Another framing question

[JohnnyC]

The floor of a 12x16 shed is PT 2x6 on top of a PT 2x8 mudsill. The bottom of the floor frame varies from 6" to 12" above the ground due to a ground slope. The mudsill is on solid concrete blocks. The decking is 3/4 ACX.

Do I need to seal the underside of the ACX with thompsons water seal or something similar? I've read a couple of differing opinions that floors will rot from underneath.

Also, is it required to put a layer of stone under the frame? I packed gravel under the concrete blocks but not the entire width/length of the floor frame.

Thank you for your time.

[kzin]

What is your climate like? Answers will be different for Oregon vs. Arizona. I'm in San Diego. My shed is very similar to your but on patio stones. I didn't water seal the flooring plywood and it is just fine after one of the rainiest winters we've had since I moved here. One thing that can help is making sure there is a bit of a gap between the trim boards along the bottom and the ground. This ensures airflow underneath. Yeah you might get some squirrels moving in underneath but if they want they'll move in anyway.

good luck ml

[JohnnyC]

Rhode Island. zone 5.

[Joe]

Thompson's products have had a sorry reputation for years starting with a Consumer Reports test some years ago and experiences of users in this NG IMO your logic for protecting the ACX is sensible. In your situation I would likely spray on a coat of the cheapest oil based polyurethane varnish I could find, Maybe even a PU porch paint. It should take around 2 gallons for average coverage. Some polyfilm on the ground to keep the humidity down might be modestly helpful (and cheap).

Joe

[RicodJour]

Here's what the NY Code (a minor variation of the IRC) has to say regarding the first question:

=A72304.11.2.1 Joists, girders and subfloor. Where wood joists or the bottom of a wood structural floor without joists are closer than

18 inches (457 mm), or wood girders are closer than 12 inches (305 mm), to the exposed ground in crawl spaces or unexcavated areas located within the perimeter of the building foundation, the floor assembly (including posts, girders, joists and subfloor) shall be of naturally durable or preservative-treated wood.

AC plywood is not naturally durable.

I'm not sure I understand your shed construction - it sounds like the foundation consists of some block sitting on gravel, which wouldn't pass inspection around here. Under a certain size the requirements are as stringent but when you go above that size you have to comply with the standard requirements of the building code.

It would be cheap insurance to put down a layer of plastic under the shed and cover it with gravel.

R

[Wayne Whitney]

Use PT decking.

Wayne