Fully enclosed foundations for raised wood floor construction are typically specified with continuous foundation walls, often called stemwalls.
Stemwalls require continuous footings, but this design replaces the need for girders providing continuous support to single sill plates and the structure above.
As with pier construction, stemwalls may be built with a variety of materials including concrete masonry units (CMUs), formed concrete, as well as wood foundation walls, each providing versatility of design and many options for exterior finishing.
Wood Stemwall on Spread Footing
Stemwall foundations – enclosing the entire perimeter of a crawlspace – can be built most efficiently using pressuretreated
wood. This foundation option may save time and money by eliminating the need for masonry work. Also referred to as “pony walls,” wood foundation walls should be built on continuous footings finished above grade and backfilled to below the face of the foundation wall.
The exterior of wood foundation walls may be finished with all commonly used materials as appropriate for contact with or proximity to surrounding finished
Wood stemwalls perform well in vented crawlspace construction, but may also be specified for closed conditioned/semi-conditioned crawlspace construction. For either application, close attention to the specification and details is required along with optional vapor retarders. In cases where wood foundation walls are required to finish below grade, design specifications will need to meet all relevant requirements of a Permanent Wood Foundation (PWF).1
Masonry Stemwall on Spread Footing
Masonry foundation walls are probably the most common method used for enclosed crawlspace construction, whether the crawlspace is to be vented or unvented. Construction techniques for masonry foundation walls vary little by climate or region in terms of the required rebar reinforcement, the concrete or mortar fill to the finished height of walls, and the loads they are designed to support and resist.
Masonry foundation walls require vertical and horizontal reinforcement, subject to their finished height, concrete or appropriate mortar fill in the voids, and (again specific to height of the walls) strap or anchor placement for properly fastening the structure above to complete the load path.
When compared with other foundation wall options, construction of masonry foundation walls will typically require the use of more construction labor at the site, in addition to possibly necessitating more visits by the building inspector at the foundation stage.
Concrete Stemwalll on Spread Footing
Poured concrete foundation walls are an option used by some builders for enclosed crawlspace construction, and are suitable for both vented
and unvented crawlspaces. The construction of poured-in-place concrete foundation walls is typically done as a second stage to the concrete footings in order to allow for correct placement of all required wall reinforcement. Additional inspections and approvals prior to the concrete pour may be required. Straps or anchors to secure the structure above are normally wet-set into the top of concrete foundation walls.
Although complex, requiring construction of forms and temporary bracing, concrete foundation walls offer high integral strength that may be necessary in high-wind and/or flood-prone areas. Poured concrete foundation walls are preferred by some builders where unbalanced backfill heights of finished grades can be an issue.
Care must be taken to prevent inconsistent or incomplete placement of concrete within the forms; otherwise, voids or “honeycombs” in the finished foundation walls may result.
Adequate time for the concrete walls to sufficiently cure prior to the commencement of construction above the foundation is necessary for both structural integrity and worker safety.