Do soffit vents work?
Getting ready to paint soffit and fascia so I decided to replace some vents and add more.
When I pulled the vents on the front of the house where they’re close to the live oak tree and the red oak, the vents were completely clogged. The sides and back of house were basically clean.
I can obviously feel the air flow into the opening and now know it may be important to clean every year or so. It’s been about 4 years since I added more vents and they were definitely clogged.
I’d love to seal it all up and foam it, but my 2300 sq ft house with hip roof would cost a fortune.
Hosed them out and dipped them in soapy water and cleaned them up to paint.
Pete
Replies
I usually clean mine every year. I use a toothbrush and have a very strong shopvac.
I also found if adding new eve vents, to installed them over windows so you can check for blockage and might help when cleaning. Hate working from a second story ladder whenever I can.You will also find that adding more vents will decrease on the debris being collected in the existing ones. You might not have enough incoming vents.
When starting from scratch I prefer the continuous channel vents and they usually don't have screens to plug. The perferrated metal, I guess is small enough to keep out bugs.
Do soffit vents work?
That depends. Define "work" <g>.
Depends on "where" you are, too. Building Science only vents the roof in Cold and Very Cold climate regions.
Down here at 29ºN latitude, the short answer is "no." Just not that much difference between my marginally vented attic and the neightbors fully-to-spec-vented attic--theirs probably runs 130-135º in the summer versus mine at 135-140º (I have more shade than they do, too.) Note that the difference is about the same as a car in the sun with windows "cracked" open versus shut.
Hey Cap,
I live in Plano, TXI was trying to be cute when I said, "Do soffit vents work." Actually trying to say that they do work based on the amount of crap sucked into them. I have 2-3 times more vents than any of my neighbors. They still have the original venting from '83 when houses were built. My attic is still hot, and you're saying the difference in my attic temp and theirs isn't that big a deal? If that's the case, I sure put in a lot of hours cutting holes, etc.Pete
I live in Plano, TX
I know some folks up there, and in Frisco & First Colony (along with a raft of people in the Mid Cities <G>). Spent a good bit of time in Dallas County, too.
My attic is still hot, and you're saying the difference in my attic temp and theirs isn't that big a deal? If that's the case, I sure put in a lot of hours cutting holes, etc
Yeah, could be. I've put in continuous soffit vents & matching ridge vents in Dallas County, to no great change in attic temperature. (Back to cracking the car windows open a 1/4 inch . . . )
The volume, the amount of air, you can exchange is just not going to be very high. It's ambient temperature, too, so, it's hard to get a lot of cooling out of 95-98º outside air. The roof assembly, shingles on skip sheathing or asphalt tab on solid deck (the two typical roofs around there) heat up far beyond what 10-15cfm of venting could reduce.
But, that's my bias, too. The more I consider it, the more I like adapting the Building Science recommendation of insulating the roof deck to the wall plane. (Even if that's not ever going to be real easy with the tract builder 10/12 & 12/12 roofs sprouting all over Colin County--I'd be afraid to install the thermocouples up at the top of some of those 18' tall attic spaces . . . )
I'm certain that, after the financial miracle that gets my electrical problems fixed, the next financial miracle after that will see my roof deck foamed right over, and tied into the walls in some sensible way.Occupational hazard of my occupation not being around (sorry Bubba)
Cap,I think you're probably right.
When it's 100 out and with the dark shingles---it probably is a losing battle.When we re-roofed after our last big hail storm, I wanted to go with real light shingles. Wife said, "No way." Of course ours would have been the only light colored shingles in Collin County. And of course my vote only counts 1/2 against wifey's vote.Pete
Attic ventilation at the code levels makes no real difference to attic temps. If you went with full gable end vents and a couple of powered roof fans, you will have an effect on temps but impractical!!
This retrofit study on a Florida house is instructive:
They put in attic vents to reduce attic temps and thus A/C costs. The payback time on vent costs: 113 years. RIP!!!
See: http://www.fsec.ucf.edu/bldg/pubs/cr978/
See summary chart near end of document.
