Cantilevered Room Insulation [Updated]

About: I'm a husband and father that loves working in the garage. From sewing to welding to wrenching on engines and everything in between.

My house was built in the late 60's and was always cold. I had seen some articles online about the lack of or improper insulation under the floors of cantilevered rooms. Since half of the front of my house is cantilvered, I figured it was a good possibility that this was my problem, so last spring I decided to see if there was something that could be done about it. This process took several weeks of evenings/weekends to complete, but some time was added because I ended up doing more that just the insulation. Here's a two part video showing how I sealed up the cantilever. If any part of your home is cantilevered and your home is cold, I'd highly recommend checking your insulation. The videos are fairly lengthy, but worth a watch.

Now that it's fall and we've have had a few weeks of "furnace" weather, I can definitely notice a huge improvement in the comfort level of our house. Last year, I was bundled up indoors all through the winter. Now, I can walk around in shorts and t-shirt and be comfortable. Time will tell as far as the heating cost savings go. I'll be tracking that and comparing it to last years heating bills. I'd appreciate your vote in the Winterize contest.

UPDATE (February 2015):

Our full time heat source is a natural gas furnace. It is the only gas appliance in our house. I just received my energy bill for January and my gas usage is 31.9% less than it was at this time last year (see photo). While we supplement heat with a wood burning fireplace insert, we are on track to use less wood than we did last year as well. There's still a lot of improvements that can be made in the insulation of our house, but this was a definite improvement. Thanks for looking and feel free to ask any questions you may have.

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    6 Discussions


    4 years ago on Introduction

    What type of rigid foam did you use and did you cover the rim joist? I ask because I used foil-faced RMAX (foil on both sides) and I was told I will trap moisture in. I installed this in a cantilever bay window. One vertical piece of the rim joist, one vertical piece above the foundation wall on the sill plate, one horizontal piece on the subfloor, then roxul in the cavity. One final horizontal piece between the bottom of the joists. Ideally I would have like to installed one continuous piece foil-face rigid board at the bottom of the joists but couldn't due to the exterior finishing issues (stucco exterior).

    Anyways I havent yet completed the project and am contemplating using unfaced rigid foam in-place of the double sided foil-faced foam that I used due to what I was told regarding trapping in moisture. Id like to salvage what I can or start over.

    Any suggestions are welcome

    1 reply
    Dustin RogersPeteS12

    Reply 4 years ago on Introduction

    I just used 1" thick unfaced foam. I only did one vertical piece over the foundation wall and one horizontal piece under the subfloor. I used expanding foam around each piece to get a complete seal. I then stuffed batt insulation in the joist cavity. I used a foil faced plywood/chipboard, caulked on all seams and joists to seal up the underside of the joists and then dressed it up with vinyl soffit material.


    Did you insulate your exterior wall after you took the siding off? Or did you just use an air infiltration barrier like Tyvek. I couldn't really tell from the video.

    2 replies

    The exterior walls have batt insulation in them and there is fiberboard on the outside of the studs. The tyvek wrap really helped with the air infiltration. The cold spot in the closet that I mentioned is gone now, but before the tyvek, that was where two sheets of fiberboard butted together. Cold air was able to get through and caused the cold spot.

    I still have more that I want to do. I want to seal air leaks to the attic as demonstrated in another recent 'ible and seal around electrical outlets, etc in the walls. I have never been in the attic above the upper level of my house because the access hole is too small to get through. I haven't even been able to get my head up there to look around due to closet shelving. So that is on the radar for spring.

    Thanks earz_cd, good luck with your future insulating. To take a quick survey of your attic, put a camera on the end of a stick set it to movie record mode, poke it through the attic hole and do a slow 360 it should give you a rough idea of what you may be up against next Spring.

    Dustin Rogers

    4 years ago

    Thanks. It's definitely a never ending project.