Insulation- rim joist area?
Keeping with the theme of the week– not-so foamy homes– I am trying to come up with a solution for insulating a rim joist area with open web floor trusses that does not include foam.
Has anyone tried to wet spray cellulose onto the rim joist between/around the floor trusses? I would imagine that wet sprayed cavities need to be incapsulated on all six sides to avoid settling, but I could wrong about this.
Dense packing the area with insulweb and cellulose would a nightmare– it would be dang near impossible to fasten the insulweb around the webbing of the floor trusses.
Obviously fiberglass batts in this application wouldn’t be the best solution either.
Any thoughts?
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The first insulation contractor I knew of who used damp-spray cellulose had insulated the interior of his house with it and left it uncovered as the "finished" wall. It held up remarkably well as I recall. It might require adding a bit extra wheat paste or some such binder.
Brett,
We need to be green, but we also need to be wise. I don't know any Americans who live without consuming any fossil fuel or who never buy anything containing plastic. We all make compromises.
If there is one place on a house where foam makes sense, it's at the rim joists.
It's great to minimize foam use in new construction, but we all need to look at our own lives with clarity and decide whether we are being consistent. A little bit of foam, when used to save energy and maintain the integrity of your sill and rim joist, helps the planet.
Martin,
I agree. My life is certainly not void of plastics.
My thought was if there is a material/solution that performs well (and is less environmentally destructive) why not use it?
more support for Avoiding Basements and 2nd floors ;--)
= No Rim Joist Issues
course we still need a thermal break at the slab
This is where Martin and I diverge. To me, true green is the wisest strategy. To Martin, apparently, they don't always coincide. I use small amounts of foam, but for the sake of convenience not wisdom.
Yes "we all make compromises", but let's at least recognize them as such and not pretend that our compromises "help the planet". If we acknowledge that our compromises, in fact, hurt the planet (which they do), then we will strive to make fewer of them (as Brett is trying to do here).
Slab thermal break.
"the insulation is moved to the exterior of the rim joist by using modified double walls where the inside frame carries the roof loads."
I would like to do this, but I don't know if it would work in a heavy seismic zone.
I posted this question in a different thread and Robert never responded (probably too busy cleaning the 16 inches of snow off his hot tub)
At any rate, I'll post it again...
Robert, I really like the version of the double wall posted above.
But I wonder... will some of the weight from the trusses transfer to the inner wall? And 12 inches of cellulose in a two story wall seems prone to settling. Any concerns there?
Also would this wall work in a heavy seismic zone? Or do the floor joists need to tie into the exterior wall with the CDX sheathing for shear?
Here is the wall I refer to:
Brett, I like your attitude.
I think the answer to "why not use it?" is often that it's not the easiest way - for a variety of reasons.
I think the building industry could dramaticaly reduce the use of foam without giving up anything in terms of performance if more effort was put into dealing with thermal breaks and air-sealing at the design stage.
(I uploaded a .pdf in the Affordable Cold Climate thread that has some vintage details by Harold Orr, all of which show open-web trusses and no-foam insulation of the rim joist. In all cases, the insulation is moved to the exterior of the rim joist by using modified double walls where the inside frame carries the roof loads.)
It's interesting to look back at the vintage stuff sometimes...
Edited to include bracketed portion... The spam filter has a hate on for me today - again.
Brett,
Not all foam insulations are created equal. We used netted cellulose in projects up until about 10 years a go. We found that it was much more labor intensive, and expensive to do cellulose than spraying foam and it provided a better seal job. Since then all my rim joist designs have open cell, soy base foam.
Are you talkin' to me? ;-)
Yes, it's true, which seems odd in that the concept for the solution is in hand (illustrated at the floor above). All that needs to be done is to design a better interface with the foundation (illustrated in your image as reposted by Brett).
I think John's approach might be better yet - avoid the rim joist altogether by building single story slab on grade with FPSF.
For the record, I concede that the use of foam is almost unavoidable for below grade applications - although there are some mineral wool products that could work where compressibility isn't an issue. The way I see it though, since it's hard to avoid foam below grade, that's all the more reason to start eliminating it's use above grade.
John (er, I mean Lucas - from that northern Texas),
Two out of three of those Saskatchewan wall sections still have rim joist issues on the first floor.
