LADCBroadcasting from Nelson BC
This building responds to a complex set of constraints and parameters which create unique design opportunities. The skin of the building is still under development, as is the immediate landscaping, entrances and other aspects of the building. However, the images below illustrate the general direction.
I will describe each component in detail as we are building it, but here is a basic description.
Total Heated Floor Area: 2400 sqft
Energy modelling framework: PassivHaus (CanPhi)
Energy Use: PassivHaus mandates that total energy use must be </= 10w/sqm or 15kwh/sqm/yr.
Orientation and siting: As mentioned in the previous post, the building is sited to maximize sun access and site programming opportunities.
Insulation: The walls, floor and ceiling will all be approximately R72, using wet blown cellulose and mineral wool.
Construction: The walls will consist of a triple stud-frame system. The outer two walls will be separated to create an approximately 14″ thick insulated wall. The inside surface of this wall will hold the vapour barrier. Inside of this wall will be the third insulated stud-frame, called the installation cavity, within which the electrical and other services can be run without penetrating the vapour barrier. The roof will be a standard truss with an installation cavity. The floor will be manufactured wood I-joists. The basement will be an unheated service space and is not considered part of the PassivHaus envelop.
Air Leakage: Careful attention is paid to the vapour barrier to ensure that the air leakage rate remains below .6 air changes per hour(ACH), the maximum allowed with the PassivHouse framework. Standard construction typically achieves between 3-6 ACH. A leaky home bleeds energy, and allows moisture into the wall system, creating mold and rot issues.
Air Quality: In the ’80′s a similar approach to air leakage was developed. However, fresh air exchange technology was not up to the task, which resulted in bad indoor air quality. Today we have mature HRV technology (Heat Recovery Ventilator), that can achieve an efficiency of up to 90%. This allows for healthy levels of air exchange without significant heat loss.
Design: The basic concept of the design utilizes the ideas of core and shell. The envelope of the building is the core, around which the exterior shell is wrapped. In between the two are inhabitable spaces utilized for a variety of purposes. On the south, each suite has an enclosed solarium. On the north are substantial service spaces, used for storage, social activities and a variety of general tasks. On the east is an open deck facing the rising sun. The west does not have this interstitial space, as it is directly adjacent to the neighbouring property and to reduce the overall length of the building. The southern overhangs create the required summer shading while maximizing winter sunlight. All three decks reduce the effects of wind-wicking-increased heat loss due to substantial air movement. These overhangs also direct seasonal moisture away from the envelop of the building. The increased exterior space, built at a substantially reduced rate as compared to the insulated envelop, increases the livable space of the building and allows for the design of relatively small suites. This design approach also encourages active outdoor living.
Material Package: The materials chosen for construction are readily available through local distributors. We favour solid materials – avoiding composites, laminates and their associated adhesives. We have chosen predominantly SPF BC lumber, unpainted galvalume steel, and concrete. Our two composite materials will be plywood, which will be used for cladding and cabinetry and OSB, for exterior wall sheathing. The use of solid materials improves indoor air quality and increases the lifespan of the building. Solid materials tend to “age with grace”, acquiring a patina of use over time that adds character. Composite materials tend to chip, fade and delaminate over time, requiring replacement and renovation.
Durability: The materials chosen for the skin of the building, being galvalume steel, glass and polycarbonate, will not fade, rust or rot, resulting in an almost zero maintenance building. In addition, galvalume steel has been shown to not leach into the rain catchment tank.