I recently remoldeled the exterior of a rancher that had two gable vents only and one hot attic. I did away with the gable vents and added a continuous vented soffit and continuous cobra ridge vent. The attic still seams to get very hot. I know that attics get hot but when i stripped the old shingles there was heat damage to them. I don’t want the same things to happen to the new shingles. I also know there is a formula for adequate attic ventilation and even though I’m not sure of the formula I am almost certain there is enough ventilation. So I guess what I’m asking is what is the exceptable temp. in an attic and should I add a gable vent with an electric fan to be safe?
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Sometimes passive venting is not enough or is just sub-optimal.
You might consider a thermostat-activated roof vent (or vents) as a back-up/supplement to your current arrangement.
If you are in a place where it gets really hot or if you have a flat pitch on your roof (or definitely where you have both) these are a really great investment.
They make the house much cooler during hot periods and save on cooling costs if you have air conditioning.
I put a system like this in a house I owned and it made a huge difference in the comfort of the house, especially during the late afternoons and early evenings.
Spend a bit more money getting the quietest system possible.
Thanks for the info. I've been leaning toward adding an alternative ventilation system and it sounds like even if it is not necessary it will still be a benifit to the AC.
Along those same lines...In my current house we not only have passive+active venting in the attic space, but have two thermostat-activated Panasonic whole-house fans along the top floor ceiling ridge (the highest point where the heat pools). When the heat starts to build up, it automatically pumps out the air and draws fresh air up from the basement. Add that to ceiling fans in all the bedrooms and we have no real need for air conditioning where we live.Your best investment of course, is lots and lots or insulation in the attic. Great for comfort and for ROI given today's fuel prices. I think we have about R-72 or something up there.
Can you provide details on the Panasonic fans? are they "whole house" fans, or generic Panasonic fart fan being used in place of a whole house fan?
Thanks
Good question. I let my electrician handle this so I am not completely sure, but looking up at them, it seems they are just a tad bigger than the Panasonic fart fans we have in the bathrooms. I don't see a reason why you couldn't use regular Panasonic fart fans. They are really quiet and they really seem to move a lot of air. Obviously this internal fan system would create issues if you have air conditioning since it would suck conditioned air out of the house-- although it would be the hottest conditioned air in the house. It works great for us without air conditioning.I did not really understand the other posting saying that if you had thermostat activated attic venting that it would pull conditioned air out of your house. Assuming you have a decent amount of insulation between house and attic and assuming you have adequate soffit venting, this seems highly unlikely.
"I did not really understand the other posting saying that if you had thermostat activated attic venting that it would pull conditioned air out of your house. Assuming you have a decent amount of insulation between house and attic and assuming you have adequate soffit venting, this seems highly unlikely."It is not the insulation, it is the air sealing.In a typical house you have lots of areas where where there are air leaks between the house and the attic.Any depressization of the attic will cause more conditioned air to be sucked out of the house..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
I will defer to you on this. I live in Seattle and virtually nobody here has air conditioning. It just doesn't get that hot in the summer. Also our codes require that there is no virtually no air leakage from living spaces to attic spacesI think as time goes by and energy prices rise, people will be looking harder and harder at building without air conditioning. My guess is that if you have a house that is really well insulated, breathes properly and has ceiling fans in most rooms, you will be very comfortable most of the time without it. Unless you live in Phoenix.
"Unless you live in Phoenix."
or other parts of the United States like mid atlantic states, all southern states east of New Mexico, and part of the mid west to name a few...
Assuming you have a decent amount of insulation between house and attic and assuming you have adequate soffit venting, this seems highly unlikely.
It's very likely. If there are any poorly or inadequately sealed areas (ceiling penetrations such as gas vents, plumbing, electrical boxes, can lights, fart fans, interior wasll top plates, etc.) they will leak conditioned air to the attic if negative pressure is created by power vents.
Foam insulation and cellulose to a lesser degree perform better than fiberglass in this aspect, but there will be leakage from the conditioned space to the attic. Power vents increase it.
If he has enough sq ft of venting (inlet and outlet) then his best option is to add more insulation which I'm guessing may be somewhat lacking in this scenario.http://grantlogan.net
"I could have had Miss September...... I couuld have had Miss May. I could have had Miss November, but I waited for December....." ZZ Top.
Thanks....
If you don't have soffit venting or some other type of inlet, no venting system will work very well. You didn't mention inlet, only outlet.
I would avoid power vents if possible. They can and will suck conditioned air out of the living space.
Look in the top right hand corner of this page. Do an advanced search for "attic venting". This subject has been discussed in detail.
http://grantlogan.net
"I could have had Miss September...... I couuld have had Miss May. I could have had Miss November, but I waited for December....." ZZ Top.
He did mention the soffit vent.
He did mention the soffit vent
Oh yeah. I missed that the 1st time. I stand corrected.http://grantlogan.net
"I could have had Miss September...... I couuld have had Miss May. I could have had Miss November, but I waited for December....." ZZ Top.
