Slab on Grade Foundation/Perimeter Insulation Detail?

Richard Miller

Background… I could use some help… I am doing my own 40x70 house/shop, slab on grade in southern Missouri. In “another lifetime” I was a Master Plumber and designed and installed radiant systems. Unfortunately, after many years of severe emotional and mental trauma, I have forgotten almost everything I once knew about radiant. I simply cannot remember how I did the footer and perimeter insulation on a monolithic slab.

1. This will be stick framed, with metal siding (like a pole barn, except stick framed on a monolithic slab).

2. What the best way to do my edge and perimeter insulation?

3. Do I have my dirt guy overdig by 2” to accommodate the insulation? (There will be no backfill. The dirt will be the edge of the footer. I guess I could run the insulation up to the bottom of the 2x10 form, then insulate the rest of the way to the top of the slab after the forms are pulled. That much will be backfilled.

4. I will have about 6” of the slab/footer sticking up out of the ground. Any ideas how to insulate that AND protect it? I might be able to have my metal guys bend some trim the extends down. But that basically creates a hidden termite path.

I’m stumped… any ideas? I’m all ears.

PS. One of these days I will post some stuff I printed off from the Wall back in the late 90’s when I was a regular on here. I doubt anyone besides Dan remembers me, but man, those were heady days for me. Good times.

Larry Weingarten

Hi and welcome back! Building Science Corporation has info that might be useful to you. Here is an image I found on their site: Hopefully it's a good start. 😊
Yours, Larry

Richard Miller

thank you Larry… are you the water heater book author? If so, still got your book. A handful of books survived my dark years.

GroundUp

The best way is to pour a footer with an ICF frost wall and use that inner ICF for your slab form. If you insist on a monolithic, the best way is to overexcavate and still use forms. EZForms are awesome, but the alternative is to use typical 2" high density foam and tack it inside the wood forms prior to the pour. Using the earth as forms is never, ever going to be a good idea.

hot_rod

Welcome back!

I used the Z flashing method. Have the metal building supplier build them for you to match the building metal color. They usually come in 10' long sections so you don't have a lot of seams.

Foam adhesive will help keep the vertical piece in place until you backfill. I used a 12" wide piece for that detail.

My wife is an aggressive string trimer operator, that damages the painted edge trim quickly. I'd use Galvalume on the next project instead of painted metal.

Be sure the final grade slopes away from all the walls to keep standing water away from the flashings.

There was a method using horizontal foamboard, a 4' perimeter around the building, also. I've never seen it done however.

I would highly recommend having a pest company spray all the foam before you backfill. Ants or termites burrow into foamboard. I have a number of pics of jobs in Missouri where the foundation and edge foam was badly damaged by some type of burrowing pest. Including my own shop, where I used the ICF method @GroundUp mentioned!

I worked with a number of ICF contractors that turned me on to the pest control spray.

Years ago foamboard contained pesticides, now you have to add your own :)

Here is another option. I've tried this but the concrete breaks away easily over that tapered top edge, not a good look in a shop.

EdTheHeaterMan

Will you be installing Radiant Tubing in the Slab?

The above Diagram from @Larry Weingarten indicates a separate foundation from the slab. For a monolithic slab, there is no sure way of disconnecting the entire concrete foundation section from touching the earth. Larry's diagram will float the slab in rigid insulation while allowing the foundation solid contact with the ground.

This illustration is the best i could think of for a monolithic slab. the foundation portion is in direct contact with the solid ground, necessary for supporting the rest of the structure. (Unless the Poles holding up the walls and roof are otherwise supported)

This will offer the least amount of heat loss to the ground while still supporting the structure

Is the savings of a Monolithic poured slab that important?

Hope this helps.

Richard Miller

https://forum.heatinghelp.com/discussion/comment/1800641#Comment_1800641

Thank you… I too have done the Z channel… just totally forgot about it. I might just go with the painted, and spray paint it as needed. I got the pest control covered. My long time buddy in Seymour has a pest control business and wants to do it all at no charge. Awful nice of him…

ScottSecor

I used the method @Hotrod shows above at my house. I did have to convince the well respected mason this was the best method for my situation. The mason also happens to be an building inspector for another town a few miles away.

He was hesitant on the usage of the two inch thick vertical edge insulation with the forty-five degree at the top. He was concerned the concrete edge would easily crack, especially when we were framing the 2x6 walls. The compromise was one inch for the edge insulation instead of the two inch. In my mind, I'd rather give up a little radiant heat to outside and not have a cracked slab.

Finally, @Hotrod I like the comment about the landscaping team member. I also suffer from being a little aggressive with the weed-whacker!