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Green Building Blog

Designing for a Hot, Humid City

In an interview, architect Peter Pfeiffer shares lessons learned throughout his career as we look at a modern farmhouse his firm recently designed.

According to Barley/Pfeiffer Architecture, the driving force behind the design of this project was not just to create a comfortable, high-performance home, but to demonstrate how an empty-nester couple, who wants to reduce their carbon footprint, can be just as happy in an urban home that is less than half the size, and on a tenth of the lot of their former suburban Austin setting.

If you are interested in high-performance building for hot and humid climates, you probably have heard of Austin, Texas-based architect Peter Pfeiffer. Pfeiffer is an environmentalist, a building scientist, and an AIA fellow recognized for “ his achievements in mainstreaming green building in America over the past three decades.” He’s been recognized by the National Association of Home Builders for his advocacy of green building and by Fine Homebuilding magazine for designing “The Greenest Home in America” in 2003. He was involved in the development of the U.S. Green Building Council’s LEED for Homes program, has helped manufacturers develop innovative building materials including radiant barrier sheathing, has long been involved with Austin Energy’s green building program, and is a member of the city’s “Zero Energy Capable Homes Task Force.” A regular speaker at architecture and building conferences across the country, Peter is outspoken, opinionated, and sometimes controversial.

If you are interested in residential architecture and spend some time in Austin, you’ll soon be able to spot a Barley/Pfeiffer home. Barley/Pfeiffer Architecture is the firm Pfeiffer started with his partner Alan Barley in 1987. From the beginning, their intention was to build homes that conserve energy and water, maximize passive cooling strategies in their hot and humid climate, and offer owners healthy and comfortable indoor living. Barley/Pfeiffer homes are commonly sided with a combination of metal, fiber-cement lap siding, and native-stone veneer. They have metal roofing, deep roof overhangs, awnings, and other shading devices, which are all part of their distinctive style. Barley/Pfeiffer homes are not necessarily modest in size, though they are not shy about explaining to clients that their lifestyle is just as important as the performance of their home when it comes to environmental impact.

The 2450-sq.-ft. modern farmhouse shown here…

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  1. Sarah Burger | | #1

    The portions of the article about overhangs and the window designs were interesting. However, I think that the square footage of houses should be factored more into the conversation about efficiency. 2450 SF is a large house for two people, and the increased efficiency gains that are created by design and materials seem minimized in such a large house. Given that many of the builders who are leading the way in reduced energy use, improving indoor air quality and moisture control, are custom home builders, square footage and the size of houses in general seems to be conveniently omitted.

    1. User avater GBA Editor
      Brian Pontolilo | | #3

      I agree with you Sarah. Unfortunately, many homeowners are willing to shell out a lot of money for a lot of gizmos and materials to make their homes "green," but few are willing to live in a smaller home. Until or unless that shift happens, architect and builders like Peter and many of the folks who hang around GBA, will have to do their best to make those homes as durable, healthy, and efficient as possible, and hopefully continue to nudge clients towards smarter and smaller plans, little by little.

      1. Malcolm Taylor | | #5

        Most thoughtful designers and builders probably have a tipping point - a line they won't go beyond where the client's wishes conflict too strongly with their principles. But before that point it seems reasonable to assume if you don't do the work someone else will, and perhaps your involvement can in some way mitigate the project's shortcomings. If I sat around waiting for the perfect clients - well I'd end up doing a lot of sitting around.

  2. James Howison | | #2

    Fascinating stuff, thanks for including a hot humid article :)

    I'm intrigued by the "no dehu" argument, as it goes against others advice (e.g. Risinger). I'd love to know what the metric for air quality they use to argue for open windows vs dehumidification. We've found the dehu to be wonderful in the shoulder seasons (dewpoint of 75 at 70 degrees is fairly common, but we don't have no fancy thermal syphon in our one story house ;)

    Certainly opening windows for cross flow is great for VoCs smells and Oxygen, but given that the house is going to be closed for 6 months for AC (and 2/3 for winter) so you are going to have to manage those separately anyway. The trouble I see is that once you get a bunch of humid air in the house, it's hard to get it out other than running the AC, which then super chills the air (without a dehu).

