# XPS styrofoam board question



## XSleeper (Sep 23, 2007)

You would need to provide a UPC, or look it up on their website.


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## Rodochan (Aug 22, 2020)

Sorry, I looked but could not find it


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## SPS-1 (Oct 21, 2008)

The R value we see over here has units foot x foot x degree F X hr / BTU

Since those units would be totally meaningless in most parts of the world, they would not be used.

They would likely mark it with the RSI value , which is measured in meter X meter X degree Kelvin / Watt

Convert by 5.678


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## Rodochan (Aug 22, 2020)

Convert by 5.678. Thanks, but I got a D in math. Can you give me a formula? Is that btu to metric?


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## Rodochan (Aug 22, 2020)

To SPS-1, thanks so much. You’ve solved a problem that’s been hounding me for 8 months. I’m gutting a house here and the fiberglass insulation is 2.0(R-11.36), but it’s subpar and wrapped in plastic. Now I can go ahead with me XPS installation. Again thanks!


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## carpdad (Oct 11, 2010)

Is the house concrete or wood? Air seal maybe just as important. If wood frame inside, some photos? Just a hobby for me learning something about framing over the world.


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## Rodochan (Aug 22, 2020)

The house is 2x4 wood framed with large fiber cement panels for sheathing.


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## carpdad (Oct 11, 2010)

In usa and 2x4 is actually width of 3.5 inches. Fiberglass insulation is now nominal r13. I think rockwool insulation has higher value. XPS is r5 per inch. Just some comparison points. Foam board gives you higher insulation but it's higher cost. Foam boards also need the cut edges sealed with extra foam from spray can. As such, the cost for using foam board vs the fiberglass, insulation you get may not be as big a bang as you think. Professionally sprayed foam is the gold standard but very high cost.


Every bit helps but that's as a large groups of energy using consumers. But what does insulation mean to you? How much will you save and does it add to the house value?


Assuming the photo construction is standard, fiber insulation rolls/batts are also sold to fit into standard framing spaces. 

Old r11 encased insulation wasn't as bad as you may have assumed, although maybe it wasn't installed carefully. I don't see any horizontal siding joints, so probably the walls were better air sealed.


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## Rodochan (Aug 22, 2020)

I’m curious, you say that the cut edges of the foam board must be sealed with spray foam. Why? Certainly fiberglass is not airtight, and nobody’s sealing that, so why foam boards? Anyway, these fiber cement panels cover the exterior wall from the foundation to the top of the first floor, and at least 8 to 10 feet wide, and then layered with a thick rubber coat. There is little air infiltration.


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## SPS-1 (Oct 21, 2008)

Rodochan said:


> I’m curious, you say that the cut edges of the foam board must be sealed with spray foam. Why? Certainly fiberglass is not airtight, and nobody’s sealing that, so why foam boards?.


Actually, yes, many times fiberglass is sealed. In my area, the common method is to put a 6 mil poly sheet on the inside wall as a *vapor barrier*. The idea being, if its cold outside, the warm humid indoor air would otherwise condense when it hits the cold outdoor surface, and you end up with wet surfaces inside your walls.

But where to put the vapor barrier, and even if to put a vapor barrier depends on the climate you live in. Best to do what has been proven to be succesful in your area. That is something you should have researched before you started the project. It can become a rather complex subject.

XPS makes a pretty good vapor barrier by itself (if it is sealed). EPS not so much unless its very thick.


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## carpdad (Oct 11, 2010)

If you saw lots of gaps between the encased insulation and the studs, that would be improper install. Maybe the insulation wasn't made correctly or the stud spacing was wider than the insulation, etc. I thought the japanese quality was better.:smile:
Insulation is about tight fits and, using foam board, you can try to cut the board precisely enough for a tight fit but I personally would not have the patience.:smile: I would cut the board about 1/4" short of the dimensions (as much because it would make the work go faster), get all the boards for one wall at least, then fill the gaps with canned foam. You can learn to control the spray foam bead so you apply just enough for the gap.


BTW, use solvent based spray foam and not the water based. Water based, such as DAP, is not robust and may get crushed by the weight of the board.


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## Rodochan (Aug 22, 2020)

There is no such thing here in Japan as “quality” when it comes to home building insulation. It’s all about withstanding earthquakes. Yes, the insulation was definitely poorly installed. We have 8’ by 8’ fiber cement panels coated with thick rubber on the exterior, so there is little air leakage. The worst season here is the hot-n-humid summers, so any air sealing on the inside would create a lot of condensation right? Thanks for the help!


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## Rodochan (Aug 22, 2020)

I have a plan for cutting the XPS, using a circular saw. We’ve already replaced the whole crawl space with a taped vapor barrier but there are at least 2 open vents per side in this square house, and I have the exhaust fans and xps/spray foam to seal and vent those. I ordered a lot of R-19 pink ($700) from the US but not sure whether to use it on the 1st floor or 2nd floor. Nobody on eBay wants to deliver any insulation here anymore cuz of the corona, I’m guessing, so we have to use local supplies. Also had to order everything shower related to build my shower from Amazon. I went with Delta faucet. We are just finishing up our last room gutting and I’m putting in the new subfloor(one room only, 2nd floor), so now it’s finally remodel time. Lots of cat damage.


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## carpdad (Oct 11, 2010)

Insulating a house, there is also the vapor factor. It can get trapped in the wall and damage the lumber and start a mold. It's quite a problem here. Your exterior siding would be a vapor barrier so you don't want the interior wall covers to be another vapor barrier. Air leaks can carry lots of vapor. I would seal ALL joints between the exterior fiber siding and the studs so that each stud bay is sealed then insulate. Then interior cover (drywall?) but use some caulking along the top and bottom plates for extra air seal. Seal around any opening also, electrical boxes, vents, lights, etc. Use flat paint. Semigloss or gloss tend to be better vapor barriers. Don't use foil or vinyl lined wallpaper.


One good thing about loose insulation/no insulation is that there's more space for air to circulate and dry out the space.


What was the interior wall cover? Maybe take a lesson from there since fiberboard looks fairly clean.


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