Musings of an Energy Nerd

How to Install Rigid Foam On Top of Roof Sheathing

Posted on April 3, 2015 by Martin Holladay, GBA Advisor

A roof over a vented, unconditioned attic does not need to include any insulation. However, most cathedral ceilings and low-slope (flat) roofs are insulated roof assemblies: with this kind of roof, the insulation follows the slope of the roof.

Insulated roof assemblies can be vented or unvented. There are lots of different ways to insulate this type of roof, but one of the best methods calls for the installation of rigid foam insulation above 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. .

Walls With Interior Rigid Foam

Posted on March 27, 2015 by Martin Holladay, GBA Advisor

There are two main ways of reducing 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. through studs: you can build a double-stud wallConstruction system in which two layers of studs are used to provide a thicker-than-normal wall system so that a lot of insulation can be installed; the two walls are often separated by several inches to reduce thermal bridging through the studs and to provide additional space for insulation., or you can install a continuous layer of rigid insulation on one side of the wall.

Most builders who install a continuous layer of rigid insulation use rigid foam (polyisocyanurate, expanded polystyrene, or extruded polystyrene); a small minority of builders use semi-rigid panels of mineral wool.

Builders who install rigid foam on the walls of a new building usually install the foam on the exterior side of the wall. There are several reasons for this:

Solar Hot Air Collectors

Posted on March 20, 2015 by Martin Holladay, GBA Advisor

A solar hot air collector is basically a black box with glass on one side. Instead of heating fluid that circulates through tubing, a solar hot air collector is like a parked car. When the sun shines on the collector, the air inside gets hot. A solar hot air collector usually includes a hot air duct connection at the top and a return-air duct connection at the bottom. To improve efficiency, most solar hot air collectors have a black metal baffle or screen behind the glass that allows air flow on both sides.

A Balanced Ventilation System With a Built-In Heat Pump

Posted on March 13, 2015 by Martin Holladay, GBA Advisor

A small manufacturing company in Illinois called Build Equinox has developed a new ventilation appliance called the Conditioning Energy Recovery Ventilator, or CERV. Build Equinox was founded by an engineer, Ty Newell, and his son Ben Newell. (Ty Newell designed and built the Equinox House, which was described in a GBA article published in 2011.)

NESEA Conference Highlights

Posted on March 6, 2015 by Martin Holladay, GBA Advisor

BuildingEnergy, the annual conference sponsored by the Northeast Sustainable Energy Association (NESEANorth East Sustainable Energy Association. A regional membership organization promoting sustainable energy solutions. NESEA is committed to advancing three core elements: sustainable solutions, proven results and cutting-edge development in the field. States included in this region stretch from Maine to Maryland., recently concluded in Boston. As usual, the NESEA conference was a great way to catch up with friends and to soak up information offered by some of the smartest scientists, engineers, designers, and builders in the country.

Here are notes from some of the presentations.

Ice Dam Basics

Posted on February 27, 2015 by Martin Holladay, GBA Advisor

What do you call the weeks between Valentine’s Day and Easter? It’s ice damA ridge of ice that forms along the lower edge of a roof, possibly leading to roof leaks. Ice dams are usually caused by heat leaking from the attic, which melts snow on the upper parts of the roof; the water then refreezes along the colder eaves working it's way back up the roof and under shingles. season, of course. Eastern Massachusetts is now the wet-ceiling capital of the world, but this winter, tens of thousands of homeowners from North Dakota to Maine are struggling with ice dams.

Designing for the Future

Posted on February 20, 2015 by Martin Holladay, GBA Advisor

When an architect, residential builder, and owner sit around a table for their first design meeting, their ostensible goal is to begin designing a house. Whether they realize it or not, however, these three people are also predicting the future.

The Evolution of Superinsulation

Posted on February 13, 2015 by Martin Holladay, GBA Advisor

At the recent “Better Buildings By Design” conference in Burlington, Vermont, I attended presentations that epitomized two different approaches to energy-conscious building. I’ll call these two approaches “classic superinsulation” and “the net zeroProducing as much energy on an annual basis as one consumes on site, usually with renewable energy sources such as photovoltaics or small-scale wind turbines. Calculating net-zero energy can be difficult, particularly in grid-tied renewable energy systems, because of transmission losses in power lines and other considerations. approach.”

The “classic superinsulation” method has been around for about 35 years. It’s the approach that formed the basis of Wolfgang Feist’s PassivhausA residential building construction standard requiring very low levels of air leakage, very high levels of insulation, and windows with a very low U-factor. Developed in the early 1990s by Bo Adamson and Wolfgang Feist, the standard is now promoted by the Passivhaus Institut in Darmstadt, Germany. To meet the standard, a home must have an infiltration rate no greater than 0.60 AC/H @ 50 pascals, a maximum annual heating energy use of 15 kWh per square meter (4,755 Btu per square foot), a maximum annual cooling energy use of 15 kWh per square meter (1.39 kWh per square foot), and maximum source energy use for all purposes of 120 kWh per square meter (11.1 kWh per square foot). The standard recommends, but does not require, a maximum design heating load of 10 W per square meter and windows with a maximum U-factor of 0.14. The Passivhaus standard was developed for buildings in central and northern Europe; efforts are underway to clarify the best techniques to achieve the standard for buildings in hot climates. standard.

Split-System Heat-Pump Water Heaters

Posted on February 6, 2015 by Martin Holladay, GBA Advisor

Heat-pump water heaters are a type of air-to-water heat pumpHeating and cooling system in which specialized refrigerant fluid in a sealed system is alternately evaporated and condensed, changing its state from liquid to vapor by altering its pressure; this phase change allows heat to be transferred into or out of the house. See air-source heat pump and ground-source heat pump.. Almost all heat-pump water heaters sold in the U.S. extract heat from the air in the room where the water heater is located, transferring the heat to water in an insulated tank.

Rules of Thumb for Ductless Minisplits

Posted on January 30, 2015 by Martin Holladay, GBA Advisor

Since 2008, when Carter Scott built a pioneering Massachusetts house that was heated and cooled by just two ductless minisplits, has endeavored to publish reports from the field to guide people designing homes that are heated and cooled by ductless minisplits. We’ve learned a lot on this topic since 2008.

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