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This is the situation: We have a flat concrete roof with (from bottom to top) bituminous sheet, insulation, bituminous sheet. There's a blower to be set onto the roof, blower has a stand with a broad flange (only one side drawn):

enter image description here

My question is, how to connect the upper sheet to the blower stand? Due to thermal expansion, there will be movement between the insulating layer and the blower, so simply glueing the sheet to the blower will tear soon.

How to do the connection?

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  • $\begingroup$ Have you asked a roofing company / contractor / installer? $\endgroup$ – Solar Mike Mar 8 '18 at 8:16
  • $\begingroup$ Actually, the first idea of the roofing contractors was to build a structure so the stand is above the level of the upper sheet, this had to discarded - we could have one built from metal, but I would prefer another solution. $\endgroup$ – mart Mar 8 '18 at 8:38
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You should attach a galvanized sealed flange to the duct like an apron hanging down 3 inches going around the duct like a ring.

Then you use a 2x2 angle galvanized flashing pasted to your roofing by roofing mastic. The vertical lip of this flashing will runn inside the apron skirt which is hanging down, and it will be free to flex a little there.

This is the typical detail for moderated climates.

 flashing detail.

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