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# Questions about insulating my garage,...

## Questions about insulating my garage,...

#1
01-08-10, 12:52 AM
Member
Join Date: Apr 2009
Location: belvidere, nj
Posts: 6

I have a very big 2 car garage with a loft. Actually its a 3 car garage. About 750+sf.

I read somewhere that im in a zone where R-49 is needed for the roof of the garage. R-49? Really? I was thinking R-30 at the most. Does it REALLY make that much of a difference?

I also found the page online where this guy said that merely insulatiing the roof alone makes that much of a difference. He used R-11 for his roof. He said before the insulation his kero heater of 23,000btu's per hour would increase the temp by 3 - 4deg. After insulating there was an increase of 20 - 25deg! With R-11.

Now I know im not going to use R-11. I want R-30. If R-11 was able to increase by that much R-30 should be just fine right?!?!

About vapor barriers,... or kraft faced insulation,.... it suppose to face the heated room right?

#2
01-08-10, 05:09 AM
Member
Join Date: Oct 2008
Location: New England
Posts: 9,460
"About vapor barriers,... or kraft faced insulation,.... it suppose to face the heated room right?"
It's supposed to be a continous layer just above the sheetrock, but if it is not there. like a layer of plastic, then a Kraft faced insulation layed with Kraft to the warm side will provide some protection. That assumes there are no holes/keaks in the air barrier (the sheetrock).
Now, let's look at the numbers. A ceiling with no insulation would be a combination of plain sheetrock and some beams, let's use an average of R=2. Now add a layer of R=11 for a new total average of R=12. The wood did not get improved, just the cavity. You would now be losing 1/6th of the heat through the ceiling as with no insulation. Really rough numbers. So the first layer of insulation does have a large effect. Now add another layer of R=11 and you will only reduce the heat loss by 1/2 over the first layer of insulation. Going with R=30 would be a huge improvement over nothing, so why R=49? The amount of recommended insulation is based upon the cost of fuel and some reasonable time for payback. If you could put \$100 in the bank and every year they would give you \$50 back, that would be a very good investment. But, if they would only give you \$2 back, and remember they are keeping the original \$100, then that would be a very poor investment. Somewhere in between is the R=49.

In your case, this is a garage. What temp it will be, how good the doors are, the walls, all must be considered. Plus tomorrows cost of fuel. If you remember the last big run-up in prices, they didn't give us a whole lot of notice. If you are going to close thing in so adding more would be difficult, then go as high as possible. R=30 is not bad, but there may be more to save depending on other factors.

Bud

#3
01-08-10, 07:18 AM
Member
Join Date: Apr 2009
Location: belvidere, nj
Posts: 6
Ok I understand. Thanks for the explaination.

#4
01-08-10, 01:12 PM
Forum Topic Moderator
Join Date: Mar 2005
Location: USA - N.E.Tn
Posts: 45,813
..also the odds are you won't heat or cool the garage space as you would the living space of your home so how well you insulate isn't as critical as it would be on the inside of the home.

#5
01-08-10, 06:40 PM
Member
Join Date: Mar 2009
Location: WA
Posts: 1,052
Your heating dollars: walls- 21% leaks- 25% doors- 3% floor- 6% roof- 12% wind- 19% duct leaks- 14% ColoradoENERGY.org - R-Value Table Roof Insulation and Diminishing Returns http://www.anchorinsulation.com/pdfs...insulation.pdf
There is also v.b. primer paint for over the drywall texture if using unfaced insulation.
Be safe, Gary

#6
01-09-10, 08:50 PM
Member
Join Date: Apr 2009
Location: belvidere, nj
Posts: 6
That is true. It is a garage and not a house. I will be in there a lot though. But I definitely wont be heating is as well as the house. I just want it to be some what comfortable. I can deal with working in there with jeans and a long sleeve sweat shirt. Wearing warm clothes is dirt cheap. But right now its like 15deg out and I can even finishing some framing work because its that cold in there. Wearing 2 - 3 layers of clothing.

Now there is a sale on R-30 unfaced insulation in my area. its like \$10 for about 31sf. If I got that and used a plastic sheet as a vapor barrier would that be suffice? And what is this VB primer paint?