Accurate Home inspection of Atlanta

Recommended Nailing Practices

Wood members are most commonly joined together with nails, but on occasion metal straps, lag screws,bolts, staples, and adhesive can be used. Proper fastening of frame members and covering materials provides rigidity and strength. For example, proper fastening of intersecting walls usually reduces cracking of plaster at the inside comers.

 

Floor Framing

Floor framing consists of columns or posts, beams, sill plates, joists, and subfloor. Assembled on a foundation,they form a level anchored platform for the rest of the house and a strong diaphragm to keep the lateral earth pressure from pushing in the top of the foundation wall.The columns or posts and beams of wood or steel that support the joists over a basement are sometimes replaced by frame or masonry walls when the basement area is divided into rooms. Floors of the second story are generally supported on load-bearing walls in the first story.Wood-frame houses may also be constructed over a crawl space with floor framing similar to that used over a basement or on a concrete slab as shown in the section on foundations.

Factors in design

An important consideration in the design of a wood floor system is wood shrinkage. When wood with a high moisture content is used, subsequent shrinkage can result in cracks, doors that stick, and other problems. This is particularly important where wood beams are used,because wood beams may shrink and foundation walls will not. In beams and joists used in floor framing, moisture content should not exceed 19 percent; about 15 percent is a much more desirable maximum. Dimension material can be obtained at either of these moisture contents, when specified.

Grades of dimension lumber vary considerably with wood species. For the specific uses described in this publication,material is divided into five categories. The first category is the highest quality, the second is better than average, the third average, and the fourth and fifth for more economical construction. Joists and beams are usually of a species of second category material, while sills and posts are usually of third or fourth category.

 

Stairways and other openings that penetrate the floor structure should be located so as to interrupt as few members as possible. Stairways should be oriented parallel to floor joists so that only one joist need be interrupted with 24-inch on-center joist spacing. Wherever possible, the stair opening should be coordinated with a normal joist location on at least one side. Stairways should never interrupt a structural beam or bearing wall when it can be avoided.

The stairway design should be completed before floor framing begins, because the stairwell opening must be framed at the time the floor is constructed. The roughframed opening for a stairwell should be 1 inch wider than the desired finished stairway width. The length ofthe opening must be accommodated to tread run and stair rise, which in turn are governed by total rise.Other openings such as those for clothes chutes and flue hole should also be located to avoid interrupting framing members. Two-foot on-center spacing of joists generallyprovides ample clearance for such openings.

Sill plate

A wood-frame floor system should be anchored to the foundation to resist wind forces acting on the structure.This is usually done with a 2- by 6-inch sill plate attached to the foundation by ½-inch anchor bolts at 8-foot intervals.Floor joists are toenailed to the sill plate.The sill plate may also be attached with anchor straps that are embedded in the foundation in the same manner and at the same spacing as anchor bolts. These devices do not require holes in the sill plate; metal straps are simply bent up around the plate and nailed. Anchor straps are less exacting and do not interfere with other framing as conventional bolts often do.

 Anchoring floor system to poured concrete foundation wall:

Sill plates may be entirely eliminated where the top of a foundation of poured concrete (fig. 27B) or concrete block is sufficiently level and accurate. Joists may bear directly on a solid concrete wall or on a top course of solid concrete block. They may also bear directly on cross webs of hollow core block or on cores that have been filled with mortar. Where the sill plate is omitted, anchorage of the floor system may be provided by anchor strap devices, as described above. The straps should be spaced to coincide with joist locations so that each may be nailed directly to the side of a joist.

As noted previously, a foundation of pressure-treatedwood does not require a sill plate or special anchor devices. Floor joists bear directly on the top foundation wall plate and are toenailed to provide anchorage.

