House Planning Guide Framing - cont...
Poor wood quality- Lumber with significant defects like splits, checks, large knots, or warping can be chopped up for later use as horizontal blocking between studs. If you notice black spots or other signs of mold growth, however, these pieces should not be used at all unless first treated to destroy the fungus.
Racking- Research shows that the best way to increase a frame’s resistance to racking or distorting is in a tube. Ask your builder to use construction adhesive when applying structural sheathing to any framed surface. When used in combination with recommended nailing, this promises a wall or floor of exceptional lateral strength.
Stage 1: The floor- The first floor of your home will serve as both a staging area and a footing for interior proportion. Along with adequate nailing and proper spacing, it’s important that joints are installed crown up, which means that the usual slight curve along the edge is positioned upward. This prevents sagging floors. As carpenters install the floor frame, look at these important construction details.
Sill plates- pressure treated sill plates should be used to form the transition between the foundation and first floor joists. Sill plates must be attached firmly to the foundation wall with anchor bolts, not just masonry nails placed at regular intervals.
Stairway openings- large openings that run perpendicular to floor joists require extra support either a vertical post that runs to the lower-level floor or an alternate joist product, typically engineered wood or steel.
Notches- Holes or cuts in floor joints where pipes or wires pass through must only occur in areas of low stress, such as near the ends of spans. Generally, no notch should account for more than one-sixth the depth of a joist.
Stage 2: walls- as carpenters assemble and erect wall frames, they will set them plumb (perfectly vertical), then square the corners and nail on temporary bracing to hold each wall in place. Inspect the following details in the framing to head off trouble.
Header size- above door and window openings you’ll see heavy structural members built from lengths of solid lumber nailed face to face. Their function is to support the structure above the opening. Minimum header dimensions vary by the span and the load but look for the headers over first floor rough openings to be built from wider lumber than the same size openings on the second floor.
Stud gaps- All lumber shrinks as it dries, but vertical gaps left between studs and load bearing top plates are usually a result of sloppy carpentry. Spaces +of more than 1/4 inch above cripple studs, trimmer studs or load bearing common studs should be filled with shims to prevent uneven settling.
Over stressed 2x4s- If your home has a third floor, be sure your builder uses 2x6 studs spaced 16 inches on center throughout. A standard 2x4 frame simply might not have the strength to support a third floor.
Stage 3: ceiling- Built using the same material and techniques as floors, the basic joist ceiling will perform to a high standard. Framing lumber comes pre-cut in 8, 10 and 12-foot sections, giving you maximum design latitude in specifying the ceiling height. To reduce waste and maximize headroom, many builders now frame interior walls at 10 or 12 feet, then create a stepped recessed ceiling that drops to 9 feet near the room’ s perimeter.
Stage 4: the roof- the practice of building roofs with individual rafters has declined since the 1950s, when manufacturers introduce now familiar truss systems. Individual rafters are still used in a custom build homes. Trusses are economical, sturdy triangles assembled in factories and held together by metal plates; they are available for roofs of virtually any size and slope.
Many people, however, still treasure the tent-like space that stick built, rafter roofs provide whether for attic storage or a loft bedroom, or simply to open a ceiling above a family room. A rafter roof costs more in both labor and lumber, but attention to a few key details will make it safe and sturdy.
Collar ties- To maintain structural strength, every third in a stick-built roof should tie to its opposite partner with a short length of lumber. If you want to increase headroom, ask your architect to use plywood gussets, wood reinforcing plates, instead of collar ties to join the rafters at the ridge. These triangular plywood pieces should be glued as well as nailed in place, with a minimum base length of about 4 feet.