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Why Are Houses Built This Way?

Missing OSB sheathing, waterproofing tape attached to air, duct work and air handlers in unconditioned attics: Is this what homebuyers really want?

Posted on Jul 20 2015 by Scott Gibson

Readers of GreenBuildingAdvisor's Q&A forum, and the bi-monthly Q&A Spotlights, are probably used to thorough parsings of seemingly small details in high-performance construction. But reader Peter L. brings our attention to an elemental question: Are we still in the dark ages of residential building?

A case in point is a partially completed house near Phoenix, Arizona, that Peter says is missing only a layer of rigid insulation and building paperTypically referring to Grade D building paper, this product is an asphalt-impregnated kraft paper that looks a lot like a lightweight asphalt felt. The Grade D designation has come to mean that the building paper passes ASTM D779 (minimum 10-minute rating with the “boat test”) and different products are called out as “30-minute” or even “60-minute” based on D779 results. At times confused with roofing felt, roofing felts and building paper differ in two ways: felts are made of recycled-content paper, building papers of virgin paper; felts are made of a heavier stock paper; building papers a lighter stock. See also roofing felt. before it will be finished with a coat of stucco. The photos he sends show whole sections of wall without 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. , and a bizarre detail of using building tape to seal window flanges to nothing but air.

"Brand new build going up in Phoenix," Peter writes. "What you see is completely 100% framed and ready for stucco. The missing OSB sheathing is done on purpose. They do ‘open framing’ and use sheathing only where required. The rest is open 2x4 framing.

"They will stuff R-13 batts within the 2x4 walls, staple on some building paper, then put 1 inch of rigid 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. on the outside, and use conventional stucco to finish it off," he continues. "A recent blower door test on a home like this showed 15 air changes per hour. All of the ductwork and air handlers are installed in the 150°F unconditioned attic."

Construction at this level has some obvious problems and some not-so-obvious flaws as well. With no sheathing in spots, for example, burglars can get inside with nothing more formidable than a screwdriver.

Is this type of construction typical? And what would home buyers think if they could look beneath the skin of a house like this? Or maybe we're just generally too fussy. Those are topics for this Q&A Spotlight.

Damage to exterior foam and building paper is common

Peter describes the typical construction sequence after framing and partial sheathing this way: First, applying a layer of building paper, and second, a 1 inch layer of rigid foam insulation before the stucco crew moves in. But because some areas aren't sheathed, there's no solid support between the studs to prevent ladders and careless workers and tools from breaching the building paper, which is the weather-resistive barrier (WRB), and breaking the foam.

A lack of solid sheathing also makes a weather-tight window installation difficult, if not impossible. Window flanges should be taped to the OSB sheathing, but where sheathing is missing the tape is applied to nothing but air.

"When they stretch the building paper layer over the open void of the studs every 16 inches, they end up ripping the paper in dozens of spots because without the OSB sheathing there is no solid backing surface," Peter says. "The paper ends up ripping between the studs and they end up stapling the paper to open air since they miss the 1.5-inch stud area. They end up totally massacring the WRB."

Crews have an equally difficult time nailing the foam to the studs, so that layer, too, gets mangled. A lack of roof overhangs means that rain gets past the stucco layer, past the foam and ripped building paper, and in some cases right into the R-13 fiberglass batts in the wall cavities.

The lack of wall sheathing is also an invitation to easy entry by burglars. Once they figure out where the studs are located by tapping on the wall, it's not difficult to cut their way inside with nothing more than a utility knife.

"Yes, folks, that's how they build them in the Wild West," he says. "I come from the Midwest, where I lived in a home that was built in the 1960s. It never had a water leak through the wall and one couldn't break in by cutting a hole from the outside wall. That home that is 55 years old was better built than this junk they are putting up today."

Regional market conditions are a factor

Are shoddy construction practices the result of regional market forces? Dana Dorsett thinks so.

"My understanding is that local markets in much of the Southwest demands a very low price per square foot, which drives all sorts of cost-cutting measures (including rampant exploitation of undocumented labor) for builders to stay competitive," Dorsett writes.

"The skim-coat-of-stucco-on-1-inch EPS sheathing with the minimum amount of shear panels or cross bracing doesn't exactly offer much confidence about the longevity of the building, even if the big bad wolf doesn't show up to huff, puff, and blow the damned thing down," he continues. "But sadly, it seems to be the current standard in the region. I'm sure there are a lot of trailers that will last longer than some of these houses."