    Also I'd love to know what they do with directly west facing windows, impossible to shade with overhangs (probably pick a site and design that avoids them, I'm guessing!).

    1. User avater GBA Editor
      Brian Pontolilo | | #4

      Thanks for the comment James. I will follow up with Peter with some questions and post the replies in a couple weeks.

  3. User avater
    Stephen Sheehy | | #6

    Is there ever a compelling reason to use spray foam in a new house?

    1. Malcolm Taylor | | #7

      I can't think of one in our climate, and it does seem like it comes up here on GBA as the best solution to solve what were essentially design errors, but I don't know the first thing about hot, humid climates, so maybe this is the one region where it makes sense?

  4. Andy Kosick | | #8

    I differ with Pfeiffer on a few points to be sure, but the best thing he said (and it's going to stick with me) is "if you can air condition above the dew point, you are doing yourself a favor". I think I'll adopt this as a design criteria, comfort above the dew point.

    We just had a 78F dew point he in Michigan yesterday, which is about as bad as it gets here and that happens to be the temp we keep our house at. With a VRF heat pump and a dehu in the basement it keeps the RH at or below 50% and it's comfortable. Most homes around here have oversized ACs and maintain 70F to 72F and often only about 65% RH. Pfeiffer's statement makes it even more clear to me how problematic this is, it's honestly not as comfortable and also asking for more moisture related problems.

  5. Todd Witt | | #9

    It is my opinion that open cell spray foam is essential in the attic in building a house in a hot, humid climate. It allows the ductwork to be brought into a semi-conditioned space. I would like to know more about the details on the flash and fill in the walls. My advice is to never use closed cell foam in a wood structure in hot, humid areas. You noted that the wall assembly often becomes a steam iron and this steam will for the most part be trapped from entering the house by the closed cell foam and it will eventually rot the wood exterior sheathing. Why wouldn't you just use open cell foam in the entire wall cavity? You said the wall R value in the wall cavities is R11? How is that achieved with flash and fill in a 2 x 6 wall? In most hot and humid areas where I see flash and fill or flash and batt used most installers install less than 1/2" of closed cell foam and then do a horrible installation on top of it.

    1. User avater
      Dana Dorsett | | #10

      >"It is my opinion that open cell spray foam is essential in the attic in building a house in a hot, humid climate. "

      It's cheaper, greener, and more moisture-resilient to go with rigid foam board above the roof deck, which keeps all the structural wood inside the thermal & moisture boundary of the house. Spray foam on the underside of the roof deck is often the path of least resistance in retrofits, but less than optimal, and completely unnecessary in new construction.

      An IRC 2018 code-min roof in zone 2 & 3 would be U0.030 (which is R33 "whole assembly", including the R-values of the roofing, nailer decks, structural roof, ceiling gypsum, and interior & exterior air films.) That can be met with as little as 5" of rigid polyiso above the roof deck. If that's too thick 2-3" above the roof deck with 5-6" of damp sprayed cellulose on the underside of the roof deck gets you there.

      >"...the wall assembly often becomes a steam iron and this steam will for the most part be trapped from entering the house by the closed cell foam and it will eventually rot the wood exterior sheathing."

      Not necessarily- rainscreened well vented cladding can fix 99.9% of those issues. But the described assembly was:

      "R-5 continuous exterior insulation on the walls and another R-11 in the wall cavities, which is easy to achieve with 2×6 framing. ".

      The continuous R5 would also protect the sheathing from exterior moisture drives if done with rigid foam.

      Still the cost (financial & environmental) of closed cell foam as well as the lower performance due to the shorter path through the thermally bridging framing ( ) makes a full cavity fill of open cell preferable.

      But open cell foam is still not NEARLY as green as doing it with rock wool, fiberglass or cellulose. A continuous R5-R6 foil faced polyiso and R20 cellulose in the wall cavities would be cheaper, higher performance, and by far greener than anything that used spray foam in the cavities. The cellulose adds ample additional hygric buffering to protect the structural wood, and even a measurable thermal mass benefit.

  6. Michael Lind | | #11

    “It’s a sealed attic with a vented, radiant-barrier roof. It’s a good system,”

    Am I correct that the attic is "air open" to the interior of the house, possibly with a small supply duct from the AC ?

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