Should a 2"gap be put between rafter vents in a continuous vent channel for cathedral ceiling

Question

The product I will be using is called accuvent cathedral vent. Installation instruction on Owens Corning raft-r-mate says to leave a 2" gap between panels "to allow moisture to escape more readily into the air channel". The manufacture of accuvent and the suppliers said to overlap the joints, but I was not confident in there knowledge. Any recommendations?

Thanks,

Kevin

Answer 1

Hi Kevin,

I wouldn’t leave any gap between the panels and I don’t understand why would they recommend such installation (I found the manual that recommends that (page 2) - http://roofing.owenscorning.com/docs/raftrmate/Unheated_Attics.pdf (same as yours, I just noticed your link )

 

There are a couple of issues with gaps between the baffles that I can see:

1. Since after insulating and drywaling the ceiling you have no access to the roof decking, no way of monitoring it, any roof leakage could seep between the panels into the insulation and onto the drywall ceiling. With overlapping panels, so the upper one is under the lower one (like a gutter), it would all drip into the soffit. By occasionally monitoring the soffits you’d be able to trace that rafter space and look for the problematic roof surface area without getting your ceiling damaged.
    
2. Gap between the panels could cause temperature differential (Owens Corning recommends spacing the insulation in that area as well) and condensation buildup that could soak the insulation, cause mold growth, and result in ceiling damage.

Check this pdf, last page - http://www.buildingscience.com/documents/published-articles/pa-crash-course-in-roof-venting 

“The AccuVent soffit insulation baffle is made of rigid recycled plastic. It’s more durable than other foam-based products and installs quickly with staples. These baffles should still be air-sealed with spray foam,…”

And this one: http://blog.tayriverbuilders.com/2011/07/testing-accuvent-cathedral-baffles.html

“When installing the baffles, start at the ridge and work your way down, overlapping the baffles as you go. This will direct water leakage out of the cavity and into the soffit. Tell the homeowner to periodically check for signs of water leakage in the soffit.”

Let me know if you have more questions, just click "comment" below.