1, and systems should not be oversized (paragraph 4.9).
• Efficiency. Each new fixed building service should be at least as efficient as the minimum values in Section 5 (paragraph 4.1).
• Replacements. A replacement heat source in an existing home should be no less efficient than the minimum standards. A heat pump meeting the minimum efficiency standards is treated as compliant (paragraph 4.5).
• Controls and insulation. New guidance covers heat pump controls and insulation of heat distribution pipework.

Do I need a thermostat in every room?

Yes, in most cases. In new dwellings, and when the heat source is replaced in an existing dwelling, each room should have thermostatic room controls (2021 edition, paragraph 5.20). With underfloor heating, that normally means one thermostat per room or zone.

• A single storey open plan home where the living area is more than 70% of the floor area can be treated as one zone (5.21a).
• Two adjacent rooms with a similar function and heating need can share a zone (5.21b).
• New dwellings of 150m² or more should have at least two independently controlled heating circuits (5.14).
• Where work is done on a system with a boiler, a boiler interlock should be fitted (5.25), so the boiler and pump only run when a room calls for heat.
• Wet systems should keep a minimum flow of water to avoid short-cycling (5.18).

A UFH wiring centre handles the interlock for you. For the hardware, see underfloor heating thermostats explained.

How well insulated must an underfloor heated floor be?

The limiting U-value for a new floor is 0.18 W/m²K, both in a new dwelling and for a new floor in an existing one, such as an extension. The 2026 edition keeps the same figures as the 2021 edition.

For an extension, the floor U-value may be calculated using the exposed perimeter and floor area of the whole enlarged dwelling. A lesser standard may be acceptable where meeting it would cause significant problems with adjoining floor levels. Under the 2021 edition, perimeter insulation should be continuous and at least 25mm thick (paragraph 4.15).

The insulation thickness to hit 0.18 depends on the insulation type and the floor's size and shape, so it comes from your architect or building control calculation, not from the heating design. The insulation under the pipes also stops heat going down instead of up, which is covered in our guide to insulation under underfloor heating.

Does Part L apply to my extension or renovation?

Yes, if you are building an extension, replacing the heating system, or renovating a floor. It does not stop you adding underfloor heating to an existing home. It sets standards for the parts you build or replace.

1. Extension with its own UFH zone off the existing boiler. The new floor should meet 0.18 W/m²K. Ask building control which control rules apply to extending your system. Giving the new zone its own thermostat is the simple way to match the room control guidance.
2. Whole house heating replaced with UFH. The new wet system should be designed for 55°C or lower, sized from a heat loss calculation, with room-by-room controls.
3. New boiler or heat pump only. The flow temperature rule in 5.10 does not apply, but the room control and efficiency rules do.
4. Floor dug up and relaid. A renovated floor should be upgraded towards 0.25 W/m²K where technically and functionally feasible with a simple payback of 15 years or less.

Heating work is commissioned by testing and adjusting as needed, and a new heat source may need building control sign-off or a competent person scheme certificate. Ask your installer which route they use.

What should my UFH design show to meet Part L?

A design that will satisfy building control under either edition should show:

1. A room-by-room heat loss calculation, to BS EN 12831-1 under the 2026 edition.
2. The design flow temperature, at 55°C or lower.
3. Pipe centres and loop lengths that deliver each room's heat at that flow temperature.
4. The floor finish in each room and its thermal resistance.
5. One thermostat per room or permitted zone, with interlock to the heat source.
6. The floor build-up and insulation, matching the U-value calculation.
7. Commissioning records: pressure test, flow rates and first heat-up.

Products for this job

Prices include VAT, October 2026.

• UFH Non-Mixing Pump Set with Grundfos UPM3 Flex, for heat pumps: £207
• Auto-Balancing Stainless Steel UFH Manifold: from £62 (2 port)
• 5-Layer PERT-EVOH Pipe 16mm: £246 (400m)
• Heatmiser neoStat V3 thermostat: £77
• Heatmiser UH8 8 Zone Wiring Centre: £77
• Edge Insulation Roll 50m: £17
• Heat pump connection

Related guides: Underfloor heating with a heat pump and BS EN 1264 and BS 7671 in plain English.

Frequently asked questions

When does the Future Homes Standard start?

The regulations and the 2026 edition of Approved Document L come into force in England on 24 March 2027, and on 24 September 2027 for higher-risk buildings. Work notified before 24 March 2027 and started before 24 March 2028 can stay on the 2021 rules.

Will gas boilers be banned in new homes?

The government's consultation response does not describe it as a ban. It says boilers are unlikely to be present in new buildings, because of the new carbon limits for heating fuel, which favour heat pumps and heat networks.

Does Part L require underfloor heating?

No. Part L sets energy standards, not a type of emitter. Underfloor heating is one of the easiest ways to meet the 55°C flow temperature guidance, because floors give out their heat at low water temperatures.

Does the 55°C rule apply if I only replace my boiler?

No. Paragraph 5.10 of the 2021 edition covers wet systems that are newly installed or fully replaced. Replacing only the heat source brings in the room control and efficiency rules instead.

Do I need building control for underfloor heating in an extension?

The extension itself needs building regulations approval, and the floor and heating are checked as part of it. Ask your building control body or installer which notifications apply to the heating work.

Does Part L apply in Wales or Scotland?

Approved Document L is for use in England. Wales and Scotland set their own energy standards, so check with building control where you are building.

Sources: gov.uk: Approved Document L (2026), Approved Document L Volume 1, 2026 edition, gov.uk: Building Circular 01/2026, gov.uk: Future Homes and Buildings Standards consultation response, Approved Document L Volume 1, 2021 edition