I am not a pro but I have built or remodeled a half dozen homes in the past. Here is my question. I am helping remodel a story and a half home with a bedroom in the atic. The homeowner who will remain unnamed aka my little sis was told that she needs rafter vents at the local home center.
I am planing to remove all of the insulation, there was not very much to start with 50 year old tar paper and mostly dust!. install new fiberglass batts between the 2×8 rafters, install vapor barier, build a couple of knee walls, rock. and skip the rafter vents.
95% of the time I would insist on rafter vents but in this house there is the fashia and then siding. No soffit to install vents in. Second since the insulation is going between the rafters I am going to be losing more R value than benifits gained from a 1″ air chanel I assume?. Third probally 85% of the vloume of the atic will living space so why bother trying to vent that little space. Finally it looks like the ridge vent is only cosmetic.
So whats your opinion?
Replies
Not an expert, but I think you need the vent space for two reasons. FIrst to allow mositure to move up and out of the rafter cavity. Secondly, to move the heat. Without the venting the roof deck cooks, and your shingles (assume asphat) degrade. I have seen many cases of shingles just curlly right up. Not good.
Without having adiquite airflow I just don't see the the deck temp being lowered enough to make a diference in the life of the shingles. A couple of my freinds have homes made of sip's (structural insulated panels) and shingle life is 25 years plus. Shure if I could figure out how to get a vent into the fascia it might work. The roof is a 12 12 pitch and I dont see the roof having problems with leaks so the only source of moisture would be from the interior and as long as i do a good gob on the vapior barrier the problem should be eliminated. By the way the house is in Milwaulkee.
right, with a high r-value and good Vbar, the ventilation can be dispensed with. Some local codes require it still though.
One way to do this is to place the FG insulation and then apply a 1" Thermax ( foil faced foam sheathing board) to the underside of the rafters and foam and tape all the joints and penetrations..
Excellence is its own reward!
if there are not any eave vents then there would not be any point in installing the rafter vents. That is assuming that the insulation carries all the way down to the fascia. I would be more concerned with venting the attic space above the room. However if there are no eave soffit/eave vents now and there have not been any problems, I don't see where adding them would help.
Ok. I guess you did not need to ask the questinon, then.
However, I think I have seen 3 inch round soffit vents which you just drill a 3 inch hole in the soffit and push it in. Or was your problem that there was blocking between the rafters at the wall?
The problem is he has no soffit to install vents in, round or otherwise.
I guess going between the (covered) rafter tails or ends would look funny.
Assuming you live in a climate where vents are nice to have - you could kill two birds with one stone and use 1" pink styrofoam for your baffles. That's what we did in our loft. It loses some heat, yes, but not much. You get an R value of 5 with the vent, that way.
Instead of those cheap, flimsy baffles you get at your local home store, use 3/4 or 1" styrofoam. Cut it to the rafter bay size, put a couple of strips of styrofoam on top as spacers, (We went with 1 and 1/2 inches.) and screw or glue them in place. Finish up with some of that "spray foam" on each edge of the baffle, where the styrofoam isn't cut perfectly, and you're in business.
By the way, here in Minnesota, they claim you need at least 1 and 1/2 to 2 inches to have enough airflow to make vents effective.
Yes I like your idea, but how get enough of a opening at the ridge and fascia to make this work? remember no soffit, no overhang. I am from Mn and painfully aware of the problems that occur with ice dams. The best thing about this roof is that without a overhang the deck temp will be somewhat even. So if snow melts the water will not refreaze on a cooler overhang.
Vented metal drip edge is available for this situation, but it is hard to retrofit to an existing roof (easy to install in a reroof).
Officially speaking, you should ask your inspector what they will want to see... since WI's code (Comm 21.05 (3) and Comm 22.08) requires that the attic ventilation be there, they might insist on it. If you're using a suitable technique (like sprayed in foam) they may overlook the venting requirement but just saying that you're going to make sure to do a good job of sealing up the VR is probably not adequte.
And even if you're not pulling permits and having it inspected, it's probably not a good idea to do things that violate the local code.
It looks like to meet code they added a ridge vent when they reroofed but failed to cut away the decking to complete the job. Hey it looks good from the road. And before the bedroom was added there was windows on both ends of the attic for cross ventilation. I would rather just have vents installed in the end walls and add more insulation on the ceilings.
here in the very humid south it has been suggest that soffit vents do more damage than good. by letting the moisture into the attic space. they suggest that lock the attic up tight and just let it cook as long as efficent insulation is in the ceiling layer. This was a study done by some fla university. They also suggest getting away from the black asphalt shingle in which would lower the attiv temp some.
There are also places out here where soffit vents are forbidden because they'd potentially let fire enter the attic.
-- J.S.
The newest version of the IRC doesn't require roof venting as long as the layer of insulation applied directly below the structural roof deck is air impervious (read spray foam). Your jurisdiction may not have adapted the new code yet, and as in Florida, it may reject this particular provision. Even so, it's an argument to use with the inspector. Also, shingle warranties may require venting. (On the other hand, I've heard lots of folks say that shingle warranties aren't worth a bucket of warm spit, so make your own call here.)Andy Engel, The Former Accidental Moderator
My experience with shingle warranties is if the homeowner goes it alone, the manufacturer will try to weasel out on them. If the installer is standing beside the homeowner when they come to do their inspection, they tend to give what it takes to make the HO happy. A pissed-off installer is not gonna use their product again. I haven't been in one of these sqaubbles for 5-6 years, so things may have changed, but I've seen three different manufacturers react basically the same way.