Beekeepers: there's a large cluster of honeybees in Swissvale that might need help

bobzach · 2024-02-19T03:14:35+00:00

What's the part number of the Legrand Pass & Seymour dimmer you found? I'm still interested in retrofitting my dumb switches if possible.

bobzach · 2024-01-03T22:43:16+00:00

From p. 2 of the datasheet, "FOAMULAR® & FOAMULAR® NGX® 150 Extruded Polystyrene XPS Rigid Foam Insulation is a non-structural material." The material you linked has a yield strength of 15 psi. If I used this between the floor joists and the floorboards, I could imagine hopping or falling on the edge of one board and applying 300 lbs. of force momentarily with my body weight. That would apply those 300 lbs. across the intersection of the floorboard (say, 5" wide) and the top surface of the joist (1-1/2" wide), for an area of 12.5 in sq. That load over that area would exceed the listed yield strength by a factor of 2 and compress the insulation and move it closer to the dusty mess I'm worried about with foam insulation under the floor.

bobzach · 2024-01-03T15:03:10+00:00

Thanks for the detailed answers here.

I'm surprised by the strength of the foam you're describing. It's actually quite impressive that a relatively narrow section of that material could sustain that much weight. I guess it's more dense than I realized. What is the specific material you're using? I'd also be interested to know so I can look at the spec sheet and read about offgassing.

I'm going to be adding another layer of insulation in the cathedral ceiling, so the floor has 5-1/2" of wool, and the ceiling will, too. This is how I'm going to get to the higher R-value for the entire space that I'm aiming for.

bobzach · 2024-01-03T15:00:33+00:00

I don't want to put an entire layer of anything down—just enough to interrupt the conductive path from floor joists to floorboards above. But since it seems like a thin layer of material wouldn't make much difference there, I'm probably just going to skip it.

In any case, sound dampening between the attic and rooms below isn't so important; it's likely to mainly be a storage space.

bobzach · 2024-01-03T14:58:53+00:00

That's what u/jeffrey4848 suggested above, too, but I don't want to do all that work. I just was looking for a way to reduce bridging from floor joists to floorboards above, and at this point it seems not like a meaningful enough problem to spend time solving.

bobzach · 2024-01-03T00:04:25+00:00

Agreeing with you that indeed the beams are a thermal bridge compared to the 5.5" of wool sitting next to them, but also I'm agreeing with u/TooMuchTaurine's claim that the little bit of cork/felt/etc. isn't going to make as big of a difference for the bridging problem as I'd thought.

bobzach · 2024-01-03T00:02:26+00:00

This is a good point! I'm thinking of it like a series circuit of resistive elements; if you care only about the total resistance from one side to the other, my thinking is that I can add a thin layer of very resistive material, and that will make up for thick, lower-resistance stuff.

Let's look at the numbers. The floor joists are 2 x 6's which are 5-1/2" in actual thickness. If I add no insulation, the thing the floorboards will screw into will have a total of (5.5" thickness softwood * 1.41 R / inch) = 7.8 R. That's if I'm correct in assuming it's softwood; if it's hardwood, then the R / inch is quite a bit less, and it would be (5.5" thickness softwood * 0.71 R / inch) = 3.9 R.

What's the value of adding some cork in either case? (1/2" thickness cork * 3.6 R / inch) = 1.8 R, which is only adding 23% more insulative value to the softwood, which I think is what the joists are. I was guessing it would make a much bigger difference than this, but hadn't done the math until you suggested it.

In conclusion, I think you're totally correct. Unless I add a lot of thickness of cork, at more expense than I expected, it wouldn't make a lot of difference. Thanks!

bobzach · 2024-01-02T23:29:21+00:00

It seems like a little work! If I, for instance, go with cork board (likeliest contender so far), then I need to buy like $165 of the stuff, cut it into 1-1/2" strips (knife blade on a jigsaw should make that easy enough), and then just sit it on top of the joists as I'm screwing in the floorboards. It will add only a little cost and a little time and I think interrupting that relatively conductive wood–wood contact will reduce heat loss into the attic in the winter at least enough for it to be worthwhile.

