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Attic insulation and venting advice


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Initial post: Sep 7, 2010 12:56:46 PM PDT
I have an older home (1935) its like a "T" shape.. i have a gable vent at either end of the top of the tee and for some reason, a window at the bottom of the tee's leg. I am installing a power vent fan in one gable vent. there is no ridge vent or soffit vents. will this be enough to vent it or should I cut in a ridge vent? will the fact that there are no soffit vents be an issue? its got ope eves and the roof extends out over the outer walls about 16 inches as it was once a summer cottage near Lake Zoar here in CT. and im guessing it had a lack of gutters.. anyhow, no soffit vents were installed and id hate to ruin the nice trim work there now.

onto insulation.. none up in the attic at all except for the 1.25" ridgid foam sheets laid down on the plywood floor. none in the ceiling below the attic either. do I need to rip out the floor or just the foam sheets before i insulate with the rolls of pink stuff? there seems to be some mould on the sheething of the roof and some of the shingles on the roof look like they were super heated.. im guessing from the stack of foam sheets someone had them stuck betreew the rafters at one time.. also there is an ice melt cable in the gutter on the north side of the house. help!! oh, the house is smaller, 1200+ sq foot.

Posted on Sep 7, 2010 2:27:52 PM PDT
you absolutely need a place for the air to come FROM. Soffit vents are crucial. Also, I've seen studies that say a combination of soffit/ridge venting is much more effective at moving air than even power ventilation.

Posted on Sep 7, 2010 7:47:00 PM PDT
M. Liegey says:
if you have gable vents, just keep those if you want to use a powered fan. maybe if you cut anything in, cut a gable vent on that third leg you were talking about that only had a window - or leave the window open with a screen...? If you want to go the ridge vent route, you MUST use soffit vents for that to do anything. The whole point of the soffit/ridge combo is so that cool air is pulled up along the inside of the roof, from the soffits to the ridge vent, therefore eliminating most of the heat buildup before it can travel to the rest of the room. Honestly, if you wanted to do the best thing, you would need to add soffit vents and ridge vents in combination. Use insulation baffles and insulate the roof joists - it contains the heat to the roof itself, thereby creating a stronger hot/cold vacuum.

Posted on Sep 8, 2010 4:05:25 AM PDT
I wanted to try and cut some vents into the soffits but when I tried, there was wall behind them... i think that the roof over hang is the problem... where the soffit vent would be (at the top of the outside wall) is lower than a normal roof line. Im thinking if i cut into that wall, id be venting the living room and master bedroom...lol Ill really have to check from the attic to see if I can add them in. Also, interestingly.. the part of the "T" with the window was an add on after the original house was made and instead of removing the roof and addint the new roof, they just cut a hole in the roof at the floor line, maybe 4 feet by 4 feet.. you have to crawl through.. and the old roof is still there, will this be a problem? Im thinking that heat / moisture will be trapped in this dead space and be a problem thus why I was thinking ridge vent. Maybe I should go with the powered "mushroom" vents on the roof to pull air in from the window and gables up and out the top?

In reply to an earlier post on Sep 11, 2010 8:56:10 PM PDT
S. says:
That would be my suggestion. We had a home built in 2000 with continuous soffit aroun the entire house and ridge vents on every ridge on the roof. However, it wasn't until I had my contractor install two 1250 cfm thermostat controlled power vents did I see any benefit. You probably want to consider putting extra insulation in the attic as well. It will help to keep the heat transfer from the attic to the living space in your home to a minimum. If your A/C ducts are in the attic, it will help to reduce the amount of heat that is picked up in your system, too. The insulation on those ducts isn't but around an R-7 or so.

Posted on Sep 12, 2010 4:45:50 PM PDT
Marc Powers says:
Proper attic ventilation is crucial, especially during the winter in your climate. I don't picture where this window is as to relative elevation. If it is fairly low compared to the 2 gable vents, consider pulling air into the attic through this window and it will exit the hot air out the gable vents. All the heat then will be "pushed" out of the entire roof if I understand correctly.

Having foam insulation in the ceiling might be OK. In a cold climate, the vapor barrier should be on the "warm wall" or close to the ceiling in your case. Remember that somewhere between the inside moist air and the outside cold air is a "dew point" temperature. This is where the moisture will condense and create water. If you add enough batt insulation above the foam, the dew point should be in the batt insulation and will be taken care of by proper ventilation (see above). You should NOT use a foil faced insulation or other type with the "vapor barrier" on top! This will trap the moisture and cause bad mold, mildew, etc!!! Remember again, the ventilation is to remove whatever moisture does naturally condense into the batt insulation. I would think this would also be the most cost effective solution and minimize the aesthetic changes of your home.