Also, local building codes are apparently no help.

Most Arizona building codes are based on the 2009 version of the International Residential Code, Dorsett says, which requires an inspection or blower door test results of 7 air changes per hour at 50 pascals or less — half the leakage rate of houses built like this.

"Maricopa County (the Phoenix metro area) does not require the blower door test," Peter replies. "The county amended any codes requiring blower door tests. The blower door test that was done was merely for reference purposes to see how tight or leaky these new homes are. "

And the result is very high energy bills for residents.

"The photo at the top of the thread is of course a two-story home and around 3,200 square feet," Peter adds. "They will install two 5-ton AC units, one for each floor. The monthly summer AC bill on this type of home will average around $350 to $500 per month depending on where the occupants set the temperature at. Typically, they set it at 79°F but for those who like it colder at around 75°F, they will see the $500 a month bill."

Is the local labor pool a factor?

Writing from neighboring New Mexico, Nate G suggests that part of the problem is that undocumented Mexican workers that make up most of the labor pool are more familiar with masonry construction than wood framing. Not taking advantage of their skills, he says, is a missed opportunity.

"You tell a bunch of Mexicans to lay block and plaster it, and they'll do a beautiful job, code or no," Nate writes. "You give them a pile of lumber and tell them to build a house, and it comes out like that mess, even with codes and inspections. They simply don't have the cultural knowledge of wood construction that others do; they can do masonry, but we don't ask them to do it here. They can't understand why.

That's not it at all, says GBA senior editor Martin Holladay. "Your obsession with ‘illegal Mexicans’ is entirely misplaced," Holladay says. "The fact that this house has almost no wall sheathing, and convoluted ductwork in an unconditioned attic, has nothing to do with whether the workers on the site were born in Denver or born in Guadalajara," he continues. "I'm sure that it was the developer who approved the design and specifications, and directed the contractors to install just a few sheets of OSB on the corners, and to route the ducts through the attic."

Construction workers do what their employers pay them to do, Dorsett adds. "It's an open secret that undocumented labor is widely (ab)used in the house building industry in the southern U.S.," he says. "But regardless of citizenship or other status, construction workers do what their employers pay them to do, at the quality standard that the employer demands...

"There are crappy builders everywhere, and if nobody is calling them to task on it, that becomes the accepted standard," Dorsett continues. "It doesn't take a lot of training or time to fix most of the construction detail issues in those pictures, but it does take some willingness on the builder's or inspector's parts to make it happen."

He doubts it would be much cheaper to insulate a house built with CMUs to code minimums would be much cheaper than stick-framing, but the difference probably wouldn't be huge.

"Still," he says, "if the market isn't asking for it, it won't get built. We can all shake our heads about the insanity of it all, but that's the way it is. Code enforcement is spotty even in the best of markets, all but absent in others."

Builders would do even less if they could

Peter spoke with one of the builders on the project he's documented, and learns that energy efficiency isn't very important.

"They stated that they would leave the wall cavities without insulation if they could," Peter says. "Granite tops and fancy kitchen cabinets sells homes. R-values and energy efficiency do not."

The sales brochure for these homes, he adds, is focused on square footage, fancy tile work, cabinetry, and molding, "and nothing at all about R-values and air-sealing techniques."

"Most people buying homes are clueless about what is inside of the walls, ceilings, or windows, or the missing OSB on the walls," he says. "It's all hidden behind drywall and stucco."

Our expert's opinion

Peter Yost, GBA's technical director, had this to add:

Why are we still seeing this sort of stuff in the 21st century? I think that this video, "If Cars Were Built Like Houses," provides part of the answer. Yes, quality can be achieved on the job site, but the process is inherently more than just challenging.

In this specific instance — production homes in hot dry climates — is there really any way that high performance can be achieved? I think so, for these reasons and with these caveats:

Open-cavity face-sealed stucco homes are being built regularly in the Southwest that comply with Energy StarLabeling system sponsored by the Environmental Protection Agency and the US Department of Energy for labeling the most energy-efficient products on the market; applies to a wide range of products, from computers and office equipment to refrigerators and air conditioners. Version 3.0 and offer thermal comfort guarantees and space conditioning energy bill guarantees. (See, for example, Environments for Living Platinum homes in Phoenix.)

