What is best strategy for insulating a garage

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Old 12-19-03, 05:47 PM
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Question What is best strategy for insulating a garage

I have a typical split entry home from the late 60's with three bedrooms over the garage. It is six degrees cooler in these rooms than in the rest of the house. I do not want to get special heaters or create a third zone of forced hot water heating in those bedrooms. I presume if I insulate the garage better, than I can reduce considerably the temperature difference between the bedrooms and the reest of the house. What is a cost effective way to proceed? My garage doors are the original, old wood doors with a poor fit with the concrete floor. New insulated steel doors would cost around $2,000 in my area (NW suburb of Boston). I have no estimates on better insulating the garage ceiling. I imagine the garage walls have little or no insulation. What do you advise?
 
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Old 12-20-03, 06:16 AM
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The single most effective approach to insulating the garage from the rooms would be to increase the insulation in the ceiling of the garage (floor of the rooms) to the highest recommended level.

Is the insulation in the attic over the rooms at its peak? How about the exterior walls of the rooms?
 
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Old 12-20-03, 02:51 PM
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Question What would be maximal insulation

I have heard other people comment in houses like mine that even with insulation in the garage ceiling, thick pads for the carpets in the rooms above, and good wool carpets, they still get cold floors and a noticeable temperature difference. In trying to research the problem for my house are there good technical papers that describe ideal insulation for an unheated garage? Is lateral air flow between the garage ceiling and the floor above a major cause of this cooling effect even with reasonable insulation? I just do not want to commit real money and then be disappointed that it has done little good.

Thank you for your responses.
 
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Old 12-20-03, 06:57 PM
BSparks294
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I have the exact same problem and my kids always complain about the temperature difference in their rooms.

Their rooms do not even sit above the garage but just run adjacent to the inside eve of the garage space.

I would like to hear of a good solution, I too had contemplated sheetrocking the ceiling of the garage and putting insulation up there.

Thanks, Brad
 
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Old 12-20-03, 09:02 PM
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Overall, insulation works best in the attic, then the walls, then the floor. Rooms can be cold due to poor heat distribution or drafts.

There will likely be no air flow between the ceiling and floor if the insulation and sheetrock are properly installed, because there should be no openings to allow any.

There is much research that can be read at the Oak Ridge National Lab site.

Hope this helps.
 
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Old 12-23-03, 01:49 PM
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My experience might be helpful

I had the same situation as Richard904, with two cold bedrooms over the garage. One of the rooms had weak heat (ridiculously long ductwork path) and you could see your breath it was so cold. I agree with chfite's advice except to check whether increasing the floor insulation is cost-effective. I calculated heat loss savings so I could perform the work that gave the best improvement for the money. You can do the same:

Q(svgs in BTU/hr) = Area * (Tinside-Toutside) * (1/oldR - 1/newR)
For calculation of R, see
http://coloradoenergy.org/procorner/stuff/r-values.htm

I used average winter nighttime temps of
Toutside = 20F, Tinside = 55F
although Toutside is lower in Jan/Feb so the improvement is greater during those months.

Area of floor and ceiling of coldest room are 175 sq ft

Here is what I did 1-1/2 years ago:
1) Increased attic insulation throughout the house from R-11 to R-36, but doubled the batts to get R-61 over the cold rooms since it was easy to do.
Q(attic_svgs) = 456 BTU/hr for the coldest room. I did it myself, cost for the BR was about $0.26/BTU/hr.

2) Opened a hole in the garage ceiling, found R-11 stapled in the center of the 2x10 joist cavities for a total ceiling/floor value of R-15. It could be about double if the cavities were filled with fiberglass. However: Ripping open whole ceiling, filling cavities, then re-drywalling would increase floor insulation to R-31 but would save only 160 BTU/hr since the average nighttime garage temp was about 28F. (It drops to only 90 BTU/hr with the 40F garage temp in #4 below). Since the expense is huge and the payoff small, I left it alone.

3) Adding a Hunter-Douglas honeycomb shade to the double-glazed window was easy, and increased insulation from R-2 to R-5 for
Q(window_svgs) = 112 BTU/hr.
Cost = $0.50/BTU.
Adding the shade to a single-pane would be even more dramatic (370 BTU/hr)

After these changes the cold bedroom was same as rest of house, while the icy one improved to merely cold.

4) Last summer I insulated the garage walls with R-13 and 5/8" drywall. Mudded and taped the seams at the garage ceiling that previously let cold air up into the joist cavity. So far this winter the garage temp stays at 40F even when it's 0F outside.
Heat savings from the bedroom to the garage at 40F compared to when the garage was 28F is
Q(garage_svgs) = 130 BTU/hr
Cost = $1.38/BTU
The cost is high when considering just the one bedroom, but when I look at savings from the entire house (500 BTU/hr) it is only $0.36. So this was a winner.

My next step will be weatherstripping around the garage doors. It's dirt cheap and very effective. Then I'm done.

I had thought about adding insulated garage doors but didn't because of the high cost and small benefit. Upgrading my dual 9x7's from R-2 to, say, R-6 might raise the garage temp another 5F but the reduced heat loss from the whole house is only 430 BTU/hr at a cost of $4.65/BTU!

