Why do roof tiles slip and how are they refixed?

Why do roof tiles slip and how are they refixed?

Roof tiles slip because the thing holding them in place has failed. A tile is held by a combination of small nibs hooked over a timber batten and, on most roofs, a nail or clip fixing it to that batten, and when the nails corrode, the nibs break, the battens rot or the mortar on a bedded tile crumbles, gravity and wind do the rest and the tile slides out of position. The single most common cause is old ferrous nails rusting through, a condition roofers call nail sickness, which lets tiles work loose one by one across an ageing roof. Refixing a single slipped tile is usually done with a lead or copper clip called a tingle, which is fixed to the batten and folded up over the tile to hold it, because you cannot simply re-nail one tile without lifting the course above it.

A slipped tile is worth taking seriously even though it looks minor, because it is rarely just one problem. It leaves a gap that lets wind under the surrounding tiles and rain onto the underlay and timbers below, and a tile that has slipped can slide off entirely and fall, which is a genuine hazard below. It is also frequently the first visible sign that the fixings across the whole roof are reaching the end of their life. The rest of this guide explains exactly what holds a tile in place, why that fails, and how a proper refix is done rather than a patch that lets go again by the next winter.

What actually holds a tile on the roof

Understanding why tiles slip means knowing what keeps them up in the first place. Most tiles have small projections on the underside called nibs, which hook over the top edge of a horizontal timber batten so the tile hangs in place. Many tiles are then also nailed or clipped to that batten through pre-formed holes, particularly along the edges, at the eaves and ridge, and anywhere exposed to wind. Interlocking tiles have shaped edges that lock into their neighbours to shed water and resist uplift. Along the ridge, hips and verges, tiles are traditionally bedded in mortar as well. Every one of these fixing methods can fail, and each failure has its own tell.

Why roof tiles slip

Tiles come loose for a handful of recognisable reasons, and often several at once on an older roof.

• Nail fatigue and corrosion. Older roofs were nailed with ferrous nails that rust over decades until they no longer hold. Once the nails go, tiles rely on their nibs alone and begin slipping. When this is happening across the whole roof it is nail sickness, and it is the classic cause on ageing properties.
• Broken or perished nibs. The nibs themselves can crack or crumble with age, especially on older clay tiles, so the tile has nothing left to hang on.
• Batten decay. The timber battens the tiles hook over can rot, split or suffer woodworm, and a failing batten releases every tile on it.
• Failed underlay. When the felt beneath the tiles perishes and tears, it stops doing its job of catching any water that gets past the tiles, so slippage that would once have been a minor issue starts causing leaks.
• Wind uplift. High wind gets under a tile edge and lifts it, and one lifted tile often starts a chain reaction along a course. This is why winter weather is so often when slippage first appears.
• Mortar failure on bedded tiles. Ridge, hip and verge tiles bedded in mortar slip when that mortar cracks and washes out, which is why the state of the ridge pointing is closely linked to tiles coming loose at the top and edges of a roof.
• Age and past bodges. Simple wear, foot traffic and previous poor repairs all contribute.

We’ve found that the roofs where tiles slip in ones and twos over a few years are almost always suffering from nail sickness underneath, and the visible slipped tile is just the first of many. These are the sort of older and period homes where the covering can look reasonable from the street while the fixings have quietly reached the end of their life.

How a slipped tile is refixed

The right method depends on whether it is one tile or a symptom of something bigger.

For an isolated slipped tile that is otherwise sound, the standard fix is a tingle. This is a thin strip of lead or copper nailed to the batten beneath the tile, with the lower end folded up over the tail of the tile to grip it in place. It is used because you cannot re-nail a single tile from above without lifting the overlapping course, and a tingle holds the tile mechanically without that disruption. Where a tile has cracked or broken, it is replaced with a matching one and secured the same way.

For a small area, the better approach is often to carefully lift the overlapping tiles, refix the loose ones properly with new nails or clips, and relay the course, which restores the original fixing rather than relying on a clip.

In our experience, refixing a slipped tile with a properly fitted lead or copper tingle works better than dabbing it back into place with mortar or a smear of sealant, because mortar and mastic have nothing structural to grip on a smooth tile and let go within a season or two, whereas a tingle is mechanically fixed to the batten and holds the tile through wind and weather. A sealant repair looks fine on the day and is usually back on the ground by the following winter.

When slipping tiles mean more than a repair

If tiles are slipping in numbers, or if lifting a few reveals rusted nails, rotten battens and torn felt beneath, the honest answer is that the roof has reached the end of its serviceable life and no amount of individual refixing will keep pace. At that point a strip, re-felt, re-batten and relay, effectively a new roof, is better value than paying repeatedly for tingles across a failing roof.

It is also worth knowing that fixing standards have tightened. The British Standard for slating and tiling, BS 5534, now requires far more tiles to be mechanically fixed than older roofs ever were, particularly around the perimeter and in exposed and windy areas. A roof relaid to current standards, working to the guidance of bodies such as the NFRC, is far more resistant to slipping than the nailed-here-and-there approach common on older properties. The same principles apply whether the roof is clay, concrete or a slate roof, though slate has its own fixing methods.

Getting slipped tiles dealt with properly

A slipped tile is cheap to fix and expensive to ignore, because the gap it leaves lets water into the roof structure and the loose tile itself is a falling hazard. The sensible response is to have it looked at, both to refix the tile and to check whether it is a one-off or the start of wider fixing failure, which is the part that decides between a quick repair and planning for a new roof.

Rated Roofers are a family-run firm with over 20 years of experience working on tiled and slate roofs across Worthing, Lancing and the wider West Sussex area, fully insured and vetted through Approved Roofers, the Roofing Register and Checkatrade. Most slipped tiles are a quick roof repair, and on a tiled roof we will always tell you honestly whether that is all it needs. Get in touch for a free, no-obligation quote and we will take a look.