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Posts Tagged ‘north-america’


Autoclaved Aerated Concrete (AAC): Will the U.S. Ever Lighten Up?

Sunday, February 5th, 2012

Lighter, more fire-resistant, and a better insulator, autoclaved aerated concrete caught on in the rest of the world ages ago. It’s taking a lot longer in the U.S.

The porous AAC structure comes from being “leavened” with aluminum. Photo: H+H UK

To read what manufacturers and distributors say about it, you’d think autoclaved aerated concrete (AAC) was some kind of new, space-age environmental miracle.

Although it certainly has some nifty properties, AAC isn’t new and isn’t miraculous–but it’s certainly popular in Europe, and has been for decades; according to one source, it accounted for 60% of all new construction in Germany in 2006. It has enjoyed pretty flat market share (of near zero) here in the U.S., though, since it was first introduced in the 1990s.

Is there space for AAC in the U.S. market? Should the green building community be working to make space?

How AAC is made

AAC is similar to other concrete types, except that it contains no aggregate; sand or fly ash is included, with aluminum powder added to react with one of these ingredients and “leaven” the concrete, creating tiny bubbles just like baking soda does when it reacts with the buttermilk in your muffin batter. (Your muffins are full of carbon dioxide bubbles, but AAC is full of hydrogen bubbles.)

[Note: Robert Riversong points out in comments that sand is aggregate, which I also thought when I started researching it, but after some more digging, my understanding is that the sand is used as a reactant and is therefore not considered aggregate in AAC. For more, see here.]

The concrete is poured into molds, left to rise, and then “baked” in an autoclave, which uses steam and pressure to complete the chemical reactions and speed up the curing process significantly–completing in hours rather than weeks. The resulting blocks are so full of bubbles that a block of the same size has about one-fifth the material required by regular concrete.

Like conventional concrete masonry units, AAC is sold in a variety of block shapes and sizes, but unlike conventional units, most don’t have cores. They are porous and light, like muffins, but not hollow.

Benefits of AAC

The main advantage of AAC when it was first developed in Sweden in the early 20th century was simple: it wasn’t wood. It’s still not wood, but in North America (unlike in Sweden at the time and in most of Europe now), wood is still plentiful and cheap.

Compared with conventional concrete, AAC still has advantages, though:

  • It uses less material–important for concrete, since portland cement is one of the most energy- and carbon-intensive building materials.
  • Despite the energy-intensive autoclaving process, manufacturers say it takes about 50% less energy to make, because of the lower portland cement content by volume (we’re haven’t found anyone to challenge those claims, but are still looking for data).
  • It’s lighter, which cuts down on transportation costs and fuel use.
  • It’s a better insulator, with a steady-state R-value just a hair above R-1 as opposed to something more like R-0.2 (neither of these factors in thermal mass, which we’ll get to later).
  • Air leakage is minimal.
  • AAC also has excellent soundproofing properties.
  • It can also be used as a firebreak.

Drawbacks of AAC

In a report written for UC–Davis (PDF), Stefan Schnitzler finds few disadvantages to AAC. Here are the two demerits on his list:

  • There are few manufacturers in the U.S. (that was in 2006, and now there are almost none, since Xella has moved its Hebel operation to Mexico); this means higher costs, which is a huge barrier for adoption.
  • AAC requires a learning curve for builders, because the mortar application is more precise.

We would like to add a few drawbacks that we’ve found:

  • The barriers for builders don’t stop with the mortar. According to Derek Taylor, owner of AAC distributor SafeCrete, the only manufacturer in North America right now is a German company whose block dimensions don’t work for U.S. builders. These often need to be sawed, adding labor and fuss to a building system that’s supposed to be simple. (Taylor’s looking forward to two new plants coming online in the States in the next couple years.)
  • Since right now your AAC is most likely coming from Mexico, the advantages offered by lighter weight will diminish significantly as the mileage increases.
  • Thermal properties are better than those of conventional concrete, but they aren’t good enough to make AAC a viable wall material (relative to BuildingGreen-recommended R-values) in most U.S. and Canadian climates without additional insulation. (The European climate, where AAC is popular, is milder.)
  • Unless rebar is added–which adds to the weight and amount of material in the blocks–AAC can only be used for low- and mid-rise construction. But it seems to be popular for single-family homes as well as schools.
  • Unlike conventional concrete, AAC can’t be used as a finish; it is more porous and needs cladding or stucco on the outside so it won’t absorb moisture.

AAC is popular for residential construction but not suitable for high-rise buildings without structural reinforcement. Photo: SafeCrete

Would you use AAC?

