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  • Building Science and the Elements of Sustainable Home Design and Construction

    Posted on July 21st, 2010 don No comments

    It’s easier to follow someone else’s prescription for achieving our goals (like building a sustainable home) than doing the hard work of making the thousands of decisions that suit our lifestyle and fit our budgets. If you’re up to the task of a custom design, here are a few of my own rules to guide you in building a successful home:

    Follow physics;
    Support your senses; and,
    Don’t do stupid stuff.

    Physics

    Regardless of the size of your home, energy still crosses the building envelope in the same three ways, and those are addressed by preventing air leakage, insulating everywhere, and installing good-quality, well-sited windows. And even if we choose to fight them, water and gravity still win, regardless of our socio-economic status. So install flashing where you need it to keep water out, and provide enough insulation to keep water vapor from condensing on cold surfaces.

    If you think we can ignore those rules, physics will do what physics does—rot the materials, make your house uncomfortable, expensive to heat and cool, and send a lot more pollutants into the air than it otherwise would.

    Hey folks, I’m looking at you eyeball to eyeball. This should be where we start; nothing less will do.

    Support your senses

    Do you think saving energy and being kind to the environment are the most important goals in building a home? Then how about all the human comfort factors that affect the way we feel in our homes, like:

    space planning, ceiling height, sight lines, daylight, contrast, color, views, privacy, openness, intimacy, public spaces, texture, and sound.

    But how do you design a home that covers all that? I think that including an interior designer along with the home designer make a superb team. To find one, ask your designer, your builder, or go to furniture stores or paint stores. Chat with them to find one who has a portfolio and a personality you like.

    Bonus Insight: The Cost of Walls vs Floors

    Compared to walls, floor space is relatively inexpensive to build: you have joists, subfloor, often some underlayment, and finish flooring. To be complete, let’s add the ceiling, which consists of framing, drywall & paint, and a roof.

    Walls are a lot more complex: there’s not just siding, house wrap, sheathing, framing, insulation, drywall, paint, but plumbing, wiring, windows & doors, outside trim, extension jambs, inside casing, baseboard, and finishing. But that’s not all—the more angles in the walls, the more complex, expensive, and leakage-prone, the roof.

    • TAKE-HOME LESSON: what you save on the home’s footprint you can spend on more luxurious interiors or energy upgrades.
    • A SUGGESTION: Experiment with interior colors to balance out daylighting; try darker colors on the south rooms and lighter on the north. Use your imagination, allow yourself to make a mistake. Paint is cheap.

    Don’t do stupid stuff

    Of course, we’d never do anything dumb, so let’s wag our fingers at others’ mistakes. These are from homes I’ve investigated myself.

    An architect designs a home with a spacious solar green house for winter heat gain and natural light. Even on a cloudy day, the wonderful natural light goes deep into the house. But unfortunately, the architect forgot that the sun shines in the summer, too, and without shading, the house costs twice as much to cool as to heat.

    One home with multiple furnaces simply couldn’t keep up in either heating or cooling, so a third heating system was added, without much improvement. Only when we measured the airflow in the ductwork did we find that the return air was only half of what it should have been.

    Another new home had two furnaces, but one of them was noisy, making a wheezing sound. Again, on measuring the pressures of the airflow, we discovered a dramatic negative pressure in the return ducts, even though the amount of air was adequate. To provide that airflow, contractors often install a grille high on the wall between two studs, and cut out the plate in the floor between the studs, opening up an air path to the furnace. In this case, only a few small holes had been drilled in the plate, where the whole plate should have been cut out. And second, even though there was an adequate amount of airflow, the furnace fan installed was two and a half times as powerful as it should have been. It was like making a Marathon runner breathe in through a straw.

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