Q&A Spotlight

Can You Heat a House with Air Ducts in a Concrete Floor?

Posted on August 30, 2010 by Scott Gibson

Concrete floors with high thermal massHeavy, high-heat-capacity material that can absorb and store a significant amount of heat; used in passive solar heating to keep the house warm at night. are often at the heart of passive solar designs. The density of concrete helps it store thermal energy and helps to reduce uncomfortable swings in indoor temperatures.

Slabs collect some heat from the sun through south-facing windows, often supplemented by radiant-floor heating systems that use a network of embedded plastic tubing to circulate hot water.

Is Bubble Wrap Duct Insulation a Good Idea?

Posted on August 23, 2010 by Scott Gibson

Lora's question seemed innocent enough, but it was enough to touch off a war of words and prove that building science isn't always as dryly academic as you might guess. It can, in fact, get downright cantankerous.

Lora's HVAC(Heating, ventilation, and air conditioning). Collectively, the mechanical systems that heat, ventilate, and cool a building. installer wanted to insulate the ducts in her house with double-wrapped bubble wrap "as a cheaper way to achieve R-6." Fine, she thought, but does the stuff really work?

Vapor Barriers Are a Good Thing, Right?

Posted on August 17, 2010 by Scott Gibson

At the dawn of our current interest in building science, sheets of polyethylene were routinely stapled to interior framing before drywall was installed. The idea was to block the flow of water vapor into exterior walls. (Some builders tried to make their polyethylene seams airtight, so that the poly would do double duty — acting as an air barrierBuilding assembly components that work as a system to restrict air flow through the building envelope. Air barriers may or may not act as a vapor barrier. The air barrier can be on the exterior, the interior of the assembly, or both. as well as a vapor barrier.)

Installing a vapor barrier (or more properly a vapor retarder) was considered cutting-edge.

When is a Window Upgrade Worth the Extra Cost?

Posted on August 12, 2010 by Scott Gibson

There's no doubt that windows are getting better — much better. The double-glazed, low-eLow-emissivity coating. Very thin metallic coating on glass or plastic window glazing that permits most of the sun’s short-wave (light) radiation to enter, while blocking up to 90% of the long-wave (heat) radiation. Low-e coatings boost a window’s R-value and reduce its U-factor. units that looked so ground-breaking a few years ago seem merely ordinary now that Canadian, European and some U.S. manufacturers are producing high quality triple-glazed units.

Triple-glazed windows offer substantial benefits, including improved indoor comfort and lower energy bills.

But they aren't cheap. Homeowners who are already facing painfully high building costs have to weigh the costs against the benefits. Are triple-glazed windows really worth the added cost?

Can Heat Be Stored in a Sand Bed Beneath the House?

Posted on August 4, 2010 by Scott Gibson

David Meiland was intrigued by something he'd read in a Breaktime post at Fine Homebuilding magazine in which a Minnesota builder discussed plans for a heat-storing layer of sand 4 ft. thick below the house slab.

PEX tubing would dump heat gathered by solar collectors into the insulated layer of sand in summer, and extract it during the winter. Although sand isn't an ideal material for this type of system, it's cheap and easy to work with.

Do All Houses Need Mechanical Ventilation?

Posted on August 2, 2010 by Scott Gibson

A central aim of energy-efficient building is to eliminate air leaks through the roof and exterior walls. A leaky building envelopeExterior components of a house that provide protection from colder (and warmer) outdoor temperatures and precipitation; includes the house foundation, framed exterior walls, roof or ceiling, and insulation, and air sealing materials. not only makes it harder to heat and cool a house but also increases the risk of condensation and moisture damage.

Builders are getting the message about air sealing. But the tighter the house, the greater the need for some type of mechanical ventilation — and that raises construction costs. Is it possible to build a house with just enough air leakage to satisfy fresh air requirements without a ventilation system while still reaping some energy rewards?

In Search of the Most Energy-Efficient Windows

Posted on July 26, 2010 by Scott Gibson

It seems like a very long time ago, doesn't it, that windows were considered simple building components? As long as they opened and closed and let in sunlight most of us were content. We know now that windows are anything but simple. They're an essential part of an energy efficient building envelopeExterior components of a house that provide protection from colder (and warmer) outdoor temperatures and precipitation; includes the house foundation, framed exterior walls, roof or ceiling, and insulation, and air sealing materials.; they must simultaneously admit sunlight (and a certain amount of solar energy — but not too much), minimize heat loss or gain, prevent drafts, and last a generation or two.

Are Tankless Water Heaters Really Green?

Posted on July 19, 2010 by Scott Gibson

Tankless water heaters have one advantage over conventional storage units: no standby losses. Instead of keeping water hot around the clock, regardless of whether it's actually needed, tankless units heat water only when a tap or an appliance is turned on. By rights, this should mean lower energy consumption, a decidedly green advantage.

Bathroom Walls, Mold, Vapor Barriers, and Building Codes–Where's the Love?

Posted on July 8, 2010 by Scott Gibson

Josh, a builder in Columbus, Ohio, has been hired to add a bathroom in the attic of an existing house. Although he had hoped to use cellulose insulationThermal insulation made from recycled newspaper or other wastepaper; often treated with borates for fire and insect protection. in exterior walls, the homeowner's budget allowed fiberglass batts. Josh was counting on the kraft paper facing on the insulation to serve as a vapor retarder, but to his surprise the building inspector insists the paper be removed before the insulation is installed.

What gives? And will the inspector's decision increase the risk of moisture problems in the bathroom, surely one of the most humid rooms in the house?

Can Exterior Foam Insulation Cause Mold and Moisture Problems?

Posted on June 23, 2010 by Scott Gibson

Many builders add one or more layers of rigid foam insulation to the outside of a house to lower heat losses. Rigid insulation has an R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. of up to 6.5 per inch, but it also can be an effective vapor retarder.

Ed Welch touched off an extended discussion in the Green Building Advisor's Q&A section when he asked whether the foam would trap moisture inside walls, creating mold as well as the potential for structural decay.

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