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Floor Framing

Floor Framing

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.

Anchor bolts

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.

Joist

Beam

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

Subfloor

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.

Bridging

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.

Floor Framing Plan

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,

Gathering information from prints

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.

Section views

~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.

Checking the Foundation for Square

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.

Checking the Foundation for Square

If opposing walls are not equal the Pathagorean Therum can be used to determine square.

Sill Plates

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

Steel Columns

Posts are vertical framing members used in combination with horizontal members, such as beams or girders, to support a load.

Wood Posts

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.

Other Vertical Supports

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.

Wood Posts

Steel Columns

Other Vertical Supports

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.

Beams

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

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.

Band Joist or Rim Joist

Double Joists

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.

Trimmer, Header, and Tail Joists

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.

Lap Joist and Bridging

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.*

Sheathing

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.

Laying Out and Installing Sill Plates

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.

Procedure:

Point #1

11-1/4"

x2

1'-10-1/2"

Locating the Sill Plates on the Foundation

11-1/4"

30'

-1'-10-1/2"

28'-1-1/2"

Point #2

Corner A

  • Determine the deck dimension from the drawing

  • Compute the inside-of-sill plate dimension of the deck length and width by subtracting two times the sill plate width from the dimensions

  • Establish a control line between corners A and C by measuring in from each corner the width of the sill plate, marking these points, and snapping a control line through the points

  • Along this control line and at corner A measure the sill plate width for perpendicular wall and mark point #1

  • From this mark of intersection pull measurement determined in step 2 to locate point #2 in corner C

Point #1

Point #3

Point #1

Procedure:

E

  • From point #1, make a perpendicular line using a multiple of the 3-4-5 method that extends to the end of the foundation wall at corner B

Point #4

Point #2

44'

-1'-10-1/2"

42'-1-1/2"

  • From point #1, measure the inside-sill-plate to inside-sill-plate dimension from step #2 and mark point #3

  • Locate point #4 in corner D by measuring from point #2 in corner C and from the control line you made connecting point #1 to point #3

Corner A

  • Find E by pulling measurements from control lines connecting (A to C) and (C to D)

  • Last, check for square by checking another corner with the 3-4-5 rule or by pulling diagonals

Point #1

Procedure:

It is important that you do not cover your control lines (plate lines) with sill sealer before sill plate install.

Installing Sill Plates

  • Place a sill plate along one of the walls and tight to the bolts, align the end with the perpendicular line at the corner

  • Mark the anchor bolt locations on the sill plate

  • Drill holes or cut slots for anchor bolts or straps in sill plate

  • Place the sill plate over the anchor bolts and lightly tighten

  • Repeat these steps for remaining plates, the whole time checking to ensure plates remain square

Procedure:

Setting Posts and Beams

  • Measure down to the top of the pier footing from the dry line and record this measurement. Subtract the depth of the beam from the recorded measurement to establish the length of the center post
  • Fabricate the four-stud center post to the length measured
  • Slide the notched end of the beam into the beam pocket in the foundation wall and simultaneously set the other end on one half of the center post.
  • Lay out the locations of the center post
  • Fabricate the beams as per the plan
  • Locate the dry line approximately 6" off center of both 18'-0" foundation walls
  • Stretch a line from the top of one exterior foundation wall sill plate to the top of the opposite exterior foundation wall sill plate at the points established

Procedure:

Setting Posts and Beams

  • Measure, mark, cut, fabricate, and install the beam post that will support the notched end of the beam
  • Repeat these steps for the remaining beam
  • Secure the two beams together with metal hardware
  • Check that the top of the beam aligns with the top of the sill plate at the foundation, and with the dry line at the center post end
  • Fasten the notched end of the beam into the beam pocket and the post end of the beam to the center post
  • Plumb and brace the center post

Laying Out and Installing Floor Framing Components

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

Procedure

Laying Out Floor Framing Members

  • Measure in from the outside edge of the sill plate the thickness of the rim joist. Place a mark at each end of the sill plate.

