Keeping a garage warm: What would you do next?

[William Schmitz]

The recommended order of business is to tackle air infiltration before insulation. There is quite a bit of information available on the internet for this topic, such as:

http://www.simplehomerepairs.com/Weatherproofing.html

This means caulk and weatherstrip. Especially as you plan to heat your shop from "cold" prior to use with a convection heater (heating the air, not the surfaces); if you don't keep the cold air from continuing to come in you will end up with a hot head and freezing cold feet!

In addition, insulate the ceiling as recommended here. Insulating walls is much more work, so save that for another year.

I suspect a reason you are getting your shop up to around 52 fast, then having trouble above that is that all your heat is rising above you and shutting off the heater (mounted high with an internal thermostat, I suspect). A remote thermostat should help with this, mounted at the level of the people.

[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.

[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.

[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.

[Doug Carpenter]

In the 20 years I have been a general contractor it seems the industry has changed its view on vapor barriers several times. I have worried that any job I did in the past will haunt me later. Often it is the same subcontractor that tells me what we did last time was wrong!

I think there is no need for extra vapor barrier here. If you use kraft faced insulation put it towards the heated space. If you have some sort of vapor barrier don't use faced insulation over that. I think as leaky as a garage is it isn't a concern, especially if you open the garage door often.

My insulation has a $350 minimum and doing a garage ceiling would fall under that catagory. They buy such huge quanities of material that I can't touch it by doing it my self.

I'll bet the 15" and the 16" batts are the same size. The 16'' material is made to fit between to studs or joists so they probrably measure 14 1/2".

If you are 32" oc then it will measure 30 1/2" so you might not make it. You could do it with the 16" and leave the space and then blanket another layer perpendicular to the joists but that may be out of the budget for now. If the 16" stuff you mention is actually 16 the squishing it in isn't going to cause a problem. Or maybe you could get both sizes and one of each will do the job.

For the walls later I would check with a pro because there are other options than batts and blown in.

[Augusto Orosco]

If you are 32" oc then it will measure 30 1/2" so you might not make it. ... maybe you could get both sizes and one of each will do the job.

I decided to follow Doug and Mike's suggestion and go with a 15" / 16" combination, but once I got to the store, they had a lot of 15" R30 but no 16" rolls or batts to be found . Since the 15" rolls were so cheap per sqf compared to the rest I took the risk and bought enough for the full job (they do measure exactly 15").

Late last night I was able to cover about 40% of the attic in less than two hours (not as hard as I was expecting, even with cutting around electrical boxes). Two 15" rolls side by side seem to fill the space between joists well. I'll see how it works once the job if finished. I saved a good deal of money, so I could still find a way to make make them fit tighter if needed (such as placing a roll of 15" R19 on top, right in the middle where the two R30s meet)

[Rick Metcalf]

Agusto,
If you consult your building department and indicate that you are adding heat to a space in MA, the AHJ will require you to have a building permit and meet the state energy code for the building envelope. This will be way more costly than you now imagine. The best solution would be to fill the ceiling joist space with faced batts to fit the depth of the ceiling joists. Tape the joints, joining the batts (15" to 16") and staple the kraft face to the inside of the joists close to the ceiling to seal as best as you are going to get without removing the ceiling sheetrock. Lay another layer of unfaced R-30 across the top of the joists. Make sure the soffit vents are not blocked. Pick up some owens-corning raft-r-vent shims if you have soffit style vents and gable vents. This will keep the space above the insulation ventilated and cold to prevent mold growth on the underside of your roof. If the floor is in good condition, consider sealing it with a quality epoxy sealer. With the floor sealed, other that you sweating hard over the workbench, the moisture from internal sources in a garage environment are pretty negligible. Best of luck with the project.