Non-Treated Joists too close to ground in Crawlsapce.

[XR250]

I have a customer who re-framed a floor with non-treated 2x10 SYP joists. The bottoms are 12" above the ground surface. Code is 18" for non-treated lumber. Does anyone have any ideas on how to makes this work short of re-framing?
I was thinking exterior grade paint. Can't think of why this would not fly.

 

[SWComposites]

this is ground in a crawl space?
probably simplest to remove 6" of dirt.
who is going to go into the crawl space in a few years to repaint the joists?

 

[XR250]

He does not want to create a bathtub. Why would they require repainting?

 

[SWComposites]

well I've never owned a house that didn't require re-painting.
granted the joists would not be exposed to sunlight.
presumably there is a concern about moisture from the ground; can they put down a vapor barrier? not sure if the code allows relief for that.

 

[XR250]

Yea, I think UV is the biggest issue with paint. Have not seen anything in the code about vapor barriers mitigating this issue.
I imagine encapsulating the crawlspace would completely address the issue but he said the AHJ is not accepting that for some reason.

 

[Eng16080]

I think painting is a great idea. If it's damp down there, get a dehumidifier first and let it run for awhile. Get the wood as dry as possible and then paint. Dry wood absorbs paint very well and will create an exceptional bond.

Somewhere I have an old building construction book (from the 1920s I think) where they make the claim that painted wood (where properly maintained/repainted) will last indefinitely in an exterior/damp environment.

I would think it might require repainting at some point in the distant future.

 

[gte447f]

XR250, if 2018 IRC is the governing code, Section R317.1.1 does say 18 inches from "exposed ground" in a crawl space, so are you sure that a vapor barrier does not mitigate this requirement? Personally, I would not favor joists closer to the ground than 18", but technically it might be OK with a vapor barrier per the code. It's a question of interpretation I guess, which is ultimately up to the building official. I would say that the same (interpretation by building official) would apply for an alternative like painting the joists. Personally, I don't think painting should be considered a viable mitigation strategy, unless it's some serious marine grade paint or something and there is some data to back it up. This seems like one of those situations where the offending party should have known better, and should have to eat their mistake and redo it correctly.

 

[ChorasDen]

Separate joists from ground with a sufficiently thick moisture/vapor barrier? How do we keep wall framing in walls dry from wind driven rain?

 

[XR250]

"XR250, if 2018 IRC is the governing code, Section R317.1.1 does say 18 inches from "exposed ground" in a crawl space, so are you sure that a vapor barrier does not mitigate this requirement?"

Thanks,
I forwarded this to the contractor.

 

[Eng16080]

A sheet of plastic (vapor barrier) set directly on the ground would seemingly satisfy the code requirement.

 

[RontheRedneck]

I'm thinking vapor barrier on the ground, insulate the perimeter walls, and run HVAC ducts into the crawlspace.

 

[Tomfh]

What is the risk when joists are 12” above ground compared to 18”? Here in Sydney I see so many old places that are 12” or less.

 

[gte447f]

Tomfh, the code requirement is in the International Residential Code section titled "Protection of Wood and Wood Based Products Against Decay", so presumably the risk of decay increases if joists are closer than 18". It makes sense because the ground is the source of moisture. I'm sure 18" isn't a magic number or distance, but from anecdotal personal experience, in my area (southeastern USA) it does make a difference, i.e., higher crawl spaces perform better RE: moisture management.

 

[Tomfh]

Is it reduced airflow due to reduced cavity?, or is there an actual moisture gradient as such, with the air 18" high being drier than 12"?

 

[gte447f]

Tomfh, good questions. I don't know the answers. I have never seen any research or technical information on the topic. I would suspect that both phenomena you mentioned are probably factors at play.

 

[phamENG]

Rather than paint, I'd go for a surface applied wood preservative. I don't think it technically meets the commodity specs from AWPA U1 for floor framing, but combined with the moisture barrier (probably taped) to remove the "exposed ground surface" you should get decent results.

Regarding the distance...I'm not sure either. My hunch is that it's more for encouraging ventilation, but I wouldn't be surprised if there's a moisture gradient at play, too.

Anecdotally, my house is built over a crawl and has a 'sunken living room' typical of the late 70s to early 90s. When we bought it, only two areas had any moisture damage - a bathroom and that living room. The bathroom was obviously leaking plumbing, but the living room was a more general fungal attack from elevated moisture. Proximity to grade coupled with being stuck in a corner between the garage and a filled porch (very limited ventilation), that area started to rot while the rest of the house is high and dry despite being built over a swamp with visible condensation on the underside of the vapor barrier in some seasons.

 

[gte447f]

Good luck applying paint or surface applied wood preservative on your back in a 12" crawl space. I guess the same can be said of unrolling a plastic vapor barrier which might be only slightly easier to accomplish. A 12" crawl space is a terrible idea unless it is to be sealed up and never accessed again. Maybe the whole thing isn't 12" and its only a small section that is.

 

[gte447f]

As an aside, this topic has got me thinking about required access to under floor spaces. IRC Section R408.4 requires 18x24 opening through the floor or 16x24 opening through a perimeter wall. The perimeter wall option seems like a no-go for a 12" crawl space, so will they be providing 18x24 hatch through the floor? I doubt it, right?