Loft insulation installation and top-ups
We install loft insulation to the recommended 270mm using Knauf Earthwool Loft Roll 44, laid between and across the joists. Every installation includes eaves ventilation, hatch insulation and pipe and tank insulation where needed, because insulating the loft floor without ventilating the roof space is how you end up with condensation.
What we install
Knauf Earthwool Loft Roll 44
A glass mineral wool roll with a thermal conductivity of 0.044 W/mK. It is the standard product for loft floors, it does not itch like the old yellow stuff, and it is made with a high recycled glass content. We lay a first layer between the joists (usually 100mm) and a second layer across them to bring the total to 270mm.
Knauf Supafil 40 blown insulation
Where the loft is awkward, very shallow at the eaves, or where rolls cannot be laid properly. Blown fibre fills the gaps rolls leave.
Celotex XR4000 boards
For the back of the loft hatch and for anywhere a rigid board makes more sense than roll.
Climaflex pipe insulation
On every exposed pipe, and a jacket on the cold water tank or cistern.
Klober eaves vent trays and felt lap vents
To keep the roof space breathing.
Why ventilation is part of the job
The moment you insulate a loft floor properly, the loft gets colder. Warm, moist air from kitchens, bathrooms and breathing still rises through the ceiling, and when it meets cold felt it condenses. Left alone, that causes damp timbers, black mould on the rafters and water dripping onto your new insulation.
Eaves vent trays
Rigid plastic channels fixed between the rafters at the roof edge. They hold the insulation back so air can flow in from the soffit or the gap at the eaves.
Felt lap vents
Clipped into the horizontal overlaps of the roofing felt, letting air out through the roof covering where there is no ridge or tile vent.
We fit both as standard where the roof needs them. A lot of installers do not, and we see the result when we are called in to remove wet insulation two winters later.
Pipes and tanks
A loft at 270mm is a loft that can freeze. Pipes to the header tank, overflow pipes and any heating pipework running across the loft are insulated with Climaflex. The cold water tank gets a jacket, with insulation kept away from underneath it so a little warmth from the house reaches it. Since you have a nicely insulated floor, the last thing you want is a burst pipe at two in the morning in January.
Our process
Survey
We measure the loft area and existing depth, check the eaves, the felt, the pipes, the tank, the hatch and the wiring. If there are recessed downlights, we note them because they need clearance or hoods.
Quote
Written, itemised: insulation, eaves trays, lap vents, pipe and tank insulation, hatch, and any boarding you have asked for.
Install day
Sheets down from the door to the hatch. We fit the eaves trays first, then lay the first layer between joists, then the second across. Pipes and tank next, lap vents where needed, hatch insulated and draught-stripped. Downlights hooded. Cables lifted above the insulation where possible.
Document
We photograph the finished loft with the depth confirmed by a tape in shot, and give you your completion paperwork. A normal three-bed semi is done in a few hours.
IAA-backed guarantee
Loft insulation we install carries an IAA Able To Pay guarantee, issued through the Insulation Assurance Authority, covering materials and workmanship. The IAA offers loft guarantees in 2 and 6 year terms; the term that applies to your job is stated on your written quote and in your paperwork.
Cost and 0% VAT
Guide prices, with VAT at 0% until 31 March 2027 and 5% after that:
| Job | Guide price (0% VAT until 31 Mar 2027) |
|---|---|
| Top-up to 270mm, 3-bed semi | from £500, typically £550 to £850 |
| Full install to 270mm, terrace | from £600, typically £650 to £900 |
| Full install to 270mm, semi | from £750, typically £800 to £1,100 |
| Full install to 270mm, detached or bungalow | from £1,000, typically £1,100 to £1,500 |
| Eaves vent trays and lap vents | from £5 each fitted; typically £150 to £300 for a semi; included in a full install where the roof needs them |
| Pipe insulation | from £6 per metre |
| Cold water tank jacket | from £60 |
| Draught-strip and insulate an existing hatch | from £60 |
| New insulated hatch fitted | from £180 (20% VAT unless it is needed for access to the insulation) |
Materials and labour are included. The written quote after your free survey is the one that counts. Prices as at October 2026.
Full insulation price guideGrants
Loft insulation is one of the measures funded under the Warm Homes: Local Grant for eligible households. The council runs the scheme and appoints the installer. Our guide explains who qualifies.
Warm Homes: Local Grant guideFrequently asked questions
Can you top up existing insulation?
Yes, if the existing material is dry, clean and reasonably even. We lay a cross layer of Earthwool over the top to reach 270mm. If what is there is wet, flattened or contaminated, we recommend removal first, and we can do both in one visit.
Do you insulate the hatch and tanks?
Yes, on every job. The hatch gets a board of rigid insulation and a draught strip. The cold water tank gets a jacket, and all exposed pipes are wrapped. These are small items that make a big difference and are easy to forget.
Will it make my loft damp?
Not if the roof space is ventilated, and that is why we fit eaves vent trays and lap vents as standard. A well-insulated loft without ventilation can get condensation; a well-insulated loft with ventilation stays dry.
Is loft insulation free?
For some households, yes, through the council-run Warm Homes: Local Grant. You need to meet the eligibility rules and the council appoints the installer. For everyone else it is one of the cheapest home improvements you can make, and VAT is 0% until 31 March 2027.
How soon will I notice a difference?
The first cold evening. Upstairs rooms hold their heat longer and the heating cycles less often. On the bill, the Energy Saving Trust's figures are conservative for a top-up and much larger for a loft that had little or nothing in it.
Book a free loft survey
Ten minutes in your loft and we will tell you what you have, what you need and what it costs.