Exposed strata of a 2 ply torch-on roof with 2” insulation

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scandimod
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Exposed strata of a 2 ply torch-on roof with 2â€￾ insulation

Postby scandimod » Mon Jan 12, 2009 3:36 pm

Thought I would post these pics for anyone considering using this type of roof, although I don’t know if it is widely used further south.

We recently cut a 3’ x 12’ hole in the roof to expose and replace an area of rotted cedar decking over the former carport that is being converted to living space. From the underside, the rot became evident while we were stripping the paint. Since the carport area had to be insulated and reroofed anyway, it made sense to cut a hole in the roof and fix the rotted area just prior to the reroof. (Why these rotted boards were overlooked during the original reroof I don’t know.)

The roofing system over the cedar decking, as exposed in the pics, is waxcraft vapour barrier, 2â€￾ polyisocyanurate insulation (ISO), 7/16â€￾ fibreboard hot mopped to the ISO, and a 2 ply SBS membrane consisting of a base sheet hot mopped to fibreboard, then a granulated cap sheet torched to base sheet. All curbs (protrusions like chinmneys, etc) and perimeters also get an extra layer of base and cap sheets, called stripping.

The ISO normally terminates over heated areas (ie at exterior walls) and transitions down to fibreboard with a wood cant strip. This also creates a built-in gutter on the drainage ends. In my case, we took the ISO up to the tapered gable ends of the house as it was easier. Terminating the ISO at the walls on the drainage ends may need a rethink, per my previous post about dripping soffits.

The more recent reroof of the former carport used something called HAL Permboard instead of fibreboard over the ISO. This allows mechanical fastening and torching of the layers without the use of hot mopping. HAL is more pricey than fibreboard but eliminates the setup costs of an asphalt kettle.


Removal of roof over rotted area for deck replacement

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Reroof of former carport and repaired area - HAL board on top of ISO, before application of 2 ply membrane

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Finished integration of reroofed and repaired area with existing roof (we roofed in a couple of new skylights while we were at it)

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johnnyapollo
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Postby johnnyapollo » Tue Jan 13, 2009 2:58 am

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