How to insulate space above garage, below bath/bedroom?

[zolotiyeruki]

One of our bedrooms and one of our bathrooms are built over our (uninsulated) garage, and are quite cold in the winter.  Today, I cut a hole in the garage ceiling and poked my head up there to see what's going on.  As it turns out, there's a surprisingly large space there (see attached picture.  The ceiling of the garage is framed with 2x4's 24" on center, and the floor joists for the bathroom are 2x10's 16" OC.  The bottoms of the floor joists are a full 14" above the 2x4's that make up the garage ceiling, and all the plumbing and ductwork goes through this space.  The builder put R-30 kraft-faced fiberglass batts on top of the garage ceiling, as well as around the perimeter.  They also cut a 4" hole in the side of one of the ducts, so that it partially exhausts into this space.  The air coming out of one of the ducts (not the one with the hole) is not as warm as I think it should be, which is probably contributing to the bedroom being cold.

Would it be worth it to blow in additional cellulose on top of the batt insulation?  I'd make sure to not cover the plumbing, so there would be no danger of pipes freezing.  Given the existing R-30, though, I'm wondering if I'd be better served by paying attention to the attic insulation.  The kraft facing is anything but continuous, so i'm not convinced there would be a moisture problem if I covered it in additional insulation.

Any advice?

[GrowingTheGreen]

I don't understand why the hell they'd try to heat/cool a non-living space. That makes no sense to me. Supply air to the room--not the damn crawl space.

If I'm understanding your description correctly, there is 14-in of space between the garage and bedroom. You would notice a big difference by blowing in insulation. I have no idea where you live, but I've heard fiberglass does better with a lot of moisture compared to cellulose. Since you're trying to control the bedroom and the insulation will fall to the ceiling of the garage, look into air ceiling the crawl space so that air cannot penetrate from the outside.

Something to look into would be dense-packing cellulose. MMM actually did this in one of his posts and reported good results. This would eliminate of the floor of the bedroom not getting any insulation love since it would fill the entire space.

You could also explore close-cell or open-cell foam, though I'm not a fan. For very little rational reason, I'm paranoid about off-gassing.

[zolotiyeruki]

You're right--there's literally a 14" space there.  I'm guessing (just speculating) that since this air space is technically inside the building envelope, and there's plumbing in it, that's why there's a bit of air going to it, to avoid freezing the pipes (we're in the Chicago suburbs).  You can tell where the hole is, too--it's right under the middle of the bathroom floor, and that area of the floor is noticeably warm.

Spray foam is probably not an option, since it's so much more expensive, and it'd be hard to get it applied all the way around--this floor area is about 20'x20', with an access hole from the garage near the middle.  I can sneak a insulation-blowing hose in there no problem, though.

[Bearded Man]

One of our bedrooms and one of our bathrooms are built over our (uninsulated) garage, and are quite cold in the winter.  Today, I cut a hole in the garage ceiling and poked my head up there to see what's going on.  As it turns out, there's a surprisingly large space there (see attached picture.  The ceiling of the garage is framed with 2x4's 24" on center, and the floor joists for the bathroom are 2x10's 16" OC.  The bottoms of the floor joists are a full 14" above the 2x4's that make up the garage ceiling, and all the plumbing and ductwork goes through this space.  The builder put R-30 kraft-faced fiberglass batts on top of the garage ceiling, as well as around the perimeter.  They also cut a 4" hole in the side of one of the ducts, so that it partially exhausts into this space.  The air coming out of one of the ducts (not the one with the hole) is not as warm as I think it should be, which is probably contributing to the bedroom being cold.

Would it be worth it to blow in additional cellulose on top of the batt insulation?  I'd make sure to not cover the plumbing, so there would be no danger of pipes freezing.  Given the existing R-30, though, I'm wondering if I'd be better served by paying attention to the attic insulation.  The kraft facing is anything but continuous, so i'm not convinced there would be a moisture problem if I covered it in additional insulation.

Any advice?

How would adding insulation over the plumbing create risk of it freezing? I thought insulation was supposed to prevent that and more insulation would be better instead of worse.

[zolotiyeruki]

How would adding insulation over the plumbing create risk of it freezing? I thought insulation was supposed to prevent that and more insulation would be better instead of worse.

The current insulation sits between the pipes and the (unheated) garage.  If I put in a ton of insulation on *top* of the pipes, the pipes would be insulated both from the cold garage and from the warm indoors.  It's possible, however unlikely, that the pipes would get too cold in such a situation.

[BudgetSlasher]

Is the plumbing supply or drain?

[zolotiyeruki]

Is the plumbing supply or drain?

Both, although the supply is right up against the underside of the joists.  The drain is a long U-shape, starting with two sinks and a toilet on one side, the looping back to catch the shower and tub (yeah, they're separate, and this is a kids' bathroom!) on the other before heading down to the basement.

[windypig]

I live in Mass. we had an identical situation with the garage. Here we have a state program that provides financial incentives (significant) for energy efficient upgrades. One of the things that the contractors which the state program partnered with was to blow in insulation. They blew it in above our garage and it has made a huge difference in the comfort of the room above the garage. Check to see if your state has such a program.

