Ice and water shield
NSFRAMER
| Posted in General Questions on
I’m doing a ventilated deep rafter cathedral.
The main path for any drying would be in the ventilated cavity.
So is there a risk to coving the entire roof in ice shield?
Or in this assembly is it better to just do the perimeter and use an artifical underlayment for the rest.
Will of course have a rainscreen and its a snap lock standing seam style roof.
Thanks!
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Replies
That should be a safe assembly as long as your venting is done properly, and it's a good idea to use extra-deep vent baffles such as Accuvent's 1 1/2" product, rather than the more-typical 1" depth. Addiing a variable permeance membrane at the interior will reduce the amount of moisture that diffuses into the ceiling, and making it airtight will help a lot as well.
Asphalt shingles and standing-seam metal roofing are also impervious so a full I+WS covering isn't very different from a typical roof assembly.
Excellent, thanks boss!
Yeah I'm going with a 2" ventilation cavity using 1/4 plywood to form the cavity. 2" extension on 2x12 raters to allow for r40 fiberglasd with I" foil faced polyiso underneath to form the vapour barrier. 2x4 strapping with low profile led pot lights so nothing penetrates the barrier.
Intello plus for the walls with r20 batt and 3 inches eps continuous on the outside to prevent dew point on osb sheathing. Its on a thicken edge frost protect slab with 15mil stego vapour barrier that will be brought up the side and under the sill to tie into the intello plus.
NSframer,
There is no downside to covering the roof with an impermeable membrane besides price. I'm not sure it adds much that a good synthetic underlayment doesn't though.