Addition crawlspace insulation

Ask your questions pertaining to the interior that don't fit in the above categories
Post Reply
DIY newbie
Posts: 2
Joined: Wed Jun 12, 2019 1:42 pm

Addition crawlspace insulation

Post by DIY newbie » Wed Jun 12, 2019 2:23 pm

Hi there,

I'm dealing what is becoming an increasingly complicated reno project. I will go into as much detail as I can to explain, and include photos to illustrate.

Our home is in central Ontario, about 1.5 hours northeast of Toronto. So cold winters, and hot summers. The house is a 1970-built timber frame bungalow, with a 320 square-foot living room addition, added in 1979. The issues are to do with this addition.

The primary and most obvious issue to us, is a low point in the floor on one side of this room, and a general slight slope to the floor away from the main structure. What is the structure? The main house is cinder block foundation. The addition is pressure treated 4"x4" posts directly into the soil. Please read that twice. No footings, no sonotube, no cinderblock under this addition, just 4"x4" posts directly into the soil. Apparently that was okay in 1979.

There is also a skirt around the perimeter (pressboard with fiberglass batting inside, vinyl siding outside). The floor is also insulated and enclosed from underneath with 1/4" plywood. The soil under the crawlspace is covered with poly sheets and gravel on top of that. Generally speaking, we are on sandy, well-drained soil.

The room is on the left in the image below.
632560118_23.jpg
632560118_23.jpg (114.1 KiB) Viewed 181 times
Back to our sloping floor, with a low spot. In order to address the structural issue (wood footings directly in the soil), without rebuilding the addition from scratch (not in our budget), we've invested in having two steel beams placed under the room on top of helical piles. The piles are outboard of the walls. This has required the removal of some skirting and the entire deck, so we now have the crawlspace partially open to the elements. There is insulated HVAC ducting in this space, which I have rerouted to accommodate the steel beams. All of this infrastructure makes this a difficult space to work in now.
Here is what the opened space and new structure looks like.
IMG-20190502-WA0001.jpg
IMG-20190502-WA0001.jpg (216.21 KiB) Viewed 181 times
On to my main question. Given the details above, I have a goal of re-enclosing the crawlspace as my summer project. I'm hoping to find the best option in terms of warmth and moisture mitigation, while understanding that this space incredibly hard to maneuver in for making changes to the in-floor insulation, etc.

I've read online (dubious, I know) that the best fix, at least were this a crawlspace with cinder block walls, would be to place the crawlspace within the envelope of the 'conditioned air'. I'm not sure if this is truly feasible given that I can only install skirting around the perimeter, and not to any significant depth in the soil. But perhaps this is a good idea.
One possibility I've been considering is installing skirting beginning with some sort of composite board along the bottom, then pressboard or plywood above ground, and insulate from inside while tying an interior vapour barrier into the poly sheets on the ground. Is this a good idea? If yes, how would I best tie the vapour barrier into the rim joists? (The floor is enclosed from underneath, and those new steel beams now cover some of that enclosing plywood).

I've also read about just enclosing the room, and treating this like a sunroom of sorts. I think conceptually, that's what this room is at present.

Just wondering how best to proceed. How to address this in a cost, and time-efficient way. I'm open to tackling any project myself. One other comment: the room above is in need of updates, which is the whole reason we chose to reinforce with new beams. No point in putting in a new floor, drywall, etc., if it's going to continue to slump/sink. The point is I'm open to strategies that might involve accessing things from above, lifting subfloor, etc. That wouldn't be the most disruptive thing given future interior updates.

I'd really appreciate any of your thoughts, ideas, and suggestions in how to properly enclose this crawlspace again. I will say in advance that I wish our contractor had been more holistic in their view of the project, rather than just swooping in to install beams without considering the space as it was, and how it functioned. Unfortunately we are where we are, and I'd like to move forward effectively. We just want to fix things up as best we can.

Many thanks in advance.

User avatar
Shannon
Posts: 13373
Joined: Fri Nov 25, 2011 11:58 pm
Location: Canada
Contact:

Re: Addition crawlspace insulation

Post by Shannon » Wed Jun 12, 2019 8:50 pm

I personally think your best approach to this crawl space is treating it like the under side of a mobile home. Build a skirting around the perimeter out of PT lumber . I would excavate the soil 6 or so inches and install the wall, anchoring directly into the soil with some 24" rebar lengths. Sheet the inside of the wall and run the ground poly up a few inches and re -install the rock. You can then use rigid foam in the wall cavity. Cut the pieces about 1/2" small and seal them inplace using canned sprayfoam. Then enclose the exterior with the finish or sheeting you want. Keep this crawl space ventilated in summer and closed in winter.
Not sure if this is what you wanted but I think it would be the route I would go.
If you've found our videos or website information helpful, please considering making a donation using PayPal or pledging us on Patreon

DIY newbie
Posts: 2
Joined: Wed Jun 12, 2019 1:42 pm

Re: Addition crawlspace insulation

Post by DIY newbie » Fri Jun 14, 2019 7:42 am

Thank you for the quick reply Shannon. This makes a lot of sense, and seems like something I can handle in the coming weeks. I just want to clarify that I'm understanding your description, so I've done a quick sketch.

Is this accurate?
IMG_20190614_093900.jpg
IMG_20190614_093900.jpg (105.36 KiB) Viewed 158 times
For the sheeting on the inside of the wall, what material would be appropriate?

Once again, thank you for taking the time. Much appreciated.

User avatar
Shannon
Posts: 13373
Joined: Fri Nov 25, 2011 11:58 pm
Location: Canada
Contact:

Re: Addition crawlspace insulation

Post by Shannon » Sat Jun 15, 2019 8:02 am

pT plywood on inside . Other then that looks like you got it.
If you've found our videos or website information helpful, please considering making a donation using PayPal or pledging us on Patreon

Post Reply