That said, AAC does appear to have significant advantages for applications where conventional concrete would normally be the best material–like in the American Southwest and in other climates where thermal mass can increase the“effective” or “mass-enhanced” R-value of the wall. Even then, its performance may still be outmatched by that of insulated concrete forms, depending on the needs of the client.

Unfortunately, much of the information we have on AAC performance in the U.S. comes from manufacturers. We’d like to hear some empirical evidence from the field.

Are you using AAC on any of your projects?

If you’ve used it, how did it perform? If not, what would it take for you to try it out?

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In the UK, Even Boathouses Are Passivhaus

Sunday, January 9th, 2011

Aerial view from river

Designed to Passivhaus standard,  Associated Architects‘ new boathouse at King’s School, Worcester started on site last month.  The Michael Baker Boathouse is the eighth building to be completed as part of the architects’ ten year masterplan for the school and is located at the edge of Worcester’s historic city centre.

The existing one storey boathouse will be replaced by a two storey, 821 m² building that raises the main areas above the flood level; connects it to the school via a walled garden and improves views along the River Severn.  Facilities include boat storage, changing, training and teaching rooms and a school community reception space.

Prow perspective

The premise of reduction is adhered to here, with the annual heating demand below Passivhaus standard <15kWh/m2 and airtightness at Q50=0.6m3/m2hr. Renewable energy features prominently with a mix of solar thermal to supply 75% of hot water and solar PV for 50% of electrical demand. Heating will be supplied by a wood pellet biomass boiler.  The services engineer for the project is LEDA.

Passivhaus certification is anticipated upon completion in December 2011.

View from River Severn

Base building cost:                      £1,455,376/£1,772 per m²
Archaeology abnormal:              £43,412
Foundations abnormal:              £49,076
Renewables:                                 £44,704
Net cost including above:           £1,592,569/ £1,939 per m²
Total inc fit-out fees & VAT:       £2,500,000

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Passivhaus Boathouse

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Will Garden Shed Home Offices Catch On in North America?

Saturday, November 6th, 2010

Credit: Eco-Hab

Uncle Wilco shows us yet another british Garden home office design, the O-Pod. It’s full of green goodness like FSC timber andrecycled insulation, from Aidan Quinn , who previously built the lovely Eco-pod. There are so many of them now.


I discussed the future of sheds in America with Alex Johnson, author of Shedworking: The Alternative Workplace Revolution, and suggested that conditions were very different in the UK. My points:

  • The climate is more extreme in much of America;
  • People have greater expectations of the temperature and humidity of their workplace being stable and within a couple of degrees of ideal;
  • People have bigger houses, often with basements, so that they can find space within the home to have an office;
  • People are more security conscious and would not leave expensive hardware in a backyard shed;
  • People are obsessed with the price per square foot of everything and find them too expensive.
  • Where’s the fridge?

On the other hand;

  • Sheds provide a distance and separation that one often needs for work;
  • It is cheaper and more flexible than adding a room;
  • It is a great opportunity to experiment and mix a little modern into your life;
  • If it is used only for work it is probably fully tax deductible.
  • If you are moving home to mom because of the recession, it is a cheaper way to get a little space.

Original Post by Lloyd Alter, Tree Hugger
Will Garden Shed Home Offices Catch On in North America?

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Gorgeous Radiators From Jaga Save Energy And CO2

Sunday, March 28th, 2010

jaga hydronic heating radiators photoVery few houses have hydronic (hot water radiator) heating in North America; most have forced air systems with ductwork that does double duty as heating and air conditioning, supplying air to the wrong place at least half of the year. Almost everyone in Europe and those of us in older houses have radiators; it is quieter, there are no bulkheads for ductwork, and there is less dust moving around. But a big problem is the inertia, or thermal lag; it takes a long time for the temperature to change when you move the thermostat or the sun comes streaming through your windows. The Belgian radiator company Jaga

This green surface is full of holes
Published: March 25, 2010


Click this picture to view a larger image.

Scott Erickson, owner of Quality Conrete and Evolution Paving Resources, demonstrates how his pervious concrete products works. On the right, he poured water onto an ordinary concrete surface. Much of it remains there. On the left, he pours water onto the pervious concrete, where it is almost instantly soaked through the concrete and into the ground, which reduces rain runoff. Temperature readings showed the water poured onto the pervious surface was nearly 20 degrees cooler.


Of the Keizertimes

Who knew concrete could help the environment?

