Rafter insulation | From £1,645

What is rafter insulation?

Because the whole roof slope, the gables and the party walls now have to be insulated, this costs much more than insulating the floor and saves less heat for the money. It earns its place when you need a warm loft. We check the roof underlay first: a breathable membrane and a felt with no ventilation gap need different build-ups to avoid condensation.

Is it right for your loft?

You use the loft as a room or plan to
Heating or ducting runs through the loft
The loft floor cannot be insulated because of the ceilings below
You are converting the loft and need to meet building regulations

How we do it

We check the underlay, the rafter depth and the condition of the timber.
We design the build-up: board thickness, ventilation gap if needed and vapour control.
Boards are cut tight between the rafters and taped at the joints.
Insulated plasterboard goes over the rafters to cut cold bridging.
Gables, party walls and the floor edge are finished so there are no gaps.

What is included

Build-up designed for your type of roof underlay
Rigid insulation between the rafters, joints taped
Insulated plasterboard lining where specified
Vapour control layer where the design needs one

Worth knowing

Rafter insulation on a converted or habitable loft is building work. Building control or a building warrant may be needed, and the target U-values are stricter. We confirm the route for your nation on the quote.

How much does rafter insulation cost?

£1,645 to £2,595About 30 m² of roof slope. Free survey and a fixed written quote before any work.

Part of this work can be zero-rated as energy-saving materials until 31 March 2027, and part is standard-rated. If VAT applies, your quote shows which is which.

Work out a guide price for your loft or see every price.

Do the rules differ across the UK?

Yes, a little. Building regulations and funding schemes are set separately in each nation. Here is the short version; each area page has the detail.

Nation	Building rules	Funding to check
England	Approved Document L; insulation alone is not usually notified	ECO4 to 31 Dec 2026; Warm Homes Plan and Warm Homes: Local Grant
Wales	Welsh Approved Document L; conversions need building control	Warm Homes Nest; ECO4 to 31 Dec 2026
Scotland	No building warrant normally needed; standards still apply	Home Energy Scotland grant and loan; Warmer Homes Scotland
Northern Ireland	NI Building Regulations (Technical Booklet F1); check with council building control	Affordable Warmth Scheme; NISEP

Questions about rafter insulation

Is insulating between the rafters better than the loft floor?

Not for saving energy alone. Insulating the floor heats less space and costs far less. Rafter insulation is the right answer when the loft itself needs to be warm.

Can I use the loft as a bedroom after rafter insulation?

Insulation alone does not make a loft habitable. Fire escape, stairs, floor strength and headroom all come into a conversion, which needs building control.

Will it cause condensation?

It can if the build-up is wrong for the roof. Old bitumen felt needs a ventilation gap behind the insulation; a modern breathable membrane may not. We check before we design it.

Where we provide rafter insulation

Wales

Scotland

Northern Ireland

Often booked with it

Sources, checked October 2026: Energy Saving Trust: roof and loft insulation; Which?: loft insulation costs and savings; LABC: building regulation requirements for loft insulation; GOV.UK: extending the ECO4 end date, government response.

Rafter insulation (warm loft)