With all due respect to a NS native. As a Florida native, who happens to go into a lot of attics, I think your overlooking several bits of information when you discount the retrofit of vents. First the venting was done along side a radiant barrier.http://www.fsec.ucf.edu/bldg/pubs/cr978/#Attic%20Radiant%20BarrierSo the energy uptake of the living space mitigated in belt and suspenders approach. Had a radiant barrier been left out the ventilation would have shown more effect and faster payback.Also the type of vent added is a nail-down mesh type vent. Fine for shifting a bit of moisture up there but down here they should have gone with a more open vent. There are several options that have at least twice the free area that are not more expensive to apply and are only marginally more expensive to buy. A better vent design would have been more effective and would also pay itself off more quickly. The cost of installation would also be lower if the job was done as part of a re-roofing job. This is also a job a DIYer can handle. Lower installation costs get paid off more rapidly. This research was done in 1997. In the nearly ten years that have passed energy prices have increased. Payoff times would have to be figured lower as the cost per KWh has gone up. Future trend will be to further reduce the payoff times. And what brain-dead gomba puts a black roof on a house down here. Mostly real-estate people who understand that a dark roof recedes and makes the house look bigger. And perception gets the higher prices. Of course neither the builder nor the sales agent will help you pay that electric bill so draw your own conclusion.
I'll quote some other people/agencies views about attic venting. From CMHC, Canada's housing agency:
(1) If you have properly sealed the attic you should not need more attic ventilation. Attic ventilation is overrated. In winter, the cold outside air cannot hold much humidity or carry moisture away from the attic. In summer, attic temperatures are more affected by the sun and shingle colour than by the amount of ventilation."
See:
http://www.cmhc.ca/en/co/maho/gemare/gemare_001.cfm
(2) From Joe Lstiburek's list of "Top Ten List of Dumb Things To Do in the South"
#10- VENTING
The rationale for venting attics in the South is to "flush" heat. The dominant heat transfer mechanism in an attic is radiation. Venting attics will not "flush" radiation. The air change in a perfectly built and vented attic (code 1:300 ratio) results in an average air change rate of 3 to 6 ach. At this attic air change rate there is approximately a 2 to 3 percent reduction in heat transfer to the conditioned space through the vented attic as compared to an unvented attic insulated to the same level. This assumes an airtight ceiling and no ductwork in the attic and certainly not leaky ductwork in the attic. The moment ductwork (assumed airtight in this instance and insulated at R-6) is installed in a vented attic, the balance changes. There is approximately a 5 to 7 percent increase in heat transfer to the conditioned space as compared to my version of an unvented attic. This is due to conductive heat gains through the surface of the ductwork and air handler now located in a "hostile" location (a hot, vented attic), rather than inside a 75°F conditioned space (the "house"). The moment leaky ductwork is installed in a vented attic there is approximately a 25 percent increase in heat transfer to the conditioned space. Of course this does not happen if you have airtight ducts and an airtight ceiling (then the penalty for venting the attic is only 5 to 7 percent as previously noted).
Now, if you locate the ducts within the conditioned space and also build an airtight ceiling, this is approximately 2 to 3 percent more efficient than my version of an unvented attic. I never said that this wasn't the most energy efficient way to do it. Of course when is the last time you saw ductwork below an attic ceiling coupled with an airtight attic ceiling? Builders put things in attics because they don't leave any room in the house for the ductwork and air handler. If they continue to do this, then venting attics is a dumb idea.
So much for the energy concerns. Now lets talk moisture. What? Are you all crazy? The air outside is hot, humid and disgusting. And you want to bring this into an attic where it can diffuse through the vapor barrier-less attic insulation and get to the cold, air conditioned ceiling? What were we thinking! Before it gets there it will see those cold R-6 insulated ducts, fittings, etc. and drip all over. Give me a break. Venting attics in the South was dreamed up by some disgruntled Yankee pissed about the Civil War and wanting to get even. Be sure when insulating at the roofline in humid climates to follow moisture control principles as you would with any insulated wall so that the roof assembly is self-drying (http://www.buildingscience.com/resources/walls/exterior_sheathing_systems.pdf).
Venting attics in the South was dreamed up by some disgruntled Yankee pissed about the Civil War and wanting to get even.
Oh, now, that's a good line <g> . . .
Probably, though, the flaw is that the "model" code was written by some one in a climate with 9 months of winter and 3 of bad sledding, like Minnesota, or some such. if your sumber is only about 90 days long, and peaks in the mid 90s with 20-30 humidity, venting does little harm.