Posted on Sep 13, 2010 6:38:16 AM PDT
thanks guys.. Mark, Picture looking down on an "L" the window is at the end of the bottom on the right. one gable is on the top, the other on the bottom. the window is at the same height as the gables give or take an couple inches. my main concern is not so much heat loss but moisture and malting / freezing ice causing ice dams on the roof. Plus removing hot air in summer time. why dont they make a gable vent that sucks air out? wouldnt that work as well? The reason im thinking ridge vents is that withough haveing the soffit vents, Ill need as many other type vents as possible.. im even considering those mushroom type power vents or the ones that look like chef hatys and spin in the wind.. anything so the hot air can escape.. Im thinking that since hot air rises, venting through the roof is best.. no?

Posted on Sep 13, 2010 5:34:48 PM PDT
R. Rinehuls says:
Craig, if this is a good-sized attic with headroom and useable space you should talk to a contractor about spraying insulation between the rafters and insulating the endwalls. In other words insulate the entire attic space. Sounds like your shingles need replacing at which time the roof deck can be accessed for rot repair and would be a good time to do the insulation work.

In reply to an earlier post on Sep 14, 2010 4:18:31 AM PDT
Funny you mention the spray insul. I worked next door to a company who does the spray foam insulation.. and for over a year they had no towmotor and just a small crew of 6 guys so no one would be there in the daytime as they were all out on jobs... so I used to take in thier deliveries for them and the owner kept saying he would come spray my house for me but I declined cause
A) I couldnt wrap my head around how the stuff worked ( i always heard NEVER insulate the attic roof)
B) I had sooo much junk up there I didnt want to have to move it all out.
But that was my old house, I have moved and they are no longer next door to us. I should call and have him stop by and give me a price though, may still be cheaper than rolling out 19" of pink stuff..lol And yeah, Id love to keep the usable space.. its a good sized attic I can definetly walk around in most of it.

In reply to an earlier post on Sep 14, 2010 4:19:30 AM PDT
Oh yeah... I will be replacing the roofing after this last winter. it already had two leaks... but I believe I repaired them (clear roofing patch.)

In reply to an earlier post on Sep 14, 2010 12:37:53 PM PDT
R. Rinehuls says:
I am not an expert but am interested in this subject. If you want to learn more about insulation or consult with some experts checkout Building Science Corporation. They publish a lot of free information and you can get on their e-mail list: http://www.buildingscience.com/bsc/

Posted on Sep 14, 2010 1:42:43 PM PDT
Razzz says:
Typically you use square inches to find the area of a roof and divide by 2 and use that number for the amount of intake on the eaves/soffit and the equal number for the exhaust on the ridge(s). Continuous vent is best on the eaves and passive continuous ridge vents is preferred. Insulation of the rafters bays (between the rafters) will prevent the majority of heating in the attic space. Insulation of the rafter bays includes using standoffs to leave a space for air to travel from the soffit vent to the ridge line between the bottom of the sheeting (whatever material it might be) and the top of the whatever type of insulation being used. In other words, you don't cram/spray insulation in the space between the rafters so air can't flow directly along the sheeting upwards.

Any roofing specs. or supply house or website has the details.

Posted on Sep 14, 2010 6:23:06 PM PDT
thanks for the link!!!

Razzz, I think the spray foam stuff they did was applied directly to the roof, wals and flooring.. they even cover up any vents.. i guess their thing was to encapsulate the house.. seal the top air tight and the crawl / basement.. this way no humidity / heat can get in there.. they say it does work.. they were even on the TV show, "Extreme Make over, Home edition" or what ever its called..the one with Ty.. lol thier website is
http://ecologices.com/

Posted on Sep 14, 2010 7:04:12 PM PDT
Last edited by the author on Sep 14, 2010 9:30:50 PM PDT
R. Rinehuls says:
The venting area required for moisture control is much, much less than that required for a cooling benefit. Since you were unable to cut soffit vents don't bother with ridge vents. These vents are for moisture control and not cooling. The gable vents and the window are sufficient ventilation if the window can be left open. Mounting a fan in the window, or at the window end, would be even better for cooling, as it would DRAW air all the way through from the gable vents. Those chef-hat turbines don't work if the wind isn't blowing. Your main problem is insulation though. If you decide not to insulate the entire attic, you will have to take up the plywood and insulate the floor. You'll need a lot more than R-19. Better check your code up there. Even here in N. Florida R-25 or R-30 is standard now.

Posted on Sep 14, 2010 8:17:13 PM PDT
Razzz says:
http://www.dulley.com/docs/f668.htm

Note that venting controls are mainly dictated by the roofing materials manufactures. Ideally you would want the attic and outside air temperature to stay the same as in balanced since most building material breathe and flex, keeping relative extremes to a minimum is the goal. Even house wrap breathes allowing water vapor to pass through it but not water moisture per se. Airtight structures creates their own set of problems.

In reply to an earlier post on Sep 15, 2010 6:42:53 AM PDT
Hmmmm Putting it in the window may be a good idea also, since it is on the far end of the house away from our bed room and living room, we wont hear it either. What a PITA all this is.. lol Installing the Rollsof Insulation over the wood floor wont work, according to the lowes guy.. cant believe that a floor would hurt, rather than help.

