Advice for insulating unheated garage ceiling

[radojko]

Good day, everyone!

This is my first post, so my apologies in advance for any faux pas that I commit.

We have a huge problem with a very cold floor that is above an unheated garage. The details are as follows...

We live in a condo building in the Northeast (Boston). Our unit is on the first living level, directly above a 40-car, grade level unheated parking garage. We happen to have the misfortune of being directly above the garage door, which not surprisingly gets opened and closed a lot. In the winter, it's not unusual to see floor temperatures in the low 50's in our living room (which has hardwood floors) - this past winter was especially harsh, and I often measured floor temps in the high 40's - brrrrr! We've resigned ourselves to insulating the garage ceiling, even at our own expense if necessary.

The building was constructed in 1989. Lots of corners were cut (don't ask), which includes shoddy insulation of the garage ceiling. The building is a commercial-style structure - i.e., lots of concrete and steel. Sub-floors are 4"-thick concrete slabs that sit in a corrugated steel pan. The pan is supported by thick concrete posts and steel I-beams, spaced approximately every 20 feet. Between and perpendicular to the I-beams are 12"-tall steel lattice joists, spaced every 24 inches. The garage ceiling is finished with a suspended sheetrock surface. The cavity between the sheetrock and the corrugated steel pan is about 18" tall. The cavity was filled haphazardly with fiberglass insulation rolls, maximum thickness of around 4" and lots of gaps. Needless to say, our winters have not been warm and cozy, and our heating bills have been inordinately high, not to mention wasteful and environmentally-unfriendly.

So, I'm looking at having closed-cell foam applied to the corrugated steel pan holding the concrete sub-floor. The area to be covered is about 800 square feet. I'm told that the R-value of CC-foam is about R6-R7 per inch of thickness. I'm also told that one "set" of CC-foam yields about 4000 square feet of coverage at 1" thickness. Doing the math, our 800 square foot area yields about 5" thickness, which provides an R-factor of R30-R35. Of course, the sheetrock ceiling will have to be torn out to apply the foam properly and then will have to be replaced.

So, the $64000 question is: will that much coverage provide adequate insulation to mitigate the severity of the coldness that we experience on our floors? Even better: can we hope to experience *any* relief at all at that thickness using CC-foam? How much R-factor is "enough" - would R-70 be overkill/not worthwhile? Is there another/better insulation option? Also, the ceiling cavity contains some plumbing pipes and electrical wiring - is there any reason for concern about covering those things with the foam.

Questions, questions, questions. Your insights and recommendations will be enormously appreciated...

Regards,
-Bob-

 

[mtmgtz]

Are you saying it is going to cost you $64k to have some closed cell foam sprayed in?? I'd move. You'll never see that money back in the sale of your condo.

That said, R-70 would be overkill. You'd probably notice a huge difference with R-20 on it. I think the worst part is where do you really stop the insulation. The garage below is still unheated and you don't have any thermal break in your floor slab from the adjoining uninsulated concrete slab. The cold will still creep in from the adjoining un-insulated slabs. Maybe not quite as much but it won't be perfect.

EDIT: Just noticed you said the slab is insulated but poorly with fiberglass.

 

[radojko]

Are you saying it is going to cost you $64k to have some closed cell foam sprayed in?? I'd move. You'll never see that money back in the sale of your condo.


EDIT: Just noticed you said the slab is insulated but poorly with fiberglass.

Lol. It looks like I've really dated myself. "The $64000 Question" was a scandal-ridden quiz show from the 50's. It was sorta like an ancestor of "Who Wants to Be a Millionaire", just with a much smaller jackpot question.

In actuality, the quote I've gotten for application of a "single set" (about 5 inches) is $3200.

So, your sense is that the R30-R35 yield from 5 inches is adequate, and there's little/no value in jumping to the next increment...?

Oh, and BTW, when I said that the ceiling is insulated with fiberglass, I should clarify that by saying that the fiberglass (4" or so) lies on the sheetrock ceiling and is not in contact with the steel pan/concrete slab above - i.e., there's a significant (at least 6"-8") air gap between the fiberglass and the pan above.

