What to Know About Construction Sequencing in High Performance Projects

This post first appeared on the Green Building Advisor website.

I was a builder for more than 10 years before I attempted my first above code building project.  There was an order in the way I built early in my career that usually kept my projects moving smoothly.  That schedule went out the window with my first attempt at constructing a higher performing home.

Integrating high levels of air tightness, greater R-values, along with other elements to improve performance can result in assemblies and installation details going out of order from traditional construction practices.  The easiest and most logical construction schedules often need adjustments.

Here’s an example, performing an early blower door test.  Building codes only require a blower door test at the end of construction, after the home is finished.  This can work if your air sealing details are easy to execute and you are only looking to satisfy the code with the pass/fail test result.  When a building has more stringent air tightness requirements, like the 0.06 CFM per square foot of surface area (used to be 0.6 ACH50) requirement of PHIUS, or the home has a complicated design, it’s best to perform a mid-build blower door test or even multiple tests during the build.  This requires the air control layer to be complete.  Not too much of a problem when using the building sheathing, both walls and roof as the air control layer.   What happens if there is a vented attic?  Do you temporarily seal the attic space?  Install the ceiling drywall or a membrane before any of the mechanical/electrical/plumbing (MEP) systems are installed?

Designing the building so that only the exterior walls are all that’s required for structural support will allow for the installation of the ceiling air control to be continuous and installed before MEP systems (there are other methods to create an airtight lid).  This allows us to test the air control layer before any holes are created by the MEP.  If you are working with sub -contractors unfamiliar with this type of construction, there will be many questions and discussions.

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This photo shows a blower door test being conducted on a home with an attached garage, the separation of garage and home was needed for the test even though construction of the space was not complete.  The pillowing membrane between the spaces is the result of the pressure difference between the spaces.

Installing the membrane would typically happen after insulation was installed.  Because the home was tested early, the electrician and plumber had to adjust the methods they would typically use.  This results in out of order sequencing (and sometimes complaining, especially with subcontractors that have not bought into high-performance construction).

Here’s another example specific to projects I’m often involved in, frost protected shallow foundations.  We used to have the foundation poured with the slab edge insulation integrated with the foundation form, casting the insulation and concrete together.  Another option we’ve used is a manufactured form.

I prefer to seal the wall framing directly to the concrete slab edge using a tape designed for the application (again, there are other methods that can be effective).  This air sealing connection can’t happen if the slab edge insulation is present, the insulation will have gaps and cracks where air can move through.  I’ve changed my method to add the slab edge insulation after the exterior walls are built and slab to foundation air sealing is complete.

This adjustment to how I used to construct a home’s foundation created an extra step, leveling the ground around the foundation so we weren’t tripping over piles of dirt or having unstable surfaces to place ladders and scaffolding.  Using this method will require re-excavating the slab edge of the shallow foundation to install the slab edge and horizontal wing insulation required for the frost protected shallow foundation design after the exterior walls are constructed.

In a project I currently have under construction, there will be a layer of continuous exterior insulation installed.  Where to locate the water resistive barrier depends on the type of insulation used.  In this project, we are using fibrous rigid insulation (Rockwool ComfortBoard 80) as the CI, the WRB will be located at the sheathing layer because the WRB and wall sheathing will be our primary air control layer (there are lots of ways to design this detail).  We will need our exterior MEP penetrations in place, or at least well planned out before adding the CI so that these penetrations can be effectively water and air sealed before the insulation is installed.  This may require additional visits by the MEP contractors.

These are just a few examples of how construction schedules may need to be adjusted when building higher performing homes.  It’s been my experience that extra steps, extra visits, or at a minimum, thorough planning between a builder and subcontractors is required.  I’ve found that explaining why there is a needed adjustment in the schedule helps, often the discussions that ensue will lead to developing alternative methods to improve scheduling.  Modern building practices require understanding and cooperation from everyone involved.  Working as a team will provide the best outcome.

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