Q&A Spotlight

Planning a New Home: Where to Spend the Money?

Posted on August 22, 2011 by Scott Gibson

A tight, well-insulated 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. is fundamental to a high-performance house. So is a heating and cooling system that keeps it comfortable with a minimum input of energy. What happens when the construction budget can’t handle the added costs of high-quality windows and extra insulation as well as high-efficiency mechanicals?

That basic question is what’s plaguing Dave W as he works to complete plans for his new home.

Choosing a High-Performance Wall Assembly

Posted on August 18, 2011 by Scott Gibson

Jesse Lizer’s new house will be in Climate Zone 6, where he can expect 7,400 heating degree days a year. High R-values in the 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. are a high priority.

How to Insulate a Foundation

Posted on August 8, 2011 by Scott Gibson

Peter Fusaro is building a high-efficiency house on spec, and his plans include insulating the foundation walls. The question is how.

One option is to apply rigid foam to the outside of the foundation. That would leave roughly 1 ft. of insulation above grade, and Fusaro is concerned about how durable the foam would be.

Another possibility is to use a sandwich of 2 in. of foam between two outer faces of concrete, each 4 in. thick, making an assembly with both structural and thermal properties. He’s been told a wall built that way would have an effective R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. of 19.27.

Adding Insulation to a 1944 Roof

Posted on August 1, 2011 by Scott Gibson

Thaddeus Cox’s 1944 Cape Cod in Portland, Oregon, has a roof that needs some attention. Not only is the roof under-insulated, but it’s currently covered in two or three layers of asphalt shingles installed over the original layer of cedar. 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. consists of 1-in. thick boards.

The International Energy Conservation Code recommends R-38 for the roof in this Climate Zone 4 house, far more than the R-11 batts Cox thinks are currently in place.

How to Build a ‘Perfect Wall’

Posted on July 25, 2011 by Scott Gibson

Andrew Homoly is building a house in Kansas City, Missouri, and plans to use a “perfect wall” system consisting of 2x6 studs, IcyneneOpen-cell, low-density spray foam insulation that can be used in wall, floor, and roof assemblies. It has an R-value of about 3.6 per inch and a vapor permeability of about 10 perms at 5 inches thick. open-cell foam insulation and an additional 1 1/2-in. layer of rigid foam on the building’s exterior.

His question in this Q&A post at GreenBuildingAdvisor concerns the best way to install window and door flashing, and where to install housewrap.

Does Passivhaus Work in New Orleans?

Posted on July 18, 2011 by Scott Gibson

It is now a given that high-performance houses have high levels of insulation. It is not uncommon for a new cold-climate home to have R-40 walls and an R-60 roof, as builders do their best to lower a home's energy requirements.

But is this premise in favor of thick insulation weighted toward houses in cold climates, where heating is a higher priority than cooling? Does it make just as much sense to insulate houses as heavily in hot, humid climates? Or does a lot of insulation actually make it more difficult to keep the house cool?

How to Retrofit a Roof with Insulation

Posted on July 11, 2011 by Scott Gibson

Finding effective ways of beefing up under-insulated roofs is a perennial problem, affecting countless houses built to minimum energy standards.

Even roofs that meet minimum code requirements are susceptible to thermal bridgingHeat flow that occurs across more conductive components in an otherwise well-insulated material, resulting in disproportionately significant heat loss. For example, steel studs in an insulated wall dramatically reduce the overall energy performance of the wall, because of thermal bridging through the steel. when only the rafter bays are insulated.

How to Protect Structural Insulated Panels from Decay

Posted on July 4, 2011 by Scott Gibson

UPDATED on July 7, 2011 with comments from Tedd Benson

Jay Hersh is building a house in northern Vermont that will have a roof of structural insulated panels. Although his plans are fairly advanced, Hersh is still stumped about detailing the SIP(SIP) Building panel usually made of oriented strand board (OSB) skins surrounding a core of expanded polystyrene (EPS) foam insulation. SIPs can be erected very quickly with a crane to create an energy-efficient, sturdy home. seams to prevent the migration of moisture-laden air from inside to outside. He's also looking for a foolproof way of heading off any leaks from the outside.

How to Insulate a Low-Slope Roof

Posted on June 20, 2011 by Scott Gibson

Eric Dymond lives in a 1920s Baltimore row house that needs a new roof. He plans on replacing the low-slope, built-up roof with an EPDM membrane, and the question is how to insulate it correctly.

Currently, the built-up asphalt roof is installed over Homasote (or something similar) and a roof deck made of wood planks. Although there’s some “sparsely distributed” insulation in the space between the ceilings and the roof deck, it won’t meet current recommendations for Dymond’s Climate Zone 4 house.

The Downside of Structural Steel

Posted on June 13, 2011 by Scott Gibson

Brandon M. is building a three-story house in Seattle whose design includes cantilevers on the second and third floors. The designer has specified steel I-beams to provide the structural support in this modernist design, and this is what’s giving Brandon pause for thought.

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