Roof Structure: Getting Your Extension Watertight
PremiumHow the timber roof frame goes onto your extension: wall plate, rafters, ridge, and warm roof insulation. Covers cut roofs vs trusses, the ridge beam vs ridge board distinction that catches builders out, warm roof construction, and what building control inspects before you cover anything up.
Do this first:
Your roof structure is the single biggest milestone in the build. Once the timber frame is up, the breathable membrane is on, and the covering goes over it, your extension is watertight. Internal trades can start. The clock on weather damage stops ticking. Everything before this point is exposed. Everything after is protected.
Which makes the quality of this stage non-negotiable. A sagging rafter, a wall plate that's 15mm out of level, or the wrong timber grade might not be visible once the plasterboard goes on, but building control will catch it if you don't. And if they don't catch it before the roof is covered, they can require you to strip it back.
Your walls must be at plate height with the wall plate bedded and strapped. Your structural steels must be in position, including any steel ridge beam. If you're having roof windows (Velux or similar), order them now if you haven't already. Lead times run 8-10 weeks and your carpenter needs the exact dimensions before cutting trimmer openings.
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