I am having difficulty in understanding NYS Codes concerning PWF’s.
I have four (was three) questions. Two about specific codes, and I can’t find information in the Code to answer my third question.
First. For 404.2.3, what is meant by “height of fill”? Is this the fill INSIDE the foundation walls, or outside? Do I need a “Crawlspace” underneath joist floors, or can I have the level of dirt (with sealed sheets of plastic on top to be in between the dirt and the bottom of floor joists) at the same height as the fill on the outside of the foundation. I only planned on digging trenches the width of the required footings for the foundation walls to support the 1st and 2nd floors. Or is this not allowed?
Second, how do I determine what thickness of plywood will I need? Yes I will be hiring an architect to design the plans, but before I begin spending money on professionals, I want to make sure there are enough available funds to build this project, so I am attempting to get an estimate on the cost of the project. If the initial estimate is over the budget then the project won’t even be started. Is the spacing of the studs referred to in the table discussing the studs for the foundation, or the studs on the walls above?
Third, I can’t find in the code any mention about the spacing of the studs in the wall to support a one and/or two story building with a truss roof. I believe the foundation needs to be 4′ tall (with 8″ above the ground), is this correct as well. So for a 4′ tall foundation, what would the spacing of the 2×6 studs need to be to support both a 1 story and 2 story building. This expansion will be 1/2 – 1 story and the other 1/2 – 2 story.
Fourth question is I have gone through NYS codes, and other installation “guides” for PWF’s, and I must be misreading them because it doesn’t look like plywood is required on the inside of the pwf, even when it indicates inside fill is needed when the backside fill meets certain criteria. Since I don’t want a crawlspace (if that is allowed) then will I need to have plywood on the inside side of the foundation?
Thanks again for all the help
Ken L
Replies
A follow up question that is related to these questions. Part of this house/garage expansion involves a space where an existing Poll barn is that has a concrete floor. The building will be razed obviously, but I was hoping to salvage a good portion of the concrete floor that are in between the existing polls, the rest will be cut away and dug out. Is it possible to only dig a trench for the PWF the width of the footer's and surround the space with the foundation? And then fill/backfill after local inspector approves foundation? Or am I going to have to scrap the existing concrete floor completely? Thanks.
Ken L
Engage a design professional to translate the code and design your foundation. NY is a big state with a variety of climate conditions that anyone reading your posts can't determine. Personally I would NOT consider a wood foundation - you'd be better served with a concrete footing and and ICF foundation wall (ICF= insulated concrete forms). Utilizing the existing slab may be possible, but it has to be evaluated in the context of the entire picture.
Check out the Southern Forest Products Association's Permanent Wood Foundations design and construction guide. It should answer every question you have here and more. (I'd include a link, but it comes up as gobbledygook. The link you want is a PDF download). I know FHB editorial advisor Mike Guertin has built at least one PWF, and I believe this is the reference he used. He swears by it. Hope to use it myself. Good luck!
Thanks. That guide answers all of the questions I said so far, but there is a new one that that guide does not discuss. Because of code requirements PWF's must be 4' deep to be below the frost line where I live. A joist floor is not required for the "crawlspace" that is created, but what if I wanted to have a joist floor approximately 2 feet below grade? Is there any "guide" that helps describe that kind of construction?
Thanks again!
Ken L
By 2 ft below grade, I'm guessing you mean 2 ft. above the "basement" floor/2 ft. below the top of the foundation wall. You might need to consult an engineer and possibly get soil testing done if you want to put a floor system halfway up the pwf stem wall. Just like a regular foundation, a pwf has to battle the pressure of the soil pushing inward against it, and the pwf design in the code and the guide achieve this by restraining the top via floor framing and at the bottom via a slab. If you were to move the first floor framing below grade, there's not much to keep the soil above the floor framing from deflecting the portion of your foundation wall that's above grade. In other words, the reason it isn't in the guide or the code is because it's not a great idea. That's not to say it couldn't work in some soil conditions, but you'd need to have that designed by a professional.