It’s a dark winter evening. You leave the house and as you emerge outside you feel the cold, fresh air and you pop up, feeling sharp, awake, fresh and lively.
The operative word is ‘fresh.’
Sure, the air is cold and that helps, but in reality we’ve been building sealed buildings since the 80’s with gasketed doors and windows, old drafty houses are becoming fewer. Modern housing is very well air sealed to prevent energy loss. However, the ventilation systems have not been developed and installed at the same pace as the air sealing.
So we need to get fresh air into our houses. We’ve needed more fresh air since the 80’s and as a population we’ve become used to poor air quality.
Yes building code does require ventilation, but often it’s switched and folks don’t hit those switches. We need ‘continuous ventilation’.
The best system is the Heat Recovery Ventilator (HRV). The outgoing ‘dirty’ air is blown out of the house, but before it leaves the heat is stripped out and imparted into the incoming ‘clean’ air. The HRV is always on, and has filters so the air really is clean. HRV’s can be 95% efficient, and in the Lake Stevens house the HRV reduces the maximum building heat load from 14,450Btu/h to 12,800 Btu/h.
The Zhender HRV’s we fit can have Co2 sensors, so they bring in more air when more folks are inside breathing. Also humidity sensors so moist air, the “building-killer,” is automatically removed. Manual boost switches and wireless control are all becoming standard.
The air is still dirty!
Ted Clifton, Co-Owner and Founder of TC Legend Homes, has an air quality monitor in his home. Cooking is a real problem.
The screenshot from Ted’s Footbot monitor shows that it took over an hour for the 200cfm balanced fan to remove the particulates down to the monitor-defined safe level. Ted was cooking hash browns and eggs on a Saturday morning. It is important to note that Ted’s 200cfm fan has a second 200cfm intake fan so it’s a balanced system and can be interpreted as a 400cfm fan.
The lesson is that range hoods are critical to maintaining indoor air quality and should really be sensor-activated. At TC Legend Homes we will be specifying more powerful units; perhaps 800cfm as standard. The presence of particulates indoors is linked to asthma.
The arrival of home automation will easily address this problem and a quick Google search for wireless range hoods yielded plenty of cost-effective models.
The next part of the test is to cook the same hash browns and eggs next Saturday, leave the range hood off, then we’ll see how long it takes a modern super home (Ted lives in the Bellingham Powerhouse) to clear the air with just the HRV.
SIPs are wall, roof (and sometimes floor) panels. Fabricated from a slab of foam sandwiched between two plywood sheets. Actually, it’s not ply it’s OSB (oriented strand board).
The sandwich-panels can be up to 24’x8’ and are made in the SIPs factory, in our case Premiere-SIPs in Puyallup. The doors and windows are cut-out in the factory, a stack of pre-fabricated house panels are loaded onto a trailer and arrives on-site where the SIPs are assembled… a bit like Legos.
Because TC Legend Builds affordable Net Zero energy houses, we use our crew to assemble the wall panels, man-handling them into place, but a crane can be used for walls. We do use the crane to set to thicker, heavier roof panels.
Our goal with SIPs panels is to create a continuous foam box, surrounding the inside of the home. When you remember that there’s 4” foam under the concrete slab, the 6” foam walls and 10” foam roof trap all the heat inside the house.
The ‘S” in ‘SIP’ stands for structural and the panel-system carries the load of the house, floors and roof, and does not need the sticks of vertical lumber you see in the walls of a conventionally framed house.
How are SIP panels joined? We’ll use the walls as an example:
The SIPs panels typically have the interior foam held-back to form a 1.5” gap at the panel edges. Two panels are joined by setting a ‘spline’ into the recessed gap on one panel, then sliding the second panel over the spline, nailing the connecting spline in place through all four edges. Splines can be made of 2×6 lumber (L-spline), foam mini-SIPs (called S-splines), or an insulated TJI spline (called an I-spline).
Because a 2×6 lumber splines touches both the warm inside of the house wall, and the cold exterior of the house wall, they are said to cold-bridge. A cold-bridge creates a poorly insulated pathway for the warm inside energy to travel to the cold exterior. There a many cold-bridges in conventional framing and that’s why we don’t do it. We aim to minimize L-splines as they have an insulating value of R7.8, compared to R29 for our Neopor graphite foam 6.5” Premiere SIPs wall panels.
Last week the TC Legend Homes crew finished off the SIPs roof structure on the Lake Stevens house.
On average we take about (2) days to assemble the 1st floor SIP wall panels. We build the 2nd floor-level TJI and sheeting floor system over the succeeding (2) days. The upper level walls take a day or so, and then it’s roof-day!
On roof-day the crane arrives early, and the roof panels are rigged, swung up, and screwed in-place by Ted and Norm. The crew have pre-assembled the boundary supports, so we don’t use more crane time and belch more diesel than necessary. The boundary support is a continuous 2×10 that seats into the 1.5” perimeter recess & connects together the outside edge of the roof panels.
SIPs are very fast to assemble and incur almost no waste material onsite because everything arrives pre-cut. Most excess off-cut foam is recycled back into the process during factory fabrication and the Premiere software nests the required panel shapes for maximum efficiency, making Premiere more streamlined, more profitable and more environmentally responsible.
Air sealing is very, very important for energy efficiency.
