Insulation under osb subfloor

[travelingalice]

Ive read many different articles and read about the different types of insulation how they work and the r-value. As well as installing it is very important in order to keep the r-value.

Who has replaced part of a subfloor.( im redoing under tub and around tub due to mold) what have yall used for instulation? Do you wish you did something different?

I have bought insulation today and i just want to make sure im making a right choice before installing.

 

[Rene T]

I’ve never done it but I would assume that fiberglass would work well as long as it will stay 100% dry.

 

[Gary RV_Wizard]

What sort of space constraints do you have to work with under the floor? I mean, is it practical if I recommend 8" thickness of 14" wide fiberglass batt? That would be great R-value...

 

[Kirk]

For a floor, I'd think that Styrofoam sheets would be best? I would probably use the foil wrapped foam board.

 

[Rene T]

For a floor, I'd think that Styrofoam sheets would be best? I would probably use the foil wrapped foam board.

For foam board to be totally effective you have to cut it precisely so that there are no gaps at all. Fiberglass merely needs to be stuffed into the space and fluff it up so that it touches surfaces on all sides.

 

[travelingalice]

What sort of space constraints do you have to work with under the floor? I mean, is it practical if I recommend 8" thickness of 14" wide fiberglass batt? That would be great R-value...

Its a small space

 

[travelingalice]

For foam board to be totally effective you have to cut it precisely so that there are no gaps at all. Fiberglass merely needs to be stuffed into the space and fluff it up so that it touches surfaces on all sides.

SO i bought unfaced foam board (i dont have a truck or needed a whole 4by 8 sheet) and reflectix bubble insulation. In order for reflectix to work it needs an air space so my thought after a bunch or research was to put the reflectix on each side of the foam and then have an air space below and above the insulation. In order to have r value u did read about that so i got spray foam reflectix tape and astro foam to choose from... would this work like im thinking it will or would you do something differently with the material i bought. The foam is less than 1 inch and us expanded (eps) i think its called

 

[Rene T]

SO i bought unfaced foam board (i dont have a truck or needed a whole 4by 8 sheet) and reflectix bubble insulation. In order for reflectix to work it needs an air space so my thought after a bunch or research was to put the reflectix on each side of the foam and then have an air space below and above the insulation. In order to have r value u did read about that so i got spray foam reflectix tape and astro foam to choose from... would this work like im thinking it will or would you do something differently with the material i bought. The foam is less than 1 inch and us expanded (eps) i think its called

What will the R Value be?

 

[Kirk]

The foam is less than 1 inch and us expanded (eps) i think its called

How much space do you have to fill? My problem with fiberglass in a floor is that it is probably going to get damp if not wet and it takes forever to dry once it does. OSB does not do well if kept damp for long periods. The idea that foam board has to fit tightly in order to be effective is overblown. It certainly is better to then but that isn't that hard to do and it can easily be sealed with sheathing tape that is readily available.

 

[Gary RV_Wizard]

If you have enough space for foam + 2 layers of Reflexit and two air gaps, I would think that either thicker foam or filling it with fiberglass wool would be equal or better. In either case, make sure there is a well-sealed moisture barrier on the bottom side. And since it's a bath area, I'd seal the OSB as well, e.g. a water-resistant primer. In fact, I wouldn't use OSB - it use real plywood and prime it well.