In the rest of the house, I insulated the crawlspace under the dining room, beefed up weatherstripping and caulking, and replaced a 9' wide single-pane aluminum sliding window with a wooden low-E double-glazed French door assembly.

Insulating the garage, attic and window brought the icy bedroom to the same temp as the rest of the house. We retired the jackets and space heater, and the children are happy. Our family room is now warm. The cars are a pleasure to climb into in the morning, too. Finally, our January heating bill was $50 lower last winter than the previous, and should be lower still this winter.

Hope this helps you decide where to put you money and efforts!
 

Last edited by marcusl; 12-24-03 at 11:27 AM.
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Old 12-24-03, 01:51 PM
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Lightbulb Marcus, thank you for the intelligent reply

Thank you for the reply and the effort you put into it and your willingness to share it with others. I printed it out, so I could more easily study it and adapt your research to my situation. I am quite impressed with the serous analytics that lead you to the best steps to be done.

Parenthetically let me mention as a layperson that this shows the value of forums like this to give aid and support to the unsophisticated user.
 
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Old 12-24-03, 05:06 PM
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You're very welcome. Just for the record, I'm a "layperson" too, a weekend DIY'er like yourself. I have a background in physics, though, and I like to calculate things--can't help myself!

regards,
 
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Old 12-24-03, 09:16 PM
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That was a great post and I will be sheetrocking AND insulating my garage, walls and ceiling come this spring. Sounds like the most economical and efficient way to keep the bedrooms warmer. I do not have a heating problem, as I have dual furnaces, one in the attic and one in the basement. The run from the one in the attic, to the bedrooms in question is only about 10 feet.

Great forum, thanks---Brad
 
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Old 12-25-03, 10:25 AM
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marcusl

Regarding the 3 1/2 inch insulation in a 2x10 cavity, I doubt you could count on it having any insulation value if the insulation wasn't a good fit. If the cavity air isn't 'trapped', you don't have insulation.

Also consider the convection inside the garage. It might seem that ceilings only transfer heat, but in this case it could be argued that the ceiling is transferring cold. It might be the warmest air of the garage, but it's colder than the space above it.


What comes to my mind is the 'warmth' I feel when I stand barefoot on Styrofoam slabs. There are dense EPS foams (marginally) capable of foot traffic; with addition of the proper underlayment it's a great opportunity to install a heated floor. You would lose some interior headroom, but would gain comfort.

As to the original query, it might be a good idea to investigate what was installed between the garage ceiling joists. Maybe nothing was installed, or less than joist depth. If indeed there is insulation, how snug is it? Ripping down a drywall ceiling isn't hard since gravity is on your side. Plaster is a tedium, but drywall is quick.

If the joist cavities are insulated to the maximum and it's snug, then maybe the ceiling isn't the problem. We would all hope that the second floor walls were properly insulated, but you won't know how the walls (and the attic) were insulated until you investigate.

Remember, many of these above-the-garage rooms were originally "bonus rooms" and who knows who did the finish work.
 
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Old 12-26-03, 06:30 PM
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I have the exact same problem with cool rooms over my garage. In mine there is not sheetrock on the garage celing, just 4" insulation. This insulation has the vapor barrier. What do you recommend to help? Should I just pull this stuff down and replace with unfaced insullation and then install sheet rock? Or could I put thicker stuff over the exsitng insulation. Does any new insulation need to have a vapor barrier? I've got 2x10 rafters, is there a maximum thickness of insulation that I can put in? Packing more that a 10-inch thick bat doesn't help, correct?

thanks,

Brian
 
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Old 12-26-03, 09:14 PM
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no_sparks

You can productively add to the existing insulation with unfaced insulation another 3.5 inches, which will give you about R-22. This is about as much floor insulation as is recommended. You could add to the total space of the 2x10 and gain more R-value. The insulation should be covered with sheetrock or other fire barrier to prevent its ready combustion, as fiberglass is usually required by code to be covered. There is no point in compressing insulation as this reduces its R-value.

Hope this helps.
 
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Old 12-28-03, 12:50 PM
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It's great to see so many posts in this thread!

Brad--you're welcome and best of luck on your project. Don't forget to add to the attic insulation as chfite advised. It is the most effective and usually the cheapest way to reduce heat loss.

Steve--
a) the 3-1/2" fiberglass batts in my garage ceiling are a tight fit, but they are stapled into the middle of the joist cavity so there is a 1-1/2" space between the batt and the floor above, and the same between the batt and the drywall below. The batt gives R-11 worth of insulation.

b) Convection becomes a factor for the "dead" air spaces above and below, however. The optimum thickness of an air slab (for lack of a better word) is about 1/2" as is well-known by double-paned window manufacturers. Thicker spaces begin to support convection and so don't offer additional insulating value. The website I referenced below states that all cavities from 1" - 4" are worth R-1. I'm sure that's an approximation but a small change in value won't change the results of the calculations in any significant way.

c) There is no such thing as "transferring cold." The physical entity is heat.

d) I agree that assessing the existing ceiling/attic/wall insulation is a good idea. You can't decide where to start otherwise. However I think redoing the garage ceiling is a major job (literally a pain in the neck). Hanging 4x8 sheets of 5/8" fire-rated drywall overhead is hard work.

Brian no_sparks-- chfite gave you good advice. Most codes require 5/8" fire-rated drywall in the garage.
 
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