Slab Houses and Why Your Deck May Be Freestanding

If a contractor tells you your deck should be freestanding, that is not them avoiding work. On a slab-on-grade house it is frequently the correct structure.

The ledger problem

An attached deck hangs one edge off a ledger, a board bolted through the wall into the band joist behind it. The band joist is part of the floor framing of a raised house. On a slab-on-grade house, the floor is a concrete slab poured on the ground, and at deck height there is no floor framing behind the wall to bolt into.

You can bolt into the concrete stem wall in some situations. You can also make a mess of a wall assembly trying to attach something to sheathing that was never designed to carry it. Neither is as clean as simply not attaching.

What freestanding means

A freestanding deck carries its own load on its own posts. Instead of one ledger at the house and one beam at the outer edge, there are two beam lines and two rows of posts. It costs a little more in framing material and labour.

In exchange it never penetrates the wall, which means there is no ledger to flash, no route for water into the structure behind the siding, and no wall detail to get right. In a climate with a thunderstorm most summer afternoons, removing a wall penetration is a genuine advantage rather than a consolation.

The height question solves itself

There is a second benefit that shows up on slab houses. The finished floor of a slab house sits close to the ground, so a deck off the back is naturally low. A low deck needs short posts, minimal bracing, little or no guard, and one or two steps rather than a flight. That is a cheaper deck to build, which offsets some of the extra framing that freestanding requires.

Where this comes up around here

Slab-on-grade is the dominant construction type in newer Florida housing, so this is the normal situation across most of the recent subdivision building west of Gainesville, through Jonesville and Newberry, and around Alachua. It comes up much less on older housing in the Duckpond, in Micanopy, or in Archer, where houses are frequently raised off the ground and there is real floor framing to work with.

What to ask

If a quote proposes attaching to a slab house, ask what it is bolting into and how the connection is flashed. There are correct ways to do it. There are also fast ways that leave a wall taking water on every storm, and the difference is not visible from the finished deck.

The framing guide covers ledgers, flashing, and the freestanding alternative in more detail.