building the cabin: shallow pier post foundation

Creating a simple shelter - and living with it!

Foundation
Framing
Roof
Insulation
Floor Insulation

	Building our Cabin: Foundation
	We used simple pre-cast concrete piers on a pad of gravel as our only foundation element. With these marvelous little blocks our foundation was done all by ourselves in an afternoon, for under $100.00. This concept is probably the single most radical aspect of our cabin, as viewed by the building trade, yet the principles are ages old. Here's how it works.


Cabin Intro Cabin Images Building the Cabin Brief Building Story Heating Floorplan FAQ Construction Diary Pre-Building Notes

These concrete piers are 12"x12" at the base tapering to 8"x8" at the top. The height is 8", and they cost less than $10.00 each.
The bracket, sized for 4" lumber, comes with the piers. They adjust 3-4" in the vertical plane for ease of leveling the main beams.
To create a stable base, I centered the piers on minimum 4 pavers, measuring each 2" x 8" x 16"
The concrete piers available at the local lumber yard will certainly differ from location to location.
The ones shown here do the job just fine..

A foundation serves at least two important functions:
1: To estalish a square and level surface to put the house on.
2: To ensure this surface remains square and level for the life of the building.
The first one is accomplished relatively easy with the aid of strings and spirit levels and so on.
Number 2 is more tricky. Earthquakes, frost, seasonal flooding and erosion are factors to contend with. Careful site evaluation is definitely advised before using this shallow, gravel based concept.
Low clay content in the soil is mandatory for stability. Determining this should ideally be done before purchasing the land.
The best draining building site has a constant gentle slope in one direction or sits on a slight mound. Avoid hollows and depressions where water will pool during spring thaw or summer thunderstorms.

		What to do: Lay out a square footprint of the cabin with strings. Determine the location of the main beams, and mark the center of the pierposts with spikes. The plans will give you all the measurements, and the exact layout procedure can be gleamed from good construction manuals. Absolute accuracy is not that important at this point, unlike a poured perimeter foundation. Dig the holes. Ours were 24" x 24" and about 16" deep. The deeper the better. We hand dug them all at around 10 minutes each. Using an excavator would leave a bunch of huge, ugly craters and generally make a mess. Better to simply grab a shovel and get some exercise. Look at the pictures: It would NOT be this neat pretty with backhoes around! Moist conditions typical of early spring makes for the best digging. Use a wheelbarrow and collect all this topsoil in a pile out of the way for future gardening. Backfill with gravel. Gravel drains extremely well and will not frostheave. Stack the pavers and piers level and flat, starting at the marked location with the highest elevation. if unsure about which one this might be, pick a likely one and add an extra layer of pavers to that stack. With reference to strings and line levels as you go along, build up the lower piers to match that first one. Finally level the beams carefully individually and to each other, using the adjustment nut on the brackets. Be meticulous here. Your efforts will be rewarded later. On the other hand, having the beams absolutely parallel and square is not critical, as long as you don't fasten them to the brackets yet. You do the final squaring of the building when you construct the floor platform. That's it.


	Counting all the construction projects we have done so far, the total number of these piers I have used is close to 40! All of them were put in using the method described here. The first building was done in 2003 and I have yet to detect any settling or heaving. This whole idea places all foundation elements deep under the building where they are protected against excessive moisture from driving rain or snow avalanching off the roofs. Further insurance can be gained by skirting the cabin with corrugated metal to about 36" above the ground.