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Insulating Gable Walls in Attic


hotrod1131's Avatar
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10-11-07, 08:00 PM   #1  
Insulating Gable Walls in Attic

I am currently insulating my attic in my house (unused attic). At my gable ends the ends were only covered with siding and no other board. I was thinking of insulating the gable ends with R-11 face insulation with the kraft paper to the inside of the attic. Does anyone think that is a good idea. It seems to me that the single board (siding is letting a lot of cold air in the winter and hot air in the summer into the attic. Let me know what you think?

Dale

 
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10-11-07, 08:45 PM   #2  
Posted By: hotrod1131 I am currently insulating my attic in my house (unused attic). At my gable ends the ends were only covered with siding and no other board. I was thinking of insulating the gable ends with R-11 face insulation with the kraft paper to the inside of the attic. Does anyone think that is a good idea. It seems to me that the single board (siding is letting a lot of cold air in the winter and hot air in the summer into the attic. Let me know what you think?

Dale
First where are you loctaed and is your HVAC system located in the attic? Is your attic really finished and unused or unfinished and just ceiling joists and rafters.
Secondly, I think adding insulation there is a really really bad idea and heres why:
1. In winter you want the attic space (unfinished) to be as cold as possible and ideally the same temp as the outside temp. Keeping it cold up there with proper insulation on the attic floor and ventilation will not allow warm moist air you have paid for to reach the attic and melt the snow on your roof which in turn will refreeze on the eves and give you ice dams and damage your roof and give more headaches than you can imagine.
Make sure you have some vents on those gable ends or at least soffit or ridge vents elsewhere to help remove hot attic air in the summer (and keep it cold in winter). Putting insulation on the gable will help keep that heat and moisture there in summer and eventually that superhot attic will cause your roof to rot and your second floor temp to rise and rise again costing you more money to cool your house and making you miserable.

2. Generally speaking fiberglass is a really poor way to stop any air movement at all. It just does a horrible job of it and isnt what its designed for which is to resist the transfer of heat. Cold air washing across fiberglass ruins it R value. To stop air movement there you have to seal the leak with caulk or spray foam and or foamboard. But unless you have giant holes there you dont need to do this anyways for the above reasons i mentioned about ventilation of the attic space in both winter and summer ie you should already have streaming air coming thru your gable or soffit or ridge vents.

Just be sure you have all the correct insulation you need for the attic floor and pay special attention for any holes or penetrations of the attic floor by plumbing vents wiring no top plates of interior walls chimney chases (careful with those )etc. If you find any then seal those correctly but leave the gable ends be as well as your roof rafters.

 
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10-12-07, 08:06 AM   #3  
Insulation on gable vent

I live in Montana and the furnace is not upstairs. The attic is just trusses. The house is 1100 square feet and I have full soffits with vents to the attice, 3 - 1 foot square gable vents and a full roof vent which is 42 foot long. I thought since I had enough ventilation this insulating the gable wall was a good idea. Let me know what you think.

Dale

 
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10-12-07, 03:48 PM   #4  
OK i still think its a bad idea.Fiberglass faced or unfaced wont stop air leaks at all and with all that ventilation its going to be cold and hot up there anyways.Besides that you only insulate walls or surfaces next to a living space. Are you having a different problem keeping the house warm or cool during the winter or summer? If so, doing the gable walls will not help at all. What kind of insulation do you already have on the attic floor and what R value is it.

 
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10-12-07, 04:27 PM   #5  
Insulating gable walls

I totally agree and I am not going to insulate the gable walls, but this is a description of my problems. A insulating contractor told me that my problem was that I was not getting enough air in the attic because the soffit vents were plugged with the blow in insulation and he wants to put in larger gable vents and a twirly bird vent on top of the roof and blow in fiberglass insulation. I checked this out and he was wrong as air was flowing through the louvers stapled on the underside of the roof. Right now I have 4 inches of fiberglass batt insulations between the joists and about 3 inches of cellulose insulation on top of the the batt insulation. I have taken the time to move the cellulose insulation that is up their to underside of the louvers without plugging them up and not pushing it on the soffits. Then I was going to blow another 10 inches of cellulose insulation in. After your reply I believe the insulating contractor is misleading me. Let me know what you think and if I am on the right track. I appreciate your help.

Dale

 
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10-12-07, 04:37 PM   #6  
Finishing answering your question?

Forgot to mention that I do have other issues with heating and cooling. My windows are 1973 and doors the same, in fact here is a great one for Montana winters; my doors are not enough solid doors. This is the next project, but I'm not sure if this would change what is needed for ventilation in the upstairs. Again, thanks for your help.

Dale

 
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10-12-07, 05:09 PM   #7  
I think your plan is sound. Don't spend any time or money insulating gable ends that separate the ventilated attic from outside. But do add some on top of what you have on the attic floor. That should get you the most bang for your buck. The heat generated in your attic comes from infrared radiation penetrating the roof and hitting the top of the attic insulation. Ventilation will remove some of that heat but unless your house is sealed, a powered attic ventilator may pull more conditioned air out of your house and that is an energy waster. I would go with ridge vent and soffit vents and live with it.

Ken

 
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10-13-07, 04:10 AM   #8  
Yes your plan sounds good. You already have good ventilation up in the attic so i wouldnt change it. Adding more insulation though is crucial. In montana you need R49 at least in an attic. With 4 inches of batts and 3 inches of cellulose you really have about R24--way less. You need an additional R25 which is 8 more inches of cellulose but go ahead and blow in 10 just to be sure. Be sure to seal up with foam any penetrations of your attic space from below while you can get to them.
Your windows are old but so are mine in cold ohio. I just make sure they are tight with the locks and put in rope caulk and even insulation tape to seal out the leaks. It really makes a difference. Do the same with drafts around the doors and get some weatherstipping if needed.
I bet if you do all this your house will be more comfortable and probably wont cost you more than a 150 bucks depending on how much cellulose you buy. How much was the shady contractor going to charge you?

 
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10-14-07, 08:17 PM   #9  
Cost of Contractor

He was going to charge about $700-$800.

Dale

 
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