Chapter 1: Why are the hip and ridge tiles loose on our Popley semi, and does the whole roof need doing?
What we find
On the estate semis, the ridge (the line of capping tiles at the apex) and the hips (the sloping joints between roof planes) were set on a mortar bed of sand and cement. Mortar is rigid and tiles are not, so as the roof breathes through winters and summers a hairline crack opens at the edge of each bed, rain gets in, and frost widens it. After enough seasons the bed crumbles and a capping tile sits on little more than habit.
You can often see it from the pavement: a tile slightly out of line, a dark stripe where mortar has dropped away, or crumbs of grey in the gutter. In the loft there may be a damp mark on the timber below the ridge or a thin line of daylight. Because the estate went up in runs, the house next door is probably at the same stage, and a gust that moves one ridge tile can move the lot.
What we fix
The tiles underneath are usually fine, which is why the whole roof rarely needs doing. We lift a sample of ridge tiles to see the condition of the bed and the battens beneath, then take the ridge off and rebuild it dry. In a dry-fix system the capping tiles are screwed or clipped to a ridge batten over a breathable strip, so nothing depends on mortar. BS 5534 asks for mechanical fixing of ridge, hip and verge parts, and BS 8612 covers dry-fix systems.
Published UK guides put a dry ridge for a semi-detached house between £900 and £1,600, with scaffold extra at £300 to £900; the exact figure goes on paper after we have been up. The job takes a day or so, and it frequently removes the need for a larger repair. Our ridge tile repairs page covers the choices in more detail.