My a/c "season" runs May to October, with peak temps in the very upper 90s (45-55 days of 98 & 99 are not uncommon) with average humidities in the 60% range (dew point temps in the mid 70s). The fact that moisture does not "eat" more houses is what tends to continually surprise me. (It is also what I suspect will 'doom' the tract-built 12/12 roofed houses that have been built in the last few years.)Occupational hazard of my occupation not being around (sorry Bubba)
LOL.The link to the CMHC is quite humerous. It is also largely inapplicable to the situation in Florida. Sounds like the visiting professor of building construction that was telling me how an attic physically couldn't get any hotter than 140F. So I had my photo taken with a calibrated thermometer sitting in an attic with the thermometer clearly reading 155F. I then presented him with both the thermometer and the photo. At least he was nice about it and admitted that his assessment was based on a series of estimations based on the average home in the USA. He later modified his program to take into account the higher solar gain in the deep south. Building science is an interesting site. A lot of what they say makes sense. Some of it doesn't translate from academics to real life. My favorite claim is that a sealed attic is best. Sure except for one tiny fact: All roofs leak. It may not be enough to show but moisture always eventually gets in. Our ancestors understood this. More recently we have been fooled by our own pride and modern methods and sealants into thinking we can build a roof that is absolutely moisture-proof and one that will stay that way. Build a sealed attic. When, not if, the water gets in it has nowhere to go. Rot, mould and corruption soon follow. The issue of attic ventilation is not that there is too much down here. Seldom, never in my experience, is this a problem. Almost always it is a matter of too little. People put in venting that matches the FHA minimums and then step back and announce that 'it doesn't work'. Well, no wonder there. The FHA standards are far too low and the assumptions about how much air will go through any mesh size are far too optimistic. Such standard are fine for Canada. They help keep heat in and heating is the majority cost. Down here it is just the opposite. Hint on what works can be drawn from early an early 'Cracker' house I worked on. About 1200 square foot floor area I measure the vents in each rafter bay at 2" by almost 24" with 1/4" mesh. Hip roof with a wide porch on three sides so the vents are pulling from the shade. The steeply pitched galvanized steel roof was topped with two large coupolas. Easily 3' square with louvered vents on all four sides a bit more than 2' square also covered with 1/4" mesh. Worked out to be a vent area about 1/20th the roof area over the roughly 1200 sf living area and 1/50th the total roof area including the porches. Roughly 2500 sf. Without any appreciable wind the tall attic always had a breeze rising up from the soffit vents to the two cupolas. Standing under the hole going up into the cupola it must have been a good five, perhaps seven mile an hour wind. The ceiling, at the time, had no insulation and yet the HO seldom used AC. This house was built in the 1910s long before AC was commonly available. The only cooling in its day, I suspect retrofitted around 1940, was a large whole-house fan. Ceilings were tall and the windows were all double hung going to within inches of the ceiling. Only the north side lacked a deep porch. These folks knew how to build for Florida. This is the essence of adaptive architecture. More recently Florida was inundated with houses adapted for Nebraska. Building science adapted for Maine. The poor choice of design made marginally livable by slapping on a couple of tons of AC capacity. Sheer stupidity some of what I see. Narrow, or no, overhangs. Unshaded picture windows and huge sliding glass doors facing the South. Almost as bad facing unshielded into the East or West. Stupidity. Slap on a black shingled roof to make complete the Cape Cod look. Watch the power meter spin like its trying to take off. With all due respect to the Canadian Mortgage folk and Building science I think they need to come on down and live down here for a while. Perhaps I could stuff them into an attic or three and they would reconsider their opinions.
Of course ours would have been the only light colored shingles in Collin County.
Well, at least on your street <g>
I know of one re-roofed after the 2000 hail storm with standing seam in a very light beige galvalume. Always wondered (since I only saw it finished) if they went to the trouble to flash it properly. I do know it was one of the few that was not re-roofed after that next hail storm a couple years later, though . . .
And of course my vote only counts 1/2 against wifey's vote.
Well, that's a separate issue all together <g>Occupational hazard of my occupation not being around (sorry Bubba)