Definitely foam the room floor/garage ceiling. It makes a big difference in comfort.

In NC - we have a bedroom over a 3 car garage. Typical r-30 fiberglass in the garage ceiling and I have never noticed 1 degree difference from other bedrooms (not that I would notice 1 degree). In the winter it is a non issue - garage is typically 50 degrees and you can guess how much temp movement comes with only a 20 degree temp difference and r-30.

In the summer, 2 west windows in another bedroom totally eclipse any heat gain from the garage below this bedroom. Mind you again only a 25 degree temp differential (100 in garage, 75 in bedroom). But heat does rise so there is some heat gain to account for.

The HVAC guys don't want to get a call back to balance this room. Sure, you need more airflow in this room than an identical room over conditioned space. But the difference needed based on windows is more significant - and changes with the season (depending on orientation of the windows). So if you are particularly sensitive, this balance needs to be changed twice a year.

Lots of people have had crappy rooms over garages when it comes to temp control. I believe wholeheartedly that in our climate, foaming this area is a ridiculous waste of money as is zoning.

Something to always remember, r-30 achieved with foam is the same as r-30 achieved with fiberglass with some caveats. Sure foam seals air leaks - but tell me how many air leaks are there typically in a garage ceiling? Sure foam is less susceptible to compression from sloppy install - but a garage ceiling doesn't have much to mess up fiberglass. Usually minimal electric, no plumbing. So the advantages of foam here are minimal. If you can do r-40 in fiberglass, you might actually be better off for probably 20% of the incremental cost.

Unless detailed steps were taken early in the construction process, the interface between the garage ceiling, the band joists and the space above is far from air-tight. See detail below.

You can do a perfect retrofit by spray-foaming the ceiling and band joist area for air tightness; then spray a few more inches for insulation or use netted dense-packed cellulose. The detail below shows tightly fitted foam boards under the framing, which then has to be covered by drywall. Fiberglass batts alone installed upside down make good air filters!

Air-Sealing Details over Unconditioned Garage
Source: Building Science Corp. Building Profiles: Mixed-Humid Climate: Charlotte

This post was edited by worthy on Fri, Mar 22, 13 at 13:58

ditto worthy's post.

what stage are you at in your build?

depending upon where you are in the process
& what is to be foamed, it will be cost
effective to foam all at once rather than
multiple trips. a lot of cost is set up rather
than minimal product cost. so price is
cheaper if jobs are together.

also, keeping your posts together helps to keep
answers together, rather than reading 3 threads
on two forums.

best of luck.

They were out there foaming the roofline today. Just got the message that it would be $800 to foam the whole garage ceiling (three car garage, 792 sq ft). Will I get a good return on investment from foaming?

Just got a message that is $240 to upgrade to R-30 fiberglass. So, my question is, $240 for R-30 or $800 for foam???? What are your thoughts?

are they finished or still on the job?

if they are still on the job, then set up
and time to do fg or foam is about the
same. only difference is product used.

I'd tell them I'd go for the foam for
$600. and see what the counter offer
is. it isn't taking advantage, if they
are still set up. a large part of
the cost is set up & heating product.

at this point, the foam that is doing
the hardest job is the foam at the
roofline. foaming the floor of playroom
is for comfort & so that the amount of
air supplied will do the job in the play
area.

if they are still on the job, now is the
easiest cheapest time to do this.
in the big scheme of things..I'd go for it.
you'll never be there as easily & less
destructively as now.

so...are they still on the job?
what stage is your house in now?

best of luck.

I'm not sure if they're still on the job or not. I'm going to go by there in just a little bit. I know they were there yesterday but I don't know if they finished or not.
The house is just about dried in, zip sheathing sealed, shingles on, electrical and plumbing done and hvac will be going in this week. Builder expects to start sheetrock late next week.

The best time to negotiate on prices is before the job is started. After having built and/or lived in homes with finished space over garages--inevitably hot in summer, cold in winter--I would only use spray foam right from the start. But as long as Codes allow fg meeting nominal R values that's what builders will use.

Here is a link that might be useful: Spray Foam Garage Ceiling (video)

Well - $600 is pretty cheap. The real advantage may be sound which foam is better at.

If not r-30 than what? I'd want at least r-30 and I thought that was code but obviously you are in a different zone. I'd personally r-30 fiberglass it.

Worthy's logic again points to why people get all over foaming this area. They have lived in bad examples. Worthy also doesn't live in SC.....