Imagine a fast, cold wind blowing over the building and all the warm air streaming out through the construction cracks. The Lake Stevens house is modeled to need a maximum of 12,500Btu/ hour to heat in midwinter, if we air-sealed the envelope to 0.6 air-changes per hour. (Note: (1) air-change-per hour assumes the entire volume of the house has the air replaced once within (1) hour).
If we air-sealed the Lake Stevens house to 5.0 air changes per hour, code minimum, we’d need 19,000Btu/h of heating for midwinter! So you can see that air sealing to reduce the air-changes per hour can give over 35% reduction in heating load.
SIPs are a pre-sealed sandwich, and compared to typical construction there are far fewer construction-joints in a SIPs building due to the large SIPs panel size. The standard SIPs assembly process includes installing beads of specialist mastic to air-seal and adhere the panels to each-other. SIPs have a measurable dollar advantage with that high level of pre-sealing and easy panel-to-panel air sealing. Meaning you can buy and run a smaller heat pump. And we haven’t yet examined the standard R29 insulation in the equivalent 2×6 wall!
When we pour a slab on grade we are basically pouring concrete directly onto the earth. Sure, there is a 4” layer of foam under the concrete so we don’t lose our heat, and yes, there is 12” of sand under the foam so the foam sits perfectly flat and the plumber can easily locate drainpipes in the sand… but under that sand is the compacted native earth.
No crawl space, rats, trash or mold, just a crisp concrete slab sitting on the earth, insulated so the slab holds in heat (or cold), and keeps the temperature inside the house consistently stable.
Slab-day is stressful, because many of the affordable Net-Zero houses from TC Legend use the slab-on-grade as the finished-floor.
Concrete slab as a finished floor provides a cost-effective, durable, aesthetically modern floor. However, the concrete needs to be finished perfectly flat on “Slab Day.”
Last week at the Lake Stevens house, the second concrete truck was late and the guys had to scramble to pour and screed the last truck-load before a permanent seam became inevitable!
Disaster was fortunately averted, the 1,500 square foot (sf) floor had the seam massaged-out, was troweled flat, covered in plastic and will be scrubbed and sealed in a few months before the trim goes up.
There are other finish options for concrete floors; they can be ground down, acid etched, and stain can be added to the concrete in the yard.
The following photos are gathered from a couple other already-built jobs. Dan was too busy at Lake Stevens last week, shoveling, troweling and de-stressing the crew to run a camera.
The black slab under the mountain was poured using black dye within the concrete.
The yellow Legos are a layout grid for in-floor radiant hydronic heating, which until recently was one common heating option deployed within our Net-Zero homes (more on heating systems soon).
The TC Legend Homes fellas put up the Lake Stevens house’s insulated concrete form (ICF) walls in the rain last week over the course of just (2) days! Dan said it went well since the soil had a good consistency to seat the Form-a-Drain footing, and the blocks went up fast, as per usual, since everyone likes stacking up Lego blocks!
A Net-Zero house is insulated on all (6) sides, and TC Legend builds with structural insulated panels (SIPs), so we have R-29 SIPs walls all around, R-49 SIPs roof above, and 4” R-20 foam under the slab-on-grade.
The edge of the slab also needs insulation, otherwise there would be a weak spot and heat would leak out through the slab perimeter, into the stem-walls (which are exposed to the weather).
We solve this problem by pouring the stem-walls into R-24 ICF forms which complete the insulted shell of this affordable Net-Zero home.
Concrete has been poured into foam wall-forms since the ‘80s. The hollow blocks go together like Legos with the required re-bar clipped inside, and once full of concrete, the Styrofoam block remains in place performing the job of insulation, and containing concrete while wet. The process is fast and clean, and has lower labor costs compared to traditional concrete forming.
We use NuDura R23.8 ICF blocks to form the stem walls, and retaining walls when we need them. The NuDura blocks are great since they concertina-down to transport. ICF blocks are available in many thicknesses with many variants for different construction requirements. We use 6” walls and usually only order inside-corners, outside-corners and 8’ straight blocks. The NuDura blocks have hard plastic structural strips that accept screws for siding and drywall.
The blocks sit atop the hat-channel that spans the footing form. At Lake Stevens we used Form-a-Drain footing form which, like the ICF’s does not need a form-board to be stripped-down after concrete is poured. The Form-a-Drain replaces 8” footer boards, is hollow, and drains water away from the foundation foot.
The Lake Stevens house has a 4’ stepped retaining wall up-slope and NuDura supply a very, very sticky vapor barrier to waterproof the stem-wall. TC Legend Homes has a metal cap/ cladding system system that wraps the exterior ICF foam from the sill plate downwards below-grade with roofing metal, leaving no visually, or thermally exposed concrete.
ICF’s are great for us! They perform two functions: (1) insulation, and (2) concrete form, they are a smart solution for our thriving Net-Zero, and increasingly Net-Positive SIPs housing in Washington state!
We found out we won the Residential Energy Services Network (RESNET) “Cross Border Challenge” award for Net Zero American Home Builder. This was for having a HERS Index Score of negative 25 on our Bellingham Affordable Net-Positive Home! Big thanks to Elizabeth Coe, our go-to for third-party certification!
We fielded our first-ever Ski to Sea team!
Sustainable Connections featured a recent detached accessory dwelling unit, which they dubbed “Gentle Density,” in the NW Green Home Tour.
We updated our Portfolio with some recent projects. Links to each of them are here: