Loft insulation top-up

What is a loft insulation top-up?

Before we quote we measure the existing layer in several places and check its condition. If it is dry, even and not contaminated, we keep it and lay the top-up across it at right angles. If it is wet, dirty, matted or full of droppings, laying fresh wool on top just buries the problem, so we say so and price removal instead.

Is it right for your loft?

A ruler pushed into the insulation shows 100 to 150 mm
The tops of the joists are visible above the old layer
Patches are missing where cables or pipes were run
Your EPC lists the roof at less than 270 mm

How we do it

We measure the existing depth in at least five places and photograph it.
Gaps and thin patches in the first layer are filled so it is even.
The top-up rolls go across the joists at right angles to cover the timber.
The eaves stay clear and the tank and pipes are lagged.
We record the final depth with photos.

What is included

Depth check and photos before and after
Gaps in the existing layer filled
Cross layer to a total of 270 to 300 mm
Tank jacket and pipe lagging in the loft
Eaves ventilation kept clear

Worth knowing

The saving from a top-up is real but smaller than insulating a bare loft. The Energy Saving Trust puts it at about £17 a year for a semi-detached house going from 120 mm to 270 mm, so it is worth doing for comfort and the EPC, and best done at the same time as other loft work.

How much does a loft insulation top-up cost?

£395 to £545Terraced house, average loft, topping up from about 100 mm. Free survey and a fixed written quote before any work.

Installing insulation in a home is zero-rated for VAT until 31 March 2027 and 5% after that, under HMRC's rules for energy-saving materials (notice 708/6).

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 a loft insulation top-up

Is it worth topping up 100 mm of loft insulation?

Often, if the existing layer is in good condition and you also want a warmer house or a better EPC. On bill savings alone, a top-up from about 100 mm takes decades to pay back, so the case is strongest when it is done alongside other loft work.

Can new insulation go on top of old insulation?

Yes, if the old layer is dry, clean and reasonably even. If it is damp, contaminated or badly compressed we recommend removing it first.

Which way should the top-up layer run?

Across the joists, at right angles to the first layer. That covers the tops of the joists, which otherwise let heat escape along the timber.

Can I still store things in the loft after a top-up?

Not directly on the insulation. A 270 mm layer stands well above the joists, so storage needs raised boarding on loft legs.

Where we provide a loft insulation top-up

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.