The most recent blogs at Green Building Advisor

Three Reasons to Remove Attic Floor Insulation in a Sealed Attic

Posted on August 10, 2016 by Allison A. Bailes III, PhD, GBA Advisor in Building Science

I get asked a lot of questions about spray foam. Do I need an ignition barrier? Should I use open-cell or closed-cell spray foam? Will open-cell spray foam really rot my roof?

But the question I get more than any other on this topic is about whether or not the insulation on the attic floor should be removed when insulating the roof deck in an existing home. As you can tell from the title of this article, my answer is to remove it. Here are my three reasons, in increasing order of importance.

Looking for a Breakthrough in Cement and Concrete

Posted on August 9, 2016 by Robert Hutchinson in Guest Blogs

The toughest climate challenges involve large global industries, with no good substitutes. One of these literally produces the material under our feet — concrete. Every year, each of us in the U.S. uses about one-third of a ton. Fast-growing developing countries use far more. Globally we produce over 4 billion metric tons of Portland cement per year — the key ingredient in concrete and responsible for the majority of its CO2 footprint — driving over 5% of total anthropomorphic CO2.

Floating Solar: A Win-Win for Drought-Stricken Lakes

Posted on August 8, 2016 by Philip Warburg in Guest Blogs

The Colorado River’s two great reservoirs, Lake Mead and Lake Powell, are in retreat. Multi-year droughts and chronic overuse have taken their toll, to be sure, but vast quantities of water also are lost to evaporation. What if the same scorching sun that causes so much of this water loss were harnessed for electric power?

Installing floating 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. arrays, sometimes called “floatovoltaics,” on a portion of these two reservoirs in the southwestern United States could produce clean, renewable energy while shielding significant expanses of water from the hot desert sun.

Capillary Breaks Above Footings

Posted on August 5, 2016 by Martin Holladay, GBA Advisor in Musings of an Energy Nerd

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.

Blue Heron EcoHaus: Blower Door Testing

Posted on August 4, 2016 by Kent Earle in Guest Blogs

Editor's note: Kent Earle and his wife, Darcie, write a blog called Blue Heron EcoHaus, documenting their journey “from urbanites to ruralites” and the construction of a superinsulated house on the Canadian prairies. Their previous blog on GBAGreenBuildingAdvisor.com was called Insulation, Air-Sealing, and a Solar Array. The blog below was originally published in January. (A complete list of Kent Earle's GBA blogs is provided in the “Related articles” sidebar below.)

Why North America Needs Its Own Passive House Standard

Posted on August 3, 2016 by Allison A. Bailes III, PhD, GBA Advisor in Building Science

There's this thing called passive houseA 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.. It's a terrible name. Almost everyone agrees on that. Look at how its adherents are driven to a frenzy and you'll see that the name doesn't really fit. The houses themselves aren't passive either, but let's leave that aside for now.

When Spray Foam Goes Bad

Posted on August 2, 2016 by Greg Labbe in Guest Blogs

When spray foam goes bad, it’s hard not to feel a bit sick. Sick because this high-performance insulation has a big carbon footprintAmount of carbon dioxide and other greenhouse gases that a person, community, industry, or other entity contributes to the atmosphere through energy use, transportation, and other means. and proper installation is key to its performance. When it’s not installed correctly, it can get expensive for the client, the contractor, and the planet.

How to Vent a Dryer

Posted on August 1, 2016 by Scott Gibson in Q&A Spotlight

The exhaust from a conventional clothes dryer is full of moisture and lint, and the best place to vent it is directly outside. Matt Culik knows this, but his particular situation makes him wonder whether there are circumstances when this rule might be broken.

Culik will soon be moving into a new house, and the intended laundry room does not have a vent connection for a clothes dryer. Coincidentally, he is planning to replace an old electric hot water heater with a heat-pump water heaterAn appliance that uses an air-source heat pump to heat domestic hot water. Most heat-pump water heaters include an insulated tank equipped with an electric resistance element to provide backup heat whenever hot water demand exceeds the capacity of the heat pump. Since heat-pump water heaters extract heat from the air, they lower the temperature and humidity of the room in which they are installed. , and this has given him an idea.

Batteries for Off-Grid Homes

Posted on July 29, 2016 by Martin Holladay, GBA Advisor in Musings of an Energy Nerd

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.

Green and Cool Roofs Provide Relief for Hot Cities

Posted on July 28, 2016 by Ashish Sharma in Guest Blogs

More than half of the world’s population lives in cities, and the United Nations projects that this share will rise to 70% by 2050. During the daytime, these expanding urban areas absorb more solar energy than the surrounding countryside. At night they radiate the heat back to the atmosphere. Higher temperatures in cities compared to the areas around them create what are known as urban heat islands (UHIs).

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