Fiber Cement over 1" foam

[300Carpenter]

Hi Everyone,

I am installing fiber cement over 1" foam over existing redwood v-groove siding. Client doesn't want to maintain painted siding, so going with the Color Plus from James Hardie for siding and white trim from James Hardie around doors and windows. Climate is SF Bay Area, aka Northern California.

I have a few questions before I start.

1. What type of foam to use? (brand, foil backed, T n G?, Etc.)
2. What type of nails to use? I was thinking a 3 1/4" Galvanized #12, ring shanks
3. James Hardie's instructions say up to 1" foam can be installed under the siding, I am worried about the boards cracking or denting during installation. My client wanted the ColorPlus siding, so my boards are limited(as in it took 2 weeks to get them delivered). Do I have to pre-drill every hole?! That would take forever!
4. Vapor barrier. The siding area is basically a flat wall, with 4 windows and a door, no bays.
5. Trim I am planning on using the white Hardie Trim too.

I have done a bunch of cedar ship lap, but the insulation on the outside is new to me in northern California(SF Bay area). One thought is the use of furring strips for nailing(like pressure treated plywood). Seems like a good idea, but a bunch of extra work.

I am looking for some good building principles. I would rather do it right, than upset my client and possibly have a call back.

Thanks...

[AndyGump]

Re: Fiber Cement over 1" foam

I would suggest following this as a basic out line for your marine environment.
The Hardie siding will replace the stucco of course.
No foil backed anything.

Andy.Marine env. C.S..jpg

[NW Architect]

Re: Fiber Cement over 1" foam

Long nails are adequate - no need for nailers. Stainless better than galvy. Response to other questions depends on whats already in the wall and what you intend to do with openings to tie them in. I'd put a vapor permeable, drainage enhanced WRB between old T111 and new foam. NO vapor barrier outboard of the foam

[Ablesupe]

Re: Fiber Cement over 1" foam

Are you planning to mark stud locations on the foam?

[Stovepipe]

Re: Fiber Cement over 1" foam

I've put Hardie over 1" foam and it's been 6+ yrs now and holding up fine. I used 3" galvanized roofing nails. Not sure about using the ring shank nails unless they have a roofing nail style head. If the head is too thick and small in diameter, it will either puncture through the siding or stick too proud of the siding. Of course, mark your stud locations.

[tjseims]

Re: Fiber Cement over 1" foam

Hardie, Nichiha and Certainteed all allow for installation over up to 1" of foam, providing you achieve 1" fastener penetration in the studs. The biggest problem with foam and siding is "fastener sag". To best prevent this even under prescriptive conditions, make sure to not overdrive nails, nail at the proper nail line and do not use ring-shank nails. If you follow this and resist the urge to face nail the bottom of lap siding, your wall will hold up and look great (and straight) for a long time.

Best to you on your project!

[300Carpenter]

Re: Fiber Cement over 1" foam

Stovepipe:

When you used the 3" Galvy Roofing nails, was it a nail gun or hand drive? I am concerned about breaking the fiber cement siding, since it was Color Plus, it takes 2 weeks to get...unlike the regular stuff that takes about 30 minutes to get.

I have done fiber cement with out the foam( directly over older siding and vapor barrier) and even that broke a few corners!

Also, what type of insulation?

Thx...

I've put Hardie over 1" foam and it's been 6+ yrs now and holding up fine. I used 3" galvanized roofing nails. Not sure about using the ring shank nails unless they have a roofing nail style head. If the head is too thick and small in diameter, it will either puncture through the siding or stick too proud of the siding. Of course, mark your stud locations.

[300Carpenter]

Re: Fiber Cement over 1" foam

TJSEIMS:

Why do you recommend NOT using ring shanks? Seems like they would hold better IMHO. Whats your logic/experience behind that recommendation?

Hardie, Nichiha and Certainteed all allow for installation over up to 1" of foam, providing you achieve 1" fastener penetration in the studs. The biggest problem with foam and siding is "fastener sag". To best prevent this even under prescriptive conditions, make sure to not overdrive nails, nail at the proper nail line and do not use ring-shank nails. If you follow this and resist the urge to face nail the bottom of lap siding, your wall will hold up and look great (and straight) for a long time.

Best to you on your project!

[300Carpenter]

Re: Fiber Cement over 1" foam

Are you planning to mark stud locations on the foam?

If I am wearing my "thinking cap" that day I will....so YES. Plus, if I go over the studds, I will get more bite and the 1" penetration I want.

[Stovepipe]

Re: Fiber Cement over 1" foam

Stovepipe:

When you used the 3" Galvy Roofing nails, was it a nail gun or hand drive? I am concerned about breaking the fiber cement siding, since it was Color Plus, it takes 2 weeks to get...unlike the regular stuff that takes about 30 minutes to get.

I have done fiber cement with out the foam( directly over older siding and vapor barrier) and even that broke a few corners!

Also, what type of insulation?

Thx...

I hand drove them all. This way I don't blow through the siding and I am certain if I hit the stud or not. For the butt joints, I placed a 5x7 tin shingle behind the joint and spray painted it a flat black. 30# felt might work too. I used extruded polystyrene, the pink or blue stuff, for insulation.

Do not hang any planks that are even a little bit wet. Let them dry out first.

[Bill Robinson]

Re: Fiber Cement over 1" foam

Breakage of the corners can be reduced by making the siding is firm and flat against the insulation before nailing.
Use a good pneumatic gun and look both ways before crossing:>}

[300Carpenter]

Re: Fiber Cement over 1" foam

Stovepipe:

When you hand drove the nails, did you "pre-drill" the holes? Or were you able to finesse the nail thru the fiber cement?

[Stovepipe]

Re: Fiber Cement over 1" foam

Stovepipe:

When you hand drove the nails, did you "pre-drill" the holes? Or were you able to finesse the nail thru the fiber cement?

I didn't pre-drill them, except for when it landed close to the end. I used Hardie, and didn't need to "finesse the nail thru". Sometimes a nail would bend, but after awhile, I learned how to hold the nail to minimize the bent nails. Well, on second thought, maybe you can call that finessing.
I've used other brands of fiber-cement siding and found the Hardie brand less brittle.

[Bill Robinson]

Re: Fiber Cement over 1" foam

At this point the best thing to do is to get at it and you will quickly learn what works best for you.

Break that egg.

[tjseims]

Re: Fiber Cement over 1" foam

TJSEIMS:

Why do you recommend NOT using ring shanks? Seems like they would hold better IMHO. Whats your logic/experience behind that recommendation?

Good question. It is because ring shank nails can blow out the back of fiber cement and only have marginally improved fastener pull ratings.