Yet Scott Erickson, who has been selling pervious concrete throughout the northwest for about seven years now, says it can not only do that – it can save the customer money in the long run.

Erickson owns both Evolution Paving Resources and Quality Concrete, operating off a property just a hop, skip and a jump away from Wheatland Ferry.

In the world of stormwater runoff, large parking lots and driveways are a nightmare for environmentalists. It’s not the substance itself – it’s what rests on the concrete. With a solid concrete structure, water collects, then eventually runs off into ditches or wherever the downward slope takes it.

That water – and everything that gets in it, including oil, brake dust, cigarette butts and other substances found on roadways and in lots – then flushes untreated into local waterways, which can have devastating effects on streams and rivers.

Not so with pervious concrete technology. The water seeps through the concrete almost immediately, sinking into the soil below, which acts as a filter. This minimizes water runoff, reducing harm to local waterways.

And with new federal restrictions on stormwater runoff, it can also save money. Local governments are now assessing its households and businesses for stormwater runoff, calculated in large part by the square footage of impervious surface on a property. The roof and concrete or asphalt parking areas are among the largest culprits.

“Cities are starting to say, ‘We can’t just dump this in a ditch anymore, or even build detention ponds,'” Erickson said. “It has to be treated.”

To demonstrate, Erickson took a jug of water and poured it simultaneously onto standard asphalt and onto the pervious concrete. Not only did the water seep into the pervious surface while it pooled on the asphalt, the water was also significantly cooler.

The asphalt surface was 110 degrees Fahrenheit dry. A few seconds after pouring, the water on it was 103 degrees.

On the other hand, the pervious concrete was 103 degrees dry. And moments later, the wet area with just a trace of water was 83 degrees.

This distinction is important, Erickson said, because warmer water suddenly flowing into streams is unhealthy for water life.

“That temperature held in the pavement, when exposed to water, is deadly to fish,” Erickson said. “That’s an issue a lot of people forget about.”

The basic theory behind it has been around for years, Erickson said. He first learned of it when he traveled to Florida to see an early version of the technology.

With standard concrete, you start with different sizes of aggregate rock. Sand is used to fill the remaining gaps, creating a solid, non-penetrable surface.

The non-pervious concrete eliminates some steps. The same size of rock is used throughout, creating gaps. Erickson says to think of it as a bowl of same-sized marbles. However, the adhesive qualities that bind aggregate for concrete also binds the rocks used in the pervious surfaces.

Erickson said selling the stuff was initially difficult as the original designs were useful, but not very pretty to look at.

“I went out of my way to make it look not so harsh,” he said.

He still faces skepticism from some engineers, mostly those who aren’t familiar with the product, he said.

“Engineers are used to dealing with something they’re comfortable with,” Erickson said. “Their reputation is on the line.”

But the customers that take the leap are finding it cost-effective, he said. A residential customer in Portland, he said, is saving $55 per month in stormwater fees over similar-sized lots with impervious driveways, he said.

And while a few customers are really into the green aspect, he said many of his customers had few other alternatives.

He recently donated labor to install the driveways at two Habitat for Humanity houses in Keizer. They were nowhere near the city’s stormdrain system, and to connect would have been prohibitively expensive.

With the pervious surface, Erickson said the property wouldn’t have to be connected at all to the stormdrain system.

“If they would have had to put in a formal storm drain, their project wouldn’t have been viable,” said Bill Lawyer, public works superintendent for the city of Keizer.

Fred Meyer and WinCo stores in Vancouver, Wash., have also been using them because they would have had to install expensive pipes or find ways to retain stormwater either on-site or underground. Keeping it above ground renders a portion of the land unusable, while underwater tanks are quite expensive.

“They do it because we’re the low-cost alternative,” he said.

Original Post by Lloyd Alter, Treehugger:
Gorgeous Radiators From Jaga Save Energy And CO2

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Alex’s Cool Product of the Week: Zehnder’s High-Efficiency HRV Systems

Sunday, March 21st, 2010

Our next feature article for Environmental Building News is on the Passive House standard for ultra-low-energy buildings–a standard that originated about 20 years ago in Germany. Excitement about Passive House in North America is resulting in some really cool products being introduced from Europe. One of those is the Zehnder line of heat-recovery ventilators (HRVs) and associated components.

I had a chance to spend some time with Barry Stephens, the national sales and marketing manager for Zehnder America at last week’s Building Energy Conference, sponsored by the Northeast Sustainable Energy Association (NESEA). Zehnder is a Swiss company that specializes in hydronic heat distribution, heated towel racks, ground-source heat recovery, and advanced heat-recovery ventilation systems. Runtal, a more familiar brand in North America, is a Zehnder company.

