Insulating slab and stem walls?

[Innovate1]

Planning a 30 x 40 shop building. Still considering if I will do radiant floor. Thinking I will do gas furnace/AC but still want to insulate the slab well. Have read about running 2" foam up the walls from the footing to the top of the stem wall. My stem wall with be 24 - 30" above the floor. Not sure they will allow me to reduce the wall thickness to 4" for the stem wall. Wall above will be 2 x 6 framed. I could cover the foam with OSB or Plywood - could do drywall but seems like it would get beat up easily.

Plans call for wood strips for nailing siding - should I have nailers on the inside to secure the foam? What holds the nail strips in the concrete?

Should I be worried about the slab shifting if it only has foam around it? Slab slope is 6" in 40'. Mostly to get the high end high enough to have slope on the bathroom drain pipe. Seriously thinking of raising the low end a few inches to get a bit less slope. Need to look again but I think code requires at least 2" of slope and doesn't link that to the total length.

Plans call out all sorts of details for insulation but nothing over the interior of the stem wall (and nothing outside). Shows 2" x 24" foam on wall below floor and in 24" from outside edge under floor. Thinking I should put it across complete floor even if I don't put heat in the floor - thoughts?

Radiant floor would be great but already need ductwork and fan for AC so a furnace will be easy/cheaper than radiant. And if I want to bolt something to floor I don't have to worry about where the tubes are.

Are the apron and the interior floor supported by the foundation wall at the overhead doors? In the current house the joint is at the outside of the wall but I was told something about a taper so one slab supports the other - I think. It was a long time ago ...

 

[Montyx5]

Planning a 30 x 40 shop building. Still considering if I will do radiant floor. Thinking I will do gas furnace/AC but still want to insulate the slab well. Have read about running 2" foam up the walls from the footing to the top of the stem wall. My stem wall with be 24 - 30" above the floor. Not sure they will allow me to reduce the wall thickness to 4" for the stem wall. Wall above will be 2 x 6 framed. I could cover the foam with OSB or Plywood - could do drywall but seems like it would get beat up easily.

Plans call for wood strips for nailing siding - should I have nailers on the inside to secure the foam? What holds the nail strips in the concrete?

I had built something similar in the past. It was well insulated above a 12 in. stem wall and I did have a green patch around the exterior all winter long. If I were to do it again I would have used furring strips all the way up the walls above grade with foam panels in between just the height of the stem wall and full coverage below grade extending down to the footings. If the stem walls are poured you could incorporate the foam panels taped together against the forms before pouring and use zip ties pushed through so the free end would be embedded to secure the panels, if the contractor is willing to work with you. It will be more efficient to keep the stem wall on the heated side.

 

[Innovate1]

Protecting the foam on the outside of the foundation is an issue. Thermally that seems like a good way to go but there are issues against it.

Thinking a few hard plastic blocks around the edge would keep the slab from shifting.

 

[Montyx5]

Protecting the foam on the outside of the foundation is an issue. Thermally that seems like a good way to go but there are issues against it.

I agree that any foam that is daylight exposed needs to be protected, especially from the daylight.

 

[ForceFed70]

That foam is expensive. I looked hard at doing it, but was going to cost me $2k in material alone. 5 years later and I've only spent about $500 in total heating the garage.

If you're not planning in-floor heat, and are like me and keep the shop at *50 unless I'm in there working, you might want to consider skipping it as I doubt you'll get an ROI.

 

[jvitez]

The weather in Missouri isn't that extreme but you only have one chance of doing it right, so if there is any chance of in-floor heat you should do slab insulation.

The greater the difference in temperature the higher the rate of heat loss, so insulating the stem walls is more important than under the slab. Run 2" foam up the stem wall and onto the horizontal edge in front of the bottom plate of the stud wall. After the slab is placed, cover the vertical foam with pressure treated 1/2" plywood.

