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Floor framing consists of an interconnected system of columns, posts, girders, beams, trusses, sill plates, joists, and subflooring.
Houses and other buildings always have framed floors. The framing provides a stable platform for the walls and other parts of the structure while soundly anchoring them to the foundation.
Sill Plates are often fastened to the foundation using long anchor bolts that are threaded at one end. Part of the anchor bolt is embedded in the concrete while the threaded end is left exposed. The anchor can then be used to secure a sill plate to the foundation with a nut and washer.
Floors and ceilings are often supported by horizontal members called joists. Floor and ceiling materials are usually fastened to the joists, which help distribute loads. In most cases, floor joists rest on and transfer loads to sills and beams.
A horizontal, load bearing structural member. It rests on a column, a pier cap, a wall, or a foundation wall. Beams are typically used to support loads over an extended span.
Joist hangers are small U-shaped pieces of galvanized steel that add extra support and strength to the joists. They wrap around the floor joist and attach to the framing.
In houses and other residential structures, flooring materials are usually installed over a subfloor consisting of plywood or some other type of manufactured panel. The subfloor is attached to the floor joists.
A structural member that connects floor joists laterally to maintain alignment and to help distribute the load. Bridging is installed before the subfloor is applied.
A floor framing plan must take into consideration both dead loads and live loads. The dead load is the weight of the floor itself and any parts of the overall structure that it must support. The live load on the otherhand includes such things as equipment, furniture, and people.
Openings that penetrate the floor should be located away from structural beams or load bearing walls, because these features cannot be cut or altered. The project prints detail the size and locations of beams, trusses or joists, and other structural members.
The foundation plan is a drawing that shows the layout and shape of the foundation, the locations of foundation walls and footings, piers,
beams, columns, joists, and their locations.
The two types of drawings found in prints most essential for laying out the floor system are the foundation plan and the floor plan.
The floor plan generally contains more information than other plan views. It shows the locations of exterior walls, interior partitions, and openings.
~Typically one of the first drawings a carpenter will look at.~
Wall sections can include ceiling heights, knee wall requirements, floor heights, joist size, subfloor thickness, and sill dimensions.
Foundation walls serve as anchoring points for wooden sill plates. Usually made of treated lumber, sill plates provide a nailing base for floor joists. Before installing sill plates, the foundation walls must be checked for square.
If opposing walls are equal in length the diagonal method is commonly used to check foundation walls for square. If diagonal measurements differ from one another the frame is out of square by one half the difference between the two.
If opposing walls are not equal the Pathagorean Therum can be used to determine square.
A wood framed floor consists of a series of individual components that work together as a unit. sill plates, usually made of treated lumber, anchor the rest of the building and help it resist destructive natural forces such as high wind and earthquakes.
Sometimes sill plates are anchored with clips or straps. Like anchor bolts, these are embedded into the concrete. Once the concrete has set the straps are then bent around the top of the sill and secured with nails. Both anchor bolts and clips are spaced a maximum of 6' apart, and one placed within 1' of each outside corner.
Often foam sill sealer is used under the sill to prevent air leaks and form a tighter fit between the sill and foundtion.
Sill plates are attached to the foundation with an embedded hardware device, usually a 1/2" or 5/8" anchor bolt. Building code usually requires anchor bolts to be embedded a minimum of 8" into reinforced concrete, or 16" into concrete that is not reinforced.
Posts are vertical framing members used in combination with horizontal members, such as beams or girders, to support a load.
Round steel columns, sometimes known as lally columns, are often used as vertical members in a wood-framed building. When used with a concrete slab the base is embedded in the concrete. If supporting a wood girder the lally column is secured using with lag bolts, when supporting a steel beam machine bolts or a simple weld may do.
Posts are often made of solid wood or engineered wood products and may be pressure treated or laminated for greater durability. They must be sturdy enough to stand up under heavy loads and to prevent bowing and cracking. The bottom of the wood post may be pinned to a concrete or masonry pedestal or it may be nailed to a sill plate that has been secured to the top of a pier. The width of the post must be equal to that of the girder or beam it supports, and fastened using angle iron or another type of metal connector.
When a structure has a crawl space instead of a basement, masonry piers are sometimes used in place of wood posts. There will usually be at least 18" of clearance from the ground to the joists, and 12" between the ground and the girder.
Why are the beams in the picture notched? (right)
Why are the bearing walls positioned directly over the lally column? (bottom)
Which walls are bearing and which are not? (bottom right)
C.
A.
B.
In two story structures, floor beams from the first story support the second floor and are themselves supported by means of a central load-bearing wall. Beams and bearing walls are usually located near the center of the structure in order to reduce the distance that the joists must span.
Although beams may consist of a single piece of material, they are often assembled on-site from individual pieces of wood or engineered wood product. The length of a built up beam may be extended by butting the ends of members together, but columns or piers supporting built-up beams should be positioned within 12" of a butt joint and atleast 4" at each end resting on a load-bearing support member.
Beams are horizontal structural members made from wood or steel that provide support for joists. They are always located between primary structural supports, such as load bearing walls or posts.
Floor joists are installed after the sill plates have been anchored to the foundation walls and the beams are in place. Joists should be placed with the crown up. Positioning the joists this way will allow it to straighten as loads are applied on top. Joists should be inspected for large loose knots, severe crowns, splits, checks, and other defects that can make it useless for framing purposes.
