By its very nature, a wall is an environmental separator—it’s job is to keep the outside out and the inside in. How we do that has been beguiling architects and builders for centuries. One thing hasn’t changed: No matter what material you use to build your wall — rocks, thatch, logs, sticks, fiberboard or steel — it needs four principal control layers:
- a water control layer
- an air control layer
- a vapor control layer
- a thermal control layer
This priority order is also important. If you can’t keep the rain or groundwater out, don’t waste your time on the air. If you can’t keep the air out, don’t waste your time on the vapor, and so on.
In the last decade, the construction industry has gotten pretty good at combining the water control, air control and vapor control into a single layer that can be a coating (spray and rolled on) or a membrane (housewraps and films). We have also gotten pretty good at wrapping the exterior of buildings with the fourth control layer – the thermal control layer. In fact, some products, when installed properly, can act as all four layers.
But “pretty good” is no longer good enough. New building codes are helping reshape the perfect wall. Not only do the code changes require more insulation on the exterior of the building (called continuous insulation) and better air tightness, it forces the builder to consider different products all together. Thankfully, product manufacturers are providing more multi-functional products, i.e. rigid insulation and sheathing, which, in many ways, make things simpler.
Bottom line: whether it’s the International Code Council (ICC), International Building Code (IBC), International Residential Code (IRC), International Energy Conservation Code (IECC) or state-specific amendments, building codes are driving improved building performance.
Here’s what you need to know:
Know Your R-Value. The 2012 Code per table 402.1 code requires more insulation in/on our buildings. It smartly addresses R-value, or measure of insulation, for the WHOLE assembly taking into account thermal bridging, be it the wall, ceilings, floors, slab, basement or crawlspace. Thermal bridging occurs when framing or structural members transfer heat faster than the wall’s insulated cavities which means buildings don’t maintain their interior temperatures as well as they could. For example, the more wood framing in a wall, the greater the heat gain/loss b/c wood only has an R-value of 1. Concrete masonry units are even worse than wood with an R-value of R-0.5, and steel studs are by far the worse performing at R-0.02. The more studs, the greater the heat loss. To combat thermal bridging, all wood framed walls in climate zones 6-8 must have exterior insulation installed over the framing. Climate zones 3-4 now have to either install R-20 in the wall cavity or they can do R-13 cavities with R-5 continuous insulation.
Concrete foundations must also have Styrofoam sheets on the exterior bottom and sides to ensure sufficient insulation. Instead of calculating the amount of insulation needed just for one wall cavity, you now need to calculate the R-value of the whole wall to meet regulations: no more thermal bridging and no more air pockets prone to mold and other climate-related damages.
Know Your U Factor. A U-factor is a rating based on how much heat loss a system allows. U-factors generally range from 0.2 (very little heat loss) to 1.2 (high heat loss). The U-factor is the inverse of the R-value, which measures insulating value. One of the most effective means of achieving a low U-factor and minimizing heat loss from thermal conductivity in the wall assembly is by installing continuous insulation outboard of the metal studs or sheathing.
According to Walls & Ceilings magazine: ‘Continuous insulation’ is an insulation that is continuous across all structural members without thermal bridges other than fasteners (i.e., screws and nails) and service openings. It is installed on the interior or exterior wall system or is integral to any opaque surface of the building envelope. Builders and contractors can consider employing stucco over CI or newly-improved EIFS claddings as a way to achieve relevant U-factors.
Air Tightness Testing. An airtightness test is a whole building test that measures how easy it is for air to leak through a building’s enclosure or “skin.” Since the 1980s, airtightness testing has been performed on high-performance housing, however the 2012 IRC and the 2012 IECC® codes require testing of every new home. Given the potential for energy savings, as well as the management of indoor air quality and condensation risks, it makes sense to test buildings of all sizes for airtightness. Increasingly, blower door testing crops up as a required measure for new construction, under programs like ENERGY STAR® and the Department of Energy’s Zero Energy Ready Home. IECC lists a mandatory air leakage of ≤5 ACH @ 50 pascals in Climate Zone 1 and 2, and ≤3 ACH @ 50 pascals in zones 3-8. These specific test requirements are calculated on the flow rate of air produced by a blower door at a specified pressure (50 pascals or 0.2 inches of water).
Now Trending: Exterior Rigid Insulation. Also known “outsulation”, this is the construction practice of placing a layer of insulation on the exterior side of the building to provide thermal resistance to walls, foundations, and roofs. You can read more about exterior rigid insulation here.
How have new building codes impacted your job site or material selection?!