I have a question about RIM board insulation. My home (new const) is zone 5, metal roof, cathedral ceiling, 14" engineered joists, 2x6 walls and 1.5" XPS rigid exterior under 3/4 furring.

The foam was placed on the framing prior to standing walls. So foam seams exist between wall sections and between wall/RIM at top and bottom of RIM. These foam seams are not perfect and there are some gaps.

with 14in TJI joists, what I am considering is HD R21 unfaced batts in all the walls with intelloplus to allow interior drying and HD R38 kraft faced batts in the cathedral areas with venting channels.

For the RIM, I am debating open cell spray foam but not sure if that is what I should do. I can't really put intelloplus over these areas because there is nothing to put it over or the joists run perpendicular and I'd have to cut a zillion square pieces of intelloplus and the sealing would not have a good result anyway.

I think using batts in the RIM is a mistake. With the exterior XPS 1.5in, should I go with closed or open cell spray foam?

I would use closed cell foam at the rim joist location

Even with the exterior 1.5" XPS? If closed cell, 2" to just seal it, then fill the rest batts?

that will work.

Note that the exterior foam often ends at the top of the foundation, and that is where there can be substantial infiltration.

Well I used sill seal gasket foam for that. Should I do more? I would think its worse where the wall bottom plate meets the decking for each floor. I just sealed all that with 100% silicone. Two layers, once last week once today. The insulation guys are supposed to seal stuff so I will probably let them do it, then go behind them and do more.

Standard sill sealer foam that comes in a roll is pretty leaky stuff under a treated board used for the sill plate on top of your poured walls the sill sealer does not SEAL out anything really so make sure to apply a bead of sealant where that board meets the wall or the slab whichever and close that off. The bottom plates are also a leaky spot, but you can also seal that with silicone or a product like ECOSEAL from Knauf insulation. Just be sure not to get the caulk or whatever to think because your drywall will flare out at the bottom of the wall.

There is no current substitute of 2#foam for sealing and insulating the sill plate/rim joist area of new home home or old and no better place to start, save the attic, which is naturally number one. I specify in even when we only show up to replace a boiler and recently on a multi-million dollar new construction project.

An EDPM sill gasket (Conservationtechnology.com) is a far superior product to between the foundation and sill than those crummy foam gaskets

Bob, too late to change, the walls are built.


"make sure to apply a bead of sealant where that board meets the wall or the slab "

regular caulk? or great stuff foam?

Best: Urethane caulk, next - canned spray foam.

I agree with Bob, urethane caulk is best. Foam is a bear to get INTO that small space where the sill plate gasket lives. Caulk can be put on thick and packe/smoothed into the groove so not to interfere with drywall in the future.

"Caulk can be put on thick and packe/smoothed into the groove so not to interfere with drywall in the future" not sure if we're talking about the same thing. The sillplate/gasket at the concrete is no where near drywall. The concrete is 10" thick, the outer walls/plate are 2x6 (5.5") so there is a ledge there. I can completely fill it with foam, ten inches thick, to meet the inner plane of the foundation wall.

I'm still not sure about the 2in of closed cell foam. With XPS on the outside, will it ever condense, and if so will it dry sandwiched like that?

bump on my previous post above...just want to be sure we're talking about the same thing. Getting ready for insulation here shortly would appreciate some comments thanks.

Posted By easyrider470 on 07 Aug 2014 09:43 PM
Standard sill sealer foam that comes in a roll is pretty leaky stuff under a treated board used for the sill plate on top of your poured walls the sill sealer does not SEAL out anything really so make sure to apply a bead of sealant where that board meets the wall or the slab

If the basement wall is pretty flat foam sill seal works just fine, unless you have real cheap stuff that is paper thin.

I used to wonder about everyone hating on sill seal so I started checking it out with the blower door and what I found was that for the most part it worked great, where it didn't work great was where you shouldn't expect it to work great and installation error. Problem areas are the corners and seams/ sill plate joints, low spots from horrible foundation contractors, ect. For what sill seal costs, its a great first step. Gaskets are going to have the same weak points, they just cover more foundation sins.

Also, surprising how much air will come in from the anchor bolt holes, seems to be from over-drilling bolt holes and not cleaning out the blowout from the back of the board from spade bits.

Anyways, I was going to comment on the sealant at the bottom plate or any 90 degree corner, how many of you are putting a tiny bond breaker in the corner of the sheathing and bottom plate? Or bottom plate and wall sheathing?

I've said it before, but look at joint design and you'll probably look at other options when thinking in terms of long term durability for a lot of applications using sealant. Especially if you do the math and learn how much movement the joint will take before it fails.

If the basement wall is pretty flat foam sill seal works just fine, unless you have real cheap stuff that is paper thin.

The concrete work was actually very nice. My waterproofers and framers both asked "who did your concrete work?" The top was quite flat and smooth. I used the pink sill seal.

Since I have 1.5in XPS (approx 0.75 perms) on exterior I was more concerned about how to seal moisture from interior of home from reaching the RIM board (condensing in winter). I am already planning to use MemBrain or Intelloplus for the walls with FG batts in the 2x6 cavities to breathe toward interior. For the RIM on top of the foundation and between 1st/2nd floors, applying membrain would be difficult since the engineered "I" joists are in the way.

Everyone here wants to do open cell foam of the RIM. Couple questions as I am VERY close to doing this:

1) Is the RIM at the first floor ceiling also an important spot for good sealing?
2) There is RIM at the front entry with a concrete stoop poured against it (with two layers of rubber between the stoop and RIM) - I am wondering if I should provide the ability to dry to interior as I am doing with the walls?

All band joists need to be air sealed, including those between floors, not just the one at the foundation sill.

Open cell spray foam (ocSPF) is usually going to be just fine for that job, even with 0.75 perm foam on the exterior. The R-value of the exterior foam increases the average temp of the joist, and the ocSPF has at least some vapor retardency. If you're still concerned, spraying the interior side of the ocSPF with "vapor barrier latex" brings it's vapor retardency down to about 5 perms, even 2-3" ocSPF thicknesses. (The specified permeance of vb latex is 0.5 perms if applied to paper-faced wallboard, but only hits ~5 perms when sprayed on foam.)

Dana, thanks for taking the time to answer. How thick should the ocSPF be? The sill plate is 2x6 5.5in wide so 5.5 inches fill the cavity?

Okay I believe Agribalance is an ocSPF based on the spec sheet here:

http://www.demilecusa.com/wp-content/uploads/2014/05/Sealection-Agribalance-TDS.pdf

Looks like 5 perms at 5 inches thick. So I assume even if some vapor gets through and condenses in the 4-8 weeks period during the coldest winter weather, it will have the capability to dry to the inside eventually?