GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Overview of garage insulation based on what I learned here

thegiz | Posted in General Questions on

So thanks to everyone that has been answering my garage insulation questions, and I think I’m ready to start this project based on what I learned here.  Again I have a 2 car detached garage that I plan to heat at an hour or so during winter.  I live in suburbs of NYC.  So this is what I think is easiest and most economical.

1. walls- fiberglass batts paper faced inwards cover with osb board
2. Rebuild an osb ceiling, leave cathedral ceiling uninsulated so do not have to worry about ceiling condensation.
3. Drop in fiberglass batts paper facing down into new ceiling.  
4. Throw OSB boards on top to make attic floor
5. Finally to save money create an insulated box with OSB and scrap 2×6 to make ceiling access to attic.

Does this make sense?  If I’m complete moron just let me know, I’m no expert. -Joe

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. onslow | | #1


    If you are only planning to heat the garage for an hour or so, I think your best plan of action would be to skip the insulation entirely and focus on creating as air tight a space as possible first. Air blowing through the garage via doors or eaves will defeat most heat options. Doing the entire ceiling with OSB to reduce the total volume of air to be heated would be a start. If you did add insulation under the attic floor, it might also help keep the garage a bit cooler in the summer. Insulating the walls will temper the summer heat load if the garage is not in shadow from neighbors or trees. The value in winter will be less for the description of use you gave.

    The main problem with minimal insulation combined with minimal heating cycles is the time it will take to achieve any sense of warmth when you start from dead cold. Insulation doesn't keep heat for days, it merely keeps the input from dissipating too quickly. Even if you had R30 in the walls and ceiling, the start point for your unheated shop on a cold February morning would still be very close to whatever outside is. Heating the air contained in the garage is one way to make whatever you are doing in there bearable, but your tools and bench will still be starting as cold as the building started. After an hour the air might be up to 50F but your tools will still be much colder. If liquids are involved, you will find them taking even longer to warm.

    Warming the air can be pretty quick given enough energy input, but trying to warm an entire garage this way will put big demands on any electrical circuits in the garage. Infrared heater bars don't waste as much energy heating the air and better warm you and the tools under their beam spread. Some are much more directed than others. Whether this is the best choice for what you are doing is something only you can answer.

    One potential work around might be to isolate a portion of the garage space with a hanging curtain wall you can pull around the bench area. Then heat that much smaller volume of air with small fan heaters that are much cheaper to buy than infrared heater bars. Also less demanding of the electric circuits

    Imagine the sort of curtain wall used in emergency rooms (or less dire) conference rooms that can be separated into two rooms with an accordian type wall. It would need to limit air leaks at the ceiling, but you will find that a small volume of air can be brought up to workable temperatures pretty quickly.

    I would caution against the use of LP heaters like the type that mount on barbecue canisters. You can't be very close without discomfort or even risk of igniting your clothing, and they will produce combustion gases and lots of humidity. The ones that look like jet engines have similar problems of fumes and humidity, but at least the will warm air on a massive scale fairly quickly.

    If you are really looking for massive heat for short periods, the kind of natural gas heaters that one might see at a loading dock are an "out there" option. Lots of code things to get involved with though in addition to need a gas line.

  2. Expert Member
    Peter Engle | | #2

    With the amount of insulation you describe, it would be inexpensive to heat the garage a little bit all the time. My garage is heated to 40 degrees all winter, more to keep it dry and to keep the things stored in it from freezing. The cost to do this is pretty low. When I'm working in it, I turn on the heaters. Bringing it from 40 degrees up to 50-60 degrees is much easier than bringing it up from 20 degrees. I mostly use a woodstove for the boost heating, as it provides a lot of heat in a hurry, and scrap/found firewood is a free and limitless resource around here. Of course, there are safety issues related to that as well, but manageable with care.

