Musings of an Energy Nerd

Sub-Slab Mineral Wool

Posted on May 22, 2015 by Martin Holladay, GBA Advisor

Most green builders who need a layer of horizontal insulation under a concrete slab specify expanded polystyrene (EPSExpanded polystyrene. Type of rigid foam insulation that, unlike extruded polystyrene (XPS), does not contain ozone-depleting HCFCs. EPS frequently has a high recycled content. Its vapor permeability is higher and its R-value lower than XPS insulation. EPS insulation is classified by type: Type I is lowest in density and strength and Type X is highest.), an affordable product that performs well in this application. If a builder specifies high-density EPS rated for below-grade use, the product is very durable.

That said, many green builders don’t like EPS. Some object to the fact that polystyrene is made from petroleum, while others worry about possible health problems associated with the brominated flame retardants that polystyrene manufacturers add to EPS.

The Return of the Vapor Diffusion Bogeyman

Posted on May 15, 2015 by Martin Holladay, GBA Advisor

Fully aware that I am engaging in gross oversimplification, I’m going to offer a cartoon version of the History of Vapor Barriers. (I’m not a cartoonist, though, so someone else will have to make the drawings.) Here goes:

Panel 1: In the late 1940s, residential building codes in the U.S. began requiring the installation of vapor barriers on the interior side of walls and ceilings. These requirements had complicated historical origins but were not based on credible building science.

Books for Homeowners Interested in Saving Energy

Posted on May 8, 2015 by Martin Holladay, GBA Advisor

Two books that do a good job of explaining residential energy use issues to homeowners are Consumer Guide To Home Energy Savings and No-Regrets Remodeling. Both books have been around for years. Recently the publishers of these two books issued new editions, so I decided to give them a careful read.

Consumer Guide To Home Energy Savings

Using a Tankless Water Heater for Space Heat

Posted on May 1, 2015 by Martin Holladay, GBA Advisor

You can buy a gas-fired tankless water heater for $600 — or even $300, if you want a bare-bones model. These appliances are remarkable: they are compact enough to hang on a wall and can begin producing an “endless” flow of hot water almost instantly. Many people look at these small appliances and think, “Why can’t I use one to heat my house?”

The answer is, you can. However, just because you can, doesn’t mean you should.

Site-Built Ventilation Baffles for Roofs

Posted on April 24, 2015 by Martin Holladay, GBA Advisor

Roofs often require ventilation channels 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. — either for a short section of the roof (for example, near the eaves) or for the entire roof, from soffit to ridge. When the wind is blowing, these ventilation channels allow air to move from the soffit vents to the ridge vents.

Fixing Attics With Vermiculite Insulation

Posted on April 17, 2015 by Martin Holladay, GBA Advisor

If you're under the impression that natural insulation materials are the safest ones to use, it might be time to think again. Vermiculite is a natural insulation material — but it’s one that you definitely don’t want to have in your attic.

Vermiculite is a mineral mined from the earth, composed of shiny flakes that look like mica. When this mineral is put in an oven, it expands like popcorn. Expanded vermiculite is lightweight, fire-resistant, and odorless; since it 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 about R-2 per inch, it was used for decades as an insulation material.

Using a Glycol Ground Loop to Condition Ventilation Air

Posted on April 10, 2015 by Martin Holladay, GBA Advisor

Most energy-efficient homes include a mechanical ventilation system — often an HRV(HRV). Balanced ventilation system in which most of the heat from outgoing exhaust air is transferred to incoming fresh air via an air-to-air heat exchanger; a similar device, an energy-recovery ventilator, also transfers water vapor. HRVs recover 50% to 80% of the heat in exhausted air. In hot climates, the function is reversed so that the cooler inside air reduces the temperature of the incoming hot air. or ERV(ERV). The part of a balanced ventilation system that captures water vapor and heat from one airstream to condition another. In cold climates, water vapor captured from the outgoing airstream by ERVs can humidify incoming air. In hot-humid climates, ERVs can help maintain (but not reduce) the interior relative humidity as outside air is conditioned by the ERV. that brings in fresh outdoor air while simultaneously exhausting an equal volume of stale indoor air. The main problem with introducing outdoor air into a house is that the air is at the wrong temperature — too cold during the winter and too hot (and often too humid) during the summer.

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.

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