Hello:

In an attempt to make my not-so-super-insulated house alittle better, I have installed the Roxul 2” R-8 ComfortBoard IS so that it covers the double top-plate and extends 2 1/4” up the sides of bottom cord on my trusses. The point of doing this is to reduce thermal bridging through the top-plate. The baffles, to allow air circulation from the soffit to the roof vents, will back against this 2 1/4” Roxul extension and allow the cellulose ceiling insulation to cover the top of the top-plate.

The problem is securing the vertical exterior 3/4” stapping (16” oc) to which the Canexel sidiing and soffit channel will be attached.

In an attempt t

In an attempt to make my not-so-super-insulated house alittle better, I have installed the Roxul 2” R-8 ComfortBoard IS so that it covers the double top-plate and extends 2 1/4” up the sides of bottom cord on my trusses. The point of doing this is to reduce thermal bridging through the top-plate. The baffles, to allow air circulation from the soffit to the roof vents, will back against this 2 1/4” Roxul extension and allow the cellulose ceiling insulation to cover the top of the top-plate.

The problem is securing the vertical exterior 3/4” stapping (16” oc) to which the Canexel sidiing and soffit channel will be attached.

My worry is that the 3/4” strapping, nailed or screwed, through the 2” Roxul will not be strong enough to hold the Canexel in place.

I have considered using Simpson Strong-Tie Hurricane Tie (ZMAX) to attach strapping to the bottom cords of the trusses at 24” oc (and through to top-plate) and attaching strapping between these (12” oc) nailed or screwed through the 2” Roxul into the 7/16” OSB sheathing.

Do you think that this would be strong enough to hold the siding?

Is there a better way?

Thanks,

Rob.

Don't nail the strapping, and don't use bugle-head screws. The standard approach would be to screw the strapping to the studs on a 24" o.c. spacing 1.5" into the wood (stud + sheathing) using pancake-head timber screws such as FastenMaster HeadLok or similar. For 1x strapping plus 2" insulation you can use use either 4.5" or 5" HeadLoks. At 24" o.c. spacing it's more than enough to hang fiber cement or Canexel composite (or even stucco on metal lath), no problem at all.

http://www.fastenmaster.com/details/product/headlok-heavy-duty-flathead-fastener.html

http://www.greenbuildingadvisor.com/blogs/dept/musings/fastening-furring-strips-foam-sheathed-wall

For hanging the siding to the strapping without penetrating thermally conductive nail-points into the foam the nails need to be pretty short. In high wind areas ring-shank nails are preferred due to the limited 3/4" bite into wood.

Thanks Dana1, that's what I will do.

Rob.

I am kicking myself for not getting extra insulation placed on the outside of my house when I got it resided. I am looking into doing one side of the house at a time and doing the same. I have R11 in the walls now with 1/2 inch foil faced rigid foam over it. I would be removing portions of the siding, shooting cellulose in the wall cavities, and covering the outside with 2-4 inches additional insulation. I could then tack the siding back up.

Question is, why the roxil comfortboard instead of 2inch rigid foam that comes in 4x8 sheets at R10?

Hi kogashuko:

Basically, I 'bought' into this: http://www.roxul.com/files/RX-NA_EN/pdf/ComfortBoard%20IS.pdf

It really blocks outside noise, is easy to install (2'x4' panels) alone and should not allow a moisture issue within my walls.

Rob.

Ok good reasoning... is it cheaper or more than poly? Seems much easier to install since it is smaller. I just worry that there is no osb and might just be rigid foam on my existing home. The poly might provide more strength but I have not looked much at the roxul.

I bought 2" Roxul ComfortBoard IS for $45.00 CDN per pack. Each pack has 5 panels at 2' x 4', or, 40 sq ft. This equates to $1.13 per sf or $0.1406 per r-value per sf.

It cuts easily with a serrated bread knife but I mostly used my table saw to give me straight cuts so that I could reduce waste. I also used an electric carving knife, with a serrated blade, to trim or cut panels.

The only issue I had was that it compresses more easily, I think, than foam. This meant that I had to be careful not to over compress it at the edges, like around my window openins when I installed the strapping for my siding. I ripped 2x4's to 2" to be placed at the top & bottom of my walls to strongly secure the vertical strapping for my siding, again, to ensure no compression. If I had bought the R-6 Roxul, I could have simply used 2x2's as R-6 Roxul is only 1 1/2 inches thick.

HTH,

Rob.