Does Spray Foam Fix Slipped Tiles?

Why tiles slip in the first place

Tiles do not slip at random. Most clay and concrete tiles are held by their weight and by a nail or a clip fixing into the batten, the timber strip across the rafters that the tiles hang from. When a tile slips, one of those things has failed. The nail has rusted through or snapped, the batten has gone soft from rot or woodworm, the tile has cracked at its nib (the lug that hooks over the batten), or the tile was never nailed to begin with. On older roofs, the cause may be a sagging rafter or a roof that has moved, so the courses are no longer straight.

These are fixing and structural faults, and the repair is to deal with them: re-fix the tiles with stainless or aluminium nails or clips, replace damaged battens, and renew broken tiles. Our page on re-roofing a spray foam roof explains what is involved where foam is already in place.

What foam does to a loose tile

Spray foam expands and sticks hard to almost any surface. Applied from inside the loft, it can reach the underside of the tiles and the battens and bond them in position. A tile that was starting to slide may stop. That is the whole of the claim, and it is why some firms offer it as a fix. The tile is not repaired, only stuck.

There are several problems. The nail is still rusted and the batten is still rotten, so the underlying fault carries on, now buried in foam. The foam can pull a cracked tile apart as it cures. It fills the gaps between tile and batten that let the roof breathe. And it covers the evidence: slipped tiles can no longer be inspected from the loft, and the dampness they let in is trapped against the timber. The RICS consumer guide notes that spray foam can make a roof hard to inspect and may trap moisture against timbers.

The moisture issue deserves a second look. A tile slips because water, wind or age has worked on its fixings, and a roof that has slipped tiles has probably been letting some rain in. Foam stuck over that history seals the damp in, so the batten that was already soft stays soft, and the rot that follows is out of sight. Fixing the tile and checking the felt and batten beneath it is quicker than dealing with the consequences.

What it does to the next repair

Bonded tiles are hard to take off. To replace one, a roofer lifts the tiles around it, and if they are glued to each other and to the battens the lift tears them, snaps the nibs and cracks adjoining tiles. A job that would have cost a simple repair becomes a patch of re-tiling, with new tiles that may not match. Disposal also changes: foam-coated tiles cannot be reused, and it is a further cost to strip and sort them. If the foam is later removed, any tiles it was stuck to will often need replacing. See our guide on spray foam removal for how the foam comes off.

Some owners are told the foam adds uplift resistance, so that wind is less likely to lift the tiles. Bonding does add some grip, but a roof is meant to resist wind through proper fixing to the battens, and building standards for tile fixing assume nails or clips, not adhesive foam. A roof relying on foam has no fixing to inspect, so you cannot tell whether the tiles would stay put in a storm. If you are in an exposed spot, the right answer is a check of the fixings, not another layer on top.

What to do about slipped tiles instead

Start by finding out why they slipped. A free survey of your roof, with photographs of the tiles, the battens and the fixings, gives you the cause rather than a guess. If it is a handful of loose tiles on a sound roof, the repair is cheap and quick: re-fix them and replace any cracked ones. If the battens are failing or the nails are rusting across a whole slope, the answer may be re-battening and re-tiling that slope, which we quote at a fixed price.

If you already have foam under the slipped tiles, tell us when you book, because it changes how the repair is done. We look at the moisture in the timbers, the tile condition and whether foam needs to come off one area or more. You can see the full service on our spray foam work in Basingstoke. Whatever we recommend, we show you the evidence first, and we repair wherever repair works.