Shed and backyard office foundations: skids, piers or slab

Foundation type is not fixed by the plan. Every BlueWood design works on skids, on piers or on a slab, which means this is a decision about your site rather than about the building — and it is the decision that most affects how the building ages.

The three options at a glance

Skids

Pressure-treated timbers laid on a compacted gravel bed. This is the fastest and least expensive route, and on flat, well-drained ground it is entirely adequate for a building of this size. It is also the most forgiving if your site is slightly out of level, because you can shim and adjust as you go.

The catch is water. Skids sit close to the ground, so if the site holds moisture the framing lives in it. Get the gravel bed right, keep the timbers clear of soil, and grade the ground away from the building on all four sides.

Piers

Concrete piers or helical piles carry the floor frame above the ground. They cost more and take more setting out, but they solve the two problems skids cannot: sloping ground and drainage. Lifting the structure clear of standing water is the single most effective thing you can do for the long-term health of a timber building.

In frost-prone climates, piers need to reach below your local frost depth so the building does not heave through the winter. Your building department will tell you what that depth is.

Slab

A poured concrete slab is the most permanent choice and the best base for a building you will heat and use all year. The floor arrives flat, solid and ready to finish, which simplifies everything that follows — particularly if you are laying rubber flooring for a home gym or setting up equipment that does not like a springy floor.

It is also the most expensive option, the one most likely to need a permit and an inspection of its own, and the one you cannot undo.

Let the soil decide

Budget picks between skids and piers; soil often overrules both.

• Sandy, free-draining soil is forgiving and will take any of the three.
• Clay-heavy soil holds water and swells — push toward piers, or a slab with proper drainage beneath it.
• Ground that is wet for part of the year rules out skids in almost every case.
• Sloping ground favors piers, which can step down the slope without heroic earthworks.

What the plan set gives you

Every BlueWood construction set includes a foundation and framing layout with the floor system drawn member by member, plus the construction details for how the building meets its base. Once you have chosen your foundation type, the drawings show you how the structure sits on it — see how to read the drawings if the sheet layout is unfamiliar.