insulating cathedral with lookouts

Started by JeffnTN, January 07, 2005, 10:33:14 PM

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I have lookouts supporting the barge rafters and now am wondering how to handle the attic vent channels....

Do I ignore the vents on the end bays or try to drill them...   Roof is on...    Hate to weaken the lookouts now.....


I believe your vent guy is going to lose over the structural guy in this arm wrestling contest with a slight concession the to insulation guy. Consensus of their opinion might be to run it around the lookout with a little selective massaging with your hammer tacker to flatten the bump the vent channel makes.
Of course we could all start paying attention to vapor retarder detail in our ceiling assemblies and forget the vent channel... naw that's to hard.

Ryan B


Thanks for the reply,  But I AM The Vent Channel Guy, and the Framer and the insualtion guy and the trim guy and the tile guy, and flooring guy.and the painter etc....

Any input?


Vapor retarder (according to my EXTENSIVE RESEARCH)  are NOT  neccessary  AND MAY BE HARMFUL where I live since I am in a dual climate.


My thoughts on vented roofs.
Hot day – vents cool the roof until the underside of the sheeting rises to the same temperature as your roofing
Cold day – vents cool the roof, this helps reduce ice dams.
Any day – vents allow outside air to the underside of the roof sheeting, this has been shown to transfer snow and water vapor to the underside of roof sheeting. Its kinda neat looking when it pours out of the lower vents unless your unlucky and it drains down to the inside of the walls.

I haven't mentioned water vapor and or heat that comes from the inside of the house because in a properly detailed ceiling assembly no water vapor and or heat should enter the roof area. Of course this takes a lot of detail work and insulation so most code/design books have come to the belt and suspenders approach of dealing with water vapor infiltrating ceiling assemblies.  Prevent it, but if it gets in there, vent it.

As to your vent channels that fasten to the underside of the sheeting, just run the channel over the lookout and continue to the top. The slight loss of insulation depth as the channel passes over the lookout shouldn't be noticeable. Of course if you're in an area that venting is not required you could detail the ceiling and eliminate the vents.


Ryan,  no code here.  Just trying to build it right.

We get some snow but nothing major lately..  

Have a metal roof (12/12) so ice dams are not a real problem..  

It usually gets blown off before it can accumulate.  

Very windy here at the end of the vallley at the edge of the Cumberland Plateau.



Is the metal roofing not providing the vent channel?  Photo DCP01628 looks like air would travel nicely over the gable end lookouts.


The Lookouts are set in the top of the rafters so that the roof sheathing is flush with the top of the lookouts, aka (outriggers)  My problem was how to get the rigid plastic attic vent channels to conform to go over the  1 1/2"' lookouts  that were in the path of the attic vent channels in the end rafter bays.

I tried a few different things.

what worked best was just tacking some 7 inch long by 1 1/2" tall wedges to the four edges of the rafter bay next to each lookout  (outriggers) and stapling the vent channel down over these.

This worked out fine.  I tried cutting and piecing first to form an overlap but it was worthless.  The wedges did the trick.