This cottage-sized casita is a hybrid-earthen design, born from an effort to reduce petroleum-based insulations, while providing a comfortable and artistic interior. Best for 5000-7000', it is adequate for a family of two, but is expandable by adding on to the west side of the home.
Two adobe-arched entries lead from Living Room to Kitchen and Hall, 36" wide. These, along with the traditional viga ceiling (round beams 8" in diameter on 36" centers) may cause the visitor to say, "it may be small, but it is solid and has artistic style".
The Passive Solar features include 5, 34" x 76" Direct Gain windows and one 34" x 76" Trombe wall. There is also a small Trombe wall on the south side of the battery box, helping to maintain temperatures during winter (it has its own small solar overhang for summer shading).
Exterior walls are 14" thick with interior walls at 10". However, most of the east and west exterior walls and all of the north wall are enclosed in an additional 5 ½" of insulation (within 2x6 framing), plus stucco or plaster, giving a total wall thickness of up to 21" on those sides. The insulation layer is not deployed on the south or "solar" side where most of the wall area is in glazing, but adobe areas on the south side should be stuccoed or plastered to match the other walls for a uniform look.
Inside, only 16 linear ft. of frame walls are needed, limited to plumbing walls in Bath and Wash areas and one closet. All other walls are adobe or compressed earth block, 10" wide. This adds interior thermal mass to moderate temperature swings and makes for good sound dampening in a small home. SWSA recommends that as a money saver, all interior walls be exposed, tooled to taste and sealed (rather than plastered) which will reduce costs. However, the owner should plaster or tile suitable Bath Room and Kitchen surfaces for ease of cleaning.
877's Living Room is 16' 11" x 11' 8" with a Count Rumford fireplace in its NE corner. The fireplace is not set against an outside wall, rather an inside one, making full use of it's ability to improve thermal conditions in the Living Room, but also in the Hall and Bed Room behind it. The one Bath measures 8' 3" x 7' 8", and is located in the NW corner of the home. Only 4 doors are required for the home, two exterior grade and two interior grade, all 36" wide. There are two bi-fold doors, one for a walk-in closet (6' 3" x 4') and the other for Bed Room privacy.
The efficient Kitchen faces south, measuring 9' x 8' 6". While the window over the sink will aid in solar gain, its main purpose is for ventilation and a view. The Wash/dry Utility is 6' 3" x 8' 10" with Bedroom access. It has space for PV components in its SE corner and leads to an east side entry and the battery box (for off-grid PV). Both east and west entries have covered porches, with gentle ramps. In the case of expansion, the west porch would be modified to accept an addition.
877's wall sections show a choice of Light Clay or Cellulose insulation on the exteriors (NM has a Light Clay standard), adding R factors from 10 to 20. A few words should be said here. The least expensive method is the Light Clay insulation which produces an R factor of approximately 1.8 per inch or about R 9 in a 5 ½" cavity. The vertical studs only need to be 48" apart for light clay, saving on lumber. The lime stucco covering may go directly onto the Light Clay without wire or tar paper (very green, very direct). With the adobe or pressed block mass behind it, the system will pass the energy code for every climate zone in NM, including locales like Chama,Tierra Amarilla or Taos, which have very cold winters. The straw and clay are basic and can be gathered locally at very low cost. The light clay will not burn. Other materials needed, such as lime and Boric acid are off the shelf.
BUT R 1.8 per inch is not a high R factor for very cold winters. Our advice is to limit the Light Clay method to sites not over 6500'. Above that, consider the Cellulose method, which has an R factor of 3.4 per inch. The total wall R for this system will exceed R 24 for walls (green). However, blown Cellulose requires studs on 24" centers, a stiff sheathing (½" OSB board or plywood, etc.), 15 # grade D tar paper (felt), wire stucco netting and about 1" of Portland based plaster (not green in the pocket book!). Moreover, the cellulose approach will require the builder to raise the frame structure first, back it on the outside (with whichever sheathing was chosen) and then blow the cellulose material from inside the home (like on a concrete slab) where the waste may be vacuumed up and reused. Once the cellulose wall has been trimmed and dries to a lower moisture content, the adobe wall is built to it, again from the inside. The frame/Cellulose wall can be used as a vertical surface to lay adobes to, as long as it is properly plumbed during construction.
Regarding the Cellulose method, one argument says that while you pay more initially for non-green materials (plywood, tar paper, galvanized wire, Portland plaster, plus labor) to erect the system, it will save more energy over the years. The other argument is that if you are not in an austere winter climate, you don't need that much protection, especially below 6000'.
The home sports a 26 gauge metal hip roof that creates a suitable cavity for cellulose insulation in the crawl space above (about 3' 6" of vertical room inside the space under the ridge board- much less elsewhere). We recommend an R 50 if you will build above 6500' and R 45 for lower elevations. including warmer summer climates. R 50 will require 14" of loose fill cellulose (ask about a stabilizer for settlement).
Plan Set 877 comes in a tube and consists of 9, 18 x 24" sheets consisting of Elevations, Floor Plan, Foundation Plan, Roof Framing Plan for Vigas, Roof Framing Plan for Hip Roof, House Section, Wall Sections (Cellulose and Light Clay choices), Fireplace Section and Electrical Plan.