Flat Roofing Across Hampshire

Box dormers: Hampshire's most common flat roof problem

Thousands of Hampshire lofts were converted with a full-width rear box dormer. The dormer top is a flat roof, usually felt, usually a cold deck, and usually with barely any fall to it. Water sits there, the felt splits at the perimeter or where it turns up the cheeks, and the ceiling of the bedroom below is the first to know about it.

Replacing a dormer top properly means re-forming the fall, upgrading to a warm-roof build-up where headroom allows, and taking the membrane correctly up the cheeks and behind the cladding rather than stopping it at the trim.

Cold deck to warm roof

A cold deck relies on ventilating the void between the ceiling and the deck. In practice that void is usually blocked by insulation stuffed between the joists, so warm moist air ends up condensing on the underside of the deck. The homeowner sees damp and assumes a leak, but the roof was never actually leaking.

Rebuilding as a warm roof — insulation above the deck, membrane over it — clears the problem up entirely and brings the extension or dormer up to a standard that meets current building regulations expectations for renovation.

Drainage and the details

We check that outlets are sized and sited at the low point, that any parapet has an adequate upstand and a proper coping detail, that abutments are chased and flashed rather than just sealed, and that the perimeter trim is fixed to resist wind uplift. These are the bits nobody ever sees — and everybody ends up paying for eventually if they're skipped.