Whether building or adding on to a house, one will inevitably encounter 'framing', the structural skeleton of a building. Now the term 'framing' includes many different types of framing, wall framing, floor framing, roof framing, structural framing, timber framing, interior framing, partition framing, wood framing, metal stud framing, and many more. Framing is a building technique based around structural members, which provide a stable structure to which the exterior and interior sheathings are attached. Early structures were 'timber framed' where large wooden timbers were fitted together either as "post and beam" or panels (bents) that could be raised and connected together. Skyscrapers are large frames of large steel beams riveted or welded together to create a structural skeleton to which all of the other building components are added. Modern homes always rely on some framed elements in their construction. Even a masonry structure will have framed interior partition walls and some form of framed roof.
The materials used in framing vary. The majority of framing is done with wood; spruce, pine or fir being the most common and recommended varieties, of standard dimensions usually 2"x4" or 2"x6" called 'studs'. Light-gauge steel studs are the second most common framing material. Steel framing is used mostly in commercial construction but has also gained popularity in residential construction. Engineered lumber and composite material studs are available, but are not regularly used yet.
Wall Framing
The major components of light frame construction are the bottom and top plates, studs, headers, and trimmers, or jacks. The studs are vertical framing members that are spaced evenly in the framed wall panel. Stud spacing is dependant on the structural loads placed upon the wall. 24" on center (denoted as O.C.) is the maximum spacing for studs in a non-bearing wall or a very light loaded wall such as a small shed. 16" O.C. is the most common spacing for studs in a structural wall. The framing terms for wood frame and steel frame are similar and will serve both. Most of the framing you will encounter in a typical building is wood light frame construction. Usually this type of construction utilizes 2x4 lumber. Since wood frame construction is the most common this will be the focus of the rest of the article.
First a note on lumber. Light frame wood construction utilizes pre-cut lumber of standard sizes. 2x4 lumber is the most common and economic. 2x6 and larger lumber is used for a variety of purposes including greater strength, matching masonry construction, and providing space for plumbing and other utilities. Lumber is rough cut to the nominal dimensions 2"x4", 2"x6", 2"x8", etc. However most framing is done with dressed lumber that has been planed down to provide a smooth and straight finish, resulting in actual dimensions of 1-1/2"x3-1/2" for 2x4's, 1-1/2"x5-1/2" for 2x6's, 1-1/2"x7-1/4" for 2x8's, etc. The majority of building plans dimension walls to their nominal widths rather than their actual widths. The length of studs also varies. Frame walls are normally built to standard heights of 8', 9' 10', and 12'. Lumber can be purchased in these lengths. The lumber, however, will have to be cut to make studs for these standard heights. For example an 8' wall is constructed with one bottom plate, 1-1/2", and a double top plate, 3", such that an 8' stud will have to be cut by 4-1/2" to make an 8' wall. Precut studs can be purchased to make your framing project simpler and more economic. However, precut studs typically measure 92-5/8", which will make the wall 97-1/8" tall. This is discrepancy is reputed to be taking into account ceiling sheathing and floor coverings for finished room height of 96".
The bottom plate or sill plate is a continuous member to which the studs are attached that rests and is attached to supporting structure below. Where splices occur in the bottom plate, the splice should be reinforced with a scab at least 12" long and centered on the splice. If the supporting structure is of concrete or masonry the bottom plate is required to be pressure treated lumber
The top plate of a framed wall is a continuous member to which the studs are attached that supports the structural loads from above. In a structural wall the top plate is usually doubled to create a composite beam. Where splices occur in the double top plate the two members should overlap each other for a total of a 48" splice.
Wood frame walls are usually built lying horizontally on the ground or floor surface in panels, or bays, and then stood up into position. Where these panels meet special attention to the framing should be given to provide a good connection. At corners where two panels meet one wall, wall 'A', should extend to the edge of the slab or floor framing with the second wall, wall 'B', held back the width of the framing members to meet wall 'A'. The end stud of wall 'A' should be doubled or tripled to provide a solid connecting block for attaching wall 'B'. Wall 'B's end stud should be a single to facilitate an easy connection. The top plates at the corners should overlap and intermesh with each other. Hold the top member of wall 'A' s double top plate back the wall width and extend the top member of wall 'B s double top plate such that it will rest on top of wall 'A' s bottom top plate member. Then fasten the two walls together with vertical fasteners locking the walls and top plates together. Where two wall panels meet on a continuous exterior wall, the to panels should butt up to each other with single studs and the studs fastened to each other with nails or screws from both sides in an alternating pattern. The top plate should be spliced at this joint by holding back the top member of the top plates 24" on both walls and splicing with a 48" member centered across the joint. Where an interior wall connects with an exterior wall one of two methods can be employed. Non-structural interior walls can simply be butted up to the exterior wall with a single end stud to a double or triple stud in the exterior wall and then fastened. Structural interior walls should be attached by interlacing with the exterior wall. Frame the connection point on the exterior wall such that two single studs bracket the connection point. Frame the interior wall with nailing blocks or a double stud extended from the end stud to fit between the two bracketing studs in the exterior wall. Then fasten from both sides into the nailers.
Framing at openings, such as doors and windows, are another area that requires a little special attention. First, any opening that breaks the regular spacing of the studs requires a header, or lintel. Headers are typically constructed of at least a double ply of 2x lumber sized to support the structural loads carried. An additional ply of 1/2" plywood is often sandwiched between the 2x plies to make the total width of the header 3-1/2", the width of a 2x4, for easier framing. Headers are also often constructed with 2x12 lumber both for strength and ease of framing. To illustrate, a wall's nominal height is 96", a doors nominal height is 80", subtracting the double top plate, 3", 2x12 header, 11-1/4", and a 2x4 nailer plate, 1-1/2", leaves a height of 80-1/4" for the door opening. Smaller sized headers might require additional cripple framing to meet the desired opening height. Headers require support studs and should not be toe nailed into the adjacent stud. These shorter studs supporting the header are referred to as "jacks" or "trimmers". Although for light loads a single jack may be used at both sides of an opening, a double jack is recommended along with double studs at heavy loads or wide openings. The windowsill is a low wall, a cripple wall, framed between the structural jacks to the sill height and is non-structural.