Ducts in unconditioned space never cut it; high-performance production builders in the Southwest primarily insulate and air seal at the roofline.

If you include home security as part of the definition of a high-performance home, then “open-cavity” wall assemblies clearly don’t cut it. (Pardon the pun on “cut.”) But then there are “high-performance” production builders in the mid-Atlantic using thin-profile foil-faced panels (such as Thermo-ply who would not make the cut either.

To build high-performance buildings, you have to invest in training the trades, and when you do, they get it.

Many years ago, when I was working in the Building America program at Building Science Corporation, we did a case study on a production builder in Banning, California, who had the most amazing build team. (The guy’s name was Josh, but I can’t find the case study on the BSC or the Building America Solutions Center.) The “champion” was a very young project manager who trained, treated, and lauded every building assembly (and HVAC(Heating, ventilation, and air conditioning). Collectively, the mechanical systems that heat, ventilate, and cool a building.) contractor and their crews with 100% attention to detail. At a site meeting I was invited to attend, every single worker — right down to the young tiny guy insulating and air sealing all the lousy and tight spaces in their attics — was incredibly proud of his work and their product. These guys “fought” to stay on the crews working for this particular manager. Latino or Anglo—no one cared. It was doing good work with good results that drove this team and their work, and it really showed.

When you hear someone in the building industry say, “Buyers just aren’t interested in energy efficiency or performance,” it’s because they are not interested. I am so tired of hearing this; it is flat-out never true. Imagine someone buying a car or other “performance” purchase saying, “I don’t care about miles per gallon or horsepower or if the heater, defrost, or air conditioner works well.”

It’s not that home buyers don’t want performance or energy efficiency — they just don’t connect those attributes to their home purchase, strange as that may seem. If you make that connection for them, they move very readily from buyers interested in curb appeal and granite countertops to savvy performance-interested buyers. This would all be a lot easier for builders and buyers if realtors, appraisers, and lenders understood buildings as performance products too, but that is another problem I am tired of ranting on…

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Image Credits:

  1. All photos: Peter L

Jul 20, 2015 9:38 AM ET

Conventional stucco walls are easy to break into?
by Skip Harris

"With no sheathing in spots, for example, burglars can get inside with nothing more formidable than a screwdriver."

My understanding of a "conventional stucco wall" is wire and nearly an inch of masonry. Are you talking about eifs?

Jul 20, 2015 12:09 PM ET

Education of consumers
by Lucy Foxworth

Peter Yost pointed out something to me that I really hadn't questioned. We often hear that consumers don't really care about what is in the walls, only caring about features like granite countertops. I have always just accepted this statement as fact. Peter pointed out that this is really what builders and contractors think, NOT necessarily the truth. So what he is saying is that the consumers care, they just don't know how to evaluate energy efficiency. It's not something you can see.

My suggestion to Peter L. is to post these photos on a Facebook or blog or some other social media site called "State of the Art Homebuilding in Arizona" so people can actually see what is "under the hood". The builders do not have to be identified and really shouldn't be identified (to avoid legal issues), but people need to know how vulnerable these homes are from an energy and security standpoint. This website could also show what a "pretty good" build looks like. It has to be graphic meaning that it has to be visible, people have to see the difference to know the difference. Infrared photos comparing a normal home in Arizona and a well-built home will show how the heat infiltrates the home.

Jul 20, 2015 12:19 PM ET

Getting the word out
by Peter L

Scott, Martin, Peter Yost and everyone at GBA, thank you for bringing this to everyone's attention. As mentioned in the article, some Phoenix area home builders do care about quality and energy efficiency and are taking steps to build a better home. Sadly, they are the exception to the rule. I would estimate a 100 of these homes go up for every 5 they build.

What also surprised me is that mold was an issue in some Phoenix homes. Mold in a desert climate that sees under 8" of annual rainfall? Due to the poor building & sealing methods the wall cavities will get water damage and the fiberglass batts will get saturated with water. This happens during the monsoon season when heavy downpours hit and the outdoor humidity remains high for 2-3 months, making the wall cavity drying difficult. Once monsoon season ends, the rains subside and humidity drops so the walls will eventually dry out.

An interesting test is that once a home like this is built and it gets its first heavy monsoon rainfall where the stucco walls are completely saturated with moisture. In addition, during winter when Phoenix sees long duration rainfall that really saturates the house walls. Get a thermal image gun and walk around inside the home and you will find where all the water leaks are coming into the wall cavity. Window flashing attached to air is definitely not a good way to seal a window ;)

Jul 20, 2015 12:30 PM ET

Edited Jul 20, 2015 12:32 PM ET.

