What are the parts of my roof called, and which ones fail?

Being able to name the parts of a roof changes two things: you can describe a problem accurately when you phone a roofer, and you can tell whether a quote is addressing what you actually saw. Most of a roof is visible from the ground with binoculars and from inside the loft with a torch, and most of the failures have distinctive signatures.

Safety

What you'll need

• Binoculars
• Head torch
• Crawl boards for the loft
• Camera with zoom (optional)

Step by step

1. Start at the ridge.The tiles along the apex, traditionally bedded in mortar and on modern roofs fixed mechanically with a ventilated dry ridge roll. Mortar cracks and washes out over decades; a loose ridge tile is both a leak and a falling hazard, and it is a common and relatively cheap repair when caught early.
2. Look at the tiles or slates.They are hung on battens by nibs or nails. Individual units slip when nibs break or nails corrode, and a slipped one exposes the underlay to sun and weather. A patch of a different colour usually marks a previous repair.
3. Understand the underlay.Under the battens is either old bitumen sarking felt, which is impermeable and eventually goes brittle and tears, or a modern breather membrane, which lets vapour out of the roof space. The underlay is the actual weatherproof layer once a tile is missing, so its condition is more important than most people realise.
4. Look at the eaves.The fascia carries the gutter, the soffit closes the underside, and the underlay should be dressed over the fascia into the gutter. Underlay tucked behind the gutter drips into the eaves instead, and this is a classic cause of rotting rafter feet and damp at the top of a wall.
5. Look at the verge.The gable end edge of the roof. Traditionally mortar-bedded and prone to cracking and falling out; modern dry verge systems clip on. Open mortar at a verge lets wind and rain under the tiles.
6. Find every flashing.Lead or an equivalent at chimneys, at abutments where a lower roof meets a wall, around soil vent pipes, and around roof windows. Flashings leak far more often than tiles do, and a cement fillet where lead should be is a guaranteed future problem.
7. Find the valleys.Where two slopes meet, water from both is concentrated into one channel. Lead, fibreglass or a tile valley. It carries more water than anything else on the roof, so a valley that is blocked with moss or has a failed lining leaks badly.
8. Go into the loft and look at the same roof from inside.Daylight through the covering, staining on the rafters, wet or rotten rafter feet at the eaves, torn or sagging underlay, and where any of it lines up with what you saw outside.
9. Write down what you found before you call anyone.Which elevation, how far along, what it looks like, and a photograph. That turns a vague call into a specific one and makes quotes comparable.

Tips

• Binoculars and a phone camera at full zoom, used from two different angles on the ground, show almost everything a roofer would see from a ladder.
• Moss on a roof is mostly cosmetic, but a thick mat holds water against the tiles and blocks valleys and gutters. Scraping or jet-washing tiles does more damage than the moss does.
• A roof that has been patched repeatedly in different materials is telling you something about its remaining life. Ask a roofer for a view on the covering as a whole, not just the patch.

Common mistakes

• Judging a roof only by whether tiles are missing — The tiles are the most visible layer and among the least likely to be the problem. Ridge mortar, flashings, verges, valleys and the underlay account for far more leaks.
• Getting onto the roof to look — The roof is not a working platform. It is also the case that whatever is loose enough to be a problem is loose enough to move under your weight.

Questions people ask