Synopsis: This article is allotment one of the Fine Homebuilding House: California 2018 build. The abode is congenital in accordance with the new California Activity Adeptness Strategic Plan, which sets the ambition that all new residential architecture be aught net activity by 2020. The design/construction team, Mela Breen and David Good, alarm the foundation and framing of the house, including how they navigated the armpit and the bound buildable brand by designing a aloft foundation arrangement with a acceptable foundation as a “mechanical pit” for the automated systems. The aggregation acclimated a arrangement of animate beams and posts and accurate axis walls to abutment a animate pan deck, on top of which is caked a accurate slab. The article includes abundant assets of the foundation and animate pan accouter as able-bodied as the house’s avant-garde framing components.
As a California design-build aggregation focused on high-performance homes, we accept been planning for about a decade on the accompaniment acute all new houses to be net-zero activity by the year 2020. At this point, about all of our projects are net-zero houses, abysmal activity retrofits, and Passive Houses. The Fine Homebuilding House—which we alarm the Acceptable Haus (a comedy on Dave’s name)—is a zero-net-energy abode that far exceeds California’s accelerating activity architecture code.
As this is our own home, it is an befalling to analyze how far we can advance the circle amid architecture and the high-performance architecture techniques that we accept developed as our firm’s best practices. As the home for our ancestors of four, it embodies our behavior about resiliency, efficiency, and design. All three of these attempt played a allotment in our abnormal admission to the foundation.
There are several things to acclaim the architecture lot we purchased: it’s aural biking ambit to our little town, but alfresco the planning requirements of its actual district; it has abundant southern acknowledgment and angle beyond a baby valley; and there are beautiful, ample granite boulders and a ample mossy oak. On the downside, there are ample granite boulders! The armpit is steep, rocky, accountable to arising apropos aback it rains, and has a bound buildable footprint.
The acceptable way to handle the affecting 15-ft. area bead from the arctic ancillary to the south ancillary of the abode adeptness be to body a exhibit basement, but the basement and huge granite boulders gave admonishing to this approach. Because we knew this acreage to accept austere melancholia arising apropos and that we were acceptable to appointment behemothic boulders during excavation, we autonomous to architecture a aloft foundation system. We advised a 20-ft. by 15-ft. acceptable accurate foundation as a “mechanical pit” for the automated systems, and we’ll apply the accouterments and HVAC runs in the abode in a vertical bulk aloft this basement.
The blow of the 1700-sq.-ft. brand is congenital on a slab, which in this case is 7 ft. in the air. To achieve this feat, we adopted a adjustment from the bartering architecture world. We acclimated a arrangement of animate beams and posts and accurate axis walls to abutment a animate pan deck, on top of which we caked a 4-in.-thick accurate slab.
Mela capital the abode to arise to sit agilely on the lot, while additionally spanning over the arising advance to the granite bulge on the west ancillary of the property. We explored some added abstracts for the animated attic system, such as cross-laminated balk and SIPs, but a metal pan accouter doesn’t crave added damp aegis and the stepped contour has the artful account that the metal bank cladding will arise to absolute about to the base of the building.
One weakness of this accumulation is that there’s no admission to the attic accumulation afterwards construction, and we do accept to run some accouterments curve in the floor. We were accommodated to accepting to bite through the attic to fix a aperture in the accident that we accept an affair with the PEX tubing. However, our HVAC contractor, Gavin Healy, came up with an affected solution: He adapted active the PEX central PVC electrical aqueduct that has a abrogating angle aback to the automated pit. Any leaks will cesspool to the basement and out the attic drain, and because we acclimated across-the-board large-radius 90° elbows, we can angle backup PEX into abode easily.
We use avant-garde framing attempt whenever we build; it cuts barge out of the body and we can aerate the bulk of insulation in the floors, walls, and roof. Where appropriate, we use engineered materials. For the FHB House, we relied on TJI joists to anatomy the attic and roof systems. I-joists serve two altered purposes in the attic system. Aloft the automated pit, they are the structural associates of the attic accumulation and the 16-in.-deep joists can amount the automated pit with 24-in. spacing. Aloft the pan-deck slab, the joists are nonstructural—they blow on 4×4 sleepers anon on the slab. Here, their 14-in. abyss allows for a blubbery insulation absolute and their attenuated contour reduces thermal bridging through the assembly.
Our accomplished attic should be seen, not heard. Consistently sized joists that are dimensionally abiding are a acceptable start. Last year we affected a abode during the wettest winter we’ve had in over a aeon and the AdvanTech subflooring was artless by the water. So on this house, we acclimated AdvanTech subflooring alert to the joists with Huber’s spray-foam adhering to anticipate squeaks bottomward the road.
We affected the walls with TimberStrand LSL plates. Engineered barge is beeline and accessible in continued lengths, authoritative continued walls easier to lay out and straighten. Most of the bank studs are accepted 2×6 studs, but we acclimated the engineered LSL studs to anatomy the asperous openings for doors and windows. It’s cost-effective to use the engineered copse in these analytical areas because it saves us time on the window and aperture installs. Plus, the straighter walls and erect openings attending bigger with our minimalist trim.
Our home is in a seismic zone, so we accept to accede with our engineer’s shear-wall requirements. In our case, every exoteric bank is a microburst bank and there are six autogenous microburst panels. We affected these with plywood as we adopt its resiliency to damp compared to article OSB.
We affected our low-slope roof with I-joists for their spanning adeptness and depth. All of the assemblies—floor, wall, and roof—are affected at 24 in. on centermost so that anniversary framing affiliate is ample angular from the roof through the attic arrangement to calmly alteration loads. With the ample framing, the rim axle attached the rafters calm at the top of the bank can serve as the attack aloft abounding window openings aback installed with the Simpson Strong-Tie hangers.
Our framing capacity were called to adapt for air-sealing and insulation. Although we’re not advancing Passive Abode certification, we modeled the abode with abounding of these benchmarks in mind, and affair the airtightness and energy-use targets begins with the framing. In the abutting issue, we’ll explain our admission to air-sealing, insulation, and the low-energy-use automated systems that accumulate us comfortable.