Brett,
Sorry about missing the question elsewhere, but my truck is stuck in my dooryard right now, since I got a bit too close to the downslope when I was plowing. I'm waiting for the wrecker.
There are two versions of my "no-bridge" double wall system. The one you posted shows the outer wall sitting on the foundation sill, and would look the same if that ThermoMass foundation were the first storey double walls.
The other version would have another rim joist on the sill under the outer wall and would require gussets to tie the two wall frames together at the bottom plates. This has the advantage of identical shrinkage under both walls. At the second floor, the outer wall would be framed to match the height of the 2nd floor framing and the 2nd storey subfloor would extend out to tie the two walls and to tie the horizontal shear plane of the floor assembly into the outer, sheathed, load-bearing wall. This should meet any seismic or high wind requirements, and it's easier to tilt up the outer wall if it sits on the subfloor rather than dropping below it.
And the load-sharing problem of a double-wall system at the roof framing is not so much of an issue with trusses as it is with heavy framing. A high-healed truss will have a compression strut (as in my drawing) at the bearing point, and the light framing will flex if there is a reaction force elsewhere (plus trusses tend to rise at the bottom chord in the winter). Also, because in a 2-storey house the outer wall would not have another rim joist (and its cross-grain shrinkage) at the 2nd floor, there will be slightly less overall height loss in the outer wall as in the inner wall as the wood equilibrates.
Brett, the drawing you posted and the wall description provided by Robert are remarkably like our new house, nearing completion. Where the upper floor walls rest on a foundation wall, the outer wall studs run down to an outer sill on the foundation, and the floor joists and rim rest on a second sill also on the foundation. The inner wall is supported by the rim and floor system. The wall cavity thus runs down to the foundation, and the rim is insulated on the outside with dense-packed cellulose.
The house is set into a slope, with framed walkout front on the downhill side. Where the lower floor walls rest on the slab, there also are two sills for the two walls. The rim and inner wall studs of the upper level rest on the top plate of the inner wall of the lower level. The studs for the outer wall of the lower floor run up to the floor level above, so that the subfloor there ties the two walls together. Where there are two levels thus joined by the subfloor, the rim is insulated as the top part of the lower level wall cavity.
Well, now that I got my truck pulled out of the snowbank and got my Chocolate Oatmeal Stout for the evening, I got around to drawing up Double Wall Section #2, that depicts the 2nd floor transition for a completely shear-braced no-bridge (allright, minimal) structure:
Apples to apples, spray foam performs better, with a better air seal and less air permance. So, the individual can pick the lesser of two evils. Dense pack, requiring more heating/cooling load (read: more fossil fuel/electric consumption) or spray foam, requiring a poly-based plastic in your walls that will outlive all of us. Pick your poison.
Except spray foam IS poison and cellulose is the most non-toxic of all common insulation materials.
And "performs better" is meaningless unless all the goals of performance are spelled out. Cellulose outperforms almost any other insulation in the big picture.
Spray foam is way more expensive and so is typically applied thinner, while cellulose is affordable to a much higher R-value. And damp-spray is highly effective at stopping air movement.
Robert,
Thanks for the detail! Great for two story homes. I shall run it by the structural engineer.
For the homes that have surpassed the design phase I've been contemplating an idea for a cost saving, less environmental impacting solution for insulating a rim joist:
What about wet spraying cellulose to the rim joist and floor joist cavities. Let dry, then spray a 1" layer of closed spray foam to encapsulate the cellulose? What about a thicker layer of open cell?
What a great post! I'm not a fan of using foam primarily for the reasons Riversong stated in an earlier post. It's great to find a community of like-minded people searching for alternatives.
I'd like to revive this post.
I've got an existing 80-year old house in Pittsburgh and would like to insulate my basement. An energy auditor recommended to me that I use foam to insulate the rim joists as well as interior bypasses. My basement is about 70% subterranean, just about 3 feet or so is exposed above the ground. The basement walls are built with concrete block.
What options do I have besides foam? I love the idea of the original poster, to use wet spray cellulose to insulate the rim joists. How practical is this? Would I need to build something to contain the insulation?
Being that the project is a retrofit, I can not use the double-wall plans above since the trusses already sit on the single outer wall. Would it make sense to build a faux inner wall and insulate with cellulose or some other material there?
