Does this window strategy need flashing?
I have 2″ polyiso with foil-taped seams on the exterior of my 1,500-sq.-ft. new construction home. The jambs are all papered and the windows will be low expansion foamed on the inside. I have the window flanges on the foam, with long roofing nails driven through the foam. The window flanges are taped to the foam with Gracie Vycor Plus. There are 1×3 furring strips/strapping horizontally on the house which will be covered by 1×8 unfinished shiplap pine installed vertically. The windows are getting trimmed with 5/4 unfinished rough pine. The trim and the siding will be attached to the 1×3 furring strips providing an air space behind them.
So here is the question: Do I need additional flashing over the trim on top of the window? The sider wants to bend aluminum over the top of the peaked window trim (picture a New England Barn window) and insert it into the foam. He is concerned with the Vycor failing and water working up under the Vycor over the flange and into the house.
I feel that the house is sealed at the window flange-foam-Vycor junction, and that any water that gets behind the siding will drian and or dry out harmlessly due to the furring strips.
Looking for guidance. I have watched the video with Mike, head flashing the window, but the furring strips are not mentioned.
Thanks
Peter
Roxbury, CT
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Replies
Peter,
It seems to me that your question can be simplified. I think you are asking, "If I have flashed the top window flange to my WRB" -- in your case, the WRB seems to be your foil-faced polyiso -- "do I also need to install Z-flashing to protect my exterior head casing?"
The answer is yes. I agree with your siding contractor.
In a similar scenario, we flashed the head casing but didn't insert it into the foam. We used pre-bent aluminum drip cap and taped it to the strapping with Huber zip tape. We had horizontal strapping over each window so we also ran the tape over the top edge of the strapping and taped that to the foil. Maybe overkill, maybe not, but we are not losing sleep wondering about it. Incidently, after years of using Grace products (Vycor, etc.), we are now in the camp that feels bituthane and asphalt based tapes are inferior to butyl based tapes (e.g. Duponts Flex Wrap, Straight Flash, and Zip Tape).