  3. thegiz | | #3

    Roger, thanks for your input. The left side of garage is shaded my trees, the other side is not. When you say wall insulation would temper in summer, are you saying that would actually make garage hotter? I have a 2400 watt infrared heater, that I bought last year that would work somewhat if you stood directly in front of it even when I had 0 insulation. Building a curtain would work to help isolate an area. What about standing in a corner and pointing my infrared heaters along with some cheap heating fans towards one corner? I have a propane heater, the jet kind you are describing but I rather not breath toxic fumes and natural gas heater I know running gas lines would be a pain and costly. Not expecting temperature to feel like I'm inside but more bearable. To put things bluntly I have kids and wife in a small house, I want to be able to escape to a man cave in garage to work. Some of us are desperate enough to camp outside, but I want to be somewhat comfortable. If insulation would help cool in summer that would be a bonus I have overlooked. Thanks again for your input.

  4. Expert Member
    Akos | | #4


    Your plan is good, it is a fairly common setup here for workshops.

    I would recommend installing one of those propane or gas fueled vented garage ceiling heaters. They put out a lot of heat and get the place comfortable in no time.

    If you do have enough power out there, electric infrared heaters are another option. They work best with taller ceilings though. The 2400W unit you have right now will get the place hot, but will take too long. You need closer to 7kW to 10kW of electric heat.

  5. Expert Member
    NICK KEENAN | | #5

    I'd look into a quartz infrared heater. It warms you without warming up the space.

  6. thegiz | | #6


    I made a mistake the heater is actually 5600watts. Not sure if that will make enough of a difference. It also has automatic thermostat control, claims to be 45-95 degrees F. It doesn’t actually have numbers just a yo-yo switch for low to high. I tried it without insulation and shut off automatic control because it never switched off. I wonder if it would be too expensive to leave it on low when I’m not in garage so I’m starting at about what they claim 45 degrees.

  7. onslow | | #7


    The one problem with infrared heaters with thermostats is the thermostats rely on the air temp to tell them when enough is enough. Since infrared heaters are specifically designed not to heat the air, but heat objects instead, the air ends up getting warmed by the objects. A very slow process. That is why heating a small volume of air will always be faster and often feel warmer. As I noted, the down side is cold tools. Of course if you are out there hiding for sanity sake, then at least the beer won't get too warm too fast.

    I did a rough calc on how much insulation would cost and came up with north of $900 based on typical 2 car dimensions. Plus a couple of hundred for OSB per side of the ceiling if you want to use the attic space. You might look to see if local utilities have insulation rebate deals with the big box stores. My local one has an up to 50 cents a sf rebate sponsord by the local gas company.

    If you just insulate the corner where you are hiding (two walls and part of the ceiling) combined with the movable walls you could spend the savings an electric fan heater to go with the infrared and maybe a barcalounger as well. If you go this route, you might look at foil faced polyiso sheets as a fast not too mouse friendly choice. The foil will bounce the infrared around.

    If you do go all in with insulation, seal the ceiling well and make sure the doors are gasketed well. They will be the weak link. I noted your prior question and the pics of the existing garage. You will have earned your man cave by the time you get done. Hopefully, the raccoons will not come back to enjoy the new digs as well. You might find it possible to use a low output heater to keep the edge off during the winter, but I think you are in a 25cents/kwh region of the country so be prepared to pay dearly. Just figure the wattage times 24hrs and go from there. 5600 watts non stop is around $33.

    There will be the summer advantage to full insulation if you can open up long enough in the evening to cool things down. Or provide a fan out a hole in the wall you can plug during winter. The sunny wall will be slower to re-radiate all that warm sunshine and keep it modestly cooler in the garage during daytime. Again the garage doors will be the weak link unless you have insulated garage doors as well.

    Your situation makes me almost fond of my long behind me damp moldy basement with 6' ceilings. It did at least keep warm from the furnace and water heater. Best of outcomes for your project.

  8. thegiz | | #8

    Roger thank you for breaking it down for me. I don’t know where you are but everything cost dearly in NY materials and electric included. If I’m going to build this man cave might as well go all in with insulation and sealing. As far as heating can’t run it all day maybe just turn it on for an hour or 2 before I go in there. I can always beef up the heat as time goes on at least garage will be prepped to be heated. I can live with cold tools, I know this is a builders forum so many of you would never stand for that but like you said at least my beer won’t warm too fast. Don’t worry a cold damp basement will be my following project, going to start with this one, that will be much more complicated def going to read up on information here, thanks again.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |