Vented SIP roof — fascia detail
jackofalltrades777
| Posted in Green Building Techniques on
Trying to find a photo or a detail of a vented SIP roof fascia area. Typically they use 1x or 2x furring strips on top of the SIP and then the layer of sheathing and roofing material. How the fascia gets finished is something that is hard to find. There is a 1″ or 2″ vent gap there so how does that all come together?
I did an internet search and could not locate any such detail.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Search and download construction details
Replies
Peter,
The GBA detail library has a detail for this situation; here is the link: SIP - Backventing of Roof Cladding.
To me, this detail is somewhat unsatisfying, however.
If I were strapping a SIP roof with 2x4s to create a vent channel, I would simply continue the 2x4s vertically at the sub-fascia, creating short vertical furring strips every 24 inches. Then I would install the fascia on these vertical furring strips. That brings the ventilation openings down to the soffit, where they belong. A conventional ventilated soffit would allow air to enter the ventilation channels.
Peter,
Lucy Foxworth posted links to a couple of vented roof details in another thread. This one shows one variant on venting at the eaves:
http://www.jlconline.com/rooftop-accessories/retrofitting-an-insulated-cold-roof.aspx
Malcolm,
Do you have a link to the Foxworth details??
Peter, she included three links in her comment (#14) on this blog by Martin:
https://www.greenbuildingadvisor.com/articles/dept/musings/how-install-rigid-foam-top-roof-sheathing
The link to the fascia venting is in my post above.
Malcolm,
The problem is that all of that blog is now locked because it requires prime membership. If you could, please repost those links here on the Q&A forum so I can access them. Thanks
Peter,
Here you go:
Insulating the roof with polyiso foam boards
Retrofitting an Insulated Cold Roof
Ventilated Cold Roof
By the way, there is a solution to the problem you identify: subscribing to GBA.
What are the pros/cons of going 24" oc vs 12" oc for the 2x4 furring strips? I assume better support of the 5/8" sheathing when going 12" oc. Any other advantages/disadvantages?
Peter,
The disadvantage is clear: if you install a 2x4 every 12 inches, the intermediate 2x4 will clog up the air channel and reduce the ventilation rate.
If your roof has 24" o.c. framing, it makes sense to install a 2x4s above each rafter, and to install plywood or OSB above the ventilation channels that is thick enough to span 24 inches.