Zehnder’s ComfoAir systems are the highest-efficiency heat-recovery ventilators available in North America. They use counter-flow air-to-air heat exchangers, while most HRVs in North America rely on parallel-flow heat exchangers. With counter-flow, the ComfoAir can achieve heat-recovery efficiency of over 90%, according to Stephens. This is the only HRV available in North America that is Passive House-certified.

Both heat-recovery (HRV) and energy-recovery (ERV) versions are available. HRVs bring in fresh air, exchanging heat with the outgoing interior air; any moisture in either air stream is retained. ERVs exchange both heat and moisture, so that moisture levels in the house neither increase nor decrease appreciably as a result of the ventilation; this is important for applications where you want to either keep unwanted moisture out of a building or keep it in.

Just as interesting as the HRVs and ERVs from Zehnder are the modular, small-diameter ducting systems. The ComfoAir systems rely on “home-run” ducting. Analogous to home-run plumbing systems, home-run ducting relies on a central manifold and flexible 3″-diameter HDPE flexible ducting that extend from the central manifold to each location in the house where air is being delivered or exhausted. The ducting is small enough to install in stud cavities, and a small bending radius makes installation easy. In Europe these ducts are often installed in concrete floor slabs, but that is not typical here.

The ducting has a smooth interior to minimize friction and a corrugated exterior for strength. Lengths of ducting snap into the manifold using super-simple connections, taking just seconds and sealing extremely well without duct mastic. It’s what you would expect of Swiss engineering–clean, precise, and elegant. Simple balancing components are provided in the outlet registers.

  • The company offers various other components:
  • Silencers that acoustically isolate the ComfoAir HRV or ERV unit from the ducting to limit noise;
  • Sophisticated and elegantly simple control modules;
  • Bathroom switches that communicate wirelessly to the control modules using radio-frequency signals;
  • A unique antifreeze-filled ground-loop ComfoFond-L to temper inlet air and prevent frost (in Europe the company offers earth tubes to pre-condition ventilation air, but Stephens doesn’t recommend those in North America, due to moisture concerns);
  • Small, in-line “post-heaters” (made by Electro Industries in Monticello, MN; to condition the ventilation air–often the only heat that’s needed in ultra-energy-efficient Passive Houses; and
  • Through-the-wall baffles to passively distribute ventilation air in a home.

The ComfoAir 350 is the most common model, providing 350 m3/hour (225 cfm). A smaller 200 model delivers 125 cfm, and a larger 550 delivers 350 cfm. All use advanced ECM motors to maximize energy efficiency.

As one might expect, the ComfoAir ventilation system, with all its bells and whistles, isn’t cheap. A typical residential system for a fairly compact house will run $6,000 to $6,500 installed, according to Stephens, with installation accounting for about half the cost–plus another $2,500 to $3,000 if you want the ComfoFond-L ground loop system. An in-line electric duct heater providing about the output of a hair dryer will add another $500 to $600.

Zehnder’s ComfoAir was introduced to North America in November, 2009, and the website is just going up this week (check back next week if the site doesn’t yet include the Zehnder ventilation products). To date, about a dozen systems have been installed, mostly in Passive House projects.

For more information:

Barry Stephens
Zehnder America, Inc.
Greenland, New Hampsire
888-778-6701, 603-422-6700

Original Post by Alex Wilson, Building Green

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A PassivHaus Renovation: Heritage Meets Energy Efficiency

Sunday, February 21st, 2010

rear-facadepassivhaus britain design energy efficiency photo front

In the UK and North America, heritage buildings are under serious threat; our history is being bulldozed under the false mantra of energy efficiency when in fact, most buildings can be insulated, sealed and brought up to a much higher standard without throwing away the embodied energy stored in those bricks.

That is why this Victorian terrace house in West London is so interesting; the builders are not just doing a renovation, but are going for the PassivHaus standard, tough to do in new construction and perhaps impossible in a heritage structure like this.

The PassivHaus standard is tough to meet; it requires a lot of insulation, really low air infiltration and a compact form. Old houses often meet the latter requirement but leak air like sieves.

Tom Pakenham (and Sophie, Baby Luke and the Green Tomato Team) are “charting the epic conversion of a draughty, freezing, solid brick walled Victorian house into a cosy, efficient and beautiful home for the 21st century.” They hope to prove that “low-energy houses are not only much more comfortable living spaces than the old clunkers we live in now, but also don’t have to look like a nuclear bunker.”


