Subfloor Insulation

Stephen C.

Thanks Hot Rod I appreciate your insight and experience.You are right about the infiltration being a big unknown factor.

A propane 'woodstove' is also being installed as a supplemental heat source. Approx. 35000 Btu.

Stephen C.

Stephen C.

Subfloor Insulation

Hello all,
I have been lurking and learning here for a very long time and have very probably seen this question answered previously but cannot remember where.
I am overseeing construction of a new log home with radiant floor heating throughout.

What is the best practical and functional method of insulating the subfloors?
Does the insulation have to be tight to the subfloor or can it sit at the bottom of the joist cavity?
The floor construction is 11 7/8" TJI joists with 5/8" ply subfloor. The tubing will be stapled to the plywood followed by a 1 1/2" gypcrete overpour.
The floor finishes are tile and engineered oak hardwood flooring.
Thank you in advance for all responses and suggestions.

hr

What's below the floor

heated, or un heated space? If it is a cold crawl space I would go with an R 30 batt. If is is above a heated space R-19 6" would be sufficient.

Typically with TJI's they push unfaced batts up and use stiff wire to hold them in place, about every 2 foot or so. Usually this installation method pushes the batt up against, or near, the subfloor. Really no need for an air space above the batt with a gyp pour. A higher R value batt may fill up that 11" joist space.

Pay attention to how they insulate the rim joist. This is an infiltration area and I like to see spray foam or foam blocks held in with spray foam on the edges.

Even if you go with fiberglass batts, around the rim or band joist, be sure to use that can foam to seal the rim and the sill plate to the foundation, and where the rim joists butt to one another. As that wood shrinks you can get some serious infiltration at these framing connection.

hot rod

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Andrew Hagen (ALH)

Foam

Icynene foam works very well also. Around R3.6 per inch.

Corbond polyurethane foam is also amazing stuff if the space beneath is unheated. Around R7 per inch.

If the space is heated I'd lean toward fiberglass batts.

As hot rod said, the R-value needed depends on whether the space beneath is heated or unheated.

-Andrew

Stephen C.

Thanks for the responses and advice about the rim joist and sill plate sealing.I will definitely ensure that critical element is covered.
The house is built on an ICF foundation with 2" styrofoam under the 4" thick concrete floors and embedded tubing.
The north facing garage is part of the basement so that particular ceiling will receive a minimum of R-25 and possibly more.
The main floor is 1650 sq. ft. with 800 sq. ft.on the second floor.
I thought a minimum of R-12 fibreglass for the TJI joist space insulation above heated spaces. This house has two great rooms with cathedral ceilings 780 & 800 sq. ft. 7/12 inside pitch 10/12 outside (All scissor trusses).Very obviously I want this house to work properly and efficiently given present energy prices.Wirsbo has done the heat loss and tubing layout and a Vitodens boiler is being installed.

Thanks again,

Stephen C.

hr

Tall ceilings

small room square footage, glass, and logs throw up warning signals big time for me. Be sure that heat loss calc took all this into consideration. Infiltration can be a big, hard to define, number in log construction. Check to see what the btu per square foot is for those great rooms.

Very often rooms like that cannot be heated with just radiant floor. Throw rugs can really put you in deep! Just a heads up.

hot rod

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