Not just Arizona
by rjp :

Most of these issues are common throughout the South, including most corporate builders from Texas to Florida. It's interesting that only the "better" homes include the green tube insect injectors in the walls. You still get ducts and air handlers in the hot attic, recessed lights without air sealing and fiberglass insulation in all but custom homes. It's not the labor's fault, it's clearly the market forces (less than $100 a ft) and the builders themselves. These markets are often fast growing; the school districts are better in the new communities and building codes are not enforced or are non-existent outside of the big city. It's often a seller's low inventory market. I would like to see home inspectors step up their game and warn consumers before they sign the papers. Most buyers do figure it out later and either default during a downturn or move on when they can.

Jul 20, 2015 12:35 PM ET

by Peter L

The conventional stucco walls they do out here are a 3-coat type of system. It definetly is NOT the old school type of stucco that had rigidity and strength. The system they use in a home like what is shown above is very weak. One cannot even use a masonry screw as the stucco would simply crumble. You can easily take a flat blade screwdriver and push through the stucco.

Jul 20, 2015 2:35 PM ET

What are "green tube insect injectors"?
by Lucy Foxworth

That sounds kind of crazy.

Jul 20, 2015 2:46 PM ET

Response to Lucy Foxworth
by Martin Holladay

See Image #3 on this page.

Jul 20, 2015 3:38 PM ET

Thanks, Martin.
by Lucy Foxworth

I thought I had looked at all the photos on the original post, but apparently not. Isn't effective air sealing one of the best barriers to insects and non-toxic too?

Jul 20, 2015 4:11 PM ET

Construction in the Wild West
by w d

I want to say I just don't believe it ..... but there it is.

I read this posting and couldn't help but laugh. And I kept laughing. Then I wondered what I was laughing about. I should be crying. By then I couldn't tell the difference. Can you imagine a house like this in Zone 5? They wouldn't survive a single winter!

It reminds me of the old movie promos you'd see at the theatre: I LAUGHED. I CRIED. IF YOU ONLY SEE ONE MOVIE THIS YEAR, SEE "CONSTRUCTION IN THE WILD WEST", staring materials fastened to air. YOU'LL LAUGH. YOU'LL CRY. YOU'LL THROW UP.

Please, please tell me this house was built on SPEC and not to a designer's or home owner's specifications.

Jul 20, 2015 4:24 PM ET

That's a great title for the homeowner education blog
by Lucy Foxworth

"Construction in the Wild West"

Jul 20, 2015 4:25 PM ET

Edited Jul 20, 2015 4:26 PM ET.

Response to W D
by Martin Holladay

W D,
You wrote, "Then I wondered what I was laughing about. I should be crying."

Back in 2009, I wrote a blog with the following introductory paragraphs:

"The average new home is so poorly built, it’s enough to make an environmentalist weep.

"Windows are routinely installed without any consideration of orientation. ... In the absence of legal requirements for high-performance windows, builders regularly choose windows with appalling U-factors and solar heat gain coefficients (SHGCs).

"In the southern U.S., air-conditioning ductwork is still routinely located in attics. Most builders insulate walls by hiring a low-bid subcontractor to stuff fiberglass batts between the studs. In the U.S., unlike in Sweden, most new homes receive occupancy permits without ever undergoing a blower-door test."

For those of us who regularly visit GBA, it's easy to forget how most U.S. homes are built. These building practices have been going on for a very long time... and it isn't easy to turn this supertanker around.

Jul 20, 2015 11:13 PM ET

Edited Jul 20, 2015 11:31 PM ET.

They can't build them fast enough
by Peter L

They are slamming up another 5 of these types of homes as I drove past a new subdivision. There are probably dozens of these homes being built all over the Phoenix metro area as of today.

Funny how the "wild west" of yesteryear was the wild gunman and outlaws that had no regard for laws, civility or life. The "wild west" of today are wild builders with no regard for quality, durability, energy efficiency and a comfortable dwelling.

Those asking about "pest tubes": It is basically a "band-aid" for poorly sealed wall cavities. Since bugs easily make their way into the home via the gaps in the bottom of the walls, these tubes are installed during construction and then every 3-6 months a company comes out and injects a high-pressure mist pesticide spray into the tubes which then disperses into the wall. This then kills the bugs of which consist of roaches, earwigs, crickets, scorpions and even Black Widows.

