Idea for attic ventilation

[Jim Matthews]

Thank you.

That was clearly stated.
When I put on my roof, the ridge vent was only included in the quote that got the job.

The other three thought it was pointless.
It made all the difference in our house.

[Steven DeMars]

I live in Baton Rouge, LA area. . .

You really want to pull from the soffits up and out . . . No power vents required.

Soffit vents do work, but total area open on intake(soffit openings) HAS to exceed the total area of your exhaust vent capability.

I have (3) 14" wind spun turbines on my roof and they do a fantastic job. Home is 1600 sf. living.

They spin non-stop day & night . . . To do what the OP is suggesting would bring "cooler" air into the attic quickly. When you do this there is a very good chance you will hit the dew point during the night in the months before spring starts.This will cause all that hot "MOIST" air to condense and dump right on top of your insulation. Now you will have to deal with wet insulation, which will give you mold and an unbelievably wonderful environment for termites.

I did a lot of research on this a few years back. It became a "hot" topic in the engineering office I was working in at the time. We were all schooled by a ChemE as to what would happen. My plan was to bury 60' to 70' of duct work 18" to 24" and pull through it to cool my attic during the day. Same principal.

Steve

[Mike Lassiter]

I recently had to replace my roof and make some repairs and improvements to the 28x60 mobile home I live in. Bought it new in late 1996 and it had 4 of the black plastic vents near the ridge on the rear side of the roof. Soffit vents all around but the vents the hot air come out of was really a joke the way they were done. One had the opening in the decking cut out about 1/2 the size of the vent, another likewise, but also when the shingles were laid down the roofer ran one run over the bottom half of the small opening and left it that way. 15 seconds to cut the shingle so it wasn't blocking the opening. I patched the 4 areas and closed them off and installed 2 solar powered vents from Home Depot that required a 15" diameter opening in the roof decking.

Standing on the roof after adjusting the solar panel on the first vent in the sun I blocked the sun to the panel and the fan obviously stops running. I stood there about 30 seconds with my hand at the air outlet area then moved to let the sun shine on the panel and the fan started running again. In the brief time the solar panel was blocked so the sun couldn't hit it the air temp of the air the fan began blowing out was noticeable warm, not hot by very warm in that short time. Sun shinning on shingles heats them up. Sun shinning on the solar powered vent makes it run faster up to it's max speed in full sun. Clouds slow it down some, but I was very happy with seeing just how much difference the air temperature was with no fan running and running. I installed two of these divided on the roof. Shingles will have much longer life now due to reduced heat buildup they will see. Attic will be much cooler because the air is being pulled in at the bottom and exhausted at the top. No gable vents installed, just decorative plastic to look like one. I have considerable more open vent area for the air to exhaust from now that I have 2 full 15" openings in the roof over the 4 puny opening the manufacturer provided. Can't say it helps with cooling cost as I have R 38 I think in ceiling, but surely will some with reduced temperature difference between ceil inside and attic temp. Fans cost about $200 each I think, but cost nothing to operate and even if it's cloudy but still hot the opening allow more air to flow by convection current than could have through the vents installed.

[Mark Bolton]

There have been several studies showing that no form of roof venting can reduce attic or deck temps by any relevent amount. 10 degrees at best. Of course once the sun goes down they can help dissipate accumulated heat quicker.

In cold climates keeping the roof deck at ambient (venting leaking interior air) is the goal and in all areas venting interior moisture.

The asphalt roofing industry has tried to blame hot attics for warranty claims but the un-vented deck industries (SIPS is one) have long since undone that one.

[Kevin Bourque]

I agree with much of what has been said here. Moisture and heat are bad for an attic.

I would also like to add that gable vents are problematic too. They tend to leak, and also let in wind blown rain and snow. The powered vents are even worse. In new construction around here ( SE Pa. )they are rarely, if ever, used. Good soffit ventilation coupled with a ridge vent does a pretty decent job at exhausting moisture and keeping the roof less hot.

Also, using light colored shingles is probably the best way to keep the roof cool(er ).

[Mike Lassiter]

There have been several studies showing that no form of roof venting can reduce attic or deck temps by any relevent amount. 10 degrees at best. Of course once the sun goes down they can help dissipate accumulated heat quicker.

In cold climates keeping the roof deck at ambient (venting leaking interior air) is the goal and in all areas venting interior moisture.

The asphalt roofing industry has tried to blame hot attics for warranty claims but the un-vented deck industries (SIPS is one) have long since undone that one.

based on your saying "There have been several studies showing that no form of roof venting can reduce attic or deck temps by any relevent amount" it seems we all have no valid reason to vent the attic.

I disagree and will leave it at that.

I know how much the air temperature increased in the time I blocked the solar panel on my vent and it doesn't take a genius to know moving more air thru a given space will reduce the heat because the air that is moving thru it is carrying some of the heat gain out of the area. As pointed out by someone else, the air needs to enter at the bottom and exit at the top. Blowing air across the top may help the upper area, but does little for the lower area that the air is not moving in.

Your comment about SIPS is comparing apples and oranges. The SIPS panel is insulated and reducing the heat from building up in "the un-vented deck".

[Mel Fulks]

We had a similar thread some time back in which I said there is considerable debate among the experts. Still is. I have a cape cod type house which was pretty hot upstairs due to heat coming from under the roof behind the knee wall. Tried the venting ,fans , etc with no improvement to living space. The roof is the darkest color available short of black and is almost exactly south facing. Once I gave up on all fixes except insulation problem was fixed. I don't care how hot or cold it gets on the other side of the insulation ,the upstairs is now comfortable.

