Under floor tubing, are shields used at the end of the floor joist?

[sgschwend]

When using pex tubing under floors is there a way to stop the heated air from heating the exterior rim?

thanks for the help!!

 

[rowerwet]

depends, I have seen spray foam insulation over the whole setup, and also fiberglass bats as well.

 

[sgschwend]

Yes, I guess I should have said that the floor joist are TGIs and that there is fiberglass bats inside, that leave about 2" of air space, the pex tubing and aluminum heat spreaders are in this space. The air in this 2" space becomes warm. This warm air will move to the end of the joist run and contact the rim board which is below the home and really does not need to be heated.

So I was wondering if folks try to exclude heating that rim by means of a shield or more insulation?

 

[Dune]

Rigid foam isulation against the rim joist. At least that is how I am doing it. 2 inches thick, and sealed around the edges with great stuff.

Read all about it here https://www.hearth.com/econtent/index.php/forums/viewthread/40754/

Oh yeah, I am having someone else do it whith spay foam, guess I have too many irons in the fire to remember everything.

 

[in hot water]

the rim joist is a very high loss area. This is because you only have 1-1/2 to 2" of wood between the inside temperature and outdoor temperature. If the joist bay is 75- 85F and outdoor is 0 or below then that is a large delta t across a small r-value. I would use foamboard sealed in with spray foam, 4" or more just as you would exterior walls.

Also the infiltration at rim joist can be very high as the connection between the foundation and rim joist often is leaky. another reason to spray foam this detail.

Tiger foam and other offer DIY spray foam kits for large areas. I think most of the box stores carry it.

hr

 

[sgschwend]

Read the other posts, I see what you-all mean, but...

If you are going to spray foam where do you stop? Pay a contractor to do the hole thing? If so then there will be no air space, but I guess the heat has got to go up, just less surface area of heating I guess.

thanks for the help


Just called my local spray foam contractor. His telephone phone estimate was $4,000 for 1000 square feet of coverage. Now I see...

 

[in hot water]

just spray foam the rim, or band joist. I think fiberglass batts are fine for the joist bays inside. The perimeter of your home X the depth of the rim joist should get you an idea of square footage of foam you need.

Tiger Foam sells it by the board feet coverage , so 600 board feet = 600 square feet at 1" thick. The spray foam is really just to seal the air gaps, still use a less expensive foamboard for the filler and r-value. The spray foam seals it all up and fills any cracks that wind can enter.

Then fiberglass batt up to the spray foam.

hr

 

[rkusek]

the rim joist is a very high loss area. This is because you only have 1-1/2 to 2" of wood between the inside temperature and outdoor temperature. If the joist bay is 75- 85F and outdoor is 0 or below then that is a large delta t across a small r-value. I would use foamboard sealed in with spray foam, 4" or more just as you would exterior walls.

Also the infiltration at rim joist can be very high as the connection between the foundation and rim joist often is leaky. another reason to spray foam this detail.

Tiger foam and other offer DIY spray foam kits for large areas. I think most of the box stores carry it.

hr

Does anyone already have fiberglass batts tucked in on this rim joist areas? Both my new and last home had them. Are you adding the foamboard and great stuff in addition to this? Or did you have nothing to start with? I could see where the great stuff would make it airtight as opposed to the batts that may seep air around the edges. Maybe some thinner foamboard and spray foam to seal it up tight? I could see where this would make a huge difference if I were to install staple up radiant.

 

[in hot water]

sure, fiberglass in the rim joist area, but I would still seal with expanding foam first, just enough thickness to seal all the air gaps.

Sill seal also can leave gaps if the foundation is not perfectly level, so a spray of foam along that connection also.

What happens with underfloor radiant is any cold air that blows through those gaps hits the warmed air and it condenses, then you have moisture and potential mold, worse case wood rot.

Ive seen this happen several times on brand new homes. In all cases the insulation contractor returned and put a layer of foam against the rim, and sill seal, replaced the batts with dry ones.

hr

 

[sgschwend]

I ordered a 16 pound kit; found out that Fastenal reps a supplier, so they will pay the shipping to their local store. I will use the kits on the ends and also to seal up my outside trench which is only 12' long.

I thought I might use some packing pellets (the water proof kind) to bed my tubing in the trench. Has anybody used these? Lots of folks have them and so you can normally get them free (you don't want the water soluble ones).