Duluth and the Upper Midwest
Frost protected shallow foundations in Duluth, Minnesota
Insulated slab on grade systems, foundation insulation and the wing insulation a frost protected shallow foundation needs. Board that holds up under backfill and does not wick, so the R-value it starts with is the R-value it keeps.
Below grade
The wall is buried for a hundred years. The insulation has to last that long too
Insulation on the outside of a foundation wall spends its life in wet soil under backfill pressure. Anything that absorbs water stops insulating, and nobody is digging the wall back up to find out.
Extruded board takes on 0.2 percent water by volume. That is the property that makes it the one rigid insulation recommended for constantly wet and below grade conditions.
- Backfill pressure. Compressive strength from 40 to 100 psi, so the grade can be matched to the depth.
- It does not wick. Closed cell all the way through, rather than beads pressed together.
- Frost wings. Horizontal board out from the footing, sized to the frost depth your code requires.
What the code asks for
FPSF is a code path, not a shortcut
A frost protected shallow foundation, FPSF for short, is covered by Section R403.3 of the residential code, which also permits design to the engineering standard ASCE 32. It is a recognised route rather than a workaround, and it is specified rather than guessed at.
The sizing is driven by the air freezing index, the cumulative total of degree days below freezing across a design winter, not by the climate zone. ASCE 32 lists Duluth at a 100 year design index of 3,130 degree days.
- Vertical R-7.8 at the slab edge at Duluth's index.
- Horizontal wing R-6.5 along the walls, R-8.6 at the corners.
- Heated buildings only. R403.3 applies where the monthly mean stays at or above 64F, so an unheated garage or shop is a different design.
- Against 60 inches of footing depth for a conventional foundation in Duluth under Minnesota Rules 1303.1600.
Frost protected shallow foundations
A shallow foundation works by keeping the ground under it from freezing, using insulation rather than depth. It takes excavation, concrete and time off the job, and in this climate it has to be detailed properly to do it.
- Less excavation, less concrete
- Wing insulation sized to frost depth
- Works with monolithic slab forms
- Forms, foam and rebar on one delivery
The detail is only as good as the insulation that survives the backfill.
What gets built on one
The same detail scales from an outbuilding to a commercial pad. What changes is the wing dimension and the grade of board under it.
Heated slab and radiant floor
A heated slab is the classic case for a frost protected design, and the slab edge insulation is what stops the heat you are paying for leaving sideways into frozen ground.
Garage and shop slabs
Worth knowing before you plan one: the prescriptive FPSF path is for heated buildings. An unheated garage slab needs a different design.
Shed and outbuilding slabs
Small pours are where the excavation saving matters most, because the hole is most of the job.
Monolithic slab and footing
Stay in place insulated forms give you the form and the slab edge insulation in one piece, with no stripping after the pour.
Foundation questions
What is a frost protected shallow foundation?
An FPSF sits above the frost line and stays safe because insulation holds ground heat under and around it, instead of being dug below the frost depth. It takes excavation, concrete and time off the job. The geometry and the wing dimensions are tied to your air freezing index and your code, so it is specified rather than guessed.
Do frost protected shallow foundations work in northern Minnesota?
Yes, and the code anticipates it. Section R403.3 covers index values well past what Duluth sees, and Minnesota Department of Labor and Industry publishes guidance on frost protected foundations for the state. What changes this far north is how much insulation the design calls for, not whether the method is allowed. We set out the full table in our post on what the code requires for a frost protected shallow foundation in Duluth.
Can I use one for an unheated garage or shop?
Not on the prescriptive path. Section R403.3 applies to buildings held at a monthly mean of 64F or above, because the method borrows the building's own heat. An unheated structure needs a different design, usually to ASCE 32 with an engineer.
Which grade goes below grade?
It depends on the backfill depth and what sits above. ECO 40 covers most residential foundation work. Deeper backfill and loaded conditions move it up. Tell us the detail and we will tell you the grade.
Does it need protection above grade?
Yes. Rigid board exposed above grade needs a protective finish or a coated board, both for impact and for sunlight. That part is standard practice and your builder will have a preferred detail.
Will insects get into it?
Rigid foam on the outside of a building wants a termite or bug screen detail at the base, which is normal practice for any exterior foam and worth designing in rather than adding later.
Can I get the forms and the rebar with it?
Yes. Send the plans and we will do a takeoff covering the forms, the foam, the rebar, the lumber and the poly, and put it on one delivery.
Duluth, Minnesota
Frost protected foundations, supplied from Duluth
Frost protected shallow foundations get specified and supplied out of our Duluth shop, in a climate where the frost depth driving the whole detail is something we have dug through ourselves.
We spent more than ten years on concrete crews before we ever sold a sheet of board, so we know what a late delivery does to a pour day. Reliable delivery is what we grew this business on, and it is why contractors here keep calling back. We have been in the trenches with them, so we already know what the job needs.
- 10+ years on concrete crews before we supplied them
- Duluth stocked and dispatched from McQuade Road
- On the date delivery you can set a pour day against
What customers say
Trusted by the crews who pour the concrete
Five out of five across every Google review, from contractors across the Upper Midwest.
I have used them and their materials several times. Not only is their material far better than their competitors but the service is as well. I was in a jam and Caleb hand delivered what I needed within the hour. I highly recommend.
Amazing product! It is the only foam we will use beneath our concrete. It performs far better than its direct competitors at a similar price. Service has been excellent, and our materials always show up on time.
EFS is a top-notch supplier. Their high-density eco foam is an excellent new product, strong, clean, and reliable. Great quality materials and service we can count on. Highly recommend.
Eco foam in my opinion is the only foam worth using. The quality and strength of the foam impresses me every time I work with it and use it. I will be using Eco foam for all of my projects. [excerpt]
Best foam on the market. Great service and fast delivery.
Solid product and support.
Who builds with us
Pick your material, pick your delivery date
Order online or text your reorder. We schedule the drop and it lands on site when your crew needs it.