Should I Insulate My Garage Ceiling

Should I Insulate My Garage Ceiling

Should I Insulate My Garage (Or Insulate it Better)?

by Erik North on October 14, 2011

I often have discussions about garages and even more often about the finished spaces above them. These finished rooms are the source of frequent complaints about cold rooms, drafts and heating problems. I had one customer who couldnt get their FROG (awesome acronym Finished Room Over Garage) over 55 F. Brrr.

Why Is The Finished Room Over My Garage Cold?

The question then becomes what is the problem and how do we fix it. I mean, whats the problem besides needing to wear socks in your over garage bedroom. A quick multiple choice: The problem is:

A. The heating system has been sized improperly for the houses heating load.

B. The attic insulation is insufficient.

C. The garage ceiling insulation is insufficient.

D. The garage walls should be insulated better.

E. There are air leakage issues that need to be addressed.

If you answered all five, youre kinda correct except that some of these are much more problematic than others.

Insulation contractors, as a whole, do a good job. I may find misconceptions/misunderstanding of what should be done but rarely find truly bad work. The problem here is that a FROG (still love saying that) faces cold, unconditioned air on five sides: top, bottom and three sides compared to three sides in a conventional second story bedroom.

Why Is The Finished Room Over The Garage Hard To Heat?

Lets list the challenges this architectural choice must overcome:

  • The heating system is often on the opposite side of the house. Think for a second most heat in Maine and in many sections of the country is oil. Oil tanks are in the basement and theres no garage-side place to locate the intake. The heating system is located near the oil tank, meaning the distribution system (which can be air or water) travels 70 or 80 feet before reaching the FROG. Even if the home is heated with natural gas, the gas line and meter will likely be on the opposite side of the house.
  • The room is insulated on five sides, dealing with wind and cold from almost all directions. It is extraordinarily difficult to insulate an attached garage. Garage doors are incredibly leaky and poorly insulated. Unless XPS foam board was included as sub-slab insulation, the garage floor slab is an enormous heat sink (see this previous article about basements ; the same logic applies to an uninsulated concrete slab).

    Added bonus time: often the heat water pipes run through the garage ceiling. If the pipes are uninsulated, youve got hot water within a few inches of cold winter air.

  • Air leaks everywhere. The attic leaks conditioned air through recessed lights, chimney chases, light fixtures, etc. First floor soffets (heres a photo example) can allow cold air into the horizontal garage ceiling bays if unsealed.

    The top of the marriage wall between the garage and main house often leaks, allowing warm air to escape. Where the garage ceiling joists join the main section of the house is often open into the building frame. Finally, cold air creeps through the garage ceiling itself, sneaking through light fixtures, holes and seams in the drywall. And remember: cold air flowing through fiberglass greatly impedes its insulation performance. As we say: Hooray!

    Check out this audit photo: The continual soffit vents are open into the garage ceiling bays. This house routinely faces stiff winds, which sweep into soffit and through the ceiling bays. And, yes, like I alluded to above, uninsulated hot water pipes were running through these ceiling bays. Meaning every time the wind blows, cold winter air is washing across those pipes intended to transport hot water to the baseboard heaters.

    Should I Insulate My Garage Ceiling

    Oh, that’s why are my toes so cold!

  • And, of course, carbon monoxide is an issue in attached garages (wait, what. ). The hot exhaust fumes from parked vehicles emit elevated levels of carbon monoxide in the hours after operating. This source of CO2 surprises most homeowners and under some conditions can present a hazard.

    And I Fix This Problem How?

    What should the slipper wearing homeowner do? Insulate and air seal and block and insulate some more. Attic air sealing means caulking and foaming gaps around light fixtures, drywall seams and anywhere there is a gap in the ceiling air barrier .

    Insulation can always be added; building codes are beefing up attic insulation requirements to R-49 and super-insulated homes aim for R-60. While insulation can be compromised by air leaks, more insulation is (almost, nearly, kinda always) your friend.

    In the garage, as in the attic, we need to airseal and insulate. Open first floor soffits and the ceiling joists open to the building frame can be sealed with foam blocks and foam sealants.

    Beefing up the garage ceiling insulation can be a large project. My recommendation is usually first pulling down the drywall and existing fiberglass (why you ask? Heres why ). Then either air sealing the garage ceiling plane with a blower door running and dense packing with netted cellulose or with 2 of close cell spray foam and fiberglass batts (if the homeowners will be away long enough for the foam curing process). The dry plywood flooring has a sufficiently low vapor permeance to act as the interior vapor retarder.

    Finally, I always recommend installing a hard wired carbon monoxide detector with a battery back-up in garages and in rooms over garages. Its a common sense way to avoid a potentially catastrophic problem.

    Insulating garages is a challenge and finished rooms over garages are a huge Achilles heel in modern construction. Theyre compromised on all sides by air leakage and insufficient insulation. Think of the thermal and air barriers on all sides of the garage and the finished rooms over them when considering re-insulating your garage.


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