AC Insulates Under Floor of 120 Year Old Crawlspace

[Daox]

Thanks for the update. I was wondering if you'd be able to tell a difference already. That is great!

I know I can tell a difference where my tile floor is and isn't insulated in my basement.

[AC_Hacker]

Originally Posted by Daox

Thanks for the update. I was wondering if you'd be able to tell a difference already. That is great! I know I can tell a difference where my tile floor is and isn't insulated in my basement.

Thanks!

My approach is to keep using the same very small mini-split (3/4 Ton), and to continue to improve the insulation in the house, room at a time, so that the mini-split can handle that additional area also.

Reducing the heat loss from the kitchen floor means that I can now expand the heated area of the house into the kitchen. Still, even in the kitchen, I have more possible energy loss improvements. Although the floor is now approaching standard, the windows are well below standard. I also have obvious infiltration from some areas in the kitchen that I can eliminate.

This seems a more interesting challenge than simply buying greater heat output.

-AC

[gtojohn]

What are you using for air film?

[AC_Hacker]

Originally Posted by gtojohn

What are you using for air film?

"Air Film" is the term that describes the boundary layer between any surface and air.

The air film boundary has an R-value ascribed to it in most thorough R-value tables.

-AC

[gtojohn]

Inside air film above floor = R-0.68
Inside air film below flooring = R-0.68
Inside air film above EPS (one surface reflective) = R-2.23
Outside air film below EPS = R-0.17
Just trying to make sense of the numbers. Above the floor, is that underlayment, under floor, tar paper? Eps are you calling the polymeric coating and foil the air film? Isn't that in the total R-value called out on the label?

[AC_Hacker]

Originally Posted by gtojohn

Inside air film above floor = R-0.68
Inside air film below flooring = R-0.68
Inside air film above EPS (one surface reflective) = R-2.23
Outside air film below EPS = R-0.17
Just trying to make sense of the numbers. Above the floor, is that underlayment, under floor, tar paper? Eps are you calling the polymeric coating and foil the air film? Isn't that in the total R-value called out on the label?

Air Film is not a thing, it is a phenomenon that results from the tendency of air that is very close to a surface to resist flow. Fluid flow is the primary mechanism of convection, therefore convective thermal loss. A boundary phenomenon that resists heat flow is considered to have an R-value which can be used in calculating total R-value.

this is from California Energy Commission:

AIR FILM -- A layer of still air adjacent to a surface which provides some thermal resistance.

AIR FILM COEFFICIENT -- A measure of the heat transfer through an air film. [See ASHRAE Table 1, ASHRAE Handbook, 1985 Fundamentals]

If you are still puzzled, you should Google "air film".

-AC

[gtojohn]

When I originally googled air film I got mostly results for the film "air". While at the store yesterday I did find Perma-R Poly sheathing with foil. The 3/8" board itself shows r-1.5 . And lists the system, with minimum 3/4" air gap reaching r-4.47. That could be multiplied for 3 3/8" for almost r-13.41 with a 1/8" thermal break before sheet rock on a 2x4 wall...if you could make it work within an 1/8" tolerance. The same could be done with 2 layers of their 3/4" board for 3" r-11.94 with a 1/2 space left over between sheetrock.

[AC_Hacker]

Originally Posted by gtojohn

When I originally googled air film I got mostly results for the film "air". While at the store yesterday I did find Perma-R Poly sheathing with foil. The 3/8" board itself shows r-1.5 . And lists the system, with minimum 3/4" air gap reaching r-4.47. That could be multiplied for 3 3/8" for almost r-13.41 with a 1/8" thermal break before sheet rock on a 2x4 wall...if you could make it work within an 1/8" tolerance. The same could be done with 2 layers of their 3/4" board for 3" r-11.94 with a 1/2 space left over between sheetrock.

Yeah, this all sounds very reasonable.

It's quite similar to the Multi Layer Insulation idea I am investigating.

However, R13.41 total R-value in a 4" wall (really 3.5") is not so amazing.

For comparison:

• Your multi-layer foil faced Perma-R Poly is R-13.41
• Dense Packed Cellulose would give you R-12.95
• Mineral wool in that same space is R-15.
• Solid XPS would give you R-17.5
• Solid PolyIso would give you about R-22

Don't forget, that if you have a standard stud wall, the stud itself has an R-value of R-1 per inch, and is a "thermal bridge", conducting unwanted heat or cold, so the stud section itself is actually R-3.5. In typical wall construction, the cumulative wall R-value will be reduced for any insulation by about 18%, so the above numbers would be:

• Your multi-layer foil faced Perma-R Poly is R-11
• Dense Packed Cellulose would give you R-10.62
• Mineral wool in that same space is R-12.3
• Solid XPS would give you R-14.35
• Solid PolyIso would give you about 18.04

If you can make your stud system non-continuous, it is a very large improvement.

-AC

[gtojohn]

it was the multi layer radiant insulation I was thinking about. After you finish with batts are you planning on sheathing for more air sealing?

[AC_Hacker]

Originally Posted by gtojohn

it was the multi layer radiant insulation I was thinking about. After you finish with batts are you planning on sheathing for more air sealing?

You have hit on a very interesting question...

I have seen seriously credible information from:

• A local organization called Energy Trust
• Opinions from this forum
• Local Oregon installers
• Building Science
• Fine Home Building
• Canadian government recommendations
• State of Alaska energy department recommendations
• State of Oregon energy department recommendations

... and they don't all agree.

I have gotten so much conflicting information from so many sources, that it is making my head spin around as I write this (yes, just like in the Exorcist movie).

We have a local organization called Energy Trust, that is funded by local gas and oil companies. They offer financial incentives for precisely following their instillation protocols, and they will send an inspector to verify your compliance, before they pay out. I have already decided that their financial incentives are insufficient to make me want to abandon my own personal ideas on this project, plus I hate the idea of an inspector... it violates my 'Pirate sensibilities'. However, I am interested in their recommendations, whether I follow them or not.

They require that your underfloor insulation be put in with absolutely no air gaps (I'm already going to 'Energy Jail' for that one), and that the lowest surface be completely open at the best, and vapor-permeable at the least.

The local 'Trade Wisdom' is that your bottom surface should be an air-tight vapor barrier.

Currently, my floor is fir, with a fir subfloor, and the only moisture barrier in the current structure is the EPS layer that I put in. Eventually however, I plan on putting in radiant heat on top of the floor, and my final top layer will be an organic high quality linoleum similar to Marmolium (German branded, organic, linoleum), if not actually Marmoleum. That will be a vapor barrier, also.

So, at that point I will be going to 'Energy Jail' on two counts of serious vapor-theory violations.

Getting back to your original question, I really would like to add another 1.5" to 2" of foil-faced Poly-Iso (foil side up) that runs in cross-direction to my floor joists, sealing all the seams with foam and tape. This should effectively stop the thermal-bridging from the floor joists. Also it would be a vapor barrier. It would also give me an effective R-value of 0.82 * (14.26 + 15) + 11.4 = 36. Since the Oregon minimum for under floor insulation is R-30, this would not really be anything to call a hyper-achievement.

[NOTE: the above calculation is assuming that thermal bridging will reduce the effective R-value of the structure that is above the Poly-Iso by 18%, and that the full R-value of the Poly-Iso will apply.]


This final act will put me in 'Energy Jail' for three counts of serious under floor insulation and vapor-theory violations.

But I will proudly retain my Pirate status.

Best,

-AC