Solar SIP Cabin Langley WA

Location: Langley, WA

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Awards/Certifications: DOE Zero Energy Ready Home, ENERGY STAR Certified, EPA Indoor AirPLUS, Passive House

The unique nature of this project was to create three nearly identical homes on a single 7,200 sq ft lot that share common elements such as, similar floor plan, same windows, doors etc. This project brings the popular trend of 'mini' homes and energy efficient living to Whidbey Island, providing a solution to the missing 'middle housing' shortage.

These cabins were unique as they were nearly the exact same layout, making the SIP construction even more efficient and quick to construct. Working in a limited space, the use of panels to build gave us the ease and ability to move safely and assemble the buildings easily. 

SIP wall thickness and core material: 6" EPS Cabins
SIP roof thickness and core material: 10" EPS Cabins

Using SIPs on this project did save us time, labor and costs as there was less preparation on site to build these cabins. Once we received the panels, the cabins were constructed quickly and the floor plans were designed with virtually no interior walls, so there was very little interior framing required. Even though the City required one unit to have it's door on the street side, and other units to have their doors on the side, we were able to use the same window and door rough openings, just switching up the locations of each.

Innovative design elements:

GWB was used only above the 8’ level for upper walls and ceilings, reducing joints and seams. A "Swing Arm” from an industrial supply catalog, made for use when unloading semi-trucks at loading docks, was used to provide flexibility in lighting the movable Kitchen Island. The movable kitchen island was made by bolting stainless steel shop cabinets together. The kitchen also featured a one-piece off-the-shelf kitchen stainless steel sink base with built-in drainboard top. We used a 24” stainless steel range, range fan, refrigerator, and 18” dishwasher, for space-savings. IKEA shelving units were used to form an armoire as a room divider, instead of having to frame a wall, and install unneeded electrical outlets.  A powered Fantech HEPA filter provides balanced air flow for the off-the shelf range fan, also providing make-up air for the Rheem heat pump water heater.

HVAC system used:

Ductless mini-split heat pump, 10.9 HSPF, 29.8 SEER, 1 indoor head, 1 outside compressor
The inside ductless head is located in the livingroom area, but because the home is completely open, the heat distributes throughout the tight building envelope. The largest windows all face east and south, with the east-facing windows help warm the home in the morning and the south-facing help heat the home during the day. The thermal-mass slab absorbs heat energy from the sun and distributes it throughout the house. 

U-values of windows:

Triple-pane U.16 (average) windows
R-10 perimeter insulation from top of foundation walls to footings, R-20 full coverage under entire floor

Energy-efficient products:

The heat pump water heater is located within the conditioned envelope of the house and within 10 feet of each of the uses of hot water, minimizing pipe runs. By drawing from the conditioned interior room air to supply the heat pump water heater, we increase the recovery rate by 50% with no increase in the total energy used. 

Solar Panels:

7,2 kW per unit, 21.6 kW total

Sustainable materials:

• Locally sourced cedar siding and exterior trim used from trees that were removed from nearby property;
• 18" porcelain tiles for elevated sidewalk and entry porches to protect tree roots, reduce impervious area, cutting carbon footprint of the walk by 75%;
• FSC-rated ACX plywood for all walls below 8' lighting cornice, reducing the carbon footprint of interior surfaces.

PROJECT DATA

• Layout: 1 bdrm, 1 bath, 1 fl, 550 ft²
• Climate: IECC 4C, marine
• Completed: May 2024
• Category: Custom

MODELED PERFORMANCE DATA

• ERI: without PV 37; with PV -33 (unit A), -32 (unit B) and -26 (unit C)
• Annual Energy Costs: without PV $350; with PV $0
• Annual Energy Cost Savings: (versus typical new homes) without PV $700; with PV $1,050
• Annual Energy Savings: without PV 5,920 kWh; with PV 8,740 kWh
• Savings in the First 30 Years: without PV $29,700; with PV $43,900

KEY FEATURES

• Walls: SIPs, R-28 total: graphite EPS 6.5" SIPs, corrugated draining housewrap, 3/8-inch plastic furring rainscreen; cedar siding or zinc-aluminum-coated standing-seam steel roofing as siding on north sides;
• Roof: SIP roof; 10.25" graphite EPS SIPs, synthetic underlayment, zinc-aluminum standingseam steel roofing;
• Attic: Unvented, vaulted ceilings, 9.35" R-46 graphite EPS in roof SIPs;
• Foundation: Slab on grade, poured concrete, R-10 perimeter insulation and R-20 under full slab;
• Windows: Triple-pane windows, U=0.16, SHGC=0.36, low-e, argon-fill. Roof overhangs;
• Air Sealing: 1.44 ACH50; all SIP panels sealed with spray foam and tape;
• Energy use intensity in kBtu/ft2: 27.3 before PV
• Ventilation: Range fan balanced to air intake with fan and 8-inch HEPA filter;
• HVAC: Ductless mini-split heat pump, 10.9 HSPF, 29.8 SEER; 1 outdoor head, 1 indoor head. Stained, sealed, insulated concrete slab and south-facing windows for thermal mass and passive solar heating;
• Hot Water: Heat pump water heater, 50-gal, 3.88 EEF. Core plumbing design;
• Lighting and Appliances: ENERGY STAR appliances;
• Solar: 7.2 kW, no battery;
• Energy Management System: Web-based monitoring of PV system;
• Other: Electric vehicle chargers. Three identical zero energy cottages on one tax lot.

To check out other Zero Energy Ready Homes, check out the Department of Energy’s Tour of Zero.

Documents

• Other: 2024_CVH_ZERH-poster-LR.pdf
• Other: Solar-SIP-Cabin-Langley-WA-Soules-Cabins-Unit-A.pdf
• Other: Solar-SIP-Cabin-Langley-WA-Soules-Cabins-Unit-C-4-.pdf

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