# Continuous back-up?

| Posted in Building Code Questions on

I am trying to understand the fire code here: http://www.cufca.ca/fire.php.

I want to put up some hardboard to cover ridig foam in my basement walls. What does the code mean by “3 mm thickness over continuous back-up?”

9.29.7. Hardboard Finish

9.29.7.1. Material Standard

1) Hardboard shall conform to CAN/CGSB11.3-M, Hardboard.

9.29.7.2. Thickness

1) Hardboard shall be not less than

a) 3 mm thick when applied over continuous back-up,
b) 6 mm thick when applied over supports spaced not more than 400 mm o.c., and
c) 9 mm thick when applied over supports spaced not more than 600 mm o.c.

Thanks!

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### Replies

1. GBA Editor
| | #1

Marc,
I'm not an expert at Canadian fire codes, but I would assume that "continuous backup" means something like continuous drywall or continuous plywood.

I think that "supports spaced not more than 400 mm o.c." means "framing members (studs, joists, or rafters) spaced 16 inches on center."

I think that "supports spaced not more than 600 mm o.c." means "framing members (studs, joists, or rafters) spaced 24 inches on center."

2. | | #2

Thanks Martin for your help. This "continuous backup" thing is confusing, because the following applies for plywood:

Maximum Spacing of Supports, mm(o.c.)
Minimum Thickness
On Supports with no Horizontal Blocking

3) No minimum thickness is required where plywood is applied over continuous backing.

How does that make sense? What could be continuous backing if plywood is the backing? So two sheets of plywood?

What I am trying to do is cover rigid foam without going through the hassle of framing the room. A pain, plus I don't have any tools.

Thanks

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