Polyiso insulation?

[bmxer883]

So I'm insulation a attic space of my old farm house had some leftover over xps I started using and needed few more sheets.

But at home Depot I noticed polyiso never really seen it before says it's closed cell foam so I decided to buy it cause of the great r value and the rest of my house is sprayed closed cell foam and its great.

Then I research and it says it looses a ton of r value in cold weather and off gases. Is this not the same stuff that was sprayed in my house cause I've never once heard spray foam lose r value in cold? I think I'll be taking it back for more xps

 

[dscheidt]

If I remember right, the blowing agent condenses at a higher than anticiapted temperature. the blwoing agent was changed for one with a much lower global warming potential, and the dew point went up. it wasn't happening at the test temperatures, so the rating didn't change. polyiso still has a high r-value per inch, it's just that if it's used where it's expose to temperatures low enough for this to happen, it won't work as well. you can accept that (which might make sense if it only happens once a year where you are) or use a layered approach, where the polyiso is inside, and something else is outside. that's common where the polyiso is used to provide an air barrier, and much cheaper fiberglass or celulose is on the cold side.

 

[bmxer883]

It says extreme climate and shows cold so if this does loose r value in cold isn't that false advertising? I'm just torn between using it or taking back to get the purple stuff. It's cold here 6months of year and gets in the negative temps

 

[jamess1562]

I used the foil faced polyiso on the inside of my garage as a vapor barrier. Unfaced batt insulation in the cavities, polyiso, then OSB. Made sure to use good foil tape on the seems to create an air barrier. Northern Michigan here.

 

[Mattilac]

From my limited research, polyiso seems to be the choice for warm climates trying to keep buildings cool, not the other way around.

I'm in the northeast and planning to insulate my garage with XPS.

 

[theoldwizard1]

But at home Depot I noticed polyiso never really seen it before says it's closed cell foam ...

Polyiso has the highest R/inch of any commonly used insulation and is usual more expensive.

It is used in commercial building for "decking" insulation under flat roofs.

Then I research and it says it looses a ton of r value in cold weather and off gases. Is this not the same stuff that was sprayed in my house cause I've never once heard spray foam lose r value in cold?

I don't believe the statement that it looses R value with temp ! Got a source ?

Off gasing may be true.

 

[billconner]

Here's one source. R6.0 in summer, R4.5 in winter.

It is generally considered to be less affected by water - hence it's popularity for roofs - and less flammable.

https://www.greenbuildingadvisor.com/article/cold-weather-performance-of-polyisocyanurate

 

[billconner]

Is this not the same stuff that was sprayed in my house cause I've never once heard spray foam lose r value in cold?

Spray foam can be polyisocynurate or polyurethane. Polyiso looses R value as it gets colder. Polyurethane does not.

My sense is spray polyiso is not readily available. And it seems chemically, they are not a lot different. I sort of loose it at the differences between isocynurates and isocyanates.

So in short no, spray foam is probably polyurethane, not polyiso.

 

[930dreamer]

I here the radio commercial for this product;

Attic Insulation in Texas and Oklahoma | MILO Insulation

MILO Insulation offers the best attic insulation in Texas made of all-natural Sorghum that is a perfect, affordable solution for your home. Contact us today!

www.miloinsulation.com

 

[bmxer883]

Spray foam can be polyisocynurate or polyurethane. Polyiso looses R value as it gets colder. Polyurethane does not.

My sense is spray polyiso is not readily available. And it seems chemically, they are not a lot different. I sort of loose it at the differences between isocynurates and isocyanates.

So in short no, spray foam is probably polyurethane, not polyiso.

Makes sense. I went with xps just 2in but no snow melts off the roof anymore so it's better than what I had another inch would probably be best tho