Many thanks,
-Bob-

 

[radojko]

This is a question for the city and your hoa.
I doubt you have legal access to that parking garage roof.
I doubt the city will let you retrofit one small portion of that roof.
Foam may be illegal. Batts may be illegal. Drywall may no longer be legal. Ceiling height may need changed to meet code. There may be plumbing issues.
This is not a do it yourself project. It involves everyone who uses that garage door.


Too many people to check with before you check with us.

You can quash my doubts by making the phone calls and asking the powers that be.

You are correct in that the area between the garage's drywall ceiling (it's not a "roof") and my concrete sub-floor is a common area that is administered by the HOA Trustees. I've already consulted with the Trustees, who ultimately have the authority to make HOA decisions like this. They are amenable to approving this project, especially if it doesn't result in a major $$$ expenditure by the HOA.

The city building inspection department is a different matter, as you've indicated. Use of CC-foam insulation is allowed. The other issues haven't been addressed just yet.

Right now, this is a fact-finding/research/feasibility exercise. I do appreciate your observations, but what would be far more helpful to me at this point in time is technical information/data that assists me in deciding whether or not to take the next steps...

Thanks,
-Bob-

 

[Andybull]

Spray foam will not only insulate, but will also take care of any draft.

 

[Stuart in MN]

My unscientific guess is that R30-R35 will be more than adequate, and you'd have diminishing returns by going to R-70. Heat rises, so there's not as much heat loss out of the floor as if you were trying to insulate a ceiling in your living space.

Oh, and I'm old enough that I got the $64,000 reference.

 

[Krodad]

You can insulate all you want, but I agree with the poster who mentioned that unless you have a thermal break in the slab, you'll see almost no benefit. A concrete pan deck will simply draw the heat you are putting in the floor… and that is what you're doing… putting energy into the concrete deck.
I would suggest that your only real alternative is to insulate from the inside in this case. If you can afford to lose an inch of ceiling height, pull up the hardwood, hope you don't have a hidden moisture problem from condensate, and lay down a monolithic layer of 25psi xps. The. Install your finish floor over that. You might need to add a 1/4 ply subfloor first.

 

[bczygan]

You need an unbroken envelope to keep heat in. And heat rises as well as seeks colder areas. You need to provide heat into the concrete structure, which would then act as a sink. Perhaps a heater that is ducted into that space between the sheetrock and concrete.

Your money might be better spent with some way of providing comfort ON the floor. I am thinking of some kind of heated pad that could go under carpet or rugs.

 

[radojko]

You can insulate all you want, but I agree with the poster who mentioned that unless you have a thermal break in the slab, you'll see almost no benefit. A concrete pan deck will simply draw the heat you are putting in the floor… and that is what you're doing… putting energy into the concrete deck.
I would suggest that your only real alternative is to insulate from the inside in this case. If you can afford to lose an inch of ceiling height, pull up the hardwood, hope you don't have a hidden moisture problem from condensate, and lay down a monolithic layer of 25psi xps. The. Install your finish floor over that. You might need to add a 1/4 ply subfloor first.

Speaking to your insightful comments... First, we do have low ceilings - about 8 feet. We replace the hardwood floors 3 years ago after a water heater mishap across the hall from us which flooded part of our floor. The original floor was "engineered" wood, layed directly on the concrete sub-floor. We decided we wanted to go with genuine hardwood floors (we chose Brazilian ipe). This required laying a 3/4 inch plywood subfloor on top of the concrete, and then the 3/4 inch hardwood - so, we lost an inch and a half of height. We told the installer about our temperature issue, and he did install a poly vapor barrier. I don't think a layer of XPS would have been feasible, given the room height.

The "heat sink" characteristic of a concrete slab notwithstanding, I really do think it's largely a problem of cold from beneath the slab, which is exacerbated by the opening and closing of the garage door directly below us. I believe that because I measured floor temps directly above the door (which showed a drop of 15-20 degrees from air temperature). I also measured a spot about 10' into the living room, away from the frigid spot - temps there were significantly higher, only a few degrees lower than air temperature. Granted it can't be definitively proven, but I have to believe that insulating the concrete from below with CC-foam will make for an improvement - not perfect (but what *is* perfect?), but much better than the current miserable situation...

 

[radojko]

You need an unbroken envelope to keep heat in. And heat rises as well as seeks colder areas. You need to provide heat into the concrete structure, which would then act as a sink. Perhaps a heater that is ducted into that space between the sheetrock and concrete.