Jul 21, 2015 3:29 AM ET

This seems to confirm the
by Alan B

This seems to confirm the adage "build it and they will come". At the time nobody thought about build as poorly as possible.
I can't get over the fact one can punch their way through the walls, or use a drywall knife and cut their way in silently within a minute.

Jul 21, 2015 9:36 AM ET

Edited Jul 21, 2015 9:36 AM ET.

Labor vs. capital
by Meyer Brendan

I can't imagine a bunch of Mexican-Americans were just walking down the street one day, stumbled on a stack of framing lumber, and decided to build a house for fun. It's more conceivable that someone with money and plans has hired them and told them exactly what to do and is satisfied with the results. If Habitat can get people with no construction experience to build a house, surely a builder could do the same with the Phoenix labor pool (if they wanted to). I'm guessing the builder doesn't want to because they know they can sell it no matter what's inside the walls.

Jul 21, 2015 10:50 AM ET

Q: What do Mexican laborers have to do with this problem?
by Sam Meyer

A: Nothing!!

Jul 22, 2015 11:53 AM ET

That's not all
by Brad Carr

What's really going to scramble your noodle is when you find out they sale these homes for at least $350k. Following the economic downturn, there's now a pent-up demand for homes in the Phoenix area. The areas of unincorporated Maricopa County that are referenced in this article are on the far fringe of the Valley. I’m not surprised that these types of construction techniques are in use there. Buyers for these types of homes are the type that travel further and further away from the city center until they reach their affordability requirement. They simple are not concerned, or informed, about what makes a solid home. They just want a home. It’s easy money for a builder. I agree with Lucy, there needs to be a conscious effort to place the spotlight on these poor construction techniques.

Jul 22, 2015 4:23 PM ET

Why Are Houses Built This Way?
by George Hawirko

No OSB, Framed with Air and No Tapes, is the Future. The only thing is that most builders don't read the main copy only the headlines. Here is the Real Future Air House.

Jul 24, 2015 7:17 PM ET

Sample of education blog
by Lucy Foxworth

I wrote a sample blogpost on my blog about this topic. I think that if we had a good name for a blog or a Facebook site that would get on the search engines, I think we could have a decent shot at doing some effective education.
I am not a good writer. I just wanted to put a sample post out there just to try to get stuff started. I am also going to post this link on the Scott Gibson article about this topic.
Let me know what you think - titles for the blog, topics, etc. We'll see if we can get one started and have an impact.

Jul 27, 2015 1:59 PM ET

Edited Jul 27, 2015 1:59 PM ET.

Quicker life cycle construction
by Brian Godfrey

Every house has a life cycle. It is built, it is occupied, it is knocked down and replaced. Since the occupied portion seems to be getting shorter and shorter, it appears that these builders have decided to reduce the building portion of the life cycle with the expectation that it will just be knocked down in a few years anyway. Thus shortening the path from raw material to dump. This is a very great increase in efficiency for the building trades which will result in greatly increased profits. I need to invest in these companies. The next advancement will be when the building suppliers deliver their materials directly to the dump.

Jul 27, 2015 2:29 PM ET

Edited Jul 27, 2015 2:32 PM ET.

Drwaings, specifications and dedicated site supervision required
by Ernest Mueller

Thanks for this great article. Such issues should be published in major newspapers and magazines to educate potential home buyers and drive their requests for better built energy efficient homes.
I have seen what I thought was inferior construction in the Northeast, so when it came to build my own home I decided on “custom built”. I spent the money to produce upfront detailed drawings and specifications. In negotiations with a builder, some specifications where “relaxed’ on his recommendations. A contract was signed and every page of the specification initialed by the builder. He said that he would personally supervise the job.
Construction progressed quickly but when I periodically visited the site I noticed that some items where not done according to drawings or specifications. Builders seem to construct and install what they are used to, instead of following drawings and specifications in detail. When I pointed out deficiencies and requested corrections, too often I let myself talk into a compromise solution – decisions I came to regret later on.
The lesson is that detailed drawings and specification for quality construction or “unique” requirements are of little use if there is not a full time dedicated site supervisor to implement them. I wish I had Josh, the “champion” young project manager, which Peter Yost mentioned in the article, at my site!

