Partly based on input from this forum, we’ve decided to insulate the foundation block wall and slab perimeter of our machine shop. The masons will be starting next week and we’ll be installing the insulation ourselves. I’ve got a few questions on how to best go about it.

Shop:
- 30x50, 8” high footer, 4 or 5 courses of block, 1 or 2 blocks exposed above grade; then 14’ 2x6 walls
Location; south central PA with long wall oriented to solar south.
Purpose: Year round use for business, but no plans for active heating system at first – hope to use solar air collectors for some winter heating and will consider additional sources after we see how comfortable (or not) the building is during winter. No plans AC. Target indoor winter temp: 60 deg F

Insulation plan:
- 2’x8’ of 2” thick XPS ‘lining’ (already purchased)
- Fasten to interior of the block foundation walls (prior to backfill) starting from about 2” above finished slab height and extending down two feet.
- Under the slab perimeter we plan to lay 2'x8' sheets of 2” XPS.
- Walls & ceiling will be insulated too, but that is a topic for another post. Ditto with thermal covers for windows and overhead doors. ;-)

Questions:

1. Does 2’ down (on the vertical wall), seem like enough depth for the XPS? Or do I need make it go deeper down the foundation wall?

2. Will adhesive only (rather than mechanical fasteners) be secure enough to hold XPS against the block wall during backfill (and forever after)?

3. On block foundation (not basement) walls, do the XPS seams need to be taped?

BabyBldr
this may be too late - just saw your post...
1. What is your frost wall depth? I'd go 4' down to get well under the cold ground
2. Getting backfill behind the XPS is a constant battle so you may want to nail it at the top. beyond that the earth will hold it in place.
3. The tapeing is basically to keep air from getting behind the foam. Not critical here, but not a bad idea.
4. Under the floor you might want to consider 4" of foam - the warmer the floor, the more comfortable it will be to work on, plus you'll loose less heat through the floor.
Bob

Bob – your’re just in the nick of time. Thanks so much! The masons finished most of the work at 4:30 yesterday and then we worked from 4:30 to 9:30 doing plumbing rough in. We’re going down tomorrow to finish the plumbing and get a start on the insulation.

As to the rigid foam insulation on the inside of the shop foundation:

1. Our code calls for 36” depth to get below frost and we have about at block and a half above grade. I could put two (instead of one) sheets of the 2’x8’ foam to give me the full four feet of depth as you suggest. It will mean using 40 sheets instead of 20, but if it improves long term winter performance for the next 30 years that I’m OK with that. My understanding of it is that we want to keep the dirt under the slab to those deep soil temps (~55 deg) and help use that to moderate the inside temp of the building during winter.

2. I got some masonry nails and large washers. In addition to liberal use of liquid nails adhesive I was going to hand hammer the nail/washer combo into to the corners and maybe one in the center. Not sure how hard that will be to do and that will likely determine how many I nail in! I hope this won’t break the block. Should I be aiming to nail into the block, or the motor in between the blocks?

3. I’ll pick up some tape to seal the seams. We’re only doing it once, might as well try do it right.

4. We’re only planning to insulate the perimeter of the slab, and we were planning on 2”. I believe we may be locked into that at this point since we’ve already got the block in and the elevations worked out for the slab and finish grade at the overhead door (you know, to account for keeping water out).

New questions for you:

5. We have a 12x12 overhead door and a 3’ people door planned. At these locations, the masons have the block stopping shorter than the rest of the wall … I think because the slab is poured out to the outside edge of the block at these locations. (?) Well, I was wondering, how to best use the rigid foam insulation at these locations. I know slab edges lose a lot of heat …but it appears that the edges at the doors will be ‘naked’ since they just meet up with the gravel drive. Not sure if you can picture that from my description and I may not be describing it correctly – but if you have any suggestions on foam at these locations I would be all ears.

6. In some places, the interior of block wall is pretty close to the dirt - like only 5" or so (even though the footer was 24" wide, masons had to adjust block layout to get building square). When the excavator shows up to backfill, is it going to be a problem getting dirt in this skinny 5" hole that now also has 2" of rigid foam attached to the block? The excvator seems very skilled with the equipment, but I don't know what is possible and where the limits are on what he can do with big machines. Also, I'm concerned that I want to get a really good backfill inside because it's critical for the slab (which will eventually have to a support structure for an overhead crane for the shop. At those locations we're making the slap thicker (going to cut out a 2'x2' section of the perimeter slab foam). But still, I've read that the prep of the base under the slab is as critical as the slab itself. So anyway, with such a tight little backfill, I'm not sure how the excavator will ever get it as hard packed as the main building area... or if he destroy the ridig foam while attempting the backfill. Any advice welcome - I'm a worry-wart. I admit it.

Thanks for your help!

P.S This is my first experience in hands-on at a construction site … in 93 degrees and 90% humidity it’s been a REAL learning experience. But we’re muddling through it and I’m learning a lot. My respect for tradesmen is climbing leaps and bounds. I think every homeowner should spend some hands-on time on-site to see how effortful this work is!

It should be easier to penetrate the mortar than the block.  Also less likely to break the block.  If nails do not work well you may have to consider using Tapcon screws.  I have used a lot of Tapcon screws in concrete but not any in block.  As a general rule, the hole for Tapcon screws should be pre-drilled before trying to insert the screw.

Alton,we will try the nails first, as I hope to avoid drilling all those holes...
Will let you know how it goes.
Thanks!

Bob I and Alton thanks for your help here. I've finished putting up the insulation. I attached it using an adhesive (lots of it) and then my husband did the mechanical fastening. We tied the nails on some left over block and they didn't work at all - broke it all to bits. Yikes. So we had to drill, as you suggested. But in the end, it all seems pretty well stuck to to the wall and will hopefully survived backfill. Thanks again!

We got it backfilled and the insulation stayed in place. Yippee. And thanks for your help!
They weren't really able to compact the backfill very much at all since it was such a narrow space in the trench. We are doing it by hand. We've found that watering it, letting it set and then going at it again seems to be packing it down, a bit at a time.