Oak pegs have been used for many hundreds of years to provide a stable way of holding a clay peg tile on a roof. This also allows for easy maintenance as the tiles are not physically nailed on – they are merely supported from slipping. The use of plain steel nails was common during the later part of the 20th Century and we are now seeing the impact of this with significant numbers of roofs requiring substantial repair projects. Unprotected steel will corrode when exposed to air and moisture. As it rusts, it expands. This causes the top of the tile to fracture in worst cases or at least for the tile to slip when the nail completely corrodes. Either way, the roof covering is at risk. The repair is very easy – the steel nails simply need to be taken out and replaced with galvanised clout nails. However, this does involve stripping the roof, causing disturbance to ridge and hip tiles, lead flashings and gutters etc. Damaged tiles will need to be replaced, but the rest of the tiles should be able to be re-used. It is certainly something to look out for on peg tile roofs.