Advanced Framing Techniques
Advanced Framing Techniques
Advanced Framing or Optimum Value Engineering refer to framing techniques that reduce the amount of materials used to build a home while maintaining the structural integrity of the home. An optimum value engineered assembly tends to use less energy for space conditioning because the omitted (and redundant) structural components can be displaced with insulation. Accordingly, the user will note that some advanced framing techniques receive points for both
Additional Information / How to Implement:
Advanced framing elements can be applied independently, or adopted in the entirety, depending upon the specific requirement(s) of the project. Framers unfamiliar with the techniques may need training, and the initial use of these techniques may temporarily slow down framing operations. In general, more planning is needed to implement these elements.
In addition to the advanced framing techniques described below for wood, homes with steel framing can incorporate similar techniques using advanced framing techniques, including 24” o.c. spacing for steel floors and walls, described in the HUDUSER’s Prescriptive Method for Residential Cold-Formed Steel Framing (see Resources section of this line item for additional information).
Some of the benefits of advanced framing include:
- Reduced first cost (3 to 5% of framing cost)
- Improved energy efficiency (2 to 5% per year)
- Improved resource efficiency (less wood consumption and waste)
Advanced framing uses engineering principles to minimize material usage while meeting model building code structural performance requirements.
The following list covers different principles that form an advanced framing system.
(1) 24" OC Framing
Details: Wall and floor framing spacing can often be engineered for 19.2" (1/5 of an 8-foot sheet) or 24" on center (1/4 of an 8-foot sheet). Roof framing that utilizes trusses is most frequently spaced at 24". This strategy can be combined with modular layout and single top plate for added economy, but can also be used independently
Installation: Installation should be in accordance with manufacturer’s specifications and model building code prescriptive methods. Bracing and fastening schedules and sheathing thickness requirements increase with framing spacing.
Careful spacing of window and door openings will maximize the economy of wider spacing. Designs that are built repeatedly should include wall framing layout drawings to guide the framing crew. When first implementing advanced framing elements, crews are likely to be slowed down until they become more familiar with the method.
Benefits/Costs: Approximately one-third of the lumber can be eliminated from the wall and floor framing of a value-engineered house, over walls and floors spaced 16 inches on center. Floor joists may need to be deeper for wider spans, but the reduction in lumber required for the building usually offsets the price increase from having larger floor joists. The need for thicker deck sheathing will also offset a portion of the savings. A careful analysis or a trial prototype is needed to determine whether the wider spans make economic sense for a particular plan. In general, simpler plans designed on a two-foot module are much more likely to result in savings with 24" on center framing than are complex plans with odd dimensions and many small offsets. However, resource savings will occur regardless of economic savings.
Wider stud spacing contributes to energy efficiency by reducing the amount of lumber in a wall cavity. Since more insulation and less lumber is used, and since insulation has a higher R-value than lumber, increasing stud spacing increases the overall R-value of the wall system. Limitations: Floor decking, wall cladding, roof sheathing and interior finish material (such as gypsum wall board) need to be sized to span the added dimension without undesirable deflection. If floor joists are chosen that have wide flanges, this will reduce the clear span of the floor decking. Material fastening schedules and sheathing thicknesses become more stringent when wider spans are employed, which may affect quantities, installation time, and cost of accessories.
One-half-inch thick gypsum board will deflect somewhat more over 24" framing than 16” framing, although it is commonly used. An alternative would be to use half-inch “anti-sag” or 5/8” gypsum board.
Some manufacturers do not make insulation batts for 19.2" on center framing. Therefore, using this spacing in an insulated wall assembly may require changing type or brand of insulation.
In some markets, there is a perception that wide-spaced framing is a mark of inferior construction. Attention to all of the details of assembly, including fastening and bracing schedules, will assure that the system performs well.
Code/Regulatory: Model codes allow bearing walls framed with 2x4 studs spaced 24" on center or single top plates on bearing walls within defined structural guidelines. Designs in high-wind zones or with tall walls may not allow 24 inch on-center spacing.
(2) Single top-plate – exterior and bearing walls
Details: Single top plates are typically incorporated with advanced framing designs that include 24" on center framing. By stacking the wall and roof framing, it is possible to use a single top plate because the top plate merely transfers compressive vertical loads to the stud below. Steel plates or straps are used to maintain continuity of the plate in the absence of a second, overlapping plate.
Installation: Temporary bracing is needed to steady and plumb newly erected walls. As with all light frame structures, temporary bracing should be left in place until the floor and, or roof is completed to permanently brace the structure.
Benefits/Costs: In a 28' x 40' two-story house, the savings by eliminating second top plates in bearing and non-bearing walls is equivalent to eliminating about 35 studs. Because one plate is omitted, the amount of wall insulation is increased, slightly improving energy performance.
Limitations: May not work on homes in high-wind or earthquake zones. Requires purchasing a longer stud.
Code/Regulatory: Meets model codes in some designs, but is more likely than other OVE practices to raise questions from building officials.
(3) Single top-plate – interior non-bearing partitions
Details: Any non-bearing partition can be built with a single top plate.
Installation: Bracing is needed to steady and plumb recently erected walls. This bracing should be left in place until the floor or roof above the walls is completed, tying the structure together.