Posts and girders

Wood posts or steel columns are generally used in the basement to support wood or steel beams. Masonry piers or wood posts are commonly employed in crawl-space houses.Steel pipe columns can be used to support either wood or steel beams. They are normally supplied with a steel

Anchoring floor system to concrete block foundation wall:

bearing plate at each end. Secure anchoring to the beam is important.Wood posts should be solid, pressure-treated, and not less than 6 by 6 inches in size for freestanding use in a basement. When combined with a framed wall, they may be 4 by 6 inches to conform to the width of the studs.

Wood posts should be squared at both ends and securely fastened to the beam (fig. 30). The bottom of the post should rest on and be pinned to a masonry pedestal 2 to 3 inches above the finish floor.

Center beams

Wood-frame floor construction typically employs a beam or girder to provide intermediate support for the first floor. In two-story construction, the beam generally supports the second floor as well via a load-bearing wall extending along the center of the first story.

For maximum benefit in reducing joist spans, beams and bearing walls should be located along the centerline of the structure. In some cases it may be desirable to offset the center support 1 foot from the centerline to provide for even-length joists; for example, in a 30-foot-deep floor system, displace the centerline to 14 and 16 feet from the two sides instead of 15 feet from both. However,as discussed later, this is not necessary if off-center spliced joists are used.

The center beam usually bears on the foundation at each end and is supported along its length by columns or piers. The spacing of columns or piers is adjusted to the spanning capability of the beam for a particular design load.Two basic types of center beams-wood and steel-are commonly used. The decision on which to use should bebased on a comparison of the total installed cost of each,including intermediate support columns or piers, and footings.Other considerations include delivery, scheduling,and ease of construction.

 Steel post support for wood or steel beam:

For equal widths, the built-up beam is stronger than the solid beam.

Built-up wood beams

Built-up beams are constructed by nailing three or four layers of dimension lumber together. The built-up beam may be made longer than any of the individual members by butting the ends of the members together. These butt joints must be staggered between adjacent layers so that they are separated by 16 inches. In addition, the built-up beam must be supported by a column or pier positioned within 12 inches of the butt joints.

Typical allowable spans for built-up wood beams are shown in table 5. Dry lumber should always be used to avoid settlement problems caused by shrinkage of the built-up beam and the joists it supports. It is not necessary to use a wood plate over wood beams, because floor joists can be nailed directly to the beam.Ends of wood beams should bear at least 4 inches on the masonry walls or pilasters. When wood is untreated, a ½-inch air space should be provided at each end and sideof wood beams framing into masonry (fig. 31). The topof the beam should be level with the top of the sill plates on the foundation walls.

Steel I-beams

Steel I-beams are often used because they have greater strength and stiffness than wood beams, which enables them to carry a given load over a given span with a beam of lesser depth and thus provides greater headroom or reduces the requirement for additional supporting posts.Allowable spans for steel I-beams are shown in table 6.However, steel beams require an additional supplier,which can complicate delivery schedules. They are also heavier and more difficult to handle in the field. The total cost of a steel beam, including columns or piers, is generally greater than that of a wood beam.Where steel beams are used, a wood plate 2 by 4 or 2 by 6 inches across is usually attached to the top surfaceby bolting or by driving nails part way into the sides of the plate and bending the protruding nail shanks over the edges of the beam flange. Floor joists are then toenailed to the beam plate to anchor to the floor and to provide lateral bracing for the beam. A beam plate is not required if the floor joists are secured by other means.

Beam-joist installation

In the simplest method of floor framing, the joists bear directly on top of the wood or steel beam. The top of the beam coincides with the top of the foundation or anchored sill, if the latter is used (fig. 31). This method assumes Wood center beams are of two types, solid or built-up.The built-up beam is preferable because it can be made up from dimension material that is drier and more stable.