Jul 27, 2015 3:54 PM ET

They Get Away With What They Can
by Rita Real

This type of construction is not limited to the Southeast. We had a luxury home built in Pennsylvania by one of the nation's top builders. No sheathing and just a aluminized paper that siding went over. Apparently more money in the builder's pocket could be the only reason. It is somewhat funny all of these homes had burglar alarm systems with door and window sensors. You could nearly puch your way through a wall.

Jul 27, 2015 4:35 PM ET

Top builders?
by Brian Godfrey

Just because a company calls themselves one of the nation's top builders, does not mean that they are. Bigger is rarely better. It's just more profitable.

Jul 28, 2015 2:22 PM ET

Rita's builder
by Chaz Steffen

Hey Rita, was your builders first name Ryan?

Jul 29, 2015 2:01 AM ET

Edited Jul 29, 2015 2:04 AM ET.

Batt Installation
by Peter L

Geez, they even butchered installing the fiberglass batts into the wall cavities. They ended up crushing and squeezing it in order to get it to fit. In one spot they squeezed it into tiny little ball like shapes and jammed it into the cavity. It's mind boggling.

Click on images to see larger picture.

BATTS.jpg BATTS2.jpg

Jul 30, 2015 4:42 PM ET

Edited Jul 30, 2015 5:52 PM ET.

Why Are Houses Built This Way?
by Eugenio Aburto

I am very impressed about the right observations of the writer, congratulations you know about the stick houses problem.
An answer to your question is the mix of tradition and ignorance. Tradition: my ancestor built with wood stick, I will build with wood sticks. Ignorance: in general people is not versed in the big range of construction materials and methods, it is not their fault. We professionals in construction need to show the advantages of other methods besides wood sticks.
I am an architect with several years of dealing with solving the people needs, as a sample, in the City of Mexico, where earthquakes are frequent, and is there a big need of affordable dwellings, I was requested to build 7,500 houses, very low cost, strong, and comfortable, the time frame was 18 month. The development site was close of a stone quarry, then I figure than masonry concrete pour in formwork will be the solution, then planed to have 25 sets of formwork to deliver 25 houses a day, the system was simple 25 crews of foundation were able to do footings and floor slab, previous waste lines to do such task in one day. The walls with the plumbing and electrical pipes, doors and windows placed on the forming using plywood panels and metal ties, were pour in one day, the next da moved to the foundation done the day before. The walls in place to receive the roof, which I design to use T-beam, the shape of the T was by having CMUs in between stems, the flange required a two inches thickness slab, preformed reinforcement was used, one day for this pour, we use concrete of fast time to reach the psi, required in the structural calcs; it made possible el removed the formwork to the next, to let the finishing people, paint, clean set kitchen and bath fixtures, electrical switches, and outlets, and cleaning the next two days, leaving the sixty day to owners receive the keys and move in.
I beat the time frame finishing the 7,500 in 15 months.
With that past experience I will try to offer to the wood stick people the alternative of have a house resisting natural disasters, a complete safe house, monolithic, and affordable.
I know it is a hard task, but I am confident that looking what concrete pour in place can do, will change the mind of some....
Thank Scott Gibson, you did great!
Some photos of the related above: a group of houses, foundation, walls done roof pouring, the roof T-beams preparation. A desert modern built in Cathedral City, California, the fist concrete house with R56 on walls and roof, saves power.


Jul 30, 2015 5:48 PM ET

The thermal performance requirements in Mexico City...
by Dana Dorsett

The thermal performance requirements of buildings in the temperate high altitude climate Mexico City are easier to manage than in Phoenix Arizona. The changes in temperature over any 24 hour period are comparable, but the year round temperate climate in Mexico City makes building with high thermal mass with little or no insulation a reasonable solution, whereas in Arizona insulation is a necessity. With the changes in season it's both much hotter and much cooler in Arizona than in Mexico City.

That's not to say that stick-building makes more sense than insulated concrete in Arizona, but it does need to have at least some insulation to stay comfortable without excessive energy use. R5-R10 rigid foam on the exterior of a poured concrete or CMU wall would be enough for most locations in Arizona, but in Mexico City even R5 might be extravagant.

I can't imagine building 7500 homes (even tiny, nearly identical homes) in 18 months, let alone 15 months. That is a HUGE project, averaging 500 houses per month! Do you have any pictures of the construction process to share?

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