Benefits/Costs: Savings depend on the design’s linear feet of non-bearing walls. In a 2,200 sq. ft. home, the equivalent of 2 or 3 dozen studs are likely to be saved on interior walls.
Limitations: If used along with a normal double plate on bearing and exterior walls, two lengths of wall studs are required on the job, which could be confusing.
Code/Regulatory: Meets codes, but is more likely than other OVE techniques to inspire questions from the building official.
(3) Right-sized header or insulated box headers
Details: Instead of sizing all headers in bearing walls to accommodate the greatest load case, size each header for its actual load and span using the appropriate wood species. Also consider the benefit of using a deeper, single-ply, and engineered wood header.
If the tedium of framing different header depths to uniform head heights at openings is daunting, use insulated box headers that facilitate load transfer above openings and use fewer resources than 2-ply solid sawn members. Typically, a boxed header design consists of a top and bottom 2x4 on the flat, some end and interior cripples and a plywood face on one or two sides. The hollows in the header interior allow insulation to be added.
Installation: Headers of various sizes require framers to pay attention to plans and customize openings. An alternative would be to site-fabricate and insulate box headers of a consistent depth and install these in lieu of dimensional or engineered wood headers.
Benefits/Costs: Material cost and usage economies must be balanced against the chance of installing the wrong sized header and slowing down the framing process by making opening head framing inconsistent. Similarly, material economies associated with fabricating box headers of consistent depth will be offset by labor involved with fabricating these on site. The need to have an additional material, insulation, on hand at the rough frame stage makes the bill of materials more complex.
Reducing the use of large-dimensioned lumber is environmentally desirable.
Limitations: Without thoughtful implementation, right sizing headers could result in uneven window and door head heights. The practice requires cutting different sized cripples over headers.
Code/Regulatory: Model building codes include prescriptive methods for sizing headers and girders, as well as sizing and constructing box headers.
(5) No headers in non-bearing partitions
Details: Although it is obvious that headers are not needed in non-bearing partitions, it is not always obvious which partitions are load bearing and which are not. Thus, framers often put headers over every opening to be safe. Eliminating these headers saves both material and labor.
Installation: If a method of identifying the bearing walls versus the non-bearing partitions is included on the plans, the layout framer can determine which openings need headers. For instance, solid blue walls can denote bearing and uncolored walls would be non bearing.
Benefits/Costs: Saves material and labor cost, and conserves resources by reducing the use of wide dimension lumber.
Code/Regulatory: Model codes do not prescribe headers in non-bearing locations, although it may be necessary to demonstrate to the inspector that a partition is non-bearing.
(6) Ladders at perpendicular wall intersections
Details: Use flat horizontal blocking between studs to secure a perpendicular wall rather than solid vertical framing. (With 24" on center wall framing, three 22-1/2" scrap pieces are set at 24" on center vertically to replace two studs.)
Installation: Cutting and nailing three pieces of blocking requires approximately the same labor as installing two studs.
Benefits/Costs: Less lumber is used, and scrap pieces can be used for blocking. The horizontal blocking stiffens the wall junction. Most important, insulation in the exterior wall can be installed continuously behind the ladder frame.
Limitations: Blocking should be set so that it does not conflict with light switches and outlets.
Code/Regulatory: The system has no impact on model codes.
(7) Two-stud exterior corner framing or equivalent
Details: Only two studs are needed at an outside building corner, one at the end of each intersecting wall end. Any additional framing is needed only to support the gypsum board at the inside corner. Gypsum can be supported either with a flat stud, to leave an open-ended cavity at the corner; or with drywall clips, thus eliminating the need for a third stud.
Installation: If using a third stud for gypsum board backing, the extra stud can be a 2x4, even if the wall is composed of 2x6 studs.
Benefits/Costs: With a two-stud corner, one stud is eliminated. In all cases, the open cavity at the corner can be insulated along with the wall, eliminating the need for the framer to insulate a closed cavity before the sheathing goes on.
Limitations: Drywall clips are unfamiliar to some builders and subcontractors. Exterior corner trim or cladding may result in being secured to the sheathing only and not to the stud.
Code/Regulatory: More studs may be required at corners in high-wind or earthquake zone construction.
Availability: Drywall clips are readily available.
(8) Doubling the rim joist in lieu of header
Details: In thick wall construction, 5 ½” or greater actual wall dimension, it is possible to have the floor system rim board act as the header, or one member of a 2-ply girder or header assembly, at the door or window openings located below that member.
Installation: The joists that frame into this structural member will be shorter than other joists if the design requires a two-ply member to carry the span across the opening. Multiple-member headers should be properly fastened to assure load sharing.
Benefits/Costs: Some labor may be saved in framing the header, but extra labor and thought is involved in fitting perpendicular joists inside the two-ply assembly and framing the opening height down. The concept works best for long spans where the extra depth of the member or additional height of the opening is needed. The design is also an efficient method for use above openings in foundations.
Limitations: If the rim joist is intended to act along with the extra member (or by itself), it must be continuous across the opening.
Code/Regulatory: This is an unusual technique and may inspire questions from the inspector.