Structural design of wood-framed single-family homes
In the United States, the conventional construction technique for residential buildings (single-family homes) is that of light-wood framing. Additionally, dimensional wood lumber has economical and environmental properties such as:
- It is readily available
- It can be packaged neatly because of its unit dimension.
- It can be easily transported to work sites
The services of an architect or construction contractor is necessary for designing a light-framed residential building. However, in the case of an alternative design approach or a design beyond the scope of the building code, a structural engineer’s services is imperative. A structural engineer’s involvement will result in improved quality, structural and financial safety of the home design. In any case, the foundation design, steel framing design, or engineered product specification are best handled by a structural engineer.
This article features the design of a typical light framed building.
DESIGNING A WOOD-FRAMED US RESIDENTIAL BUILDING
In the design of light-framed buildings, construction of the roof, floors and walls (structural assemblies) is with nominal 2” lumber members with nominal depths ranging from 4-12”. to ensure stability and safety, sheathing the structural assemblies with structural wood panels (for example; plywood or oriented strand board (OSB)) is imperative.
US homebuilders prefer the use of wood as structural materials. This is becausef:
- Wood framing method is common in the US construction industry.
- The dimensions of wood are small; therefore, they can be transported with ease.
- Erecting a wood-framed structure does not require special or large equipment.
This article will illustrate the full process of designing a wood-framed US residential building. To accomplish the design, the US methodology and basis, will be incorporated. Below are the major aspects of this article:
- What designing single-family homes entails
- Applicable design codes,
- External loading assessment for residential structures.
The load-bearing wall frameworks are the essential segments of a structure’s enclosure, and the structural properties of the wall framework are just one of the numerous conditions that must be considered. While cladding similarity, thermal execution or the hygrothermal attributes of a wall framework are significant, such perspectives are not the focal point of this article and won’t be talked about.
APPLICABLE CODES AND STANDARDS
The IRC is the predominant building code utilized for the development of a couple of residential buildings in the USA. to erect a residential building, the homebuilder should initially apply to the neighborhood code office for a building permit. It is important to give a total engineering plan set itemizing how the builder means to conform to the prerequisites of the IRC, alongside a few different things, for example, the manual J heat loss-gain figuring for the structure and determination of energy compliance path. The IRC to a great extent gives a prescriptive premise to home structure and in numerous occasions is sufficient for single-family home design. The envelope and structural parts are normally chosen by the architect, manufacturer, or mortgage holder from configuration tables inside the code. Whenever pre-assembled engineered segments, for example, I-joists, overlaid facade blunder (LVL) segments, or rooftop supports are utilized in design, a structural engineer is required to audit their specification and application.
This is normally the degree of a basic structural engineer’s association in residential design other than specific circumstances not secured by the IRC and incidentally foundational design. Whenever engineered structure is essential related to the prescriptive standards, at that point consistence with the 2015 International Building Code (IBC) necessities for those segments of the structure is required. Specialists will direct their investigation dependent on prerequisite set out in the IRC, IBC if essential, and ASCE 7-10 minimum design loads for structures and different structures (ASCE 7) [ASCE represents American Society of Civil Engineers]. The IRC and IBC likewise grant architects to refer to the 2015 AWC Wood Frame Construction Manual (WFCM) for an option prescriptive or designed methodology [AWC represents American Wood Council].
EXTERNAL LOAD DETERMINATION
Dead load (DL)
Dead load is the load that is consistently and constantly applied to a structure. Commonly, dead burden alludes to self-load of the material utilized in development/construction or a load that is applied in a lasting nature, for example, a known area of a peice of heavy gear or a huge island in the kitchen. Except if noted generally, the S&A Homes dead burden criteria will be utilized for the wood-framed design of this home
Live loading is a gravity loading that is brief or irregular in nature. The three live loads considered for the plan of this house are floor live (LL), roof live (RL), and snow load (SL). The IRC recommends the minimum uniformly distributed loads that must be utilized by architects for resident structures.
Lateral loads are loads acting on a structure horizontal to the ground. The most common lateral loads are wind and seismic loads.
Notably, In California, seismic loading typically controls the design of structural components. Therefore, in this article, lateral loads refer to wind and seismic loads. It is necessary to determine the seismic loading and wind loading.
The principle serviceability criterion considered in the design of residential homes is deflection. The IRC recommends the maximum allowable deflection of structural members and assembly. Excessive deflections can mess up the inhabitants and conceivably harm nonstructural segments, for example, cladding or fenestration. Excessive interior floor deflections are commonly seen as floor vibration or “spongy” floors. Excess deflection of rooftop individuals can prompt ponding and eventually dampness issues or over-burdening of structural members.
Combination of loads
Both allowable stress design (ASD) and load resistance and factor design (LRFD) load blends will be used for various parts of the home structural design. For instance, the ASD approach will be utilized for wood design, while the LRFD approach will be utilized for concrete foundation design. Approaches for the plans will be properly discussed. The load combination that will be utilized for design are recorded below and are recreated from ASCE 7.
ASD load combinations
LRFD load combinations
In the above load combination, the documentation is characterized as follows: D for dead burden, L for live burden, Lr for rooftop live load, S for snow load, R for rain load, and W for wind load.
DESIGN OF SINGLE-FAMILY HOMES
Wood is the most prominent material utilized in the USA for the development of single-family homes. Framing timber is effectively gotten in many areas. The units of construction can be effectively transported by contractual workers or home owners without the requirement for a particular equipment. Furthermore, the erection of a wood-framed structural system is recognizable to most and doesn’t require exorbitant measures of specific information or equipment. Ultimately, wood-framed construction has been very much documented in the USA, and many design aids are accessible.
As noted previously, a significant part of the wood-framed structural design can be cultivated utilizing design aids. The design professional will regularly utilize these design aids to the best degree conceivable and afterward perform structural analysis and design that is beyond the scope of the plan helps. This is the methodology that will be utilized for this investigation. The related calculations aren’t given because of space confinement; just the vital outcomes will be referenced.
External load transfer (load path)
- Gravity system design
- Roof sheathing
- Engineered roof trusses
- Exterior walls
- Headers within wall system
- Above-grade floor system
- Girder sizing
- Adjustable columns
- Foundation design
- Foundation walls
- Wall strip footings
- Isolated pad footings
- MWFRS structure
- Overturning and sliding analysis
- Wall bracing
- Horizontal floor diaphragms
This article describes the designing of wood-framed single-family homes. Additionally, all the external loads faced by single family homes are discussed together with applicable design codes. The use of wood as structural materials is very common in the US.
Therefore, wood-framed single-family homes can be cost effective. In the United states, building codes are very important and most building codes now require the proper designing as opposed to conventional construction methods. This building code trend can be attributed to the development of high-risk areas or seismic zones.