Negatives to Using Wood Posts in a Crawl Space

Crawl space foundations are very popular, and it’s easy to understand why. Builders often prefer this type of foundation because it requires much less excavation work than a full-height basement foundation. Crawl spaces can be built quickly and inexpensively, offering a very practical way to “get out of the ground,” in builder’s parlance.

Unfortunately, putting too great a focus on economy can lead to some substandard construction practices. Some contractors deliberately take shortcuts and cost-cutting steps, while others do it because they don’t know any better. Either way, using the wrong materials and the wrong details inevitably causes problems.

Wooden Posts: Easy and Inexpensive

A typical crawl space foundation contains at least one beam or girder that runs the length of the foundation, providing mid-span support for the first floor joists. Since the “footprint” or plan of the house is usually too wide for a single joist to span its total width, one or more centrally located girders support joist ends which typically overlap the girder and each other.

Girders or beams also require mid-span support to prevent them from sagging near the middle. Wooden posts were once used to provide this support while resting on concrete pads or piers.

This framing system has been a standard treatment used in conjunction with crawl space foundations for many years. The girder or beam can be made from a single large-dimension piece of lumber such as a 6×10 or 6×12; but the framing crew is just as likely to have built up a thick, deep beam by nailing together several 2x10s or 2x12s. Regardless of the beam treatment, wood posts were installed at regular intervals beneath the beam to keep it from sagging. For framing contractors, this all-wood structural system is simple, inexpensive and easy to execute.

Problems with Wooden Posts

The weak link in the above described floor framing system is without doubt the wood posts that are supposed to keep beams straight and strong. They often fail in this regard for several reasons.

For starters, carpenters often wedge thin wood shims (or tapered wood shingles) between the top of the wood post and the bottom edge of the beam to make the post fit more snugly in place. Usually because the post was cut slightly short, the beam lost some of its width due to shrinkage, or the natural irregularities common to dimension lumber.

While the shims may do their job initially, they too are prone to shrinkage, shifting and compression of the weight of the floor. Over time, the beam can also shrink as it loses moisture, creating a loose-fitting post. When support beneath the beam is inadequate, the beam and floor begin to sag.

Another problem that compromises the stability of the floor system is the mold and rot that often take hold in a damp crawl space environment. A wood post can easily wick up moisture from a concrete footing that’s in contact with moist soil. Since mold thrives where there’s cellulose and moisture, wood posts can weaken from decay associated with mold. When this happens, their strength and stability suffers.

The Solution: Adjustable, All-steel Supports

Anyone dealing with sinking, bowing or bouncy floors knows this situation isn’t one you want to endure for long. Home safety and property value suffer, and like the failing posts below the first floor, furniture must be shimmed up to maintain its proper orientation.

Fortunately, the problems caused by wooden support posts in a crawl space can be overcome by replacing these posts with adjustable steel support posts designed precisely for this retrofit application– so it can be raised slightly if the beam shrinks. You never have to worry about a steel post weakening because of rot, and some posts are treated with a thick galvanized coating to avoid corrosion problems.

Remember: Wood is good in many construction applications. But for the posts that support the center of the main floor over a crawl space, adjustable steel posts provide long-term stability, strength and durability that wood posts can’t match.