Building Science

In our last episode, Dr. John talked about How Heat Moves Through Homes and why radiant barriers work better in outer space than on earth.

In this episode, Dr. John talks about the history of insulation, how different materials work, and where they make sense.

TRANSCRIPT
The history of insulation comes about because of the history of structural engineering. Now, I’m a recovering structural engineer, which is probably why I like to think of it that way.

Today’s walls, roofs, and floors are better insulated, tighter, and made with a much greater variety of components than they used to be, making them a lot more susceptible to moisture problems when they get wet. Compared to the old days, today's walls and ceilings are more complicated and can be very slow to dry.

The weathering of wood is very different from decay; weathering is breakdown at the surface only. While there are a number of forces that contribute to weathering of wood—moisture, temperature, abrasion by wind-borne particles, air pollution—it’s the narrow band of high-energy ultraviolet light in sunlight that is the dominant force (see Image #1).

What bare wood looks like when cut or milled

In our last episode, Dr. Joe Lstiburek talked about efflorescence and the serious damage that water and salt can do to masonry. This week, Dr. John Straube explains how the three forms of heat flow work, and debunks the claims of a few common insulating materials.

Comfort is the Primary Purpose of Buildings

This podcast series is excerpted from a two-day class called "Building Science Fundamentals" taught by Dr. Joe Lstiburek and Dr. John Straube of Building Science Corporation.

This podcast series is excerpted from a two-day class called "Building Science Fundamentals" taught by Dr. Joe Lstiburek and Dr. John Straube, of Building Science Corporation.

As part of a new Master Certified Green Professional designation, NAHB worked with GreenBuildingAdvisor to develop a rigorous training course covering green home building, full of building science and quality construction details. This course premiered at the International Builders Show in Las Vegas just last week.

Our latest Question of the Week comes from a homeowner in New Jersey. Monica is uncertain of the best way to insulate the roof of a new second-story addition on her Cape Cod home. She wonders whether it's wise to insulate directly under the roof sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. — especially since the mounting system for her photovoltaic(PV) Generation of electricity directly from sunlight. A photovoltaic cell has no moving parts; electrons are energized by sunlight and result in current flow. array requires 54 holes to be drilled in her asphalt shingle roof.

Powerful kitchen exhaust fans do a good job of removing cooking odors and smoke. They also have the potential to depressurize a house, causing water heaters to backdraft and pulling ashes out of the fireplace and onto the hearth.

Ice dams are a familiar problem in New England and other parts of the country where winters are long and cold. Snow on under-insulated and under-ventilated roofs melts, pools and refreezes to form a dam. Water backs up under the shingles and much to the horror of homeowners often finds its way inside the building.

Spray foam polyurethane insulation is supposed to be a hedge against that problem. By forming an effective seal around rafters, and offering respectable R-values, foam should be blocking the migration of cold air into the roof where it can condense into water.