Examples of pony walls include short walls built to carry floor joists in areas where a foundation steps down, non-structural walls built as room dividers, walls that serve as guards on stairs or balconies, and walls that support overhanging countertops.
The short walls that rafters sometimes bear on in a Cape-style house are another structural example, though these are almost always referred to as “knee walls.”
What Is a Pony Wall?
A pony wall is nothing more than a short wall, and the term is often used interchangeably with “knee wall” or “cripple wall.”
Pony walls, like regular walls, have top and bottom plates, that is, the horizontal members that the vertical studs fasten to. The studs are installed on the same 16- or 24 inch spacing used elsewhere in the house. Pony walls with exterior surfaces, such as foundation walls, get structural sheathing such as plywood or OSB just like any other wall. Interior pony walls are drywalled and finished.
Load Bearing Pony Walls
Also, like regular walls, best practice is to frame pony walls so that their studs align with the floor joists below them. If the pony wall is one that extends up from a foundation wall, its studs should be laid out to fall below where the floor joists above will be.
The studs in attic knee walls should fall below the rafters. This makes it easier to run wiring or plumbing and creates what’s called a continuous load path. That means each framing member, such as a stud, joist, or rafter, bears directly on a member below it, with the path continuing all the way to a beam or to the foundation.
When a pony wall rests on a foundation or a concrete slab, the bottom plate should be made of pressure-treated lumber to avoid rot. The bottom plates of pony walls that rest on the foundation are required by code to be bolted to the concrete, just like the mudsills that tie the rest of the house framing to the foundation. This is to help prevent the building from shifting in earthquakes or very high winds.
Interior Pony Walls
Many pony walls don’t carry a vertical structural load. That doesn’t mean they don’t need to be strong. You don’t want a pony wall that serves only as a room divider to move if someone leans on it.
Because the wall itself acts as a lever when someone pushes on the top, a pony wall must be stoutly anchored. This is easy when the pony wall meets a perpendicular wall. Nailing or screwing the last stud in the pony wall to studs or blocking in the intersecting wall braces that end well.
Building a rigid pony wall is a little harder when its end (or ends) terminate in the middle of a floor. Just framing a wall and nailing it to the floor below won’t create a strong and durable attachment.
In this case, good carpenters cut a hole in the subflooring and extend the end stud down into the floor framing. If you’re lucky or have the ability to lay out the floor and wall locations beforehand, this stud should fall exactly adjacent to a joist and the two can be joined with lags or structural screws. If the stud falls in the middle of a joist bay, blocking on each side of the stud and between the joists works just as well.
Pony walls are frequently used in bathrooms, providing privacy at the toilet or shower, creating an end for a vanity, or partially enclosing a soaking tub. Because these pony walls typically get tiled, waterproofing is important as well as creating a sturdy attachment.
Stair and Balcony Walls
By code, guard rails on residential stairs and balconies must be able to withstand a 200-pound sideload. Most jurisdictions also require them to be at least 36 inches above the nosing of the stairs or the finished floor of the balcony.
The same rules apply to pony walls used for these purposes. The height is easy to check, but there’s no good way to test the side-load capacity of a guard. Carpenters just build them as strong as they can.
For stair guards, the pony wall is usually built from the floor below using continuous studs. Where these studs touch the rough stringer, the two are joined with lags or structural screws, tying everything together in a rigid assembly.
This works very well the closer you are to the top of the stair, but at the bottom, the wall again creates a lever that can overcome a simple stud-to-plate connection. Here is another place where the end stud should run down into the floor framing below.
The ends of the balcony walls almost always wind up being braced by other walls. Sometimes that’s another pony wall if the balcony makes a turn. One end often ends where it meets the pony wall from the stair. These connections create all the strength needed for most residential situations.
Finishing Pony Walls
Interior finishes are the same as for any other wall. Also, the same electrical codes apply to pony walls as to full height walls, so receptacles are usually required at least every 12 feet and within 6 feet of any opening in the pony wall.
The top of a pony wall is often finished with a wood cap. Usually, this cap overhangs the wall by an inch or so to create enough space to run molding to hide the joint. Used this way, pony walls are a great way to separate spaces while preserving long, interior views that make both areas feel larger.