Keeping a garage warm: What would you do next?

[Charles Murray Ohio]

I built my shop last year. After getting a quote, I installed it myself. A friend on my who is an air systems engineer designed the system (duct sizes and location, BTU and AC size). One of the things he recommended was to upsize the blower due to the 10’ ceilings. The system works great, better than the professionally installed one in my house. I used a 95 plus natural gas furnace, that has sealed combustion. A concentric vent brings in fresh air for the unit to burn and exhausts the gases. It took me two weeks to do both floors (the furnace is located upstairs). I also installed cold air grills that have a filter rack built in, this help keep the sawdust from being sucked through the return pipes. When it was done I saved approximately $6,000.

[Augusto Orosco]

I wouldn't worry too much about a vapor barrier since you have space between the attic floor and roof. If it was a catherdral ceiling you may want to consider the barrier.

Two contractors just told me the same thing (no need for a vapor barrier since I am insulating the floor of the attic, not the roof); but at the same time I keep reading online that kraft paper faced insulation (if fiberglass) or another sort of vapor barrier (if blow in) should be used for this application. I am a little confused now

[John McClanahan]

I watched an episode of "This Old house", where they were adding insulation to an already finished attic. Tom Silva stated that any oil based primer or paint will serve as a vapor barrier. They were blowing insulation in the walls.

John

[George Bregar]

I watched an episode of "This Old house", where they were adding insulation to an already finished attic. Tom Silva stated that any oil based primer or paint will serve as a vapor barrier. They were blowing insulation in the walls.

John

Again, I think there is a difference between an interior heated living space and a garage that goes unheated and has a concrete floor. What are is damper....your gargae or house? Also, there is a reason that they use an insulation WITH a vapor barrier on new construction, and don't simply prime and paint the walls. Drywall must be primed and painted...why not just skip the faced insulation and the added cost?

[Mark Beall]

From what I've heard/read current research on building methods is raising significant questions on whether vapor retarders are useful in walls/ceilings in many climates. The main issue that I've heard is that in areas where it is very cold and dry in the winter and hot and humid in the summer the vapor retarder is in the wrong place half of the time and causes problems due to that.

This page mentions this about halfway down:

http://www.ornl.gov/sci/roofs+walls/...on/ins_05.html

mark

[John McClanahan]

Insulation with a vapor barrier is great for new construction, but Augusto listed sheetrocked, uninsulated walls. The oil based paint is an option if he chooses to blow insulation behind the existing walls.

John

[Augusto Orosco]

From what I've heard/read current research on building methods is raising significant questions on whether vapor retarders are useful in walls/ceilings in many climates. The main issue that I've heard is that in areas where it is very cold and dry in the winter and hot and humid in the summer the vapor retarder is in the wrong place half of the time and causes problems due to that.

This page mentions this about halfway down:

http://www.ornl.gov/sci/roofs+walls/...on/ins_05.html

mark

I have been reading similar opinions, Mark, therefore my doubts. I think I will call the town and see if at least they have an official opinion on that.

[Augusto Orosco]

I would think they are 24" OC

I got into the attic tonight to double check... the joists are 32" OC. Is that standard? I guess the original builder was cheap

This is probably silly question, but I have no clue: For batts/rolls, should I get the 15" wide or the 16" wide ones, assuming that I need two batts side to side to fill up one cavitiy? The exact space in between joists is 30.5". Two of the 15" sound too short, but two of the 16" would be 1.5" too wide, and am concerced about compressing the insulation and loosing R value

[Mark Beall]

Here's another reference, although related to basements:

http://www.eere.energy.gov/buildings...s/db/35017.pdf

the conclusion is similar. Trying to stop the movement of moisture rather than allowing it, can really cause problems in some cases (even if you follow what people consider to be the "correct" rules)

Based on what I've read, I suspect that, for a garage, there's really no need for a vapor barrier since:
- in the summer (assuming you don't install AC in the garage) you're not going to have much temperature differential to deal with, so it's not really an issue at all (if there isn't a temperature differential, you can't get condensation)
- in the winter (assuming you don't install a humidifier), you're not going to have much moisture in the air in the garage, regardless of the temperature. Since you're basically going to be heating outside air, your relative humidity in the garage will actually be lower than the outside air (which will have very little moisture in it anyhow).

The only real issue I can see is that you'll have to allow for the fact that any wood stored in your garage in the winter will become very dry. Make sure you leave space for expansion when you move a piece into the house.

mark

[George Bregar]

Here's another reference, although related to basements:

http://www.eere.energy.gov/buildings...s/db/35017.pdf

the conclusion is similar. Trying to stop the movement of moisture rather than allowing it, can really cause problems in some cases (even if you follow what people consider to be the "correct" rules)

Based on what I've read, I suspect that, for a garage, there's really no need for a vapor barrier since:
- in the summer (assuming you don't install AC in the garage) you're not going to have much temperature differential to deal with, so it's not really an issue at all (if there isn't a temperature differential, you can't get condensation)
- in the winter (assuming you don't install a humidifier), you're not going to have much moisture in the air in the garage, regardless of the temperature. Since you're basically going to be heating outside air, your relative humidity in the garage will actually be lower than the outside air (which will have very little moisture in it anyhow).