Give us the specifics of your current attic ventilation. Ie:
lin ft of cobra ridge vent? Type and lin ft or sq ft of soffit ventilation? Square footage of unfinished attic floor space? What state/climate, etc, do you live in?
The house is located in central Maryland and it gets pretty hot here (high 90's) and is very humid. The roof is exposed to direct sun light all day, there is no shade. There is about 49' of cobra vent out of 50' of ridge. The soffit is Certain Teed triple 2" vented soffit and it runs all 50' of the front and back. There is also a return gable on the front that is vented the same way. I'll try to get some temperature readings today if I have an opportunity.
How much and what kind of insulation is in the attic?http://grantlogan.net
"I could have had Miss September...... I couuld have had Miss May. I could have had Miss November, but I waited for December....." ZZ Top.
It sounds like your roof is ventilated adequately and properly. I believe Cobra vent doesn't give as much ventilation as some, but it is still fine. I think it is more just a issue of expectations. I'll make a wild guess that your attic may have been 140º before you made the changes and now it is maybe 125º during the heat of the day. Not a great difference but still in the 10 to 15% range. The thing is what can really be expected? The purpose of attic ventilation is to prevent condensation in the attic and prevent ice damns during the winter as much as it is to cool the space during the summer. As others have said above, if the attic floor insulation is adequate - say maybe R-38 for your climate, and the leakage of conditioned air from the living space to the unconditioned attic space is minimal, then attic temperatures are less of a concern.
If you feel compelled to add more ventilation, and it would be aesthetically feasible, I'd lean more toward adding some wind powered turbine vents to the back roof plane or even solar powered roof vents if you could keep from choking on the high price tag.
From what I've read the savings in cooling bills with electric powered attic ventilators are most often offset by the cost to run the fan - net savings zero. A few houses ago I had a powered attic ventilator. I was up in the attic for something else and looked at the fan. There was the motor spinning away with 3 broken off fan blades laying on the floor. Granted it was an older house and no telling how old that fan was, but needless to say I wasn't impressed. The easiest thing at that point was just to install a new fan as I was getting ready to sell the house anyway.
Right now I'm building some to be Energy Star certified homes here in Raleigh NC. It's a full zone south of where you are. With the program they give a full page+ list of proposed energy saving upgrades with points values assigned to each item (these items are above the base requirements of good construction). Power roof ventilators are not on the list.
Proper attic penetration sealing and proper insulation installation are part of the base ES requirements. A problem with retrofits though is it is difficult to seal attic penetrations once the loose fill insulation is installed. Some of this can be done on the ceiling from a ladder; taking down ceiling light fixtures and HVAC register grills and caulking around the openings. Plumbing and electrical penetrations through partition wall top plates can only be addressed from the attic once the sheetrock is hung.
If you want a quick and dirty temperature measure, you can get a $10-12 digital that records maximum & minimums. Stay away from the wireless remote units, most max out at 120º.
Now, that peak temperature is not as informative as a proper thermograph, as the number of hours at a given temperature can really help. If the attic stays in/under the 90's, and then rolls up to the 120's for a couple hours, what you might need is another tree providing shade. Or a lighter color roof, maybe a metal oen that is less emissive, can help.Occupational hazard of my occupation not being around (sorry Bubba)
Your venting is OK, now you can go with other insulation options.
1st, are you sure your rafter bays are open to allow air flow from the soffets? Sometimes they get stuffed up with insulation.
There was a method for adding ridgid foam board to the underside of your rafter bays posted here awhile back. If your rafters are 16" o.c., you cut pieces of 1" thick foam board to be 16.5" wide, then slice each edge 1" in lengthwise and fold over that small cut strip. These folded over strips will space the foam board away from the roof deck for ventelation. From there you can press fiberglass or denim batts up tight to the foam, then cover the underside of the rafters with (optional - another layer of foam board then-) drywall or OSB.Rebuilding my home in Cypress, CA
Also a CRX fanatic!
Save the Whales! and Guns!
Where do you live; what kind of exposure does the roof get; how hot does it get in the attic (measured)?
Remember Mary Dyer, a Christian Martyr (Thank you, Puritans)
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Lighter colored shingles may make more difference than the venting.
My code book says: "The total net free ventilating area shall not be less than 1 to 150 of the area of the space ventilated except that the total area is permitted to be reduced to 1 to 300 provided at least 50 percent and not more than 80 percent of the required ventilating area is provided by ventilators located in the upper portion of the space to be ventilatedat least 3 feet above eave or cornice vents with the balance of the required ventialtion provided by eave or cornice vents."
Not entirely sure what the last part of that means.
Do not add gable vents, as they will "short circuit" the flow of air from eave vents to ridge vent and make it worse.
Insulation will not help--insulation on the attic floor may help keep the living space cooler, but it won't help the roof deck or shingles, and in my opinion, neither will something like spray foam or radiant barrier on underside of roof deck. As another poster mentioned, lighter colored shingles will help.