Larkspur Shed Pad Contractors

Pull the topsoil off a shed pad footprint on a wooded Larkspur lot and you'll find three or four inches of dark, springy material that looks like dirt and behaves like a sponge. Needles, duff, decayed roots, decades of it. That layer holds water, compresses under load, and rots away, so anything set on top rides a cushion that keeps changing thickness. Every leaning shed we get called about started right there.

The interesting part of a pad job happens before concrete shows up. Where the water comes from, where it's headed, what's left once the organics are stripped, and how deep we go to reach something that holds still. Get those right and the slab is almost an afterthought. Get them wrong and you're shimming a door in three seasons.

Strip it, then look at what's left

We over-excavate the footprint about a foot in every direction and take the cut past anything organic. On some Sage Port lots that's four inches. Under a heavy stand of trees it runs twice that, and now and then we find an old fill pocket somebody pushed there with a tractor, which comes out entirely. Then we proof-roll and watch for spots that pump or spring back. Those get dug deeper and replaced.

Back in goes road base, in lifts of a few inches, compacted wet rather than dumped in a pile and driven over. Six inches is normal, deeper on cut-and-fill spots. That layer carries the load and breaks the water's path up from below. Loose gravel isn't a base. Neither is native soil knocked flat with a bucket.

Water is the real enemy of an outbuilding slab

Nothing on these properties sits on level ground, so every pad has an uphill side. Water arrives from there during the melt and after every summer storm, and without somewhere to go it collects along the slab edge and sits in the base. That's how a pad heaves: saturated material under a corner freezes, expands, lifts one side of the building an inch. Come spring it settles back, not quite all the way, and the door quits latching.

Our answer is boring and it works. The finished slab stands a couple inches above surrounding grade. Ground gets shaped to carry water around the pad instead of into it, with a shallow swale on the high side where the slope calls for one. Where the shed sits below a roofline, gutter discharge moves well past it, because a downspout emptying beside an outbuilding is a frost heave generator.

Unheated buildings deserve one more thought. No warmth inside means frost gets under the whole thing every winter. For a light garden shed, a base that drains is usually insurance enough. For a shop, a barn, or anything holding real weight, thickened edges or footings go below frost depth, and at 6,720 feet that's deeper than what people see from a metro contractor.

Where the pad goes, and what that ground demands

What we put under and into a pad

• Footprint over-excavated a foot past the building on all sides
• Organic layer, roots, and soft fill stripped and hauled off
• Subgrade proof-rolled, pumping spots dug out and replaced
• Six inches or more of road base compacted in lifts
• Grade shaped to route water around the pad, plus a swale where needed
• Number four rebar on chairs for anything heavier than a garden shed
• Four inches of air-entrained 4,000 PSI mix, five to six under a shop
• Anchor bolts set wet where the wall plates land, off your building's plans
• Joints cut the same day, broom finish, spoil raked back clean

Sequence and season for outbuilding work

Order matters. Buy or spec the building first, then pour, because the anchor pattern, the footprint, and whether the slab wants a thickened edge all come off the manufacturer's drawings. Pads poured to a guessed dimension are why people drill and epoxy anchors into hardened concrete later. Custom or site-built, we work from the framer's layout instead.

Season runs mid-May into October, later than the metro because the ground opens later. Early fall is our favorite window: dry weeks, cool nights, a slab cured before the first serious freeze. Spring works once the frost is out for good, and that's the real gate, not the calendar. Frozen subgrade is out, because the thaw underneath drops the slab and you'll never get it flat again.

Give the pad time before the building goes up. Walking on it the next day is fine; framing under load, we like to see about a week. And keep ice melt off it the first winter. Sand works without pulling chemistry into a green surface.