In a typical residential floor frame, the joists rest on and transfer loads to sills and beams. Usually the joist size, spacing, and direction are specified in the foundation plan or in a wall section in the project prints.
In most cases, floor joists are made from lumber selected primarily for strength and stiffness. Floor joists range in size from 2"x6" to 2"x12". The size used is determined by the load, the length of the span, the space between the joists, and the species and grade of lumber from which the joists are made.
To prevent floor joists from rolling or twisting when placed under loads, continuous pieces of lumber the same size as the joists can be nailed along the ends.
Interior partitions, heavy equipment, or furnishings such as bathtubs, hot tubs, water heaters, or safes can place tremendous stress on the floors. They can cause excessive deflection of joists and can even cause the floor frame sytem to fail.
When nailing the two joists together, it is important to make sure that the tops of the joists are flush. Nails are placed in a staggered pattern about 2' apart from the top to the bottom of the joists. To keep them from protruding, nails should be set at a slight angle.
Tail joists are members that run from the header to a supporting wall or beam.
Trimmers, also called doublers, are double joists placed on each side of a floor or ceiling opening.
Double joists that are nailed between the trimmers of floor or ceiling openings are called header joists. Header joists support the floor joists that have been cut to create the opening. They do this by transferring the load to the trimmer joists.
Bridging
Lap Joists
Bridging is a structural member made up up of either wood or metal that connects floor joists laterally in order to maintain alignment and to help distribute the load. Bridging is needed when the span of the joist is longer than 8'-0". The two types of wooden bridging are: wooden cross bridging and solid wood bridging.
Codes typically require a minimum overlap of 3". In some areas building codes may dictate that solid blocking be installed between the joists that lap over a beam or wall to further stabilize these framing members. To prevent splaying the ends and avoid problems with the subfloor or ceiling finishes, overlapped joists should not overhang the wall or support by more than 6".
Cross bridging is usually used where the floor joists are 16" O.C., smaller width generally will have solid blocking.
*When more than one row of bridging is used, the bridging is spaced an equal distance in the span.*
Structural panels called sheathing are installed on top of floor joists in order to provide a base for the finished floor material. The tongue of the sheet is always on the outside of the framing, and the groove side is always on the inside.
Installing a wood framed floor, often called a deck, is a complex process. The floor must bear the weight of all the loads that will be placed on them. Sill plates are used to anchor the floor to the foundation. They must be carefully laid out and installed to ensure the deck is stable and able to support the necessary live and dead loads.
Point #1
11-1/4"
x2
1'-10-1/2"
11-1/4"
30'
-1'-10-1/2"
28'-1-1/2"
Point #2
Corner A
Point #1
Point #3
Point #1
E
Point #4
Point #2
44'
-1'-10-1/2"
42'-1-1/2"
Corner A
Point #1
The wood selected for joists must be squared and trimmed to the proper length before installation. Joists have a crown, which is a slight curve or bow along the edge of the joist. The crown can be found by sighting along the length of the joist from one end to the other. When placed with the crown side up, the joist will settle and straighten under the weight of the floor deck.
In a typical residential floor frame, the framing components, commonly referred to as joists, rest on and transfer loads to sills and beams. When placed correctly, the top of the beam will be at the same elevation as the sill plate.
Layout
Flagging
Laying Out Floor Framing Members
Openings in floors are typically planned by the architect so that the long dimensions of the opening are parallel to the joists to minimize the number of joists likely to be interrupted during framing.
Framing of Floor Openings
Framing of Floor Openings
If the floor has an opening in it, after the opening is framed, the next step is to install the remaining floor joists. The two main methods used to install floor joists are known as clear span and lapped framing. When one joist is used to span the entire width of the opening it is known as a clear span while the lapped has joists that lap over one another in the center of the span.
Installing Floor Joists
Band board or rim joist, help stabilize the floor joists and prevent them from twisting when placed under load. The band joist can be butted and centered on a floor joist or butted in between joists and reinforced with a block.
Installing Band Joists
The two most common types of bridging used in residential construction are cross and solid. Cross bridging is typically used for joists that are spaced on center and solid bridging is used for odd-spaced joists. Cross bridging is typically made of 1x3" material whereas solid bridging is typically made from the same material as the joists.
Determining the Length of the Cross Bridging
Most building code requires bridging for floor systems with joists that span 8'-0" or more. Bridging should be equally spaced though, so a span of 14'-0" would have bridging at 7' while a span of 18'-0" would have two rows of bridging 6' apart. Cross bridging should alternate and a small gap should be left between cross bridging to eliminate possibility of floor squeaks.
Cutting and Installing Bridging
111ft/8ft = 13.875
next whole number = 14
111/14 = 7ft 11-1/8" -H.H.
It is important to remember that the ends of the bridging do not extend beyond the floor joist, this will interfere with the sheathing or drywall.
Engineered wood panels, such as plywood or oriented strand board (OSB), are used for subflooring and come in
standard sizes of 4'x8'. These panels may be standard with squared edges or tongue and groove.
A subfloor serves as the base for the finished flooring material. The subfloor is fastened with glue in addition to either nails or screws to reduce or eliminate floor squeaks caused by the subfloor rubbing against the joist when placed under shifting loads.
Installing a Tongue and Groove Subfloor
Installing a Tongue and Groove Subfloor
Installing a Tongue and Groove Subfloor