flat roof junction with pitched roof eaves

4 Feb 2012
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United Kingdom

Looking to replace a felt covering over a flat roofed extension (4m x 5m). However, I'm unsure how the detail where the flat roof meets the pitch of the (tiled) main house roof should work.

At present the old felt is fixed to the fascia boards of the main house and a gutter fixed over it (concerned though that gutter brackets will puncture the new felt here). I've looked at other examples where flat roof coverings run up below pitched roof tiles without any guttering at the junction (the height difference between the flat roofs in this case and adjoining pitched roofs is not much, where as there is about 150mm between the top of my flat roof and top of my main house fascia board).

Which is the best option?


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When a flatty joins a pitched at eaves level i.e. no upstand then you would have a ply layboard going up the pitch of the roof the equivalent of 150mm vertically.

The high end of the ply layboard will have a cocking fillet fixed to it so that it provides a kick for the bottom course of roof tiles. The flat roofing material should go up and over this cocking fillet.

If the flatty joins lower down at fascia height then it is a case of taking the flat roof material up an upstand and onto the eaves enough to weather and then let the tiles drip onto the flat roof. Either that or dress a lead flashing down from under the eaves tiles and over the flat roof material upstand.
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