Interior non-structural walls, partitions, do not require the same framing as structural walls. Single top plates can be used and headers at doorways are not necessary. The wall widths can be reduced by either turning the 2x4's sideways in the framing or using 2x2 lumber.
There are two styles of framing with light frame construction, balloon and platform..
Balloon framing is utilized in two or three story structures where long lumber components are available or tall open areas require continuous framing members. In balloon framing the studs are continuous from the first floor support to the second floor top plate with the floor joists faced nailed to the inside of the studs. There are disadvantages to balloon framing. First the availability of the long lumber required. Balloon framing was popular in the nineteenth century when long lumber from virgin forests were readily available. Second is the lack of an integral working platform during construction. Until the floor framing is in place, scaffolding is necessary to reach the top of the walls. Third is the creation of a path for fire. Unless mitigated by the use of fire stops, a fire can travel readily from floor to floor in a balloon framed building.
Platform framing utilizes shorter lumber to make wall panels for the individual floor levels. The floor framing is then set on top of the framed walls to create a platform that can then be used as a work area to build the next level. Platform framing is the most common framing method in modern construction and eliminates the disadvantages of balloon framing.
Fastenings
How framing is fastened together is as varied as the types of framing. Early light framing, such as huts, would be lashed together with leather strips or twine made of fibers. Timber framing required skill intensive dovetail, or mortise and tenon joints pinned together with wooden pegs. Modern timber framing still makes use of mortise and tenon joints, but often utilized metal spikes, screws and bolts instead of wooden pegs. Steel framing can be riveted, screwed or welded. Modern light gauge steel framing typically uses self-drilling, self-tapping screws. Wood Frame construction typically used nails for its basic fasteners. Wood screws can be used in lieu of nails.
Metal nails have a long history in civilization. Nails were first made by hand forging. In the eighteenth century nails were cut from sheets of metal. Modern nails are extruded metal wire with a head and chisel point. Nails come in standardized sizes of diameter and length that are referenced as penny sizes. The term comes from pre-industrial England where a price per 100 nails was set in pennies, such that 100 3-1/2" nails could be bought for sixteen pennies, or 100 3" nails for 10 pennies. The penny size is denoted as the small letter 'd', which is believed to have come from the name of a roman coin, the denarius, the equivalent to the English penny. So, a sixteen-penny nail is noted as 16d, a ten-penny nail is noted as 10d and so on.
The rule of thumb on fastening wood is to use a nail twice the length of the wood thickness being fastened. So to nail 2x4's you should use 10d nails. When constructing a wood frame wall panel the studs should be attached to the top and bottom plates by nailing through the top or bottom plate into the stud using two 10d nails per stud. The second ply of the top plate should then be attached using 10d nails at 8" O.C. minimum with the splices nailed at 3" O.C. Attachments at corners and wall panel joints should also be 10d nails at 8" O.C. Headers should be nailed together from both sides using 10d nails minimum at 3" O.C. edges and 6" O.C. throughout. Although nails should always be driven perpendicular to the face of the wood, there are times when you must make attachments by driving the nail at an angle through the wood into the nailer piece. This type of nailing is called toenailing and is used to attach rafters to ridge beams, retrofit studs into walls, etc.
Screws and bolts can also be used to fasten wood framing. Wood screws can be used in lieu of nails in framing and have superior pull out strength, but screws do not have the shear strength of nails and should be used only where shear forces are minimal. Larger lumber and timbers can be fastened together using lag bolts or thru bolts. Primarily used to attach beams to the face of posts and columns or to connected the plies of a beam or girder together, lag screws and thru bolts are used where large shear loads are present.
Diagonal Bracing
Wall framing is a rectangular construction and therefore susceptible to racking. To prevent racking some form of diagonal bracing must be applied. One method is to use 1x4 diagonal bracing nailed onto the studs. This brace can be simply nailed onto the face of the studs on the inside if you are building a shed or garage and not planning on sheathing the interior of the framing. If both faces of the framing are to be sheathed, you can inset the 1x4 into the studs. This done before standing the wall section up. Lay out and mark the diagonal brace, then set the saw blade on your circular saw to a 3/4" depth and cut a series of cuts to remove the wood for a notch where the bracing will go. Set the 1x4 in the notch and nail to the 2x4's with 8d nails. Metal straps can be substituted for the 1x4 and will eliminate the need for notching the 2x4's. If you are utilizing a sub-sheathing under stucco, lap siding or masonry veneer, the sub-sheathing ca be applied at a 45° diagonal. Shearwall corners are another option. Applying plywood panels at the corners of the framing will create a shear panel and effective diagonal brace. The rest of the wall will have to be sheathed with an insulation or other cheap board the same thickness of the plywood. Plywood panel skin stressing is an effective diagonal brace and can eliminate stud clips in hurricane prone areas. Applying 1/2" cdx plywood to the exterior of the framing and fastening it on with 8d nails at 8" O.C. and 4" O.C. at panel edges serves as both shearwall panel and uplift connection from bottom plate to top plate.
Well, that's the basics to framing a wood wall. A continuation of theis article about framing floors and walls will be following shortly along with diagrams of the framing techniques. I hope this has helped and that you have enjoyed it.
Happy building!
Written by: Geoffrey M. Duggan