Do you need a new roof after spray foam removal?

Taking foam out of a roof does not oblige anyone to re-roof it. When the foam went onto clean rafters, or onto an underlay that can still slide a little, the whole job happens in the loft. It comes out in pieces, the wood is examined, and the tiles overhead stay exactly where they are.

This is the route we weigh up first, because it leaves your house least disturbed and costs least. It assumes the covering is healthy in its own right. A foam survey can easily turn up slipped tiles, split slates, tired flashings or a rotten batten, and each of those needs fixing whether foam is present or not. A roof that was overdue for attention before the foam went in does not become a different roof once the foam is out.

There are really two separate questions here. Will the foam come away without the covering, and does the covering deserve to remain? We answer both from pictures taken inside the roof and outside it, and you see the pictures too.

The difficult case is foam that has seeped through the overlaps in the underlay, the sheet that sits beneath the battens and tiles, or that was blasted against the back of the covering itself. It cures hard and holds like an adhesive. Tugging it from inside rips the underlay, and anything that rips the underlay is liable to shift battens and crack tiles on the way.

If that is what the survey finds, the roof is opened from the top, one section at a time. Tiles come off, the foam and glued-down felt are cleared, the rafters are inspected in daylight, and fresh underlay and battens go on before the tiles are laid again. Working slope by slope keeps rain out of the house meanwhile. On a small roof the outcome is a re-roof in all but name. On a larger roof it might only be a couple of slopes.

RICS cautions in its consumer guide that stripping the foam could do harm to the timbers beneath. That is a good reason to decide with the roof in front of you instead of guessing from the garden.

Tiles and slates in good order can be stacked and relaid, but foam clinging to the underside of a tile seldom lets go without a fight. Expect some breakages, and expect the survey to say whether matches are easy to buy. Modern concrete tiles are simple to replace. Old clay, handmade tiles and natural slate are not, and that shifts both the method and the final total.

Where the covering is already tired, a strip is a sensible moment to renew the covering instead of relaying tired material. On concrete tiles, Marley's figure is a life of about 60 years, though the same page calls it no guarantee. Age is only a clue. Condition is the test, and we would sooner tell you a sound roof can go back on than sell you cover you do not need.

Our answer on when a roof is due for replacement lists the signs we look for, and the spray foam insulation removal page explains the service as a whole.

Relaying a covering counts as roof work, so the usual thresholds apply. The Planning Portal's rule of thumb is that no building control application is usually needed when under 25 per cent of the building envelope, and under 50 per cent of the roof, is touched. Stripping the lot goes beyond the roof half of that test. Arun District Council also names the replacement of roof coverings among the alterations on its approval list, so put the question to its building control team.

Two more triggers are worth knowing. The Planning Portal also brings approval into play for a covering that makes the roof 15 per cent heavier or more. And once the renovated area passes 50 per cent of the roof surface, Approved Document L 2021 can ask for the insulation to be improved, towards 0.16 W/m²K where the roof is now worse than 0.35. We explain the notification and handle it where the work is notifiable. Our page on re-roofing and the Building Regulations goes into more detail.

What makes a strip dearer comes down to access, covering and area. A full strip usually needs scaffolding, and scaffolding across a pavement needs a highway licence, issued by the council. West Sussex County Council issues it and wants a minimum of 10 working days' notice, so allow for that early. Then there is the covering itself, with new underlay and battens, and the number of slopes being lifted.

You receive a written quote after the survey, giving one total price. When you compare prices, see whether each one includes VAT and the scaffold. If part of the work is insulation, the VAT turns on whether it is supplied inside one job or separately, and the quote says which applies to yours.

Pictures of the foam, the underlay and the timber travel with the quote, so the case for a strip can be seen and not merely claimed. Our answer on removing foam without stripping the roof covers the lighter route.