Typical built-up wood beam installation.that basement wall heights provide adequate headroom below the girder. When a forced-air heating system is to be installed, this arrangement of beam and joists provides space for the main duct to be run parallel to the beam and for the laterals to be run between the joists above the level of the beam.As previously noted, beams and joists should be constructed of dry lumber to reduce problems caused by settlement resulting from shrinkage. This is of particular concern when wood joists bear directly on top of the wood beam at the center of the house while bearing on the concrete foundation wall at the outer ends. In order to equalizethe depth of wood at the beam and at the outer wall-and thereby equalize shrinkage potential-joistss hould be attached to the side of the wood beam using joist hangers or supporting ledger strips (fig. 32). The simplest method is to use steel joist hangers . Where ledgers are used, joists must always bear on the ledgers. It is important that a small space be allowed above the beam to provide for shrinkage of the joists.Joists may be butted to a steel beam in the same general way as is illustrated for a wood beam, with joists resting on a wood ledger that is bolted to the web.

Floor joists

Floor joists are selected primarily to meet strength and stiffness requirements. Strength requirements depend on the load to be carried. Stiffness requirements place an arbitrary control on deflection under load. Stiffness is also important in limiting vibrations from moving loads-often a cause of annoyance to occupants.Wood floor joists have generally nominal thickness of 2 inches and nominal depth of 8, 10, or 12 inches. The size required depends upon the loading, length of span, spacing between joists, and species and grade of lumber used. After the sill plates have been anchored to the foundation walls and the center beam installed, the joists are laid out according to the house design. The center-to-center spacings most commonly used are 24 inches or 16 inches.Span tables for floor joists, provided by the NationalForest Products Association or in local building codes,can be used as guidelines. Table 7 is a simplified version for joists spaced 24 inches on center and table 8 for 16 inches on center. The sizes shown in the table are minimal;it is sometimes desirable to use the next larger lumber size than that listed in the table.

Allowable spans for built-up wood center beams

Length of maximum clear span Minimum required Minimum required bending stress (9 bending stress (9 Width of of 1,000 psia of 1,500 psib Beam structure composition (ft) One-story Two-story One-story Two-story

Joists should be inspected for straightness visually, as they are being placed. Any joists having a slight crook edgewise should be placed with the crown on top. A crowned joist tends to straighten out when subfloor and normal floor loads are applied. Those joists that are notcrowned should be inspected for the presence of knots along the edge. The largest edge knots should placed on top, because knots on the upper side of a joist are placed in compression and have less effect on strength.The header joist is fastened by nailing through it into the end of each joist with three 12d or 16d nails. In addition, the header joist and the stringer joists parallel to the exterior wall in platform construction are toenailed to the sill with 10d or 12d nails spaced 16 inches on center. Each joist should be toenailed to the sill and

Allowable spans between columns or piers

supporting steel center beams beam with two 10d or three 8d nails, then nailed toother joists with three 12d nails where they lap over thecenter beam. If joists are butted over the center beam they should be joined with a nominal 2-inch scab nailed to each joist with three 12d nails.An off-center splice may be used in framing floor joists. This system often allows the use of one smaller joist size when center supports are present. In off-center splicing, long joists are cantilevered over the center support and spliced to short joists (fig. 35). The locations of the splices over the center beam are alternated. Depending on the span, species, and joist size, the overhang varies between about 2 feet and 3 feet. Metal splice plates are used on each side of the joints. Selecting the proper plate size and installing the plate must be done by a truss fabricator.

Allowable spans for simple floor joists spaced 24 inches on center for wood with modulus of elasticity

FLOOR FRAMING;

Floor framing includes setting columns,beams,sills,headers,joist and applying the subfloor.These form a strong,solid base on which the interior and exterior walls rest,and carry other loads such dead loads,live loads,etc...The floor also forms a diapham to resist the lateral pressure from the earth and subsurface water that is pressing on the fondation wall,tending to push it inward.

FLOOR BEAMS; Usually the span from the foundation wall to the other is so long beams are installed to shorten the distance.Steel beams are often used,as well as solid and built-up wood beams.

Parallel Strand Lumber; Parallel strand lumber is used for beams,headers,columns,and post.It can be sawed,drilled,and nailed like solid wood.It has been accepted by building codes in the united states.