The height of tight: Vapor and control layers

 “Wow, that 3D image Dave put in the drawings of that tricky over-framing looks tight!” “Can you believe how tight that sauna came back together at Chris’ project?” “We need to get those cabinets installed to keep the tight schedule with our countertop subcontractor.” These are commonly heard uses of the word “tight” at A1DesignBuild.

When we talk about things being tight, we usually think about schedules or how well Eric installed the crown moldings on some kitchen cabinets, or the level of detail put into one of Sharon’s designs. Tight! Achieving tightness means having excellent systems, a well-developed plan, and a team of designers and builders that can execute their craft with precision.

Designing, specifying and installing control layers

In the high-performance home realm “tightness” takes on heightened meaning when it comes to what we call the control layers — the building envelope components that manage air, water and vapor. The tighter these components are, the better the home’s energy performance, air quality and durability.

Chief among them are the weather resistant barrier and the tapes used to seal seams and penetrations to the building envelope. Which is why designers are now faced with creating tighter drawings with details that define how these control layers are designed, specified and assembled. These details and products will determine the durability and performance of your home.

The accuracy of these drawings and details enables our builders to install with precision. Once designed, A1’s estimating and project supervision staff research what are often new products and techniques, so we can have the tightest understanding when it comes time to build.

Project schedules, from design to build, must be developed so that we can meet the tight deadlines of our clients and subcontractors. Current tightness in supply chain and staffing shortages need to be understood. High performance home products are not always readily available, and some can take several weeks to receive. We must also ensure that our builders and subcontractors are all trained to understand what it takes to properly execute the assembly of these systems.

Testing

Once our builders have installed all the necessary components, the tightness of these control layers is not easily seen. Sure, we know the water will not get in — that’s easy to see during construction. But what about air, and vapor? We can see that the building wrap is installed properly with no visible holes. Looks tight. The windows have all been taped and sealed properly. Tight. We have connected the layers to create a continuous “balloon skin” envelope. More tightness.

How can we be sure the work will be tight enough to meet high-performance standards? Washington state building code requires air changes under five per hour. We target under 0.6 and have achieved exchanges as low as 1.1 per hour. For a house that meets code, the collection of holes that leak air through the envelope would be the size of a three-foot circle; on a house that meets the high-performance .6 per hour standard, that hole would be equivalent to the size of a business card—thus netting a 60-70% reduction in the building’s energy consumption (Passive House Institute US).  

Because we use products for our air control layer that double as vapor control, we can test the tightness of our air control layer to be sure we are tight enough to control vapor. We have special equipment to test the envelope at key stages of the project to understand how much air leakage exists and where it’s coming from. We not only collect important data to ensure the control layers are at standard, we also collect thermal imaging of the building envelope and perform air quality tests of the conditioned space.

We at A1 have always taken great care in having things look tight; we are accustomed to tight schedules, can work in tight spaces (some from home for over a year now), and now we create some of the tightest buildings in Whatcom County. We understand one of the most important measures of a high performing home is the level of comfort you feel inside it.

The tightness of the control layers is what provides this comfort, and we take extreme care when designing and building them.