[jackpine]

Quick question. I am about to take the batting insulation out and replace it with rigid foam and great stuff. I live way north, rural, so it is cold. I have a lot of air leaks and loss of heat in these joists. I have a bunch of 1 1/2 inch foam, I don't know the r value off hand but think it is 7 or 8.

My question is should I double it and will that double the R value? Is it worth the hassle to double it up?

 

[Beepster]

As part of my basement buildout, i actually put in three sheets of 1" XPS from all the scraps I had leftover. Maybe overkill, but that's the way i roll. It would be best to caulk in place due to expansion/contraction, but i think by using Great Stuff you are at 99% instead of 100%.

B

 

[hammerlane]

My question is should I double it and will that double the R value? Is it worth the hassle to double it up?

DOubling it will increase the R-value. Why not do spray foam in all the rim joist cavities? I use to have the fiberglass batt insulation in all the rim joist cavities. Then did all spray foam in them. Cut down on air infiltration and insects in the basement.

 

[concretemasonry]

When I insulated my rim joists, I cut pieces of scrap 2" XPS a little short (1/4") of what was needed. I then used as little expanding foam as I could to seaql the joints around the rim/plate/ joists and subfloor. I immediately grabbed a pre-cut piece and forced it into the space to let the expanding foam expand/seal and hold the foam in place. If I had extra XPS pieces I used them up. No need to be precise about cutting and fitting and the odd lengths could also be roughly cut to an approximate length.

I also used up some scrap FG batt pieces later, although they probably did not really add any insulation after the 2-4" of XPS, but I did not have to throw them away in the trash.

It is not a fine, precise method, but is certainly effective and has worked well for me on several homes.

The rim is probably the area of the home with the greatest heat/air loss per square foot. This method is certainly many times better than the simple, lightweight, leaky wood stick and FG structure above the foundation that is exposed to the real cold air temperatures. I did not go to those extremes for my basements because the temperature between the soil and the interior is far less than the difference between the wind above grade in cold climates.

Dick

 

[jackpine]

I agree spray foam would be ideal, but around here the cost is crazy high for that application. Even buying the do it yourself tanks is just cost prohibitive for me when I can get the xps so cheap and doing it myself. Yours looks great though.

 

[concretemasonry]

Using a couple of cans of expanding/adhesive foam and some XPS scraps is certainly much more economical that having a full-blown spray job.

Dick

 

[hammerlane]

Using a couple of cans of expanding/adhesive foam and some XPS scraps is certainly much more economical that having a full-blown spray job.

Dick

For about 80 rim joist cavities...all spray foam was probably a lot quicker than cutting scraps of XPS and using great stuff around the edges.

 

[cleveman]

You'll be fine with 1 1/2" in each cavity, then at least r13 of fiberglass on top of that.

If you have some more scraps, put them on as well.

I sheathe the outside with 1", then take all my door and window cutouts and put them in the rim joist cavities, doubled up. I rip them to the depth of my floor joists first, then cut each to fit, 14 7/16, 14 1/2, 14 9/16, etc. I cut each snug and often have to force them in with the handle of a hammer.

I can see how the expanding foam could be useful. I will also smear some caulk on the edges if I have a tube open.

 

[Gary in WA]

Either way, DIY, and figure in the affordability. You need to stop the air infiltration/exfiltration as said already; from MN;

"The data thus clearly demonstrates that it is not prudent from a condensation management perspective to fill the rim joists with batt insulation, regardless of whether they are covered with a vapor retarder or not. Free circulation of interior drying air in the rim joist cavity, particularly during the summer, would inhibit condensation as well as prevent moisture accumulation. Exterior insulation is effective in controlling winter rim joist condensation but tends to exacerbate summer condensation conditions, particularly in the presence of an interior vapor retarder. With the absence of interior batt insulation and an interior vapor retarder, the negative consequences of exterior rim joist insulation are mitigated. However, especially in retrofit situations, the amount of exterior insulation that can be installed (if any) may not be sufficient to provide adequate thermal insulation (at least R-10). Thus in these cases, the alternative is to install rigid insulation (such as foil-faced polyisocyanurate) flush against the interior side of the sheathing. This still allows air drying of the rim joist cavity but reduces the potential for interior summer condensation by decreasing the condensation surface to the bare minimum of the interstices of the insulation/ sheathing interface. In the winter, the insulation is protected from interior-sourced water vapor by the foil-facing. These considerations are reflected in the recommendations of section F." From: http://www.buildingfoundation.umn.edu/RimJoist/rimjoistphenom.htm

$$$; http://www.buildingscience.com/docu...joist/files/bscinfo_408_critical_seal_rev.pdf

$$; http://www.finehomebuilding.com/PDF/Free/021189072.pdf

$; Fig. 2; http://www.buildingscience.com/documents/information-sheets/crawlspace-insulation/

