Colin wanted me a build a lean-to greenhouse on existing walls at his farmhouse. The roof would need to be low-pitched to fit under the existing barn but robust enough to cope with all the water coming off the barn roof as well.
This is an exposed spot - high winds, horizontal rain, snow loads all have to be catered for...so the roof windows have upstands to ensure a tight seal, I installed a lean flashing far under the tin shed roof and constructed with 4x2 structural grade timber for the rafters with noggins and a post to give greater stability and strength.
There are also no flat surfaces for wall to sit on. Rather than a timber wallplate or cill everything is vertical and I laid Ruabon red clay tiles for a cill on completion to push water away from the structure and wall.
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