Musings of an Energy Nerd

High Humidity in Unvented Conditioned Attics

Posted on August 26, 2016 by Martin Holladay, GBA Advisor

If you convert your vented unconditioned attic to an unvented conditioned attic by installing open-cell spray foam on the underside of your 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. , you may be surprised to discover that your attic is now the most humid room in your house.

Why? We don't know. Although building scientists haven’t achieved a consensus on the answer, we do have enough information to paint a picture of what’s going on.

Attaching Corner Trim on Walls With Rigid Foam

Posted on August 19, 2016 by Martin Holladay, GBA Advisor

Many GBAGreenBuildingAdvisor.com readers have built homes with 4 inches or 6 inches of rigid foam on the exterior side of their walls. Typically, these walls include vertical 1x4 furring strips, 16 inches or 24 inches on center, on the exterior side of the rigid foam. The furring strips perform at least three functions: they hold the foam in place, they create a rainscreenConstruction detail appropriate for all but the driest climates to prevent moisture entry and to extend the life of siding and sheathing materials; most commonly produced by installing thin strapping to hold the siding away from the sheathing by a quarter-inch to three-quarters of an inch. gap, and they provide something for the siding to be fastened to.

My House is Too Hot

Posted on August 12, 2016 by Martin Holladay, GBA Advisor

During the summer, your house is too hot. What’s the solution?

The simplest thing to do, of course, is to get a bigger air conditioner. That crude solution certainly works: if you blast enough cold air into a building — even a leaky, poorly insulated building — you can lower the indoor air temperature. (Of course, adopting this approach is no guarantee of success, since central air conditioning systems are often poorly designed and haphazardly installed.)

Capillary Breaks Above Footings

Posted on August 5, 2016 by Martin Holladay, GBA Advisor

Builders routinely install several types of barriers to avoid damp basements. Examples of these features include a layer of crushed stone and polyethylene under a basement slab; asphaltic dampproofing on the exterior side of basement walls; and sill seal made of thin closed-cell foam between the top of a foundation wall and the mudsill. All of these materials are used to reduce the transfer of moisture from the damp soil surrounding a foundation to the interior of the building or vulnerable framing lumber.

Batteries for Off-Grid Homes

Posted on July 29, 2016 by Martin Holladay, GBA Advisor

Is solar electricity cheap or expensive? There are two parallel stories circulating these days. One version of the story — the older of the two — is that electricity from a 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. (PVPhotovoltaics. Generation of electricity directly from sunlight. A photovoltaic (PV) cell has no moving parts; electrons are energized by sunlight and result in current flow.) array is more expensive than grid power, and that adding batteries makes PV even more expensive.

The newer tale, oft-repeated on GBAGreenBuildingAdvisor.com, is that PV is cheap and getting cheaper, and that any utility that tries to limit PV installations is doomed to failure — because homeowners who are disgruntled by a PV-hostile utility will choose to install batteries, cutting the cord to the grid.

A Researcher Looks at Insulated Roof Assemblies

Posted on July 22, 2016 by Martin Holladay, GBA Advisor

Kohta Ueno knows a lot about insulated roofs. As a researcher and engineer at Building Science Corporation in Westford, Massachusetts, Ueno has seen plenty of well-designed roofs, as well as plenty of rotten 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. . For a building science researcher like Ueno, rotten sheathing isn’t a disaster; it’s data.

Comparing the Properties of Insulation Materials

Posted on July 15, 2016 by Martin Holladay, GBA Advisor

We’ve all seen tables that list the R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. per inch for a variety of insulation types. These tables are handy, of course, but because old information is endlessly republished, in some cases long after the old information becomes obsolete, the tables are often flawed. Most authors make little effort to update these tables in light of the latest information from researchers.

Construction in Cambodia

Posted on July 8, 2016 by Martin Holladay, GBA Advisor

A few weeks ago, I accompanied my wife Karyn, who is a pediatrician, on a three-week trip to Cambodia. She volunteered her services at the Angkor Children's Hospital in Siem Reap, in response to a request from hospital administrators. The hospital invited her to Cambodia to provide two weeks of specialized medical training for the hospital staff.

Lucky me: I got to tag along.

Siem Reap is a bustling town in northwest Cambodia, only a few miles away from the world-famous temples of Angkor Wat.

Can Rural Living Be As Green As Urban Living?

Posted on July 1, 2016 by Martin Holladay, GBA Advisor

Rural residents are surrounded by greenery and breathe fresh air. Urban residents are surrounded by concrete and breathe polluted air.

On the other hand, rural residents live in wasteful single-family homes and depend on private cars for transportation. Urban residents live in efficient apartments and use public transportation.

So which lifestyle is greener? According to most analysts, urban living is better for the planet than rural living. But a few aspects of the question remain unsettled.

Resilient Food Supply Systems

Posted on June 24, 2016 by Martin Holladay, GBA Advisor

GBAGreenBuildingAdvisor.com has published a lot of articles about resilience — for example, articles pointing out that well-insulated buildings with low levels of air leakage are more resilient than code-minimum buildings. In other words, in the event of a disruption to energy supplies, such a building can ride out a cold spell — even one lasting for weeks — without risking frozen pipes.

A few GBA bloggers, including Alex Wilson and Tristan Roberts, advise anyone concerned about resilience to consider where their food will come from during an emergency.

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