You don't really need to have insulation under the entire slab. You can **** foam boards horizontally against the vertical foam, but run 4 x 8 sheets lengthwise around the full perimeter of the slab. This way you'll have the stem wall insulated, and 4 ft of horizontal insulation at the point of maximum heat loss. You will have more heat loss in the uninsulated portion of the slab, so you'll put more heat into the ground when you start up an in-floor system in the fall, but it will reach an equilibrium and stay there all winter. In the spring, the slab will gain heat from the ground as the weather warms so all in all it's the same. The only reason to insulated under the entire slab is for more rapid response to thermostat set point changes.

Check out "frost protected shallow foundation."

https://www.finehomebuilding.com/2010/11/11/frost-protected-shallow-foundations-2

 

[Innovate1]

Here is what the plans currently show and what I am thinking should be done. Still thinking I need some hard plastic blocks between the slab and foundation wall in a few places to keep things from shifting. And not sure about how to handle the large doors. Thinking I won't do tubing for slab heat so may just do foam under the slab in about 4' rather than all over.

The plans don't currently have any insulation on the foundation wall above the slab. My diagram footing isn't to scale and I don't show covering over foam - probably plywood or osb.

 

[Innovate1]

While one the subject of slab edge insulation how should the walkout be done? Seems like what is called out in this image is not very effective. Would also like to see cross sections or details of what people have done at overhead doors.

 

[Innovate1]

No comments? jvitez, what I sketched up (first image) is what I think you described. The link you gave seemed to be other configurations - I didn't see how they applied. The nailing strips are just vertical strips every 16". I can get 2" foam for $25 for a 4 x 8 sheet so not too bad. Might go for the whole slab to make it more comfortable. Still thinking I need some blocks around the edge to keep things from shifting but perhaps the rigid foam is enough. If the floor slopes toward the overhead doors the wall area there will be a lot less and the pressure will be in that direction. Maybe I shouldn't be concerned about this - I just looked up the compression strength of the foam: 15 PSI. If the slab only has 3" high contact at the OHD side along 9 feet (30 ft wall minus width of doors) that would be 4860 lbs pressure it would withstand. Along the other walls it has more contact area so will withstand significantly more force.

 

[Randy in Maine]

I ran my 2" of foam insulation on the inside to about 10" above the finished floor and hid it with behind a piece of 1x12" pine with a 1x3" pine ledge. Worked well. Looks great.

 

[yeldogt]

That's always a tricky detail --- On a 2x6 wall we have extended the framing out over the foam .... I don't like the ledge outside. Frankly -- it's like the lip at a large door on a heated slab .... Its a detail I will to give a little for looks.

In the mid atlantic's -- we are typically in the high 20's low 30's in the winter -- it can and does get into single digits some winters for a couple weeks ... I find a thermal break inside on slab and something inside on the block/concrete is enough. Most houses have a bigger problems with the sill leaking air. Outside we do typical spray waterproofing -- thin foam and traditional stucco. If you get snow -- the need is less.

The need for insulation when doing radiant slab is because the delta is so high --

 

[maxpat82]

2" styro below the slab.
2" styro on the whole height of the wall on the outside. (4' frost wall+2' over the slab)

I have 6" fondation wall + the styro on the outside.
(I had to shorten the outside dimension 4" to allow for the styro(2" all around) on the outside of the wall and still been whitin my max allowed dimensions)

Had to have Alu drip edge custom bent to go over the styro before putting the siding on.
I'll be covering the outisde of the styro with lightweight concrete board next summer.
I have alligned my 2x6 to be flush with the concrete wall with the strapping installed..so that I can install my inside wall finishing(sheetmetal) to be right against the concrete a couple of inches below the wood.

28x44
https://imgur.com/XJi9nW9

https://imgur.com/Yaa2XfV

https://imgur.com/dviaNs2

 

[Innovate1]

I find a thermal break inside on slab and something inside on the block/concrete is enough. --

Our winters are colder than yours but I am having a bit of trouble following what you said. You seem to be describing several very different things - one being external insulation of the foundation and the other internal.

