Open Cell Spray Foam - crawl space and interior walls

[Rusty]

Originally Posted by ChrisStratton

Hi WinniPeople!

We are looking at getting a small cottage above a lake.
Chris

What does "cottage above a lake" mean.

Thank you

[DickR]

Spraying foam upward calls for a certain amount of clearance below the floor for the applicator to crawl under and work. While closed cell foam provides more "R" value per inch, roughly 6 to 6.5, it must be applied in "lifts" of no more than about 2" at a time, due to the need for the heat released in curing to be dissipated by conduction. Open cell foam provides typically 3.6 to 4.0/inch of R value, which is similar to what you would get with a blown cellulose or fiberglass insulation, but it can be applied in thicker lifts. I'd certainly advise waiting until warmer weather, for best results. Also, with either open or closed cell foam or any other insulation, you won't get the same overall R value as you will between joists, due to thermal bridging of the framing. The R value of framing wood is roughly 1.2/inch, only a third that of porous insulation or just a fifth or less of what closed cell gives.

Considering the difficulty of application in a tight space, you might consider having a contractor do a dense-pack of borate-treated cellulose through holes cut in the sheet goods underneath the joists, much as is done when insulating a wall from the outside through holes cut in the sheathing. As a side benefit, the borate treatment of the cellulose provides a deterrent to rodents and insects.

After installing insulation between the joists, consider also installing a vapor-permeable insulation layer below the joists, such as Roxul board (https://www.homedepot.com/p/Roxul-Co...1224/206789748). This will provide an additional amount of insulation below the whole floor assembly, eliminating a lot of the thermal bridging effect of the framing.

Finally, another option is to change the skirt material to something that will keep out the weather and insulate those walls, especially if you have any utilities down there. For sure, apply that 6 or 10-mil vapor barrier over the ground. If you do go the route of building a weather-proof and insulated skirt, and the ground is flat or nearly so, consider also laying down at least 2" of closed cell insulation board, then the vapor barrier, and finally some course material like crushed stone over that for protection of the insulation and vapor barrier. With the skirt and ground insulated, there would be no need to insulate between the floor joists.

[winterh]

I had a cottage with a concrete block foundation and a dirt floor crawl space with clearance ranging from 2 to 3 ft from dirt to floor joists. It was damp and smelly and you could see the batt insulation in the joists was absorbing the dampness and beginning to drop. After much research I did whats called an encapsulation. Had a company come in and lay heavy plastic on the floor and up the walls. They then sprayed the walls and rim joists with closed cell foam. No venting at all, totally closed up. I left the batt in the floor joists but I think I could have removed it as well. Crawl space is now dry and no more smell or dampness. I do have an insulated door to enter and I run a small dehumidifier during summer months that drains to the outside. Overall I am very happy with the results. I also have my hvac, water heater.... in the crawl space. I had the block walls but I think you could apply concrete board inside your slat walls, spray foam to that and achieve the same effect.

[ChrisStratton]

I keep re-reading the comments above... and closing in the crawl space seems to be the consensus approach?

Originally Posted by winterh

concrete board inside your slat walls

Do you mean like hardie backer?? https://www.homeadvisor.com/r/hardie-board-siding/

[ChrisStratton]

This runs to ground/grade at the back upper corner.

[winterh]

I was thinking of something I believe they call duo rock board. It is about 3/4 inch thick concrete with mesh in it to hold it together. It is often used under tile applications but I was thinking it may be a good choice. I would do more research into what is best product but if you decide to encapsulate you want something that looks ok on the exterior and that will allow you to spray and hold the foam on the inside. If these were put inside of the slats I think you could keep the current look on the outside. I will be heading up mid week and will take some pics and post them or PM me and you are welcome to come by and take a look. It was not cheap but it was worth it. About $5000 for a 1600 sq ft footprint if i remember right.

[ChrisStratton]

Originally Posted by winterh

About $5000 for a 1600 sq ft footprint if i remember right.

Hi Winterh - i'd be interested in learning more about your company and how much foam they applied, etc. Sounds like the right approach, if they can get under the farthest reaches. Right now, I'm in FLA and prolly won't be up until the snow is gone (April)?

Thanks for the help in this, and the kind offer to visit!

[DickR]

The cement board product referred to by Winterh is Durock (eg. https://www.homedepot.com/p/DUROCK-N...2965/202263276). If you use that on the inside of the skirt, then you might consider cut/glue application of foam board (2-4") over the Durock for insulating, with beads of can foam at the edges and joints to seal them.

Some good reading on building an unvented crawl space can be found here: http://www.greenbuildingadvisor.com/...ed-crawl-space. In addition to the info in that blog, there is a long "Related Articles" list of links to more info on the general subject.

When I mentioned the use of borate-treated cellulose, what I had in mind was dense-pack blowing of the cellulose into the joist cavities, using a sufficiently powerful blower, like the contractors would have. Sometimes the blowers available at the big box stores are ok for a loose blow into an attic, but not powerful enough for dense packing to upwards of 3 lb/cuft density, needed to counter settling of loose-blown cellulose, as in an attic. If you are redoing the floors inside anyway, then you have more options for insulating. If you have sufficient ceiling height to lose a couple of inches, you could lay down rigid board over the present floor, then a layer of T&G plywood, and finished flooring. But if you see this structure as being regularly occupied year round, then overall comfort might be better with an enclosed and heavily insulated crawl space, with no floor insulation at all, since the floor and crawl space would be reasonably close to interior temperature.

[SIKSUKR]

Looking at those pics, if that were mine I would probably lean towards insulating the perimeter walls with rigid and laying a poly vapor barrier on the ground.

[ChrisStratton]

Thank you, each/all!

[VitaBene]

Wow, what a great thread! Thanks to those who contributed, it was very informative!

The end result is what a lot of the 4 season campers do with hay bales between the floor and the ground come winter, I guess.

[ChrisStratton]

Hi Dick & Winterh,

Thanks for a careful and informed responses! It sounds as if Dick is suggesting some sort of air "tight" skirting, with 2" foam on the "dirt floor" and "walls", covering the lot w/ 10mil poly and gravel on the floor, over the poly and foam board.

Winter H seems to be along the same lines - basically encapsulating the crawl space area.

Do I have that right?

You'd mentioned the borate treated cellulose sprayed up option. Since the floors will be redone - could I just spray that down? I guess the joists will still be cold 'bridges' in that case. https://www.homeadvisor.com/cost/ins...in-insulation/

Chris

[ChrisStratton]

Originally Posted by Rusty

What does "cottage above a lake" mean.

Thank you

Sorry for confusion. It means on the ground, upland a few hundred feet. Bad choice of words on my part.