Our insurance company required us to replace the roofs on our rental and on our primary residence
Our insurance co. required us to replace the roofs on our rental, a 1985 Jim Walter home, and our primary residence, a hand-built log cabin. Our question is what is the best ridge vent, and is there any reason to put something like GAF Deckarmor above the new above – roof insulation?
The rental has two upstairs bedrooms that were unusable due to summer heat. The largest sq. ft. of the roof faces south, at about the perfect angle for a solar collector. The builder used Kraft faced 6 x 24 fiberglass, gable vents, and soffit vents without any air channel to the peak. Squirrels degraded the insulation ( from our point of view), and there is no vapor barrier between the insulation and sheetrock.
We laid down 3 1/2″ of paper/ fiberglass backed polyisocyanurate on top of the one layer of fiberglass shingles, ripped 2×4’s and secured them to the existing rafters with 8″ hardened pole barn nails ( not many misses) and then came across horizontally with 1×4 pine strapping or purlins on 18″ centers, and then Kynar finished metal.
At the soffit we put painted galvanized 1/4″ hardware cloth across the entire horizontal length. We had to make an edge all around, 4″ for the height of the polyiso and existing shingles, 1 1/2″ for the 2×2, 3/4″ for the strapping. The drip edge and a piece of 7″ wide trim cover the new height and disguise the mesh opening without blocking the continuous 1 1/2″ opening.
We studied the internet (local contractors were kind but ignorant, in the best classic, not perjorative sense) and found most help from this site.
The ratios for attic ventilation did not apply, and it seems that the opening at the ridge must be smaller than the combined soffit vents, to prevent backflow (or downflow).
The log house is similar but steep – 12 in 12, and 19 in 12, about 4,000 ft of cedar shakes that are about 2 1/2″ thick which we are leaving on.
It seems to me that a lot of the baffles I see on the market defeat the purpose. We have the ridge caps but haven’t put them on yet, construction is slow with two 65 yr. olds.
Thanks for reading!
Chip Chandler
Carlton Ga. ( north Ga.)
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Replies
Chip,
Almost any commercial ridge vent will work. In your climate, you can't really choose a bad product. (Some ridge vents let in a lot of wind-blown snow, but snow entry through your ridge vent won't be much of a problem in Georgia.)
You've added about R-19 or R-20 of polyiso to one of your roofs. That should help. Are also going to be removing and replacing the squirrel-damaged fiberglass with something else?
You didn't really describe your plans for the log house. If you want to add ventilation channels to the roof assembly on your log house without affecting the roofing, you will, of course, have to do all of the work from inside. Here is a link to an article that may help you:Site-Built Ventilation Baffles for Roofs.
Thanks, Martin,
the log house is going to be the same - I meant that the 24" shakes would stay on and the polyiso added above. We can't work from the inside without a complete rebuild. It has round peeled rafters, then 1" roughsawn lumber, a vapor barrier, then another dimensional rafter above the first with fiberglass between each rafter, then 1x4's 4" o.c., then the shakes with 18" strips of perforated 30# felt between each shake course. We thought about removing the shakes and did a trial on 400 sq. ft. over the kitchen, half pitch, and it took 6 hours to remove the shakes, one at a time, and nails. We salvaged about 50% of the shakes that can be used again on a horizontal wall. So regarding the squirrels we are thinking about dense pack cellulose or fiberglass put in through the roof peak when it is opened up.
What did you think about a membrane over the polyiso and under the metal? Necessary or not with the underlying existing roof covering left on?
Thank you,
Chip Chandler
Chip,
As far as I know, roofing underlayment (either asphalt felt or synthetic roofing underlayment) is a code requirement. I think that it's a good idea to install roofing underlayment above the rigid foam and below the metal roofing.