How We Set Up a Crawl Space Foundation With a Pony Wall

The parts of a house that carry the most weight are the parts you rarely see. If you are planning a custom home over a crawl space foundation, this post explains how we frame that space, what a pony wall is, and why it matters for the life of the house.

We set this up at the end of the framing stage of a custom build, before the mechanical, electrical, and plumbing trades move in. At that point you can see every piece of the support system.

The crawl space holds up everything you will see later.

What a crawl space foundation with a pony wall looks like

Our crawl spaces have typically sat on a pad and pier system. In that setup, the floor rests on beams carried by piers, and each pier stands on its own concrete pad. Every pad works alone.

We recently started building a continuous footing and a pony wall instead. A continuous footing is concrete that runs unbroken from one end of the house to the other. A pony wall, also called a cripple wall, is a short framed wall. Ours sits on top of the continuous footing and also runs the full length of the house. The floor joists rest on top of that wall.

What we like about this system is that it is all locked together. The footing ties the support together down the entire length of the house, and the pony wall connects the floor to that footing.

The footing itself can be poured two ways. An in-earth footing is poured straight into a trench dug out of the dirt. A formed footing is poured inside forms, set up much like a foundation wall. On this build, we used a formed footing.

How a pony wall spreads the load from roof to footing

Our floor joists sit on 16-inch centers. We lay out the pony wall on the same 16-inch spacing, so each joist lands directly on top of a stud. That stud carries the load straight down to the footing.

Every joist has somewhere to land.

Because the wall and the footing run the full length of the house, the floor load spreads evenly through the whole floor system.

Some spots carry more weight. Where a wall above carries load up to the roof, we add blocking or pack in extra studs below it. That gives the load a path all the way down to the footing, so the house is supported from the footing to the roof.

We frame the pony wall like a foundation wall

We build the pony wall the same way we build the perimeter of the foundation. A pressure-treated plate, the green-tinted lumber you see on job sites, sits on the footing, with traditional framed members above it. Treated wood is what the code calls for where framing sits on concrete close to the ground. We fasten that plate to the footing with concrete anchors along its length, with one near each end of every plate section, as the code requires. Footings and foundation anchoring are covered in the foundations chapter of the International Residential Code, and we hold the interior wall to the same method we use at the perimeter.

A wall that runs end to end on 16-inch centers has one tradeoff. It can block the path to other parts of the crawl space. To keep the whole space reachable, we cut access points through the pony wall and header them off. Those openings make room for utilities and bulkier equipment, such as a furnace or a pressure tank.

Most homeowners only go into a crawl space when a utility needs maintenance. When that day comes, the path is already there.

This crawl space will also get a full encapsulation later in the build. A vapor barrier covers the floor and wraps up onto the footing and the pony wall. At the perimeter, it runs up the foundation wall to meet spray foam that ties into the insulated walls and roof. Building Science Corporation's guidance on crawl spaces makes the case for treating this space as part of the house, kept dry and warm, instead of part of the outdoors. A sealed crawl space also needs a way to keep its air dry. The residential code requires a small supply of conditioned air, an exhaust fan, or a dehumidifier in any unvented crawl space, so that piece gets planned with the HVAC system.

Why the framing under your house is worth asking about

A rock fireplace or a custom shower gets the attention on a tour. The crawl space does not, but the structure starts there.

Your lot shapes the foundation, too. The grade decides whether a house sits on a slab, over a crawl space, or into a walkout basement on a sloped 417 lot.

If you are getting ready to build, talk with your builder about how the framing underneath the house will be put together. Ask how the floor is supported, how the load reaches the footing, and how you will reach the utilities later. Those belong on any list of questions to ask a custom home builder.

We chose a continuous footing and pony wall for the longevity of the homes we build.

It starts at the footing, long before anyone sees the finishes.