I'm not a builder, by the way. Just learning this stuff as I go.
Stephen,
It's hard to say from the information given what your best options are...
Though I do encourage you to investigate as many non-foamy options as possible.
With respect to basement walls:
Is your basement damp or have other moisture issues?
With respect to non-foamy insulation at the rim joist:
Beware: In your climate, air-permeable insulation requires a warm-in-winter side air barrier...
Insulating between joists does not eliminate thermal bridging through the joists to the rim joist...
With respect to stick framed above grade walls:
Are you planning to upgrade these as well?
What is the existing construction?
What type of roof do you have and how does it interface with the exterior walls?
My basement is currently damp. I'd like to learn how to fix that.
For the air barrier, that would go between the wall and the insulation? Or the insulation and the conditioned space? Would I use foil for this material?
"With respect to stick framed above grade walls: Are you planning to upgrade these as well?"
Yes, I'll be putting cellulose in the walls. The most I can fit will bring it up to R-13.
"What is the existing construction?"
I'm not sure what you mean by this?
"What type of roof do you have and how does it interface with the exterior walls?"
I have a hip roof and I'm not quite sure how it interfaces. I don't have access to the house yet. (I'm just buying it and haven't close yet.) Can you give me a couple of possibilities and perhaps I can remember what I saw.
Stephen,
If you have a damp basement, you need to take measures to address the basement's moisture problems.
And you have only two choices for insulating your rim joists, in my opinion: spray polyurethane foam or rigid foam. If you install cellulose insulation in a damp basement, then moisture can accumulate in your rim joists, leading to mold and rot.
Steven,
Sorry if my questions weren't clear.
By existing construction, I was wondering how the existing walls are constructed...
I'm guessing 2x4 walls... with board sheathing?
I was thinking that if you were planning a more extensive retrofit, you might consider using a Larsen Truss.
I think it is possible to do more with less foam using a Larsen Truss.
If you establish the "pressure boundary" - crate an air barrier - at the outside surface of the rim joist/sheathing, a Larsen truss can extend down far enough to insulate the rim joist as well as provide upgraded insulation for the rest of the above grade walls as well.
Using a Larsen Truss, it is possible to add enough insulation to the exterior of the rim joist/sheathing that air permeable insulation (like cellulose) can be used in the joist bays - assuming that the "pressure boundary" is established as I mentioned above.
Extending the Larsen Truss up into the eaves might be problematic depending on how your roof is attached to the house...
It s hard to say, but ideally you either want the Larsen Trusses to extend up past the top plates of the existing wall or have the attic insulation to extend outward over the the top plate.
Of course, if you are not planning an extensive retrofit, then as Martin suggests, spray foam is probably the only other way to go.
Wet basements work best with drafty existing structures.
What you are not reading so far is that updating an older home like yours to superinsulated is a major project.
First project is drying up the basement. Next is airsealing the attic, then the rim and basement, then walls, windows and doors. The Larsen truss idea is a large labor project and large cost project if contracted.
Budgets $2,000 might get you DIY started. Contracted.... Complete.... Tens of thousands. DIY complete would be very reasonable as the project is heavy on labor and light on materials if the right materials are used.
Least expensive, NG heat and good airsealing and or add a pellet stove.
Lucas,
My existing first and second floor walls are brick. I don't know if they used board sheathing under the brick in the 1930s? I'm guessing no?
Also, since the walls are brick it looks like a Larsen Truss may not be possible unless I want to cover my brick. (I don't.)
I'm now thinking of using a method like in the following link:
http://www.buildingscience.com/documents/information-sheets/high-r-value-wall-assemblies/high-r-wall-04-double-stud-wall-construction/images/highr_wall_04_web_rev02.jpg
One difference is my home doesn't have homewrap, and like I mentioned above I'm not sure if it has board sheathing either. For the above-ground walls, what would be the best way to deal with vapor and air if I went this method?
For the basement it looks like the leaks are coming from the downspout so close to the house. I'd take care of that first, obviously. If no more leaks, would I be able to build a false studded frame inside of the concrete blocks and fill the cavity with cellulose? Would I put up a vapor barrier or retarder between the insulation and the concrete blocks? Would I need to put a drainage cavity between the blocks and the vapor barrier?
AJ,
I don't mind doing the work myself.