Gary

 

[Gary in WA]

For Grand Rapids, MN, you need more than 1-1/2", to control any condensation issues. Figuring your 3 coldest low temps average for the year, 1*F, and interior room temp at 70*F, with R-10= 24% RH and below for no condensation on the interior of the f.b. This would dry to the joist space, heated above and below. Because it's a much wider joist cavity (w. more insulation width), not a wall, my figures may be off slightly. I figured the dew-point with R-13 (3-1/2") cavity insulation, in all cases. R-15 = 34% RH ----- R-20 fb = 37% RH and below. Of course, this all depends on no exterior insulating sheathing.

Minimum code requires, for your Zone 7 and different wall cavity insulation; http://www.buildingscience.com/docu...ulating-sheathing-vapor-retarder-requirements

Page 62, Fig. 45, for the temperature slice- of Boston at 8*F; http://www.buildingscience.com/docu...ybrid-foundations-retrofits-measure-guideline

Gary

 

[Beepster]

For Grand Rapids, MN, you need more than 1-1/2", to control any condensation issues. Figuring your 3 coldest low temps average for the year, 1*F, and interior room temp at 70*F, with R-10= 24% RH and below for no condensation on the interior of the f.b. This would dry to the joist space, heated above and below. Because it's a much wider joist cavity (w. more insulation width), not a wall, my figures may be off slightly. I figured the dew-point with R-13 (3-1/2") cavity insulation, in all cases. R-15 = 34% RH ----- R-20 fb = 37% RH and below. Of course, this all depends on no exterior insulating sheathing.

Gary

GBR, I love you to death (as a man to love another man he knows from the internet, in a non-sexual way) for the vast wealth if knowledge you have in helping people at this site. But sometimes you just overwhelm me with the way you throw things out there. I really have no idea what the above numbers mean. When people come to me with tax questions (I'm a CPA), I try to explain it so that they understand and can make knowledgeable decisions.

B

 

[Windows on Wash]

Don't worry Gary can sometimes overwhelm people with his knowledge sometimes. At the end of the day, you'd rather have too much than too little.

That relatively small about insulation at that location will provide neither enough thermal resistance to hold off dewpoint and will likely have, depending on the type of insulation used, too much beeper permeance at that location and will allow condensation to happen on the actual structural wood.

The easiest thing to do would just be to spray at least 2 inches of closed cell polyurethane foam at those locations and cover with an un-faced fibrous insulation like Roxul to get the total R-value up.

 

[Gary in WA]

Lol, sometimes I have to slow down to think. I hate typing, hence the short answers and links. This should explain it fully; http://www.buildingscience.com/documents/reports/rr-0410-vapor-barriers-and-wall-design

Gary
PS. WoW explained it well.

 

[Windows on Wash]

Lol, sometimes I have to slow down to think. I hate typing, hence the short answers and links. This should explain it fully; http://www.buildingscience.com/documents/reports/rr-0410-vapor-barriers-and-wall-design

Gary
PS. WoW explained it well.

We work well as a team.

 

[jackpine]

So I am doubling the rigid foam, ending up with R14, and leaving the option open to put some batting up there before I do the concrete walls. Walls are getting xps and then 2x4 with bat insulation no vapor barrier.

Had to move some wires, the builder 40 years ago attached some of the electrical to the inside face of the bottom plate. I ended up having to cover the exposed concrete block top and the bottom plate with foam too, the air coming through that was crazy. This way I will have continuous xps from the rim joist all the way to the concrete slab when completed. Using lots of great stuff to get a good tight seal with no air movement.

Next summer I will be gluing xps to the exterior block, installing drainage and backfilling. It gets damn cold up here and I am sick of the shoddy construction the builder did 40 years ago. Everywhere I turn I find shortcuts and mistakes. Doesn't anybody build stuff to last anymore?