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Pushing the Envelope: Technically Speaking

The intent of 58 Upper Hillsborough was to design a cost effective, sustainable home. Instead of focusing on some more costly active green systems such as geothermal heating, solar panels and wind turbines, Open Practice Inc., instead chose to focus on optimizing the Building Envelope, taking advantage of cheaper passive green systems and employing a smaller, specifically-sized heating system.

The Building Envelope is what separates the interior of the building from the outside: your perimeter walls, roof and foundation. Think of the home as a thermos, you need to contain the heat in an insulated continuous shell. Heat loss can happen in different ways. One way is through air leakage. At 58 Upper Hillsborough, there is an emphasis on fine-tuning the building envelope, sealing the house from cold air infiltration and minimizing heat loss. The average newly constructed house today has air leakage equivalent to a 1’ x 2’ opening in the wall. (A major source of heat loss.) A reduction in air infiltration will be achieved through taping and spray foaming the window openings, using spray foam insulation at hard-to-seal places (which has a higher insulating value and creates an air and vapour barrier), insulating under the basement concrete slab and using insulated concrete forms for the foundation walls.

Another major source of heat loss is through transmission, one material conducting cold to another. Windows are a major culprit of this type of heat loss. Where possible we have selected triple glazed windows, which have a higher resistance to heat loss with surprisingly little increase to cost. Another form of this heat loss is due to Thermal Bridging, a connection from interior to exterior of building that funnels heat out of the home. This more obviously occurs when concrete or metal runs from interior to exterior, but it also occurs with wood framing. In a conventionally-built home, a 2×6 stud touches the sheetrock on the interior face of the house and also touches the plywood directly behind your siding. This framing, which can comprise as much as 40% of you wall area, can leave next to no insulation in your walls. In order to address this situation we framed the wall with a technique called a “double stud wall”. Framing this way minimizes the thermal bridging and provides a cavity for 9” of dense packed spray cellulose insulation. In the double stud wall two 2×4 walls are spaced 2” apart (while staggering the studs) allowing a minimum 5.5” of insulation at all points (compared to 0” in most homes). 58 Upper Hillsborough also uses an ICF (insulated concrete foundation) with insulation underneath the basement slab and the home will have a roof with 16” of dense packed cellulose insulation.

Newer sustainable homes are often associated with costly green systems, but with a little planning and minimal cost more passive green systems can be used to lower both the operating costs of a home and its environmental footprint. 58 Upper Hillsborough takes advantage of the heat from the sun (solar gain) through large south facing windows that allow sunlight to penetrate the building and warm its concrete floor. The surrounding trees shade these windows during the summer to minimize the added heat when it is not needed. Water will be collected off the roof and stored in a buried, re-purposed milk tank for watering plants and washing cars. Passive cooling will be employed by installing operable windows on opposite walls within a space which can be opened in the summer to allow for cross ventilation and a central open staircase will allow warm air to rise and be vented through second floor openings.

The following section illustrates some of the key elements that will contribute to the energy efficiency and environmental design.

Image Source: OpenPractice Collaborative Architecture Inc.
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Discussion

One thought on “Pushing the Envelope: Technically Speaking

  1. You briefly touched on it with the operable windows, but do you foresee any issues with it getting too warm in the summertime in the house due to the insulation?

    Also, I think you’ve already mentioned this to me, but what are your plans for the rain water collection? Will that low temp radiator (on top floor in figure) use the water down that wall as a sort of heat exchanger to provide heat?

    Looks awesome Aaron! Making good progress!!

    Posted by Patrick McKenna | February 5, 2012, 10:33 am

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