In reply to an earlier post on Sep 15, 2010 10:15:34 AM PDT
R. Rinehuls says:
I don't see any problem with insulating over the floor if you don't want to take it up. I wouldn't rely on the advice of a store employee. You can research a lot of this. Check out www.greenbuildingadvisor.com. They have a great deal of in-depth information about all topics, including differences between types of spray foam insulation.

Posted on Sep 17, 2010 8:02:47 PM PDT
Cowboy1836 says:
In 1970 I did an experiment with roof ventilation in Houston, Texas. During the hottest part of the year, August, I measured the temperature of the attic floor for two weeks or so with a thermocouple. The house had gable vents at each end of the roof. I installed three wind powered ventilators on the roof of the attic. When I measured the temperature of the attic floor the temperature was the same as before the wind turbines were installed. So I installed one powered ventilator in place of one of the wind powered units. No difference. Conclusion: Go with good fiberglas bat insulation and don't worry about the ventilation.

In reply to an earlier post on Sep 17, 2010 8:31:06 PM PDT
R. Rinehuls says:
Right. Gotta have the insulation to block the heat being radiated to the attic floor by the hot roof. A radiant barrier like aluminum foil on the underside of the roof would reduce this heat a lot but gotta have that insulation especially given that the house is in the Northeast and heating in the winter months will be the greatest expense.

In reply to an earlier post on Sep 19, 2010 9:43:39 AM PDT
SJG says:
I am a BPI Certified energy auditor, NATE Certified Technician, NCI Certified CO analyst, et.al., and a licensed HVAC/Home Performance contractor. I suggest you stay away from power vents. They can suck conditioned air out of the house, raising energy cost during the summer, and cause all kinds of negative pressure problems, particularly in houses with insufficient attic intake venting. I've seen numerous situations where attic fans create enough negative pressure in homes to cause back drafting flues, and even sucked sewer gases through shower traps in a house like yours where the soffit is not vented into the attic. If you can get a free foam job, grab it! The most critical aspect of home energy loss comes from air leakage, and foam, in addition to a very high R value per inch, seals the air leakage better than any other method. They foam against the roof deck. The sealed attic becomes part of the conditioned space, and ventilation is not necessary. Put on a new roof first, then spray in R-31 or better depending on where you are located. Pay attention to local codes, if the attic space is used for storage or has mechanical equipment in it, you may need to install an ignition barrier over the foam. Mold is evidence of moisture. Make sure you bathroom vent are ducted out of the attic, through a roof or sidewall vent. They should be insulated and pitch up to the outlet. Make sure dryer vents are metal, without to many bends, and they too should be insulated through an attic. The best book on the subject is Residential Energy: Cost Savings and Comfort for Existing Buildings (5th Edition) [Paperback] ISBN 0135125413

Posted on Sep 19, 2010 1:19:36 PM PDT
Last edited by the author on Sep 19, 2010 1:19:54 PM PDT
R. Rinehuls says:
All the various posts point to the complexity of the subject and the need to understand the issues specific to a given building, including its geographical location and site.
Using SIP's or Structural Insulated Panels when replacing the roof would be another option to consider. Despite acceptance of SIP's and foaming in some circles, some experts say there is concern for buildup of moisture between the foam and roof deck, were the roof to develop a leak.

In reply to an earlier post on Sep 20, 2010 5:14:37 AM PDT
well, this weekend I was able to cut in five 12 x 5 or 6" vents into the soffits on one side of the house.. next week i will do 5 on the opposite side.. at least one part of the house will have them.. thats also the part that has the window. if I use some Fiberglass Batt with the barrier above the floor, could I then use it under the floor, between the down stairs ceiling and attic subfloor? We will be re doing the ceiling with 1/2" sheetrock next year so id have: 1/2 Sheet rock, insulation with the paper barrier, 3/4 tongue and groove subfloor, dead space, 3/4 (or 1/2, not sure) plywood flooring and more fiberglass w/ vapor barrier.

In reply to an earlier post on Sep 20, 2010 5:59:44 AM PDT
Dan Edson says:
Only use 1 vapor barrier. In the Northeast that would be on the living space side.

Two vapor barriers = mold sandwich.

Any water that gets in (and it will get in) has nowhere to dry to to get out if there are two vapor barriers.

In reply to an earlier post on Sep 21, 2010 8:42:38 AM PDT
R. Rinehuls says:
I wish I could see a diagram because I am a little confused, but after you put a vapor barrier against the ceiling sheetrock don't use another one above it. Additional insulation could be loose blown-in type or batt/roll insulation without facing.

In reply to an earlier post on Sep 22, 2010 7:40:31 AM PDT
Do you have adequate soffitt ventilation? Usually one every 4 feet (not every 8 feet as usually installed).
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Discussion in:  Home Improvement forum
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Initial post:  Sep 7, 2010
Latest post:  Sep 27, 2010

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