[Mark Bolton]

based on your saying "There have been several studies showing that no form of roof venting can reduce attic or deck temps by any relevent amount" it seems we all have no valid reason to vent the attic.

I disagree and will leave it at that.

I know how much the air temperature increased in the time I blocked the solar panel on my vent and it doesn't take a genius to know moving more air thru a given space will reduce the heat because the air that is moving thru it is carrying some of the heat gain out of the area. As pointed out by someone else, the air needs to enter at the bottom and exit at the top. Blowing air across the top may help the upper area, but does little for the lower area that the air is not moving in.

Your comment about SIPS is comparing apples and oranges. The SIPS panel is insulated and reducing the heat from building up in "the un-vented deck".

No one, including the studies, say that temps cant be reduced. The issue is are they reducded in any amount relavent to shingle life or that of conditioning the interior space while the sun is out. The answer is no. There is no reasonable venting that can offset the gain when the sun is shinning by more than 10 degrees. Many of these studies were done because shingle manufacturers were trying to void warranties over unveted decks and the results proved and showed clearly and scientifically that venting can not in any substantial way reduce the attic or roof deck temperature when sun is shinning. You can question the science or get yourself a thermometer and a laser thermometer and stand on your roof and take readings with your vents running and not.

The venting is for a reason, I install it regularly, but it has nothing to do with cooling the roof when the sun is shinning or for the life of the shingles. Ice dams, moisture, yes.

[Paul McGaha]

I do think it's a good idea to get the hot air out of your attic. It makes the upstairs level of your home markedly more comfortable.

I was an electrical contractor from 1992 to 2002. For the 1st 3 years of our company we did residential service work and providing roof fans was one of our biggest sellers in the warm months of the year. A typical installation would be a home with soffet vents and ridge vents and no motorized fans.

In the summers the outside temperature here in the Washington DC metropolitan area would be usually in the 90*'s and some days in the 100*'s. The temperature in the attics would reach about 130* to 140*.

A roof fan will drive the attic temperature down considerably, I'd say to around 120*. This makes the upstairs level of your home much more comfortable during the daytime. Say about 7 PM, when the sun is down and the hot part of the day is over, it takes a roof fan about 1 hour or less to cool the attic off to the point the fan reaches the set point on its thermostat (110*) and cycles off. At this point the upstairs level of your house is very comfortable, like it's not even hot outside, although it still is.

I'd guess we did maybe 500 roof fan installs. We used to furnish and install a very good roof fan (Nutone RF59N) for $220. Everybody liked them. I wouldn't be without one if I lived in a warm climate.

I'd highly recommend installing roof fans.

Gable fans do a similar job but I like roof fans better because I like the location of the fan better (backside of the house, centered left to right, up as high as possible but not so high you can see the top of the fan from the front of the house). Back in those days anyways roof fans used to have larger motors and move more air than a gable fan.

Gable fans do have the advantage of being easier to install though. And certainly better than not having any fans.

Good luck with it.

PHM

[Mark Bolton]

I do think it's a good idea to get the hot air out of your attic. It makes the upstairs level of your home markedly more comfortable.

After the sun goes down powered or even turbine ventilation will do a lot for bringing the roof structure and attic space closer to ambient more quickly and most definitely helps eliminate heat from the attic/ceiling structure from continuing to radiate into the living space in the evening. But again, this venting does virtually nothing when the sun is shinning. The solar gain is far greater than can be dissipated in daylight hours. Taking a roof deck or attic space from 140 to 130 or even 120 will provide little comfort to the occupants though it will reduce the load on a cooling system slightly.

The real issue is if possible, had the same dollars that were spend on the powered venting, installation, and electricity to run (for a non solar vent), been invested in additional insulation the space would be far more comfortable than any powered venting would achieve because it wouldnt get hot in the first place. Of course many structures simply dont allow for additional insulation so venting can surely help to cool the structure more quickly after the sun goes down.

[Harry Hagan]

I’ve skimmed the other comments and agree that venting your attic via the crawl space would be a big mistake—too much moisture being introduced in both areas unless you live in a low humidity climate.

Adding ridge vents made a 20° difference on the upper level of our house when we did away with the existing box vents and opened up the existing wooden soffits before covering them with vented vinyl soffits.

One sure way to vent that attic during summer months would be to add a whole-house fan; but high humidity makes them impractical in most areas.

[Todd Burch]

Mark, I would like your opinion on my idea for insulating the roof via rigid foam. Please see this thread and comment:

http://www.sawmillcreek.org/showthre...ation-Question

Thanks.

[Mark Bolton]

Mark, I would like your opinion on my idea for insulating the roof via rigid foam. Please see this thread and comment:

http://www.sawmillcreek.org/showthre...ation-Question

Thanks.

Todd,
I read that at the time and agree with the comets that said even though you had the ISO, a much better idea (if your in this for the long term) would be to have foam sprayed internally and encapsulate the structure. As with any of these options, they have to be looked and and approached as a system as opposed to the individual components.

Personally I can't see how the expense of installing rigid foam and the deficiencies that will inevitably be part of the install (gaps, seams, accessory costs) could compare even to the pricey cost of spray foam. But you hAve to factor everything fairly.

If your not planning on staying in this residence for a ver long time, or are not in a market where you have the potential to recoup you investment, you are best to measure your approach.

[Mel Fulks]

In the situation I had I used ordinary fg batts in the knee wall roof rafters with the plastic toward interior. Some said it
would soak up water ,but it has stayed dry and is used for storage and checked at least yearly.

[Jason Roehl]

http://www.amazon.com/Maurice-Frankl...2+soffit+vents
Hole saw, some work, a few bucks.