I want to add attic venting to my house. The attic is 825 square feet, and has 3 24″x 6″ soffit vents per side. There are no vents near the ridge. I don’t know what the pitch is, but it is a very walkable, not steep, gable roof with fairly worn out asphalt shingles. I was considering 2 gable end vents, but I read that they will only supply ventilation near them. Apparently, the goal is to make a “curtain” of air rising up and evenly cooling the underside of the roof.
I am trying to decide between a ridge vent, and 2 or 3 eyebrow vents per side. It seems that a ridge vent will be best, but will it be substantially more work than eyebrow vents? With eyebrow vents, it seems that you would have to “reweave” new shingles around them, which I don’t know how to do. Is a ridge vent perhaps easier?
aidenbug
Replies
Foist...a question for you.
What is the condition of the existing sheathing? Do you notice a problem with mold, or condensation?
If you've no problem to this point, perhaps it isn't necessary.
You mention the shingles are rather worn...and yet, you question if they'll need to be weaved if you add a ridge vent. I wouldn't recomend adding ventilation to a roof that may (or may not) be in need of replacement within a short period of time.
If you are planned on redoing the roof in the not too distant future, perhaps that would be the best time to address your ventilation concerns.
In general....a ridge vent, paired with continuous soffet vents is the best way to go. But you mention a shallow pitch to the roof. You may not want to have a ridge vent in that case depending on your location and weather patterns. (i.e. heavy snows, driving rains)
I would recomend you get a few roofers out to the house to give some hands on (eyes on) inspections to determine your best course of action.
J. D. Reynolds
Home Improvements
I live in Marin county, where it gets very hot-100 degrees in the summer. Snow is not an issue. I don't think that there is any mold or moisture problems. I want to do this to reduce attic temperature, I am not too concerned about reducing moisture. I don't want to reroof for at least a few years. The roof is definately steep enough not to worry about rain washing in.aidenbug
I want to do this to reduce attic temperature...
In that case, I would suggest looking into some active ventilation alternatives as opposed to the passive you are considering.
A thermostatically controlled attic fan in conjunction with soffet venting would give you the benefit of venting the space as needed, without having to disturb what sounds like a tenuous roof condition.
J. D. ReynoldsHome Improvements
The problem with the fans is that they have a limited lifetime -- 3-4 years in my experience.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
Really?
I've never had that problem. Granted....I haven't installed a ton of them....but the several I have are still going strong to the best of my knowledge.
J. D. ReynoldsHome Improvements
Finally got tired of repairing/replacing the one in my garage and installed ridge vents.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
Really?
I've never had that problem.
I should not speak for Dan, but, I'll guess that he's put some of these powered units in where it gets warmer than average.
Let's pick a place like Wichita Falls, which has almost exactly an even split of HDD & CDD. If we set the powered fan's stat for, oh, 78º--that fan in WF is going to run from July to September. It will run in daylight hours for about two, almost three more months. It will likely kick on in the afternoons & early evenings of early December and late March, too. Few of those fans are rated for quite that much run time.
I'm on just memory here, but average low temps in WF are mid 70s for June; a couple degrees more in July, and high 70s for August. The low is reached jsut about 0545-0615, as well. This leaves precious few hours to get any 'cool' air into the attic.
But, that's a guess.Occupational hazard of my occupation not being around (sorry Bubba)
I think I had the thermostat set for 85-90, which is probably lower than the factory setting (probably about 105), but I wanted to cool the open garage. It would typically run 6-8 hours/day for 2-3 months in the summer. After 3-4 years the motor would stop running, and checking it would reveal gummed bearings. So I'd squirt oil in the bearings and it would be good for another year or two. Do this 2-3 times, then replace the motor, then start the cycle over again.On the plus side it wasn't as unpleasant to climb up in the trusses in the open garage to work on the thing as it would have been to work in a closed attic. Plus, being in the garage and not in the house, the noise wasn't a problem.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
I think I had the thermostat set for 85-90, which is probably lower than the factory setting (probably about 105),
Ah, and all those poor, abandoned, wore out power gable vents I've seen with ridiculously low set point stats . . .
