How Should You Insulate After Removing Spray Foam?

Check the timber before covering it

Foam removal leaves rafters, battens and felt exposed for the first time in years, and that is the moment to inspect them. Insulation of any kind is only as good as the roof beneath it. We read the timbers with a moisture meter, look at the underside of the covering for leaks and stains, and repair or replace anything damaged. Putting new insulation over damp wood repeats the original mistake, which is why this step comes first and why we photograph it so you can see the condition for yourself.

It is also the time to deal with the roof covering. Slipped tiles, perished felt and failed flashings are far easier to put right with the loft open, and a repair done now saves opening the new insulation later. If the covering has little life left, it may make sense to combine the work. Our page on re-roofing a spray foam roof explains when that stacks up.

Option one: a cold loft

The traditional answer is insulation laid between and over the ceiling joists, with the roof space above left cold and ventilated. Mineral wool is the usual material, laid in two layers, the second across the first, to a depth that meets the current standard for the property. The roof then dries naturally, because air enters at the eaves and leaves at the ridge or through tile vents, as it did before any foam was added.

Details matter. The insulation must not block the eaves, where a vent tray or spacer keeps a channel open. Pipes and tanks in the cold space need lagging or protecting from frost, and the loft hatch needs insulating and sealing against warm air rising. Gaps around light fittings and cables are filled so humid air from the house cannot get up. This is a cheap, forgiving build-up, and it is what we usually recommend where the loft is only used for storage. Our guide to warm loft versus cold loft weighs the two approaches.

Option two: a ventilated or breathable warm roof

If the loft is a living space, or storage you want to keep warm, the insulation has to sit at the rafters. The safer method uses rigid boards, such as PIR, fitted between the rafters and over them, with a ventilated gap above or a roof membrane designed to let moisture through, depending on the build-up. Each layer needs to suit the others, because a vapour-tight layer in the wrong place can trap moisture exactly as foam did. A design is only as good as its detailing at the eaves, ridge and hips.

Where the roof covering is also being renewed, the insulation can go over the rafters under new battens, which keeps the rafter space clear and dry. That is a bigger job, and its cost reflects it. See spray foam alternatives for the other materials and when each makes sense.

Building Regulations and the rest of the roof

The Planning Portal sets a test for re-roofing: work touching under a quarter of the building envelope and under half of the roof generally sits outside building control. Beyond that, approval is required, and because a roof counts as a thermal element under Approved Document L, you may be asked to upgrade the insulation across the entire roof. Removing foam and adding insulation in one loft is a different thing from re-covering the roof, but if the two go together the thresholds may apply, and where an application is required we put it in for you. Your building control body, either the council or a registered building control approver, can confirm in your case.

Cost and disruption differ between the two routes. Mineral wool at ceiling level is the cheaper job and can usually be done in a day for an average loft once the foam is gone, with no change to the roof covering. A warm-roof build-up costs more, takes longer and needs more detailing, so it is worth the outlay only where you want the loft space heated. We lay out both in the survey so you can compare them on the same page.

One more point to settle early is access and storage. A cold loft with deep insulation needs raised boarding if you store things up there, so the insulation is not squashed, and it is better to plan that now than discover it later.

What we do

We remove the foam, check the ventilation and talk through the options with the numbers in front of you. Because we are roofers, we look at the timber and the covering as well as the insulation. A common fear is being left with a bare roof, so we plan the re-insulation before the foam comes out and agree it in writing with the price.

Start with a look at what is there. The method for taking the foam off is on our spray foam removal page, and the overall service is on our spray foam hub. Where the loft suits a light specification, we will tell you, and we will not recommend a heavier specification than the loft needs.