Most Common Mistakes:
- Not checking to see if the slab foundation is square.
- Using badly bowed stock.
- Not leveling sill plates.
- Not cutting the top plate so that it breaks at the center of a stud.
The sill plates for a garage are usually 2" x 4" pressure treated or redwood horizontal framing members that are bolted or attached by foundation anchors or anchor bolts to the foundation (or concrete slab). These are also the sole or bottom plates of the stud garage wall. The purpose of the sill plate is to anchor the garage framing to the foundation, to level the foundation wall, and to keep the untreated framing members out of contact with the concrete where standing water could cause them to rot.
The metal foundation anchors or anchor bolts will have been encased in and should be protruding from the foundation after the concrete was poured. These devices will anchor the sill plate (bottom plate), and thereby the wall, to the foundation. Local code will specify placement of sill anchors or bolts. Usually foundation anchors should be embedded a minimum of 6" into the concrete with the upper position split into 5/8" wide tabs which will strap over the 2" x 4" sill plates. These upper tabs have holes to accommodate special fastener nails 1 and 1/4 inch in length. Two nails are driven into each side of the sill plate through the holes in the tabs. The upper ends of the tab are then bent over the plate and nailed into the top of the sill with a minimum of one nail on each side.
Choose the order in which you will build your walls. We suggest you begin with a wall that has no windows or doors, if possible.
Select your sill plate stock so that it is as straight as possible. When ordering, specify good straight plate stock 12" to 14" long. If it is longer than this, it is likely to have some warp or bow. If the walls are longer than 14 feet you will want to use more than one piece of stock. When doing so, we find these guidelines to produce the best results.
1. Do not use pieces under 6' in length if possible.
2. Bottom plate splices may be anywhere but top plate splices may only occur in the center of a stud to ensure the strength of the top plate.
3. Splices in top and bottom plates must be separated by a minimum of 4 feet on the horizontal and splices in the cap plate (the uppermost of the two top plates) must be at least 4 feet from any splice in the top plate.
4. Before you choose your sill or bottom plates, check code to see if redwood or pressure treated stock is required or preferred. Place them with your wall top plates to do the wall layout. The entire wall is built first, then lifted into place before the sill plates are attached to the slab.
5. The total length of each plate equals the total outside length of the walls less 3 ½ inches (the allowance for walls overlapping at the corners). The end of one wall stops at the end of the platform on one side while the other end of the wall stops short by 3½" and is overlapped by the intersecting wall which goes to the end of the platform.