Books could be written on this topic, so for the sake of time and space we will concentrate on the basics you as a customer should look for, ask about and insist upon from a contractor or builder you hire to construct your garage. We will assume we are building off a monolific turn down slab, although framing off a block foundation is very similar with the exception of the seal plate being a 2×8 treated instead of a 2×4 treated. In both cases ½” anchor bolts should have been installed about 3″ above the slab or blocks when the concrete was poured.
In most cases walls will be framed of 2×4’s 16″ OC unless the wall exceeds 10ft. then 2×6, s will be required. The bottom plate of the wall should always be treated, since it will be in direct contact with the slab or blocks. The top of the wall should be doubled, for extra strength. Corners should be triple 2×4’s creating nailers for future interior finish.
Walls should be sheeted with OSB or ½” plywood. Most codes require that structural sheeting be nailed every 6in. along the edges and 8in oc in the center of sheeting.
Headers are simply the head piece for your framed opening, doors, windows, the size of these headers as determined by the with of the opening. for standard walk in doors and windows a double 2×8 is usually adequate. Garage doors also require headers but must be much more substantial, again based on the width, and placement. Garage door framed in gable ends will require less of a header, than those framed in the eve side, since the eve side will be carrying the roof loads. Garage door headers in the gable end are usually doubled 2×12’s, those framed in eve side walls normally will require a double LVL type header. Most lumber yard can assist you in sizing your headers, just ask. All headers should have jack studs. Jack studs are studs that extend from the bottom plate to the bottom edge under your header.
You basically have two options here, trusses or stick framing. Trusses are simpler to use and very common in garage construction. Trusses are pre-engineered for structural and snow loads for your particular area.
Common installation allows for trusses to be set on 2ft. centers. You can have trusses built with the desired overhangs built in, which simplifies over hangs drastically. Stick framing will require that rafters be sized according to the span. A Ridge beam must be used when stick framing and should be a min. of one size larger than the rafters. The ridge beam is the peak member that the rafters are attached to at the top. When stick framing collar ties should be used to prevent the rafters from separating. Collar ties are attached from one side rafter to the other. Weather you are using trusses or stick framing gable bracing, which is angled from the gable wall back to the bottom cord or collar tie should be used. Roof sheeting is generally 7/16″OSB or ½” plywood. If your roof system is framed 2ft. on center plyclips should be used at the butt edges of roof, sheeting, to prevent sagging of the sheeting between rafter or truss bays
This article is not intended to be a do it yourself step by step, framing instructions, its intended purpose is to educate a home owner of what to look for and questions they should ask a prospective contractor when building a garage. As always you should make sure your contractor is licensed /bonded/insured and pulls all appropriate permits to insure your garage is built following all city, county, and state regulations.