Tightening up to Zero: the Blower Door test Blowout!

Creating a tight envelope is a critical goal in shooting for a zero energy home. And it is not enough to simply apply the correct techniques and materials, it is essential that we have a measure of their effectiveness. This is where the blower door test comes in. A blower door test is a diagnostic tool designed to test the air tightness of buildings.

A blower-door fan is sealed into an exterior doorway, all the house vents are temporarily sealed, and the calibrated fan blows air out of the house creating a pressure difference between the inside and outside, which draws air into all of the inadequately sealed cracks, holes and penetrations. A pressure sensing device is used to measure the rate of pressure change/leakage. The data is entered into a standardized formula and the number of Natural Air Changes per Hour (NACH) is derived. Typical production-built homes built under current building codes will score at about 0.5NACH or higher (one complete air change every two hours). A well built, near zero energy home aims for a score of 0.1-0.2NACH. EarthCraft Virginia officials, including Chuk Bowles, Technical Director (tending to the pressure monitor above) and KC McGurren, Executive Director, supervised the testing of our home this week.

As KC is indicating in the picture, the results were encouraging! We registered a score of 0.16NACH, reflecting approximately one complete air change every 6 hours, approximately 3 times tighter than a well built new conventional home! Mark Waring, our builder, said that he was very pleased with this performance, which reflects the tightest home he has built to date. This tightness will minimize the heating/cooling load, reducing the demand on the geothermal system and putting less draw on the solar PV array.

Insulating our way to Net-Zero: Loose-Fill Cellulose

The last piece of the insulation puzzle is wet-spray cellulose's "poor relative", loose-fill cellulose. Loose-fill cellulose is made of up to 85% recycled paper and is sprayed dry with air, providing an R-value of 3.8 and blocking air leakage. Less expensive than both Icynene and wet-spray cellulose, our builder used it primarily in accessible, flat areas, sometimes using netting to hold it in place or offer support.

And the last piece of the insulation puzzle, would be fiberglass. To quote our builder, "in the inside walls for inexpensive sound insulation, that is the only place you will find fiberglass in one of my homes." He exaggerated a little, as he also used it (CertainTeed DRYRight) in the outside eaves, to form a barrier to spray the cellulose against. His opinion is that fiberglass is poorly suited to do its primary job, to provide insulation and to prevent air infiltration. To accomplish these tasks, the fiberglass must be installed perfectly, fitted precisely into all the nooks and crannies and sealed consistently around each and every opening and penetration. This is very time-consuming, labor intensive and challenging, as anyone who has attempted to apply fiberglass batt insulation can attest. It also tends to lose R-value across time and offers minimal thermal mass.

Insulating our way to Net-Zero: Icynene

Another integral part of creating a well sealed and insulated space involved the use of Icynene spray foam insulation. Icynene is a 100% water-blown insulation that sprays on as a liquid and immediately expands to 100 times its volume in soft foam that fills every crack and crevice while providing a flexible seal and a R-3.7 insulation value. It does not out-gas or emit any harmful fumes and it retains a stable R-value across time. It is an open cell foam, so it does not block the movement of water vapor. Icynene is a petroleum-based product (Icynene-R is a new product based on castor oil)that is a flame retarding material that will be consumed by flame, but contributes no fuel and will not sustain fire upon removal of the flame source. It must be covered by an approved thermal barrier, which our builder will accomplish by seperating it from living space with drywall.

More expensive than wet-spray cellulose, but less expensive than closed cell spray foam, our builder chose to selectively use it in hard to access or otherwise challenging areas, like the vaulted ceiling, where it clings tightly in place, helping form a continuous, insulating air barrier. Seven inches were sprayed along the roofline, for an R-25 insulation rating. EarthCraft specs say R-20 Icynene is equal to R-30 of fiberglass or cellulose on vaulted surfaces.

Note in the pictures that all ducting is being kept in conditioned space, increasing energy efficiency.

Insulating our way to Net-Zero: Wet Spray Cellulose

Our builder put a lot of thought into deciding what insulation to put where, balancing effectiveness against cost. One of his favorite products is wet-spray cellulose insulation, in this case from Applegate Insulation, a product that requires one fifth of the energy needed to produce an equivalent amount of fiberglass. Made from 85% recycled paper content, largely newspaper, and treated for fire and mold resistance with borate and with a dry adhesive, it is sprayed under pressure into the cavity with a small amount of water, completely filling all the nooks and crannies, reducing the flow of heat and virtually eliminating air infiltration. After completely filling the cavity, a rotating stud scrubber brush is run over the area, leveling it even with the tops of the studs. The cellulose will dry over the next 24 hours, becoming firmer to the touch. No dangerous outgassing is involved, as it does not contain any formaldehyde or respirable microscopic fibers.

The finished surface is quite smooth and spongy to the touch, and the 3.5" of cellulose provides an R-value of 13.3, which when added to the R-3 of the SIS (Dow Structural Insulated Sheathing) on the outside, results in an overall stable R-value of 16.3 for the walls. Our builder believes that the superior air sealing power and the added thermal mass provided by the wet spray cellulose make that R-value a conservative estimate. It is notable that contrary to initial impressions, wet spray cellulose is quite fire retardant, a result of both the fire retardants applied to the paper and its heavy oxygen-limiting density, providing up to a 50% increase in fire resistance. It is also a very good product with respect to air quality, as indicated by the American Lung Association of Virginia choosing to use it in it's Breathe Easy headquarters.

Richmond Virginia Zero Energy Home Progress & Appearance

It seems time to show how far the house has progressed and at the same time illustrate that a ZEH does not have to look unconventional. Placing the Schuco PV panels on the back of the south slanted garage roof aided in this outcome, as they are nearly unnoticeable from the street. I would add that the unusual ceiling planes of the pictured great room have caused Mark, our builder, a lot of thought in terms of where to set the boundary for the conditioned space, how to keep the HVAC ducting in those confines, and where to use loose cellulose versus spray foam insulation. It is becoming increasingly apparent how challenging it is to take the basic principles of a ZEH and translate them into a workable application.