Makes a person wonder, what with a setpoint of 110º about the protestations of the shingle makers about "hot" roofs degrading their products . . . (gee, aren't all their UL tests done at, what, 70-72º . . . ?)Occupational hazard of my occupation not being around (sorry Bubba)
>>>>I want to do this to reduce attic temperature...>>>>>In that case, I would suggest looking into some active ventilation alternatives as opposed to the passive you are considering.>>>>>>>A thermostatically controlled attic fan in conjunction with soffet venting would give you the benefit of venting the space as needed, without having to disturb what sounds like a tenuous roof condition. I've seldom run across a power vent that is still working after 3-4 years and I once had to go into my attic at 1AM and disconnect one that the bearings went out on so the neighborhood could go to sleep. Opening up the ridge on a questionable roof would be less likely to cause a problem than cutting a hole downhill from the ridge. Only the ridge caps would be disturbed. I vote ridge vent.edited to add: I'd first look at blowing some cellulose on top of what ever insulation is in the attic now and add the ridge vent in the next reroof.http://grantlogan.net/
Edited 6/5/2007 4:49 pm ET by seeyou
If you could give us a tad bit more information, it woudl be helpful.
Is this a hip or a gable roof. Hip roof will have a much shorter "run" of ridge vent.
Region/location? Ridgevent is typically easier to install, especially if you are reroofing anyway (since you use the term "fairly worn out"). But, if you were on the windward side of a coastal hill, wind blown rain can be an issue. Lake-effect snow can be an issue, too. Living in NW Florida is an issue, too--so location matters a bit.
It will be worth a bit of your time to go browse buildingscience.com under houses that work, and look at their recommendations. You don't have to follow them, but you will be informed, at the minimum.
You can find the pitch middling easily. Go in the attic and put a speed square against a couple few rafter bottoms is pretty quick. Or, balance a level on the roof and measure down from there; dividing by the length of level in feet. (So, if a 3' level, and 13"± measurement; 13/3 rounds to give a 4/12 pitch.)
None.
Forrest
a ridge vent is easy to install-just remove the ridge caps and cut the sheathing back a few inches on each side, then install the vents and cover them with new ridge caps
http://www.hammerzone.com/archives/roof/maintenance/reshingle/install_2/ridge_vent.htm
That is what I was thinking might be the case. By the way, thanks, everyone, for your input. Also, I have about R-38 insulation in there. It is a gable roof, about 25 feet long. Once I researched it a little, it seemed like it might be less work to put in a ridge vent than 4-6 eyebrow vents.
Does anyone have suggestions for brands, or models(how much flow)? Do you just nail shingles over the vent to form the new ridge cap?Aidenbug
The molded plastic ones are pretty much interchangeable, the main difference between brands being in the baffles used -- all of course claim to be better than all others. I had Certainteed on before and now (new roof) have GAF, IIRC. Both seem to work fine.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
O.K., I just spoke to the carpenter who will probably help do it. He said that instead of cutting off the top 2-3 inches of the sheathing, which is 1x8 planks, he would drill holes-2 1.5" holes per joist bay (2' on center). He said that cutting off the top of the planks would weaken the structure, and the holes would provide enough flow. He is an excellent carpenter, a foreman with a top local company, but it seems to me that making holes would have substantialy less flow. Would cutting the sheathing really compromise the integrity of the structure?Aidenbug
That sounds like a bunch of crap. You only need a gap of about 2" total - 1" per side. If you have a 2x ridge board, the total gap would only need to be 3 1/2" total. He doesn't want to get his saw dirty.http://grantlogan.net/
Anyone else have an opinion on holes vs. cutting back the top of the sheathing? Keep in mind that it is 1x8 planks, not plywood. Would cutting out a strip at the top really compromise the strength of the structure?aidenbug
I can't see how it would. It's done every day. I also can't see how boring a bunch of holes is going to be near as effective as cutting out a strip.http://grantlogan.net/
First off, we should know if there is a ridge beam between opposing joists. If so, then the hole will need to be wider by the width of the beam. You want at least 1" clear, preferably 2", on each side -- 2-4" total.But removing even an entire plank (though obviously that would be much more than needed) shouldn't significantly affect the structural integrity of the roof. More likely the problem the guy hopes to avoid is simply cutting the brittle wood.Since presumably this is a stick-built (non-truss) roof, you might want to take advantage of the opportunity to install metal tie straps across every 2nd or 3rd pair of rafters -- significantly increases the roof's resistance to wind damage.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
drilling holes seems a little odd to me and may not give you enough open vent space, cutting 2" off of a 1x8 would just turn it into a 1x6, i dont see where you would be making the roof weaker by doing so
Rip the 1x's in place. There won't be any strutural compromise, at least no more than every other house with ridge vents. The drilled holes will restrict the flow and limit the effectiveness of the vents. How much soffit venting did you say you have?
Where's Marin County?
There are 3 6"x22" screen soffit vents on both sides. I guess that we could sawzall out a couple of the blocks between the rafters to add more, if necessary. Marin county is just across the Golden Gate Bridge from San Francisco. Hot, dry, and sunny in the summer, cool and rainy in the winter. Aidenbug