The only real issue I can see is that you'll have to allow for the fact that any wood stored in your garage in the winter will become very dry. Make sure you leave space for expansion when you move a piece into the house.

mark

Your source was about basement walls, which are a different animal. As for the rest, this idea that you won't have "much moisture" in the winter...work in your garage in th winter and watch the water form on the windows. Car exhaust is mostly water. Human exhale water vapor. The concrete slab is going to put moisture in the air. And there is moisture in it already...right now its 17F in Madison, and 67% RH.

In the summer you have high humidity, but not equal temperature. At night outside temps will cool much faster than inside because of the insulation in the walls.

And there are four seasons...the others are spring and fall. Both generally have higher humidity and cool temps.

There is a reason that insulation manufacturers and those that install it use vapor barriers. And don't tell the painting contractors "you handle it".

[Mark Beall]

Your source was about basement walls, which are a different animal. As for the rest, this idea that you won't have "much moisture" in the winter...work in your garage in th winter and watch the water form on the windows. Car exhaust is mostly water. Human exhale water vapor. The concrete slab is going to put moisture in the air. And there is moisture in it already...right now its 17F in Madison, and 67% RH.

In the summer you have high humidity, but not equal temperature. At night outside temps will cool much faster than inside because of the insulation in the walls.

And there are four seasons...the others are spring and fall. Both generally have higher humidity and cool temps.

There is a reason that insulation manufacturers and those that install it use vapor barriers. And don't tell the painting contractors "you handle it".

Yes, basements are different, that's why I said "although related to basements", however the reasons and the conclusions are similar.

If you take air at 17F and 67% RH and heat it, the relative humidity will drop very quickly. That why, in the winter, the RH in your house can be extremely low in that kind of climate. All of the sources of moisture in a house (people, cooking, showers, etc. ) are not enough to bring the RH levels up to comfortable levels (at least 30%) in most cases. Running your car in the garage to raise the humidity level could be a bad idea...

Vapor barriers are most often used currently since that has been the recommended practice. Research in the last 10 years or so is indicating that this is actually quite a bad idea in some cases. The rational was that if you have hot, moist air on one side of a wall and cool, dry (dry in the absolute sense, not in terms of RH) air on the other, that you want the vapor barrier on the hot side so that you prevent that moisture from moving through the wall, to cooler temps (which raises the RH) to the point that it gets to 100% RH and condenses. (note that these conditions generally only exist in winter and summer, there isn't enough temperature differential the rest of the year) There are several problems with this idea: You cannot stop all moisture movement, it will still happen, you will still get condensation in the walls. If you have a vapor barrier in place you then are making it harder for the walls to dry out when the conditions that caused the condensation have passed. Also in areas where it's cold in the winter and hot and humid in the summer, half of the year you have the vapor barrier on the wrong side of the wall, so it's actually making the situation worse.

If you had a new house built today, they would most likely use a vapor barrier. As the research that has been done gets incorporated into standard building practices that will most likely change in some parts of the country.

As for the situation asked about in this thread, the original rational for a vapor barrier barely exists since the RH levels in the garage will be quite low and it will only be heated part of the time. Due to both of these things, I'd be surprised if there would be any significant moisture migration into the walls.

mark

[Doug Swanson]

+1....and nobody wants to admit that vapor barriers are bad (building codes) because then you would could have a huge liability to contend with...my brother is in that line of work and it is a sticky issue to address in the codes...

[Augusto Orosco]

I spent a few minutes tonight making a couple of platforms so it's safer to move around the attic. Because the joists are 32” OC, I didn't feel that a piece of plywood would be sturdy enough to support my weight. I ended up reinforcing a couple of pieces of plywood with 2x4s and brought them up the attic space.

Moving around is going to be a challenge. The attic is not high enough to stand straight in most places, and with the joist being so apart from each other, I really need to rely on the platforms, which are not the lightest things to move around, given the reinforcement.

We'll see how it goes... I will get the insulation this weekend and will try to tackle the project at nights. I had the heater running today and brought the shop to 50F (pretty good, since the outside temp was in the low teens, and very windy), but every time I went up the ladder, I could feel how much warmer it was higher up. I think insulating the ceiling will make a big difference.

[Bill Clifton]

Ceiling - I paid $0.48 /sf for R-30 fiberglas blown in by a reputable company. It took 2 men no more than about 1 1/2 hours. Best thing I ever did was to hire it done.

Ask the same company you call for blowing in the attic about the walls. I bet they can drill holes through the sheetrock and blow it into the walls cheaply and quickly.

[Augusto Orosco]

Ceiling - I paid $0.48 /sf for R-30 fiberglas blown in by a reputable company. It took 2 men no more than about 1 1/2 hours. Best thing I ever did was to hire it done.

Ask the same company you call for blowing in the attic about the walls. I bet they can drill holes through the sheetrock and blow it into the walls cheaply and quickly.

I would like to know where all of you are getting these quotes... I decided to do it myself, because I can't get anyone to quote me less than $1,250 for 500sf.

Labor in Boston is very expensive!