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pasichnyk 11-27-2010 09:23 PM

Insulate finished garage ceiling or condition garage?
I have a drive in garage (basement level) with slab cement floor and walls (top few feet of walls are wood framed with brick exterior). My living room sits directly over the garage (about the same size too) with hardwood floors. The living room floors are noticably cold, due to the unheated garage and uninsulated floor cavity. Our forced air furnace can keep up just fine, but this room is always colder than the rest, due to the floors mostly. Air could be warm (even too warm), but you "feel cold" from the floors. I'd like to even this out and just get a overall warmer feeling to the room.

Hardwood Floor to garage ceiling are like this:

FLOOR JOISTS (~10") - Currently air space
SUBFLOOR material (yeah, again...)
1/2" drywall
1/2" plaster (in a metal mesh lathe)

I see that I have a few options here:
  1. Insulate the floor cavity
    1. Seeing as the cavity would need access holes drilled to blow in insulation, I believe I'm stuck with either cellulose or fiberglass? Suggestions on which would be more cost effective/insulating effective?
    2. Anyone have a acceptable price range for this? Just to keep the estimators in check. :)
  2. Condition the garage (as much as possible)
    1. Garage door insulation kit
    2. insulate walls with something (sprayfoam, rigid foam, ...)
    3. better seals on the bottom of the garage door, etc
  3. Both
    1. Not sure if it would be overkill (is there ROI?) but I could start off with one of the above, and then do the second to help in the future, but I think there are other areas of the house which could use the attention/money first...
I'm in Seattle, so usually in the 30-40's in the winter, +/- depending on the day.... Slab walls are mostly underground, maybe 1.5ft or so above the dirt.

I was thinking that it would probably be most effective to get someone to come bore some access holes in the ceiling and spray in the cavities, but just wanted some opinions on the best approach from an ROI point of view.


jklingel 11-28-2010 02:06 AM

After doing a lot of reading on and about this, I would be inclined to condition the basement, esp since you would have to retro-insulate the floor. Mineral wool is apparently good against basement walls, if you air seal well. Look up ADA (airtight drywall approach). Or, rigid foam w/ spray foam at the edges to fill gaps. No vapor barrier. Your statement "even too hot" typifies what happens in your situation, as warm air (forced air heat) will rise like a banchi and leave the floor cold.

pasichnyk 11-28-2010 12:40 PM

So you think I would get more insulation for my money/effort with conditioning the basement alone? I didn't aim to fully finish the garage anytime soon, so if I went this route id probably just glue/seal foam boards to the walls (at least the top section) and insulate the door. However I would still be left with an uninsulated area on the exterior wall in the 10" floor cavity which I'm assuming would leak a lot into my "conditioned" space. The only way i could insulate that section would be to cut access holes in each floor joist section and try to can spray foam each section. do you think this is necessary?

My exterior walls are wood framed with a single layer of brick face, and the cavity is uninsulated currently, but I don't want to blow in insulation until i can pull out and replace all the old knob and tube wiring.

Anyway, I understand this is going to be an incremental process and I'm just looking to do peices of it that will all add up to a good finished product.

Scuba_Dave 11-28-2010 12:52 PM

I'm going to insulate my garage fully
Planning on insulation under the slab, insulated garage doors
I may never heat the garage, but I do have a kerosene heater I could use out there
Or a few electric heaters if I needed to work out there
Insulating the garage ceiling would have a noticeable effect on keeping the room above warmer
Make sure that the drywall is 5/8" when it goes back up to meet code

My garage is not insulated yet, but its a lot warmer then outside

jklingel 11-28-2010 01:11 PM

It's hard to define anything w/ out being there, and you have your own criteria to meet, too; we all do. So, insulating the ceiling will sure help, but can be problematic. Conditioning the crawl space is apparently the best way to minimize problems w/ vapor. If you can't finish, it may be best to wait till the money and time are all there and do it as best you can, once. That'll have to be your call.

pasichnyk 11-28-2010 03:19 PM

In my case the slab is poured on dirt, so there is no crawl space to condition. However its a drive in to garage below grade, so the slab is actually about six feet below ground, so I wouldn't expect huge loss there as compared to the walls near or above the surface, or the door itself.

Money is not as much of a concern as doing the project correctly, bug at the same time I'm not going to throw it away on a solution that is way more expensive but doesn't really get me anything extra. ROI is important...

If I start off by conditioning the walls and door of the garage, is gluing and selling foam board to the walls A good approach if I don't plan on framing in the walls, or so I need to frame (adding unfaced batts) and drywall on top of the foam to be up to code?

jklingel 11-28-2010 03:34 PM

If you can get the foam to stick permanently, then it outta do ya some good. Give 'er a go. j

pasichnyk 11-28-2010 11:29 PM

Is there any pretreatement of the concrete walls that should be done prior to glueing the foam board to the walls, such as sealing paint, etc? The walls appear to be fairly (if not totally) dry...

Is there a certain type of foam board that would be best? What about glue and tape?

jklingel 11-29-2010 12:21 AM

Generally, you don't want a concrete wall sealed on the interior, since it can';t breathe to the outside. It could not breathe at all, then. If painted for aesthetics, they should be painted w/ a latex paint that is vapor open. I do not have the goo name off the top of my head, but there are specific ones for each kind of plastic. I think EPS (white, "bead board") is probably OK to use, and it is more permeable than XPS. No foil faced. Since your walls appear dry, I THINK you'll be fine w/ EPS. I used to think it was XPS only, but that seems debatable now. Apparently EPS only absorbs about 0.2% of its weight in water. Myself, I'd stick w/ XPS unless someone more knowledgeable says EPS.

pasichnyk 12-05-2010 01:28 AM

what about foil backed polyiso for the garage door? What about the walls, would the foil backed stuff be ok, or stick with the pink/blue board?

jklingel 12-05-2010 01:33 AM

same problem. door is a vapor barrier. i'd use regular foam.

pasichnyk 12-05-2010 02:08 AM

regular meaning blue/pink or white?

jklingel 12-05-2010 12:20 PM

i'd be inclined to use white (EPS) as it is more vapor permeable. you may even want to try one section on the door and see if you get any condensation problems before you insulate the whole door.

pasichnyk 12-05-2010 12:33 PM


Originally Posted by jklingel (Post 545875)
i'd be inclined to use white (EPS) as it is more vapor permeable. you may even want to try one section on the door and see if you get any condensation problems before you insulate the whole door.

Does the metal door itself not act as a vapor barrier? Is the point for more permeable insulation here to let anythign condensing on the metal itself to escape? You know, the kits that i have see are all white board, so maybe that is the way to go anyway. I just wanted to get the extra R value if i could, but seems maybe too much risk.

That said, you mentiond earlier that the blue/pink board is what you'd use against the poured concrete wall. That still stand?

jklingel 12-05-2010 01:12 PM


Originally Posted by pasichnyk (Post 545878)
That said, you mentiond earlier that the blue/pink board is what you'd use against the poured concrete wall. That still stand?

Yes, and I can't rationally explain why. XPS has been "the standard" because of fear of EPS absorbing water, but apparently the water absorption is minimal. I would expect a wall to be more likely to condense, so I'd go w/ XPS on a wall. If you ever dig into this on, or some other site of good reputation, let us know what you find. j

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