There is a lot more than a lot of insulation going into this house; it has solar thermal, solar photovoltaics, (all carefully integrated into the slate roof) a green roof, ground tubes for preheating and precooling fresh makeup air; a green roof and rainwater harvesting.

Along the way, they have to fight with those nasty heritage officials who like chimneys and slate roofs and brick exteriors. Maintaining the historic character means that they have to insulate the front facade inside, with 130 mm of high efficiency rigid insulation. This eats up a lot of space, and these houses are not very big to start with. That is one reason so many older houses get wrapped in that horrible exterior styrofoam and stucco.

But there is another problem with interior insulation of this magnitude: heat loss through the exterior walls will be virtually eliminated. A little bit of heat loss through old brick walls drives out moisture; if you get rid of it completely, there is the possibility of freeze-thaw cycles causing the brick to deteriorate. Fortunately London doesn’t get too many of these.

The new roof.

The real challenge with Passivhaus design is controlling air infiltration; the detailing around those bay windows will be interesting. Tom notes:

Because we are renovating and have to fill lots and lots of gaps and cracks, this component is likely to prove the biggest challenge. About halfway through the build, we will bring in a special door called a blower door and test the whole house for air leakage. We hope to fill or tape up any leaks that we find.

Good luck; it is almost like building a house within a house.

Rear Facade

The PassivHaus standard is difficult to achieve, but is an important goal, using less than a tenth the energy of a typical home. To do it in a retrofit of a protected heritage building is a real accomplishment; I am not sure that it can be done, and I don’t think Tom is either. But even if they get close, it is still a spectacular achievement. We will be watching closely.

More at the Ecohome by Green Tomato

Post by Lloyd Alter, Tree Hugger

Standard 189.1 to Provide a Strong Foundation for High-Performance Green Buildings

Sunday, January 24th, 2010

ATLANTA—A new standard for the design of high-performance green buildings is set to revolutionize the building industry. Published by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), in conjunction with the Illuminating Engineering Society of North America (IES) and the U.S. Green Building Council (USGBC), Standard 189.1, Standard for the Design of High-Performance, Green Buildings Except Low-Rise Residential Buildings, is the first code-intended commercial green building standard in the United States.

The standard, published Friday, provides a long-needed green building foundation for those who strive to design, build and operate green buildings. From site location to energy use to recycling, this standard will set the foundation for green buildings through its adoption into local codes. It covers key topic areas similar to green building rating systems: site sustainability, water use efficiency, energy ef­ficiency, indoor environmental quality and the building’s impact on the atmosphere, materials and resources. For complete information on the standard, including a readable copy, visit

The energy efficiency goal of Standard 189.1 is to provide significant energy reduction over that in ANSI/ASHRAE/IESNA Standard 90.1-2007. It offers a broader scope than Standard 90.1 and is intended to provide minimum requirements for the siting, design and construction of high performance, green buildings.

“The far-reaching influence of the built environment necessitates action to reduce its impact,” Gordon Holness, ASHRAE president, said. “Provisions in the standard can reduce negative environmental impacts through high-performance building design, construction and operations practices.  Ultimately, the aim is not just energy efficiency but a balance of environmental responsibility, resource efficiency, occupant comfort and well being and community sensitivity, all while supporting the goal of sustainable development.”

“IES is pleased to be a cosponsor of this standard that will have a significant impact on requirements for high-performance green buildings and the building industry as a whole,” Rita Harrold, director of technology for IES, said. “We congratulate the Project Committee for the tremendous effort and dedication of its members in the fast track development of a consensus standard.  We look forward to continuing the partnership with ASHRAE and USGBC as the standard continues to evolve through future continuous maintenance proposals.”

“Greening the building code is fundamental to the U.S. Green Building Council’s goal of market transformation and is also a critical factor in how the building industry is working to mitigate climate change,” said Brendan Owens, VP, Technical Development, U.S. Green Building Council. “We’re extremely excited to see our collective efforts over the past three years come to fruition in the form of this important standard.”

Standard 189.1 has been written by experts representing all areas of the building industry, including engineers, lighting designers, sustainability experts, building owners, designers, architects, code and compliance officials, utilities, materials experts and equipment manufacturers. The technical requirements in the standard were also supported by input from the building industry during the public review process.

To order, contact ASHRAE Customer Service at 1-800-527-4723 (United States and Canada) or 404-636-8400 (worldwide), fax 404-321-5478, or visit

The cost of Standard 189.1 is $119 ($99, ASHRAE members)
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