  • Snap a chalk line between the marks made in the first step

  • Repeat the first two steps on the opposite foundation wall
  • Lay out the openings on the sill plate and beam using the plan dimensions

  • Measure and mark the locations of the trimmers on the sill plate and beam

  • Mark on-center spacing for standard joist on the sill plate and beam, being careful to offset the joist location on the opposite foundation wall sill plate when using overlapped joists

Procedure:

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

  • Position and fasten the inside trimmers with the ends aligned to the chalk line on the sill plate

  • Mark the position of the double headers

  • Place the outside header pieces between the inside trimmers

  • Fasten the header to the trimmer with 16d nails

  • Mark the position of the tail joists on the headers

  • Fasten the tail joists to the outside header using 16d nails driven through the header into the ends of the tail joists

Procedure:

Framing of Floor Openings

  • Double the headers and drive 16d nails through the trimmer joists into the ends of the double header pieces

  • Nail the double header pieces to each other with 16d nails, using a staggered pattern

  • Double the trimmer joists, and fasten them with 16d nails staggered 16" on center

  • Install joist hangers

Procedure:

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

  • Set the floor joists with the crown up on the layout with their ends aligned to the chalk line on the sill plate

  • Toenail the joists to the sill plate

  • Lap the joists on the beam or wall, fasten them down with 16d toenails, and face-nail them to each other

Procedure:

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

  • Position the band joist against the end of the floor joists flush to the end of the sill plate

  • Fasten the band joist to the end joist with three 16d nails

  • Square the next joist up from the sill plate and mark its position on the top edge of the band joist
  • Face-nail the band joist to the floor joist with three 16d nails aligned with the mark established prior

  • Locate the rest of the joist layout by marking the on-center spacing from this point

  • Attach the band joist to the remaining floor joists, trimmers, and tail joists in the same manner

Procedure:

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

  • Verify the width of the floor joists and the spacing between the floor joists
  • Position a piece of material used for bridging on edge
  • Hold the framing square with the tongue of the square in your left hand and the blade of the square in your right with both ends facing away from you
  • Position the tongue of the square on the edge of the bridging material, align the width of the floor joists on the edge of the cross bridging furthest from you
  • Position the blade of the square on the edge of the bridging material, align the spacing between the floor joist on the edge closet to you in your right hand (so for 16 o.c. you would hold at 14-1/2") and the width of the joist in your left on the furthest away side of bridging
  • Scribe a line on the tongue side of the framing square
  • Mark the point where the spacing between the floor joist dimension intersects the edge of the bridging closest to you
  • Slide the square down to where the tongue is now on this mark and scribe a line, the whole time keeping the dimension of the joist in your left hand and the spacing between joist in your right
  • Measure the length of the bridging, and determine the angle cut on the bridging using a speed square

Procedure:

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.

  • Cut the bridging to length and start 6d nails at one end of the bridging

  • Snap a line on the top of the joists at the location of the bridging

  • Fasten the bridging at alternate sides of the previously snapped line in each joist bay

  • Fasten a second piece of bridging to the adjacent joist in the same joist bay

  • The bottom ends of the bridging are nailed after the floor receives all the additional loads

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.

Installing a Subfloor

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.

Procedure:

Installing a Tongue and Groove Subfloor

  • Snap a line the length of the floor system 48-1/4" away from the band joist on the side that you would like to start

  • Position the first sheet on the joists, aligning the square edge of the sheet to the end of the band joist and the grooved edge of the sheet to the chalk line

  • Verify that the other end of the sheet breaks on the center of a joist

  • Fasten the sheet to the band joist and to the joist at the end of the sheet
  • Lay out 16" on-center marks on the top of the sheet along the grooved edge and align joists to these marks

  • Fasten sheet to joists on these marks 3" back from the edge

Procedure:

Installing a Tongue and Groove Subfloor

  • Finish attaching the sheet to the joists using a nailing pattern as instructed

  • Position the second sheet on the joists, butting the squared edge of the sheet to the squared edge of the previously fastened sheet and the grooved edge of the sheet to the chalk line

  • Pull layout and continue with nailing pattern

  • Measure from the last sheet to the end of the deck and cut a sheet to this size
  • Install this piece to finish the installation of the first row of sheathing

  • Using the cutoff from the previous step, begin the second row, making sure that this piece breaks on the center of a joist. A portion of this sheet will extend beyond the deck and will be cut later

Procedure:

Installing a Tongue and Groove Subfloor

  • Stand the sheet with the tongue edge on top of the joists against the grooved edge of the fastened sheet

  • Lay the sheet down on top of the joists and verify that one end of the sheet covers or extends past the end joist and the other end breaks on the center of a joist

  • Drive the tongue of the cut sheet into the groove of the fastened sheet with a sledge hammer and a 6'-8' long 2x4 placed against the grooved edge of the cut sheet

  • Fasten the sheet to the joists 3" away from grooved edge of the sheet
  • Verify that the seam is centered on the joist

  • Finish attaching the sheet to the joists using a nailing pattern as instructed, Repeat process to finish deck

  • Snap a line from one edge of the deck to the other on the ends of the deck where the sheathing overhangs the end joist, and cut along these lines

  • Secure the sheathing to the end joists, making sure to align the end joists with the cut end of the sheathing

Wall Framing

Running Joists

Roof Framing

Jack Rafters

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