Flat roof adjoining pitched roof

31 Jan 2005
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United Kingdom
Hi all, I'm a having an extension built on my bungalow, but the new flat roof adjoins the house on the actual pitched roof.

How is this done? Are the new flat roof joists bolted to the existing rafters, with the overhang cut back? Then with the new flat roof covered is flashing run down from under the existing tiles onto the flat roof?

The reason I ask is because I'm having a loft conversion later in the year, with a dormer, and don't want any work done incorrectly that would compromise this.

Thanks in advance
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The flat roof joists should sit on the wall plate to keep the ceilings level. The deck is then run up the pitch 300mm as is the flat roof covering. The pitch roof felt then laps this ensuring that water that gets under the tiles can drain onto the new flat roof covering.

If your dormer is to be built up from the main walls (ie the wall plate) then the flat roof will need to be adapted and flashing fitted

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