Centennial Shed and Outbuilding Pads

The shed in your back corner is probably not the original one. On an established lot the sequence usually runs like this: builder puts the house in, a homeowner adds a wooden shed a few years later on timber skids or a thin unreinforced pad, that building rots along the bottom plate after twenty-five winters, and somebody hauls it off. Now you are standing in the same corner with a new steel or vinyl kit on order, looking at a cracked rectangle of old concrete, wondering if it can stay.

We get that call a lot. Walnut Hills and Foxridge lots have the depth for a real workshop out back, while plenty of Willow Creek yards fit a compact storage building along the fence line and not much else. Different sizes, same question: what does the ground under the new building actually need?

Why the original pad usually cannot stay

Almost every first-generation pad has the same three problems. Poured thin, often three inches or less, because somebody was buying concrete by the bag. No reinforcement in it. And it sits on stripped sod with no aggregate underneath, resting on soil that changes volume with the seasons.

Sometimes it survived anyway. We do occasionally find an old pad that is flat, uncracked, and still bearing, and when the new building matches the footprint we tell you to keep it and save the money. That is not the common outcome. Usually the slab has cracked into two or three pieces with a corner tipped into a low spot, and it has grown a lip that will hold water against the new building's bottom rail from day one.

Cut into the hill or build the low side up

Very few back corners are flat. These yards got graded to push water away from the house, so the far end of the lot is usually the low end, and that is exactly where people put the shed. One choice comes before all the others: cut into the high side, or fill the low side.

We cut, almost always. Ground nobody has disturbed makes an excellent bearing surface, and digging into the slope gets us onto it. Fill is the opposite, loose material that has to go in thin lifts and be compacted properly to be worth anything, and even done right it never matches native ground. Where a lot forces us to build up, we use aggregate in controlled layers rather than the spoil we just dug, and we run the slab edge past the wall line so the fill is not carrying the building. Then the uphill water: a shallow swale above the pad keeps sheet flow from arriving at your door during a storm.

The slab spec follows what lives inside

Sequence and season

Order of operations saves people money. Pour the pad first, then take delivery of the building, never the reverse. A shed sitting on pallets in your driveway is a shed getting hailed on, and no delivery crew will set a kit on green concrete. Give us the drawings before pour day and the anchor bolts go into wet concrete right where the wall plates land, which holds far better than anything drilled in later.

April through October all works, with the shoulder months best. Small pads are quick, so they slot between larger jobs and lead times stay short. Late fall is fine until the ground starts freezing overnight. Winter pads happen with warmed water, accelerators, and blankets, though frozen subgrade is a hard no no matter how badly you want the shed up before Christmas. Give the slab a week before the building goes on, and a month before a loaded trailer crosses it.

What happens to the old pad and the ground under it

• Old slab broken out and sent to a recycler, never buried on site as fill
• Irrigation located, and any line crossing the pad rerouted before we dig
• Soft or organic pockets excavated down to soil that holds under a boot
• Base aggregate placed and compacted in lifts, checked before forms go up
• Anchor bolts placed wet, positioned off the manufacturer's plate layout
• Surrounding grade left below the slab so runoff cannot cross it