I'll be building a Timber Frame/SIPs house in the future. I may not be able to get a foundation in and first floor deck on until November. I would then wait until the Spring to get the TF/SIPs up. I've been told that by using a subfloor product like Advantech, and then keeping it covered with plastic sheating/tarps, it should be ok through the winter. I live in CT so there's a good likelihood of snow. Is this a reasonable approach, or will the subfloor get ruined? Thanks.

I would not reccommend it. If you have to do it the floor can be sanded after its dry to level out the swelling. Some exposure during winter time framing is not too bad but to let it sit out all winter is not a good plan. It's what happens when plans fail. In other words to do it on purpose would be crazy. Covering with plastic won't work either, it will just trap water underneath it and prevent drying. And because wind, ask me how I know.

What are you using for the floor support? In some cases, such as wood I-beams, the weather warning applies to them as well. But, sometimes the building progress can be slow so you need to do what you need to do. If you do have to proceed thru winter, you can plastic tarp it. Use heavy plastic like 6 mil which will withstand you walking on it a little better, and carefully clean off any debris before you spread the plastic. You also need to plan a way for it to drain, and put stringers over the floor to pull the sheeting over. If it is an open floor deck, this is relatively easy as you can use practice golf balls and line to tie on weights to hang over the edge to keep the tarp pulled tight. The stringers(2X4's?) leaves some air gaps between sheeting and subfloor, and if they extend out over the edge a little will give it a chance to dry a little as air will be able to get up under the edge a little. Put any seams on top of a stringer so it is at a high point. This won't be perfect, but it will be better than nothing at all as long as it has a path to drain away rain or snow melt. Wind is also not your friend, you will have to keep regular tabs on it to make sure the sheathing stays in place. As mentioned, you may have to do some more work to deal with any moisture swelling after you get things closed up and allow the moisture content to stabilize.

The only way I'd do a project like that would be to add a sloped, plywood and tarped "roof" above the floor, so that rain and snow run off by gravity. Placing tarps and/or poly on the deck does not work - does not work - for keeping a deck dry. .

The other issue is that it will probably take two or three days maximum to build it, so when you consider all the time & cost you'll spend covering it, why not just wait?

Got it...not the thing to do. Thanks.

Use Fir not pine T&G plywood and forget about it. We do it all of the time with no issues, especially on Timber Frames, do to the length of time they stay exposed.

Good to know about it...