Insulating a Garage

Question Icon
Posted by: from Kingston
4/13/2020 at 8:53:58 AM

I have a garage that I would like to insulate and heat but it has an exposed screened porch above it. So, if I insulate the ceiling of the garage do I need some sort of air space above insulation between the joists? Will moisture condense against the underside of the porch floor?

User Icon
Date/Time4/13/2020 at 10:51:07 AM

You are required by Code to ventilate the space above the insulation. If you have an effective continuous vapor barrier plus effective ventilation (cross-ventilation) it is unlikely condensation will occur. Perhaps you could install a removable access panel in the garage ceiling in order to check.

User Icon
Date/Time4/13/2020 at 11:04:50 AM

Yes an air space is required.

I think the best option is installing R10 ridged foam insulation sheets between all the trusses. Use tuck tape to intall these. Leaving spacing of 11/2" between them and the lumber onder the deck. Then you can install R20 batt insulation on the interior side of the ridged foam. This will take care of it and give you great r factor.

User Icon
Date/Time4/14/2020 at 1:05:09 PM


Venting flat roofs does not work effectively.

Best to foam the ceiling of the garage, which does not require venting.

The floor of the porch is solid, yes?

If not, make it solid with plywood over, then whatever finish you would like for the porch floor.


Andrew Parker

Insulating a Garage

Search the TrustedPros directory and discover the best contractors in your area.

Find your home service pro
Great renovations start with a great contractor.

Since 2004, TrustedPros has been helping homeowners find the right contractor for their home improvements and repairs.

Post Your Project

Within hours you'll be comparing offers from top-rated professionals. It's free to post and you're under no obligation to hire.

Trustedpros Inc. does not warrant the accuracy, completeness, safety, legality or usefulness of any Content, or Whether Content is Current and up-to-date, and TrustedPros Inc. Shall have no liability whatsoever with respect to your use or reliance upon any content or for content being removed or otherwise ceasing to be available. Please refer to the terms and conditions of use of this websites for more details.

Get quotes from top-rated contractors