Fiber Cement over 2″ Rockwool Comfortboard 80
qofmiwok
| Posted in GBA Pro Help on
I’m finding a lot of older articles on this, but not recent ones since it’s become common.
Is wood battens the current state of the art for installing lap siding fiber cement over 2″ exterior mineral wool board? Are 1×4 battens recommended over 1×3, and are nailing patterns well established?
In some places we would be installing it above synthetic stone veneer, which we planned to install on Dorkin Delta Dry & Lath directly over the rockwool. Any tips for detailing that border?
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Replies
qofmiwok,
The first place to go are the installation instructions for whatever brand of siding you are using. They all have specific requirements for backing, nail penetration, etc. for different substrates.
I started there. Allura only has instructions for up to 1" external insulation.
James Hardie specifically addresses installation over up to 4" exterior insulation in this document. (Method 2) But says: "For applications with mineral wool insulation, please contact the mineral wool manufacturer for advice on engineering and design values regarding the furring attachment back to the structure."
https://www.jameshardiepros.com/getattachment/f580da6b-a3b5-4962-8548-5671e761034a/19-jh-over-advanced-framing-or-continuous-insulation.pdf
Interestingly, Rockwool never mentions the words "fiber cement" in it's general installation instructions, but they have this document which shows it over 2 1/2" Comfortboard.
https://www.rockwool.com/north-america/syssiteassets/o2-rockwool/documentation/construction-details/residential/constructiondetails-woodframe-construction-lightweight-horizontal-cladding.pdf
So clear as mud, and yet I know that many many people are doing fiber cement over 2" rockwool.
Clear as mud is a good description.
You may find this useful, starting at page ten: https://www.victoria.ca/assets/Departments/Planning~Development/Permits~Inspections/Example~Plans/Illustrated-Guide-R22-Effective-Walls-In-Wood-Frame-Construction.pdf
You want this link:
https://www.rockwool.com/siteassets/o2-rockwool/documentation/technical-guides/commercial/rockwool-cladding-attachment-and-support-details_en.pdf
Cement board siding falls into light weight category.
1x3 tend to split easily, I would not go with anything less than 1x4.
For siding fastener, you need to do some digging on Hardie's site. They have fastener tables for almost any wind load, building height and substrate. Not easy to find, ESR 2290 or 1844 but it is there.