Insulating garage workshop floor?

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Forum topic by Nate Finch posted 08-13-2015 01:37 PM 1917 views 1 time favorited 18 replies Add to Favorites Watch
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Nate Finch

29 posts in 3435 days

08-13-2015 01:37 PM

Topic tags/keywords: garage insulation

I have a garage set into a hill that is my workshop. I’m looking to insulate it so I can use it year round (it gets really cold in the Massachusetts winters). However, I need to be able to occasionally park our truck in one bay of the garage. Having trouble figuring out if there’s a way to insulate the floors and still be able to park vehicles in the garage. Is 3/4 ply over 1-2” XPS going to be ok with an F150 parked on top of it? My guess is no.

Anyone done this? Wondering what my options are.


-- Nate, Harvard, MA

18 replies so far

View a1Jim's profile


117722 posts in 4088 days

#1 posted 08-13-2015 03:16 PM

Nate as a 30 year contractor I’ve done something similar with 2×6s and a concrete ramp for access of the car.
You don’t say but I assume your existing floor is concrete. I’m not sure you will get enough r-values with 1×2s . I would use at least 2×4 PT material.
Things to keep in mind,use a vapor barrier under you 2by material like 30 lb felt or better yet 6mil plastic,make sure you sleepers (2bymaterial) is close together perhaps “12 on center. I would suggest pressure treated 3/4” plywood ,
Check your overhead clearance before adding the floor to make sure your car or truck will clear once the floor is in.
I would install the ply with some good screws (not drywall screws)say a short version of deck screws.
If you build a small ramp to enter the garage it can be mad of the the same PT material,concrete or even rock depending on what’s outside your shop already

View BinghamtonEd's profile


2298 posts in 2880 days

#2 posted 08-13-2015 04:26 PM

This in no way answers your question, Nate, but…

Does your truck need to be inside? I live in southern tier NY (still “upstate”), and also have an F150, and it is too tall for the garage door. I have an auto starter in it, so by the time I get out on those cold mornings, the truck is warm, and any ice/snow on it just slides right off (well, if there’s a foot on top, you have to get the brush out). The other thing that comes to mind is that I would imagine that there would be a good chance of bringing snow/water in, so whatever flooring you put down would have to mitigate that factor.

It took two years, but my wife begrudgingly accepted the fact that her car no longer goes in the garage, as well.

-- - The mightiest oak in the forest is just a little nut that held its ground.

View MT_Stringer's profile


3183 posts in 3742 days

#3 posted 08-13-2015 04:35 PM

+1 for the remote start function. Both of our vehicles have it as a factory option. Car Toys can install them if needed.

-- Handcrafted by Mike Henderson - Channelview, Texas

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Nate Finch

29 posts in 3435 days

#4 posted 08-13-2015 04:38 PM

heh.. the truck only goes in the garage during snowstorms (which are plentiful in central-ish Mass). I guess in theory we could leave the car outside during a snowstorm, since we barely ever use the car (and it’s a POS)... but it’s kind of nice to have it hidden away.

FYI – I didn’t mean 1×2’s I meant 1” or 2” XPS foam insulation on the concrete floor with 3/4” plywood directly on top of it. I had hoped to avoid needing sleepers at all, so as to provide a full thermal break… Some more googling about compressive strength comes up with Foamular 250, 400, 600, 1000 with 25, 40, 60, and 100 PSI compressive strength. Given that an F150 is about 5000 pounds spread across 4 wheels (call them 8×8” squares each, to be conservative)... math gives me about 20 PSI from the truck. Which is actually not too bad, especially with 3/4” ply spreading the weight around some.

If their compressive strength numbers can be interpreted as “it’s ok to squish this product with this amount of force” then in theory the regular 250 would be ok, though I’d probably go with 400 just in case.

-- Nate, Harvard, MA

View johnstoneb's profile


3130 posts in 2683 days

#5 posted 08-13-2015 05:12 PM

You really don’t need to insulate the floor of your garage. The cold comes in through the foundation on the side and through and around the overhead door. The best thing to have done was during construction insulate the inside wall of the foundation and in a foot or two under the floor. Now your best bet would be to insulate and seal the outside of the foundation with at least 2” preferably more insulate the overhead door if it isn’t and seal around it.
The ground under your garage doesn’t freeze in fact it will act as a heat sink releasing some heat back into an unheated garage at night. My garage doesn’t freeze overnight until it gets welll below zero overnight and then it might get into the low twenties.
My shop is 16×24 on a monolithic slab. 4’ fiberglas in the walls, 6 or 8” in ceiling depending on area and an insulated 8’x8’ overhead door I did put an extra inch of insulation board in the overhead door. Even at -20F overnight with the heat off it has only gotten to 32. I don’t have a problem with cold feet when working out there. I did put down 1/2” rubber mat from HF in the traffic areas for cushion.

-- Bruce, Boise, ID

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Nate Finch

29 posts in 3435 days

#6 posted 08-13-2015 05:16 PM

Thanks for the info, Bruce. Maybe I am over thinking it. It would probably be a good idea to insulate the rest of the garage, try it out for a winter, and then worry about the floor only if it appears to be a problem in practice.

-- Nate, Harvard, MA

View BinghamtonEd's profile


2298 posts in 2880 days

#7 posted 08-13-2015 05:40 PM

How cold does yours get, Nate? Our garage has insulation in the ceiling (bedrooms over it), shares 1 wall with the basement (kept at 55), two walls have 3 feet below grade, and the other has 2 garage doors. It will usually stay above 40 well into November. Come December, it starts dropping, and by January, it’s usually in the 30’s. During the ski season I don’t spend a great deal of time out there anyways, so I try to save the cold months for cleaning, jigs, and other things that don’t require much glue/finish. For glued parts, if I keep them small, I can bring them in and do them in the basement.