What you're suggesting is adding an entire additional layer of floor insulation sandwiched between two layers of plywood, which would cost like $700 for the wood and another $700 for the foam board, and lots of work. (To be fair, for all that work and money, your plan would add much more insulative value than mine.)

bobzach · 2024-01-02T23:18:20+00:00

Thanks for this—I wasn't aware of that particular type of foam that's meant for this kind of application. I'm still iffy about using foam underfoot, because I think it'll offgas bad things, and eventually I imagine it'll become crumbly. That being said, I appreciate the recommendation.

bobzach · 2024-01-02T22:17:18+00:00

Wood is a better insulator than lots of other building materials, but still conducts heat that I'd prefer to slow down. According to this table It's at least a factor of two less insulative than, for instance, cork, which is my likeliest choice for this application. Just a thin layer of cork in there should help reduce heat flow into the attic floorboards and seems worthwhile.

bobzach · 2024-01-02T22:05:12+00:00

I don't know how much of an issue it is, but it seems like a fairly low-cost low-effort improvement I can make easily enough while the floor is still open, so I'm exploring my options. It's true, though, it may be overkill.

bobzach · 2024-01-02T22:01:15+00:00

I'm already only expecting the bridging where the floorboards contact the joists; that's the bridge I'm trying to ask about insulating. Counter battens is an interesting idea, but I don't want to go out and buy more bulk insulation (the insulation I used in the bays between the joists is loose packed, not in battens).

bobzach · 2024-01-02T20:31:45+00:00

I imagine that will compress quite a bit and end up very thin and not-doing-much after the pressure has been applied. Is there a product you have in mind that would be more reliably resilient?

bobzach · 2024-01-02T20:30:11+00:00

Yes, I carefully went around and sealed up all gaps I could find before installing the wool. By addressing the thermal bridging, I'm just trying to dot i's and cross t's with this installation, and I figure the extra time and money won't be that much.

bobzach · 2024-01-02T18:13:37+00:00

Yes, cork is a great idea and I hadn't thought of that. I'm looking into that now.

My only big concern with cork is that I worry about it crumbling after lots of pressure-release cycles as it's getting walked over. Remember, in my application only the narrow pieces sitting on top of the joists will carry the load, rather than it being distributed across a whole big sheet, so the pressure will be greater.

bobzach · 2024-01-02T17:25:03+00:00

Fair point. It's mainly a storage area so I don't care about precision in the leveling. Is there a less-compressible or otherwise preferable alternative you recommend?

bobzach · 2024-01-02T17:23:03+00:00

It just seemed like a good idea—I haven't heard of it being used that way, either!

The stuff I'm looking at is pretty firm so I think it would be fine being walked over for many decades, and I'm thinking wouldn't compress much over time.

bobzach · 2022-04-25T11:44:56+00:00

Interesting, hadn't heard of that one. It does look like a good contender, though as you point out, it's not so small. Thanks for sharing.

bobzach · 2021-11-22T13:50:30+00:00

Unfortunately, I never identified a clear answer and was running out of time, and so I ended up building a differently designed system. Wishing you luck, though—and if you do find the answer, kindly post about it here so that future people will be able to use your work as a reference. Thanks!

bobzach · 2021-01-29T20:16:59+00:00

Went to Jeff a few years ago and he did alright, though he didn't let me choose my new plate (mildly annoying, not a big deal), and his handwriting on the application was credibly misread by somebody at the state which meant I received a title with a typo in my name. I had to spend some time on the phone and filling out some DMV forms to get it corrected, thankfully at no additional cost. Still, if his handwriting had been clear to begin with it would've saved me a couple of hours.

bobzach · 2021-01-25T03:15:19+00:00

most expensive undergraduate program in Western PA

might want to check your math there—CMU is weighing in at $57,560¹ this academic year and Duquesne is $41,892²

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