[zolotiyeruki]

I live in Mass. we had an identical situation with the garage. Here we have a state program that provides financial incentives (significant) for energy efficient upgrades. One of the things that the contractors which the state program partnered with was to blow in insulation. They blew it in above our garage and it has made a huge difference in the comfort of the room above the garage. Check to see if your state has such a program.

Illinois does have such a program, but it suffers from a couple of inadequacies: #1, there's a limited amount of funds available for rebates. If you don't submit your claim early enough, you lose the chance; #2, there's still no state budget, so I'm not sure I'd receive a rebate even if I was early enough, and #3, DIY blown-in insulation isn't eligible--you have to pay someone to do it for you.  It would probably cost about $150 total (insulation plus free blower from Home Depot) to fill the entire cavity with cellulose, and probably several times that much to pay someone else to do it.

I'm treating this as a sort of dry run in preparation for blowing a whole lot more insulation into our attic.  If I can talk DW into helping me with this smaller one, it opens up the possibility of doing the much larger project in the attic.

[Fishindude]

Something is wrong here.  That R-30 fiberglass insulation directly atop the garage ceiling should be pretty good insulation to keep the cold out of this space and to keep your upper floor warm.  I'm betting that insulation is not placed correctly and there are large un-insulated gaps, the perimeter walls of this space are poorly insulated, or there are openings or gaps where outside cold air is getting into this space through the walls or ceiling.

[lthenderson]

The existing bat insulation probably wasn't installed the best and even if it was, cold can transfer through the 2x4's and up into the space. I would blow some insulation up on top of it, not covering the pipes. Because it will cover everything on the garage ceiling, you should be able to keep the bathroom floor warmer. If that still isn't enough, I think putting in floor heating in a bathroom is just the nicest thing on your feet.  I put an electric system between our sub floor and tile and hooked it up to a programmable thermostat so it only comes on for a couple hours in the morning and a couple hours in the evening when we use the bathroom. I turn it off during spring, summer and fall.

[zolotiyeruki]

Something is wrong here.  That R-30 fiberglass insulation directly atop the garage ceiling should be pretty good insulation to keep the cold out of this space and to keep your upper floor warm.  I'm betting that insulation is not placed correctly and there are large un-insulated gaps, the perimeter walls of this space are poorly insulated, or there are openings or gaps where outside cold air is getting into this space through the walls or ceiling.

My guess is that you're right.  When I stuck my head in that space, it looked like the batts stuffed in the bays against the rim joists were...just sort of stuffed in there, not filling the whole space, and the insulation on top of the garage is compressed in some spots by the electrical conduit (yes, our village requires EMT in residential :rolleyes:).  And nowhere does it appear that the batts are taped together, so it's entirely possible that there are gaps between the batts (which blow-in insulation would help resolve).

The outside of the perimeter is actually still under a roof, so I could conceivably add insulation around the *outside* of the perimeter as well.  That would be easier than trying to blow insulation into all those nooks and crannies from the inside.  So maybe I'll blow insulation on top of the garage ceiling (relatively easy), and add insulation around the outside of the perimeter, so I don't have to worry about that rim joist.

[MasterStache]

Here's a great article and actually what I used as a guide when I insulated my garage ceiling.

http://www.finehomebuilding.com/design/departments/energy-smart-details/how-to-insulate-a-cold-floor.aspx

I have 3 bedrooms and 2 bathrooms that sit over my unheated garage. Last winter (first year in the house) we nearly froze to death. Our floors were freezing cold. Turned out they had shoved, many decades ago, R-11 fiberglass batts into 2x10 floor joist. They simply laid on the ceiling with a gigantic air gap between them and the floor. Essentially they provided no insulation value.

This past year, I ripped down the entire ceiling and insulated everything with first R-23 Roxul stone wool insulation. Then added a 2nd layer of R-15 Roxul insulation. Both of these together fit perfectly into a 2X10 joist, with no gaps. Minimum insulation for my area is R-30. I have R38. Roxul is great because you can compress it to fit it into the space and it will expand leaving essentially no air gaps.

At the ends of the joist bays, where the joist sit on the foundation, I cut pieces of 2" thick rigid foam and glued them into place. I spray foamed (can spray foam) around the edges of the rigid foam pieces. This ensures absolutely no air is coming through the foundation into the joist. They look like this:


A lot of homes just throw pieces of fiberglass batts in these areas. Truthfully fiberglass is terrible at stopping air flow. I also have HVAC ducts, which I insulated as well. I am finishing up with the third layer of insulation which is a layer of 1" rigid foam across the entire underside of the joist. Drywall will be next. The layer of rigid insulation acts as a thermal break for the ceiling joist themselves.  Since the insulation really only insulates between the joist, this is a great way to insulate the joist itself. Your wood joist are pretty good at transmitting hot/cold up to your floor, no matter how much insulation you have between the joist. 

Even though I still have some work to do, our floors have been nice and toasty this year. It's made a world of difference.