Concept and Application : Frost Protected Shallow Foundation System

I had some relatively unusual conditions, a loose stone foundation, vermin getting in through it, flies nesting in ground around kitchen, crawlspace as low as 2 inches, sill plate UNDER soil level in areas.  While there are hundreds of thousands of building much like this, far more have concrete, concrete block and brick foundations.

Frost Protected Shallow Foundation System.


The idea is to keep footings and the area under the building warm in the winter and avoid digging. 


Here's what else will a FPSF system do for your eco-sensitivity:


  1. Substantially eliminate excavation, run off, compaction, diesel fumes, oil and gas spills, save tree roots, preserve the water table.
  2. Cut construction materials, especially energy intensive concrete!
  3. Save all the money associated with excavating, installing, water proofing, heating, lighting, etc.,  deep concrete foundations, walls, and a basement, which really, is a poor choice for living in, or even storing junk, I mean, mementos.
  4. Keep the area around the building dry, decreasing the likelyhood of termite damage and other insect / vermin problems. 
  5. If you live in an really old house with rubble or even wood foundations, a FPSF will eliminate the long, risky, and costly process of hand excavation, underpinning, and segmental pouring of an insulated grade beam around the entire building.
  6. If you live in a 1950's - 70's era house, with no foundation insulation, this is something YOU can do easily, that will make a huge difference in energy use and comfort with a pay back in under 5 years! 
  7. Many do not have the money to hire a GC to excavate around the entire house and insulate vertically.
  8. It is difficult to justify economically the cost of the excavation technique, you can end up with payback times closer to 10 yrs.
  9. If the GC botches the job, you'll have a lawn ripped up by heavy equipment, and as the badly placed backfill settles, a moat around the house to collect and channel water into your foundation.

Construction Sequence : Frost Protected Shallow Foundation System - The Practice

Frost Proof Shallow Foundation System Design

Research Notes



It's an old European technique.  It gets alot of use in colder climate countries.  There seems to be a move afoot in the states but it hasn't gotten alot of traction, yet.  I have to say Googling this subject for a decade or more, I used to turn up almost nothing, now, dozens of citiation, in the US no less.  Now it's even being used at Fort Drum in upper NYS. 


Design / Insulation Thickness / Width: 

I have noticed in my research that designs and requirements being put forth by standards agencies and groups assumes a building is always heated, and that the heat from the building will migrate outwards through the earth under it and  counter freezing.   This allows designers to minimize the amount of insulation.  Now insulation isn't cheap, and it's got an enviornmental footprint.  However, this seems short sighted. 


1.  The cost of energy is only going up.  Insulation levels that were fine 10 yrs ago is now too little.  It's unlikely energy will drop in cost, nor will oil based insulation like foam (no, NO soy foam in ground contact.  Can you say termite food?). 

2.  Buildings aren't always heated.  Often during construction it's only when people are in the structure.  After occupancy, there are power outages, which in the NE are now stretching into many days.


Therefore, is seems prudent, and a long term investment, to design your FPSF system to eliminate the need for the heating system to keep the footings ice free, instead relying on ground temperature.  I'd increase the insulation thickness from the 2 inches generally recomended to 3 inches.  Then I'd increase the width outside the building to 4 feet, well past the depth of the deepest frost line in NYS at least.


Emergency Heating System:

I don't need no stinkin emergency heating..............

One might argue that earth temperature, around 47 degrees in NYS isn't warm, but it is in the winter.  This house, with a partial FPSF survived 3 days without heat and the interior temp dropped only to 40, with outside temps from 10 to 20 degrees.  With more roof insulation and a full FPSF, we may not need emergency power to keep the heating on during power failure.


Experiences w/

Old House Rehab


It is saving me the $40,000 or so it would cost to underpin the house, install a foundation and insulate it.  Nor would this have addressed the rim joist, a major source of heat loss.


For those concerned with vermin and bugs, termites, etc. in the skirt.  I've had one element in 3 yrs, in a vermin and bug heavy area, with only a few spiders taking up residence.  I suspect in addtion to being pretty well sealed, it's dry and foodless.


We have noticed that we no longer have ants invading the kitchen every spring, and flies infesting the area outside the kitchen in the summer.  There might even be fewer mice.


In addition, the boxout is a great ledge for planters at a real easy height to maintain, with the plants and flowers visible from inside.


I'm going to try some parsely and carrots that we can't grow in the garden, the moles keep eating them.