Your money might be better spent with some way of providing comfort ON the floor. I am thinking of some kind of heated pad that could go under carpet or rugs.

Honestly, I don't think trying to heat the concrete makes a whole lot of sense - whether I heat the floor from above or heat the cavity from below, it still represents a substantial wasted expenditure of heat energy. Not environmentally responsible, and certainly not financially prudent.

As for providing comfort ON the floor... We do have an area rug in the center of the room. It definitely helps. But we have beautiful hardwood floors - why would we want to cover them even more? So, wall to wall carpeting is out of the question...

 

[Chuck]

I would think you'd see at least some improvement in doing a single R35 layer. mtmgtz is right that you're still going to have heat loss at the edge, where the edge of the slab abuts the exterior envelope of the building. How much depends entirely on how the building was put together at that joint. However, conduction loss through a 4" maximum slab at the edge is still going to be less than convection loss across the bottom of 800 square feet of uninsulated floor. I wouldn't expect a perfect fix, but I'd expect your cold spot to shrink noticeably.

I wouldn't want to embed plumbing or electrical in the spray foam. The electrical under the slab won't be harmed by the colder temperatures due to loss of heat from your apartment. The plumbing might see more freeze problems. I'd make sure all the piping under your apartment is well insulated before the ceiling downstairs is reapplied.

Hope that helps!

Chuck

 

[rslaback]

I think the best option you have is probably to rip out the floor in your condo (if done correctly, most of it can be reused) and then put in a radiant floor system before putting the flooring back in.

 

[sean Buick 76]

I vote that you consider moving, it will always be an issue by the sounds of the concrete slab.

Our house had a non insulated garage, and our bedroom was right above the garage... The floors were cold and the bedroom was always colder than the rest of the house, especially when it was -40 F... We insulated the garage and that helped, but only once we added a heater in the garage did the bedroom stay warm...

 

[radojko]

A bit of an update...

I got a quote of just over $5k to apply 5" of CC over 800 sq ft. He won't have to tear out the entire ceiling - just several 3'x3' sections to allow him to apply the CC fully over the 800 sq ft area. Also, it's not likely that any pipes or wiring will have to be covered.

As soon as the HOA trustees give their approval (just a formality at this point), we'll move forward with the project...

 

[Stuart in MN]

Be sure to report back in January on the results.

 

[Paul1956]

The plumbing should be on the warm side of the insulation
otherwise you may have freeze issues.

Verify both the electrical & plumbing do not need work
before encasing either in foam.

The whole slab from the parking garage side is getting
chilled so I expect insulating only the part under your
unit will not stop the whole slab, including the portion
under your unit, from getting chilled. With the insulation
it will take longer under your unit. The whole space would
need to be insulated to have good effect.

Have you discussed with the other owners on your floor
the possibility of group action to have the whole slab
insulated?

 

[radojko]

Have you discussed with the other owners on your floor
the possibility of group action to have the whole slab
insulated?

That is a very sore subject for me...

About a year ago, I (as a conduit for the HOA) arranged for a FREE energy audit for the entire development. In addition to all the freebies that we all got from the utility company, we got a quote for insulating the ENTIRE garage ceiling - about 9000 square feet. And here's the kicker: the utility company was willing to subsidize NINETY PERCENT of the cost of applying the CCF insulation - a mere $7.5K was left for us to pay. BUT... not included was the cost to remove and reinstall the ceiling -- about $15K. So, we could have had the entire job done for $22.5K - a real deal, if you ask me.

Unfortunately, the HOA was unwilling to make that expenditure out of cash reserves, and wouldn't consider assessing each of the 24 units about $1000 to pay for the job. So, I have to go it alone... sigh.

B.

 

[buddyboy]

So, we could have had the entire job done for $22.5K - a real deal, if you ask me.

you should consider going back to the HOA and split this cost, also look into if you could also take/get tax credits for the portion you are paying.

yes if you just do the portion under the room in question it will help, but not as much as doing it correctly. heat moves to cold... hot AIR rises... the heat in the section of concrete you are warming will always move to the colder areas of un-insulated concrete.

or

if the HOA won't spend the 22.5k maybe talk them into heating the garage and splitting the gas bill with all the owners... most of them will think a small monthly bill during the winter months is a better deal than paying some big chunk up front. and their cars will be toasty warm