Platform House Framing
Category Construction Glossary
Platform is a light-frame construction system and the most
common method of constructing the frame for houses and small
apartment buildings as well as some small commercial buildings in
Canada and the United States.
The framed structure sits atop a concrete (most common) or
treated wood foundation. A sill plate is anchored, usually with 'J'
bolts to the foundation wall. Generally these plates must be
pressure treated to keep from rotting. The bottom of the sill plate
is raised a minimum 6 inches (150 mm) above the finished grade
by the foundation. This again is to prevent the sill-plate from
rotting as well as providing a termite barrier.
The floors, walls and roof of a framed structure are created by
assembling (using nails) consistently sized framing elements of
dimensional lumber (2×4, 2×6, etc.) at regular spacings (12″, 16″,
and 24″ on center), forming stud-bays (wall) or joist-bays (floor).
The floors, walls and roof are typically made torsionally stable with
the installation of a plywood or composite wood “skin” referred to
as sheathing. Sheathing has very specific nailing requirements
(such as size and spacing); these measures allow a known
amount of shear force to be resisted by the element. Spacing the
framing members properly allows them to align with the edges of
standard sheathing. In the past, tongue and groove planks
installed diagonally were used as sheathing. Occasionally,
wooden or galvanized steel braces are used instead of sheathing.
There are also engineered wood panels made for shear and
The floor, or the platform of the name, is made up of joists
(usually 2x6, 2×8, 2×10 or 2×12, depending on the span) that sit
on supporting walls, beams or girders. The floor joists are spaced
at (12″, 16″, and 24″ on center) and covered with a plywood
subfloor. In the past, 1x planks set at 45-degrees to the joists
were used for the subfloor.
Where the design calls for a framed floor, the resulting platform is
where the framer will construct and stand that floor’s walls (interior
and exterior load bearing walls and space-dividing, non-load
bearing “partitions”). Additional framed floors and their walls may
then be erected to a general maximum of four in wood framed
construction. There will be no framed floor in the case of a single-
level structure with a concrete floor known as a “slab on grade”.
Stairs between floors are framed by installing stepped “stringers”
and then placing the horizontal “treads” and vertical “risers”.
A framed roof is an assembly of rafters and wall-ties supported by
the top story’s walls. Prefabricated and site-built trussed rafters
are also used along with the more common stick framing method.
“Trusses” are engineered to redistribute tension away from wall-
tie members and the ceiling members. The roof members are
covered with sheathing or strapping to form the roof deck for the
finish roofing material.
Floor joists can be engineered lumber (trussed, i-beam, etc.),
conserving resources with increased rigidity and value. They allow
access for runs of plumbing, HVAC, etc. and some forms are pre-