I built my daughter’s bed when it was too cold to glue in the garage, and I broke down a sheet pizza box to protect the kitchen table and glue up the legs. It worked well, and I had pizza. Win win.

-- - The mightiest oak in the forest is just a little nut that held its ground.

View turbov6camaro's profile


19 posts in 1852 days

#8 posted 08-13-2015 05:50 PM

air seal and insulatin is best, are your doors insulated?

View Nate Finch's profile

Nate Finch

29 posts in 3435 days

#9 posted 08-13-2015 08:54 PM

My garage is built into a hill, with barn space above (accessible from the back of the barn, up the hill). See the picture below. There’s no insulation anywhere, so it gets pretty cold. Certainly warmer than outside, but still not really usable past September (where usable means I can work for a couple hours without losing feeling in my hands). I haven’t put a thermometer in there, so I don’t know exactly. What’s great is that it stays cool even in the hottest of days in the summer.

The garage doors are insulated, though mice have chewed the corners of the bottom weather stripping, so I should replace that. The ceiling and walls are totally not insulated, so obviously that’s something that needs to be remedied. My thought was fiberglass bat between studs & joists and XPS over the inside surfaces as added insulation and an air seal. The walls are 2×6 and ceiling is 2×12 (both 16” on center – the past owners really overbuilt the barn!)

I don’t really want to have to install a full furnace or anything, so hoping I can insulate the heck out of it and heat it with something smaller than you’d normally use for that space (it’s 35’x28’x7’8”).... maybe build a wall to enclose just the left two bays… but not sure if that would actually be cheaper than just insulating the whole thing (the left two bays are what I use for a shop… well, officially just the left bay, but I hope to be able to annex the center bay, too).

-- Nate, Harvard, MA

View johnstoneb's profile


3130 posts in 2683 days

#10 posted 08-13-2015 09:08 PM

I would put 6” in the walls, 8’ or more in the ceiling. You probably will need to fir out the concrete wall that is against the hill and insulate that if you go with 2×4 or 2×6 on that wall you could use fiberglas on it also. I think before I walled anything off I would insulate the whole thing then give it a winter or two to see what it is like. I think with full insulation and seal the doors well you proabley would be able to heat it with a wood stove. You might need to hang some plastic sheeting around if it doesn’t heat as well as you would like. It is really nice in the winter to go into a garage and get into a veihicle that has fully thawed off during the night. They will thaw off pretty well even without heat. I have a two car garage fully insulated attached to my home with an old electric furnace in it. The vehicles thaw off really well without heat. If it gets well below zero I will turn on the furnace in the evening for an hour or so just to speed up the process.

My shop is 16×24 and i use a wood pellet stove in it I will go out early in the morning sart the fire and in about 2 hours it it is at a comfortzble temp 64F or so I will turn it down work all day some days I have to turn it off it will get up around 70. That even when tihe temp is around zero.

-- Bruce, Boise, ID

View splatman's profile


586 posts in 1910 days

#11 posted 08-13-2015 09:49 PM

Insulating all 3 bays would be the way to go. Think of it: You just brought home a load of lumber, and parked the truck inside. If you partitioned off 1 bay, you would now have to maneuver your freshly-bought sheets of plywood thru a door.
And what if you need to work on your truck? Changing the oil or swapping out parts in the cold does not sound all that exciting. Of course, that’s assuming you do your own truck maintenance.

As far as whether any type of XPS can withstand a truck parked on it: Get a sample of XPS, put it on the floor where the front driver-side wheel usually ends up, put a piece of 3/4” plywood on it, build a ramp leading up to it, and park on it overnight. Measure the thickness of the XPS with a calipers, before and after the test. No reduction in thickness? Pass. Regardless, the floor probably is the least of your cold garage issues.

+1 A woodstove for heat. A great use for scraps.

View Dabcan's profile


255 posts in 3182 days

#12 posted 08-15-2015 02:34 AM

I live in Canada, winters are cold. My shop has some insulation in the walls, roof, and the garage door is insulated. This is not R2000 quality, I think the walls are only 4” thick so pretty limited. The floor is concrete and has no insulation. I do have a propane furnace and while the floor is cold, I put on a warm pair of socks in the winter and only ever notice cold feet if I stand around for a long time. I also only keep my shop at about 12 degrees Celsius and wear layers cause long underwear is cheaper than propane…

-- @craftcollectif ,,

View firefighterontheside's profile


20581 posts in 2367 days

#13 posted 08-15-2015 02:44 AM

The thing with the concrete floor is that once you warm it up, it won’t take much to keep it warm. Thermal mass. The same theory applies to my log home where R value doesn’t really apply. I agree with just insulating the walls and ceiling. When you open the garage door it will get cold in there obviously, but the heat stored in the concrete will help to heat it back up quickly once the door closes. With that said, you might look into one of the snap together tile floor systems. I believe they are about an inch thick, will support a vehicle and have an air space which will afford some insulation.

-- Bill M. "People change, walnut doesn't" by Gene.

View ElChe's profile


630 posts in 1847 days

#14 posted 08-15-2015 04:19 PM

Can I live in your garage when you’re done insulating it? Very cool structure.

-- Tom - Measure twice cut once. Then measure again. Curse. Fudge.

View buildingmonkey's profile


242 posts in 2058 days

#15 posted 08-16-2015 11:01 PM

I like your barn. If it were mine, think I would put the shop on the upper floor. Easy to insulate the floor and walls with fiberglass batts, and blow the ceiling with cellulose.

-- Jim from Kansas

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