STRUCTURE
The load bearing structure on OPEN_2 is designed very simply, utilizing glue- laminated lumber. Partially visible steel connectors are used to join the individual components. The components themselves are milled completely off site on CNC (computer numeric controlled machines), allowing them to be quickly assembled on site. The advantages of glue-laminated lumber lie in its efficient use of smaller size lumber to make larger beams, as well as in its accuracy and stability.
WALLS
Most of the challenges in a super-insulated envelope become apparent in the walls. Walls consist of very different kinds of construction. With their opaque, highly insulated areas, transparent window areas with lower insulation values, and doors and other openings, diligent efforts are required in the insulating and the proper sealing of transitions.
Openbuilt strategies separate layers that fulfill different functions. The walls on OPEN_2 use an accessible strapping layer behind the interior finish material, which allows for efficient and organized installation of electrical wiring as well as the potential for easy alteration later on. The structural layer of the wall includes framing and sheathing on both sides to provide bearing capacity for lateral loads, stiffness against bending of the panel, and support for windows and doors. The cavities are filled with dense pack cellulose insulation, using the extra space for increased thermal performance of the wall assembly.
Outside the structural part of the wall, an air/ moisture barrier is applied before insulating foam board is installed on the outside. The continuously sealed layer of foam board eliminates any convection and provides superior thermal insulating performance. A strapping system helps to keep the foam board in place and serves as a base for a siding system on which to attach the the exterior wall. Careful, detailed overlapping of the moisture barrier and specially developed gaskets provide the certainty that the large pre-finished wall sections fit right and joints provide highest performance in regards to tightness and insulation values.
FLOORS
The flooring in this single-story residence is comprised of a finished-surface concrete slab that serves as a heat sink for any passive solar gain achieved through the southern facing glass doors and windows.
The mechanical bar on the north side of the house concentrates all the utility systems of OPEN_2. The pipes and ducts are run in a framed floor system above a crawl space to allow access for connecting the 2 prefabricated modules, as well as for long term maintenance and upgrades.
ROOF
To minimize the heated volume of the OPEN_2 prototype, the decision was made to eliminate cathedral ceilings in favor of a flat roof over the walls and structure. The individual pre built panel sections are constructed with a structural layer consisting of TJI frame work insulated with dense pack cellulose.
The decking is covered by a TPO roofing membrane and extruded polystyrene foam board is layered over top. To hold the foam board in place ballast in form of pavers, gravel or any green roof system.. This disentangled configuration protects the moisture membrane from potentially damaging sharp objects or UV radiation and with the thermal properties of XPS not effected by moisture it provides additional insulation.
The width of the mechanical bar allows for a shorter span of the roof panel. A 10" thick structural foam core panel is used to provide the deck for the TPO roofing membrane and additional XPS foam layers with ballast to copy the concept of the other roof areas.
WINDOWS AND DOORS
Windows and doors are potentially the weakest areas in a well insulated enclosure system. The goal is to minimize the impact of these transparent areas by using super insulated windows and to optimize installation to minimize thermal bridging. For OPEN_2, a triple-glazed fiberglass frame window was chosen for its superior performance (Thermotech windows, Canada )
INTERNAL FINISH AND MILLWORK
Interior fit out and finishing in conventional construction takes a significant amount of time. In an effort to evaluate the potential for increased efficiency in this part of the construction process, Bensonwood has developed systems that can be pre-built and pre-finished off site, and then quickly installed into the prepared building shell.
The most challenging areas for time saving are the areas of wet finishes such as drywall taping, plastering, tile work, etc. These processes and applications include long drying and curing times, some of which preclude other finishes from being applied. If wet finishes are desired, the goal must be to apply them prior to the delivery to site. Dry finish systems applied to pre-applied substructures save time on site.
EXTERNAL SIDING SYSTEMS
Standard finishes on exterior walls are usually come in board,and shingle, and sometimes in sheet form. All these finishes lend themselves to covering large areas seamlessly, but can be very time and labor intensive,, requiring special access considerations (staging, lifts, ladders). OPEN_2 features three different types of siding materials and systems. All three are pre-finished and either pre-cut or pre-assembled.