Over the past week, Envinity has been sealing the home with expanding spray foam in preparation for the first blower door test. The home envelopes are designed to be very tight and let in as little air as possible–so little that fresh outdoor air will be mechanically supplied to and exhausted from the home. All penetrations from the outside to the inside are inspected and sealed so that the homes can run as efficiently as possible.
Envinity has finished installing the ductwork throughout the homes! All of the ductwork in each home is for the Energy Recovery Ventilator (ERV); since the homes are designed to be so tight, mechanical ventilation is required to bring in fresh outdoor air into the home. The ERV does this in a way that transfers the temperature of the stale, outgoing air to the fresh incoming air. This means that the homeowners get fresh air without having to use additional energy to heat or cool that air. Whatever additional heating or cooling that is required in the homes is done by a series of Air-Source Heat Pump Mini-Splits. There will be four ductless Mini-Split supplies throughout the home (one on the first floor and one in each bedroom) to efficiently heat and cool the home throughout the year.
Over the past week, Envinity installed the roof trusses to the GreenBuild homes. Similar to the walls, the roofs use ZIP panels to combine the sheathing and the weather resistive barrier into one building element. The interior framing use a combination of construction techniques. The previous post described the Optimum Value Engineered wall framing; the second floor structure uses open-web trusses with 16″ spacing while the roof uses manufactured trusses with 24″ spacing. The second floor structure is closer together to provide a bit more rigidity to the floor.
Over the past two weeks, the Envinity team has endured the cold and framed two homes! Each home is constructed with 2×6 studs using Optimum Value Engineering (“Advanced”) framing techniques, meaning that studs are aligned 24″ apart rather than 16″, which is seen in most residential construction. This allows Envinity to use less wood and leaves more room in the wall for insulation. The homes also have insulation on the exterior of the walls. The homes use a 2″ ZIP panel that combines the weather resistive barrier, the structural sheathing, and exterior insulation into one building element. The panel Envinity is using has a 1/2″ ZIP panel glued to 1 1/2″ polyisocyanurate insulation. When completed, the full wall will have a total R-value (the insulation value) of 28; the building code requires a home to have a wall R-value of at least 20, so the walls of these homes are nearly 50% more insulated!
The construction crew completed installation of the underslab insulation today. This insulation, 2 inches of extruded polystyrene (XPS), will keep heat from escaping the concrete floor slab into the ground, and it will help to keep the concrete slab dry. Below the insulation is a layer of crushed stone to ensure that all water is able to drain away from the slab, keeping it dry and free of cracks. Before Envinity pours the concrete slab, they will lay down overlapping sheets of 6 mil polyethylene as a final layer to protect the concrete slab from water and moisture. All of this protection will make the slab warmer but will also keep it lasting for decades without issues of cracking or breaking.