I’ve been writing (yet to be published articles) about wall framing techniques off and on for a few weeks and haven’t defined your basic wall. These are the 2×4 framed walls contractors have been building basically since forever (or at least since the end of World War II).
The push for new housing in the Baby Boom era meant the need for fast, easily repeatable construction. Mass production of nails, lumber and finishing materials moved jointly with rapidly standardized building techniques. Decades of different style houses were constructed with fundamentally similar bones. A 40′s Cape Cod has the same triple stud corner as a 60′s Ranch or a 2000′s McMansion. It is this baseline which all our advancements in framing concepts are measured.
What is a Standard Frame?
Standard framing is 2×4 vertical studs (later 2×6 studs) spaced 16 inches on center (for non-nailing folks, 16 inches on center means 16 inches from the center of one stud to the center of the next one). There’s a single stud bottom plate and a double stud top plate for strength. In the corners, a third stud is added to hang dry wall. The cavity is insulated with either fiberglass or cellulose. The exterior is sheathed in plywood or OSB, then wrapped with a water resistant barrier (#15 building felt in older homes, Tyvek in newer construction), then finished with whatever siding/cladding is desired. As construction goes, pretty straight-forward and definitely time tested.
The advantages of standard framing stems from its familiarity. All the bugs have been worked out and odds are any contractor doing the work has been building these walls for decades.
Moisture – The first test for any building assembly is moisture. Odds are good (depending on the climate), that a building will be rained on before, during and after construction of the building frame. Moisture management is all in the details and with standard framing, those details were hammered out decades ago.
The exterior siding physically protects the house from driving rain and elements, while the water resistant barrier and rain screen allow draining and drying.
The vapor controls are located based on the climate zone, generally speaking on the inside in heating climates and the outside in cooling climates (the South). All of these points along with necessary flashing and exterior detail work are a well-understood piece of standard framing.
Ease of Installation – Another advantage closely tied to familiarity is the ease of construction. Other techniques can be installed faster or more easily. Advanced framing has much less wood and many less joints to fasten and SIPs arrive on site with the entire wall assembled. But the speed of those systems depends on a knowledgeable installation crew. Standard framing excels because of the universal comfort with all contractors involved. Additionally, all materials and supplies are standardized and universally available.
Cost – I love when I run into redundant statements. For all the reasons I just mentioned in the ‘Ease of Installation’ section, standard walls are very affordable to assemble. This is huge since for many homeowners, up front cost is the first, last and only consideration.
Let’s just say that there are reasons we’re moving to other framing techniques and skip to the particulars.
R-Value – 2 x 4 framed standard walls have thermal performance woefully below that of modern code insulation requirements and that of any comparable modern wall assembly. Even bumped up to 2 x 6 studs, allowing 2 extra inches of insulation, the thermal performance is still substandard. All the extra and redundant stud board results in heavy thermal bridging, deeply compromising whole wall R-value.
Thermal Bridging – Closely tied to R-value is thermal bridging. Any attempt to improve the insulation of a standard framed wall is hamstrung by the heavy thermal bridging of all the wall studs. Newer energy codes have requirements for continual insulation to attenuate thermal bridging. All advanced wall construction approaches improve on it.
ICF and SIP walls are constructed from continuous insulation elements, external foam board installs a sheet of insulation over the wall and advanced framing eliminates a great deal of extraneous framing wood, reducing the thermal bridging. All these other approaches address thermal bridging and have better whole wall R-values.
Air Leakage – Standard wall framing can be quite air tight but rarely are. The challenge lays in the interior wall facing which in cold climates also serves as the vapor barrier. The interior air barrier needs to be sealed around outlets, windows, doors, wiring chases, plumbing, heating pipes, the baseboard, etc.
By contrast, SIPs come pre-constructed and air sealed around all windows and doors, reducing the air sealing needs to the connecting splines. The insulation used is another air sealing advantage. EPS, XPS and spray foam are all air barrier materials. The fiberglass and cellulose most often used in standard construction are not air barriers. Standard framed houses can be made quite tight but newer approaches are inherently more so.
Materials – The standard wall framing is just that; the standard against which we judge other walls. That said, advanced framing eliminates excess wood studs.
Green – Standard framing is not the greenest of options. The frame includes loads of excess material compared to advanced framing, the fiberglass has much higher embodied energy than cellulose and the R-value is vastly inferior to just about any other option. That means much more energy use.
Standard stud walls are a tested, yes, standard for residential construction. They work and work well as far as they go. As the energy code standards, other insulation approaches and wall assembly techniques are coming to the fore.