What I quoted above seems to be exactly what I show in my first image.

Here are a couple links I think are good on the subject:

https://www.finehomebuilding.com/2014/07/09/insulating-a-slab-on-grade

And fig 4-12 here:
https://foundationhandbook.ornl.gov/handbook/section4-2.shtml

 

[justinjoyal]

2" styro below the slab.
2" styro on the whole height of the wall on the outside. (4' frost wall+2' over the slab)

I have 6" fondation wall + the styro on the outside.
(I had to shorten the outside dimension 4" to allow for the styro(2" all around) on the outside of the wall and still been whitin my max allowed dimensions)

Had to have Alu drip edge custom bent to go over the styro before putting the siding on.
I'll be covering the outisde of the styro with lightweight concrete board next summer.
I have alligned my 2x6 to be flush with the concrete wall with the strapping installed..so that I can install my inside wall finishing(sheetmetal) to be right against the concrete a couple of inches below the wood.

28x44
https://imgur.com/XJi9nW9

https://imgur.com/Yaa2XfV

https://imgur.com/dviaNs2

Ah ouin t’es sur Garage Journal toi... [emoji849][emoji2937]

 

[maxpat82]

Ah ouin t’es sur Garage Journal toi... [emoji849][emoji2937]

Oui M. Plenty of good info and discussion here

 

[Bclinehand]

I had a hard time deciding which side I wanted the stem wall insulated on...... Inside was less initial work and less cost as the foam only had to go down to meet up with the underfloor insulation, but on the outside was to go down to top of footer ( 4’ ).
Con to inside was that it needed to be protected from damage and sealed against water damage.......
In the end I chose to insulate the outside ,used a construction adhesive and glued both layers of EPS foam to stem wall before backfill (4.5” total ) I then covered the exposed foam with
1/2 “ pressure treated ply attached to my sill plate with 6” screws.
Capped the top with a custom “Z” flashing that runs over the ply and is nailed to the studs.
Yes it makes a ledge on the outside but I will live with it


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You can sort of see it in this pic

 

[Innovate1]

Just talked to a concrete contractor. Said they had never done the inside insulation running to the top of the concrete but they could do it that way. Normally do it on the outside. They have done insulation under the slab for radiant heat. Also said they normally pin the slab to the foundation walls at regular intervals. My current garage floor isn't pinned and has settled about 1/4" over the 15 years since built. I can live with that.

I figure I am going to have a step on the inside anyway (although I suppose I could hold the framed wall to the inside of the foundation. Would make a larger step on the outside) so why not protect the insulation and covering by putting it on the inside.

 

[Bclinehand]

Don’t pin the slab to the walls.......better that the slab is compacted correctly to ensure no movement.
If the compaction is subpar the pins in the walls can cause cracking of the slab under load.
Just my opinion but have poured a few floors


Sent from my iPad using The Garage Journal mobile app

 

[jvitez]

To the OP: yes, your first photo in post #7 is what I was describing. This was what the HVAC contractor recommended when I was planning in-floor radiant heat in our attached garage (didn't happen for various reason's which still bothers me to no end).

Detached shop was built as a frost-protected shallow foundation. It was placed as a monolithic slab with thickened edge. 2" XPS was put under the field and angled part of the thickened edge, none actually under the thickened edge itself due to the required re-bar bracing. After the forms were stripped, the contractor Tapcon'd 2" XPS vertically along the outside of the thickened edge. The 2x6 stud wall has exterior 2" EPS abutting the XPS for 2" of rigid foam from soffit to grade, overall quite similar to Maxpat82's photos.

 

[OldNeons]

I would definitely insulate the whole slab, and include tubes for radiant heat. I have never heard anyone who has done it and regretted it. Many have not and wish they had. If you've ever worked in a shop with floor heat, there is nothing quite as nice.....

I insulated floor and inside of stem walls in mine. 2x6 walls. I'm going to fir out 4' up so I can run FRP all the way around to make wash outs nice and easy. Good luck