A house's frame1) provides the framework for exterior coverings, gives it shape, and enables it to withstand loads like wind and snow. House framing18) involves fitting pieces of engineered wood, structural steel, or wood together to create the structure2) on which the ceilings, floors, roof, stairs, and walls are constructed. Exterior doors and windows are usually installed during this process.
Wood3) is the most commonly used material to frame houses. It is inexpensive, readily available, strong, and versatile. Three types of wood house framing have been used to build houses: timber, balloon, and platform.
These methods along with the components (known as members) used to construct floor, wall, roof, and stair frames and the steps involved with constructing the basic frame are discussed below.
House Framing Methods
Timber framing is the oldest form of wood framing. It was used to build most houses until the late 19th century. In the 1970s, the timber framing tradition was revived4) and developed into a design style for the modern era.
This type of house framing involves using mortise and tenon joints5) to tightly connect beams and posts and seal them with wooden pegs. A mortise6) is a groove, hole, notch, or slot cut into a piece of wood for the purpose of holding a tenon with the same dimensions. A tenon7) is a projection created on the end of a piece of wood to be inserted into a mortise with the same dimensions. Joinery8) involves fitting pieces of wood together to create complex items like house frames. The wood used for timber framing is generally 6" x 6", 8" x 8", or 10" x 10" in size, which is more substantial than the standard 2" x 4"s used to construct other types of house frames.
Although timber framing creates the strongest frames, there are disadvantages. The large pieces of wood required for framing are not always readily available in some locations. They can also be more expensive than the standard lumber used to construct frames, but eco-friendly lumber provides a less expensive option. Timber framing requires a housewright9) (i.e., "a builder of wooden houses") or master craftsman who has the skills to make the very precise joints required to construct a secure frame. The cost of labor and materials makes timber framing the most expensive of the three methods; however, costs have begun to decrease.
Timber house framing was commonly used until the late 1800s when balloon framing became more popular.
Balloon House Framing
Although it is rarely used today, balloon framing was the most common method to frame houses for about 40 years. It was developed in the 1800s as an alternative to timber framing when people began to want less expensive houses that were built faster. At the same time, the Industrial Revolution and railroad construction created demand for dimensional lumber (e.g., 2" x 4"s, 2" x 6"s, etc.), and manufactured nails were becoming regularly available. Balloon house framing enabled builders to use these materials to construct houses faster and for less cost than timber framed houses.
This type of framing10), which was generally used to build two-story houses, involved nailing small members together to create the frame. It used long 2" x 4"s (or studs) for the exterior walls that extended from the sill plate on the foundation to the roof rafter.
Balloon framing provided a practical alternative to timber framing, but it had a serious drawback: fires could spread quickly and without much notice. This occurred because wall cavities usually did not contain insulation. In addition, they spanned the entire height of the house, so fire burned faster (and sometimes without detection until smoke billowed from the eaves of the roof).
Although balloon framed houses were not as strong as timber framed houses and posed a fire risk, balloon framing was the most common house framing method from the 1890s to the 1930s.
Platform House Framing
Platform framing was developed as an alternative to balloon framing. Instead of using very long studs that run from the foundation to the roof, studs only span one story. Therefore, each story of the frame is built individually—with each floor providing a platform11) for building the walls.
Platform framing prevents fire from spreading as quickly as it can in balloon framed houses; however, vertical shrinkage12) is a cause for concern. This occurs because a thick layer of wood with horizontal grain is used to construct floors. When the wood dries, the frame can shrink and cause stress on finished surfaces.
Within a few years of its introduction, platform house framing became (and remains) the most common form of house framing.
House Framing Components
Floor frames13) distribute structural loads across the house to its foundation or load bearing walls. The following components are used to construct floor frames:
- The sill plate, which is typically made of treated wood, attaches to the top of the foundation. Joists14) are attached to this component. They are horizontal members15) that span the open space between the beams that carry loads to vertical members.
- Rim joists, which are placed around the outside of the floor's structure, are laid on their narrow ends and fastened to the sill plate.
- Floor joists that are generally the same size as rim joists are placed on their narrow ends, spaced evenly, and fastened to the sill plate. The subfloor is attached to the floor joists, which then transfer floor loads to the load bearing walls.
- A header consists of several wood members attached to one another. It is used to frame openings in the floor assembly, which interrupts the joists.
- Bridging is comprised of small wood members that are fastened between joists to provide lateral stability.
Wall frames are used to construct load bearing and non-load bearing walls. Load bearing walls carry and transfer loads from above to floor frames. Non-load bearing walls have no structural function. The following components are used to construct wall frames:
- A bottom or sole plate is a horizontal wood member attached to the wall's base and fastened to the floor's frame.
- The top plate is a horizontal wood member attached to the top of the studs.
- Studs are vertical wood members that attach to both the bottom and top plates. They are spaced 12, 16, or 24 inches apart on center.
- A header consists of several wood members attached to one another. It is attached to adjoining studs to uniformly distribute a house's loads around the opening.
- A sill is a wood member placed under an opening and fastened to adjoining studs to support a window.
- Blocking involves fastening small wood members between studs to attach finish hardware or prevent fire from spreading within the wall cavity.
- The king plate, which is a secondary plate attached to the top plate, interconnects corners and interior wall frames.
The roof frame distributes structural loads on the roof across the house to load bearing walls. The following components are used to construct a roof frame:
- Rafters are diagonal wood members on which the roof sheathing is attached. They are evenly spaced 12, 16, or 24 inches a part. Various types of rafters—including common, hip, jack, and valley—are used to create roof shapes and styles.
- A ridge beam is a horizontal wood member on which the tops of rafters are attached.
- A collar beam is a horizontal wood member placed between rafters to provide vertical stability.
- Ceiling joists are horizontal wood members used to frame the top story's ceiling and the attic's floor.
- Fascia boards that add lateral stability are attached to the bottom of the rafters.
Stair frames carry active loads to exterior walls or the vertical studs that support them. The following components are used to construct stair frames:
- The stringer consists of several diagonal wood members that form a stair's rise and run. They are placed on the outer edges and often the center of a stair to support the tread.
- The tread is the horizontal wood member that forms the rough surface of a step.
- The riser is the vertical wood member placed between steps to form their height. No vertical members are used when the steps have open risers.
House Framing Steps
Three steps16) are involved with constructing a house frame.
1) Select the lumber.
The fewer defects and knots in lumber17), the higher the grade and cost. Common grades of softwood lumber are as follows:
- #1: Construction grade
- #2: Standard grade
- #3: Utility grade
- #4: Economy grade
Construction grade lumber is the highest quality because it has a more even appearance and is less likely to shrink over time.
2) Pour the foundation.
Before house framing can begin, the site is prepared for construction and the foundation is poured. The concrete footings that support the foundation must be properly installed and sealed to help protect it from moisture.
3) Build the frame.
Constructing a frame begins with installing three basic components:
Sill plates are anchored to the foundation. They prevent ground-related problems like bug infestation, water damage, and wood rot.
Once the sill plates are attached, vertical studs are installed between bottom and top plates. Spaces for doorways and windows must have the proper dimensions.
Horizontal joists that support floors and ceilings are attached to the studs' bottom and top plates.
A solidly built frame helps to ensure that a house can withstand structural loads like wind and snow over its life cycle. Wood is the most commonly used house framing material. Platform framing is the most common framing method. Timber house framing creates a traditional look and feel. Balloon framing has not been widely used since the 1930s because of fire hazards, but some of these homes still exist. They should be retrofitted with fire blocking and insulation to slow the spread of fire.
To learn more about home construction including site preparation and foundation construction, visit RealEstatece.com.
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