Can blown loose insulation be used in cantilever floor?

Hi all,

Happy New Year!

Question-- can blown insulation be used in cantilever floor? Extends 3 to 6 feet. Climate: Atlanta, GA

Mom has lived in home since mid 90's and I just found this. She only this year complained of cold edge of the house in two rooms. Then I went exploring. Found 2 inch gap running length of rear of home just past sill plate. And zero insulation. The insulation under home ended at foundation wall and sill.

I covered and foamed the gap length with each joist bay. Now, can I blow in loose insulation?



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Chris-----------We blow cantilevers all the time. They are prevelent in splits and second story overhangs. It sounds like you have the perfect opportunity to dense pack this area as you have already sealed the joist bays. Access sounds easy and all you will have to do is drill through your blocking and blow.

Ed Ballard

Thanks Ed. I appreciate your help. I can do nice, tight, smart A/C installs all day but insulation knowledge for me is still growing. Thanks.


Chris- you should note the difference between your term "loose" and Ed's description. Dense pack is the way to go.

How can I diy this?

Chris-----DIY may have some challenges. You will need to find a blower that has air and feed adjustments. Most box stores that have loaner equip. do not have this capibilitie. The idea of DENse pack is just that. To install the cellulose at a density that will prevent it from settling and to inhibite air flow through it. If you try an open blow into the cavity you will end up with a gap between the top of the insulation and the bottom of the subfloor. NOT GOOD.

Get on your favorite search engine and olok up dense pack cellulose insulation. It will be quicker than me trying to explain your air/feed setting. To know if you are getting in the range/pack needed push your finger into the blow . If you have trouble pushing your finger into it you are heading for bullseye.

Good luck--------just do it

Loose fill at this point will help, you have minimized the air movement with your air sealing and considering the delta T in your location you may be ok. Up where I come from it would have to be dense packed not loose filled.


The perferred solution is closed cell foam combined with a joist cavity  air seal R board located in line with the exterior shell sheathing. The extended joists create a building shell problem with generally heavy air leakage. The 2nd option would be dense pack cellulose either netted or packed behind R board and exterior sheathing applied over the R board or netting. Fiberglass is a poor choice in a cantilevered space particularly in colder climates as you need both a good thermal and air boundary. Again, you need to air seal/insulate the joist cavity for a good thermal shell boundary at the exterior framing sheathing.


I continue to find cornice crews are taught to install soffit vents at preset spacing regardless of conditions. A vented panel along a cantilevered extension can cause air infiltration in that area. We then have air/pressure into the wall section or joist cavity. In the South moisture is a concern, but I consider sealing the soffit vent so to create a true thermal barrier when insulation is installed. ....Allan


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