by • April 10, 2014 • Building Science, Housewrap & Waterproofing, Insulation & Air SealingComments (20)15021

Joe Lstiburek’s “Perfect Wall” concept. (The 500 year house!)

  What if I told you I could build a house that would have a life cycle of 500 years?  A house that would be so durable that the usual issues of rot & decay would take generations to break down this house… 
  I’d like to introduce you to “The Perfect Wall” by Joe Lstiburek & Building Science Corporation.  This blog post is a summary of an article that Joe wrote and is available for free on their website from this link.   
  It wasn’t that long ago that houses were built from rocks.  Think about the Roman Colosseum, that structure has stood the test of time!  Rocks were an separator between the outside and the inside.  Rocks are certainly durable, but they aren’t great at keeping the weather & water out of a house.  Construction has evolved and houses today need 4 basic layers to control the inside from the outside.
  These four control layers (in order of importance) are:

  1. a rain control layer (water)
  2. an air control layer (air)
  3. a vapor control layer (vapor)
  4. a thermal control layer (heat)

  This order is really important because if you can’t keep the water out of your building who cares what insulation you’re using.  If air is leaking into your building who cares about your vapor control layer.
  The best location for these layers is outside the building.  When we had buildings made of rocks there wasn’t much issue if the rocks (structure) got wet, but now that our houses are mainly wood & steel we need to move these control layers outside of our structure.
  But what about the insulation, aren’t we typically putting that inside the house?  Yes, but is that the best place for it?  Will it protect the structure from the heat/cold extremes if it’s outside?  What if we put the insulation on the OUTSIDE of the building, then it would do a terrific job of protecting the structure from expansion, contraction, corrosion, decay, & UV.  If it’s a chilly day outside, would you put your fleece jacket on your body OR would you eat your fleece jacket so it would be in between your ribs?  That’s not a perfect analogy, but you get the picture.  Insulation on the outside makes perfect sense. 
  Next, let’s talk about air control.  Doesn’t air carry with it moisture?  When air leaks into our buildings it tends to drop that moisture when it hits a condensing surface.  Water is bad for both wood & steel’s longevity so we need to do a good job controlling air if we want to control water in our buildings.  It’s also important to control air flow through our building because of what the outside air might have floating among it.  In Texas we have some nasty allergens, pollens, molds, etc.  If air is leaking into our buildings those nasties are coming along for the ride.  Once we control the air flow we can properly heat/cool, dehumidify, filter, and bring in fresh air when we want to & on our terms.  The best place to control this air flow again is outside of our structure. 
  That’s the Perfect Wall!  The rain, air, and vapor control layers are all outside the structure; then the thermal control layer is outboard of those layers.  That Insulation layer outboard of the other layers means that the control membrane also gets protected from heat/cold extremes. 
  Now, we’ve only been talking walls here.  The physics doesn’t change with floors or roofs, so to get the perfect roof just pitch the wall, same for the slab.  

I’ve been thinking about this concept for years, but I’m finally building a “Perfect Wall House”.  Here’s a wall diagram to whet your appetite.  But, Stay tuned for The Perfect Wall Austin blog posts next week….

The Perfect Wall.  Concept by Building Science Corp.  Executed in Austin by Risinger Homes & Rauser Design
The Perfect Wall House Austin – Architecture by Rauser Design – Construction by Risinger Homes

Matt Risinger
Risinger Homes in Austin, TX

Risinger Homes is a custom builder and whole house remodeling contractor that specializes in Architect driven and fine craftsmanship work. We utilize an in-house carpentry staff and the latest building science research to build dramatically more efficient, healthy and durable homes.
Be sure to check out my video blog on YouTube, and follow me on Twitter @MattRisinger
You can also check out my new Amazon Store here with Matt Risinger approved items.      

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  • rj

    Houses built from rocks: Most European and Chinese homes are built from ‘rocks’ or rock like materials including masonry and steel. It seems the ‘disposable’ mentality of the US combined with a need to get everyone a standalone home has perpetrated the culture. Along with plenty of trees to harvest, at least initially.

    • rj, I agree on the disposable mentality. I also get frustrated by the lending situation that uses “comparable” houses and purely price/foot appraisals. It’s hard to get a well built house to appraise compared to a poorly built house of 5-20 years ago. But, enough of the rants. It’s time to do something about this situation! That’s where my blog comes in, I hope that I can reach enough like minded people who are interested in building to a higher standard but don’t know the path. This “Perfect Wall” concept is ready to take off around the country. Thanks as always for reading and commenting. Best, Matt

    • The Perfect Wall and the best blog on the web!! Let me know how much for the DVD of the seminar.

    • Ryan, Too funny! Here’s my first video on this topic!

  • One of the concepts I took from Lstiburek’s book on building in hot/humid climates like Austin is that we have to control from the outside-in, which this wall seems to do very well, but also provide the ability to dry from the inside-out. With vapor barrier over OSB how does this wall dry from the inside?

    • Paul, With the air/water/vapor barrier on the outside we need to ensure that anything that gets past that barrier can dry to the inside. We are in an air conditioning dominated climate so we are generally dehumidifying our houses 9 months of the year. I’m also installing a stand-alone dehumidifier in all my houses that’s set to 50% RH and left there all year. So, if anything wets the OSB on the outside it can dry to the interior. In this particular house we aren’t installing inside insulation, nor are we installing drywall. It would be VERY easy for this house to dry should it ever get wet. On a typical house using this method you’d want to be careful not to use any vapor barriers on the inside. No plastic visqueen, no faced insulation products, no vapor barrier paints on the sheetrock, etc.
      Thanks for commenting! Matt

    • “… nor are we installying drywall.” – Matt

      Do tell more. Sure sounds interesting.

    • James,
      Yes indeed. No interior insulation, no sheetrock. Stay tuned. Many more blog posts to come. It’s a pretty awesome house. Matt

  • Matt,

    Your corrugated siding is nothing more than a rain screen, with the thousands of screw holes and terrible flashing details that go with it. So what keeps the insulation from getting wet? Don’t you think you need a water barrier behind the metal siding?

    The treated 1x4s will cause the fasteners to fail. Even stainless and galvanized will corrode and fail in a short amount of time. Have you seen the NRCA position on treated wood?

    • John, Thanks for commenting and for your concern. Yes this siding is indeed a rain screen. Like all claddings water will get behind it and that’s why the rain screen system is so important. The 1x battens provide a free flowing drainage plane for air to circulate and dry the assembly. The water barrier is the CCW 705 which is on top of the framing.
      Regarding the treated 1×4’s, they are treated with Micronized Cooper Azole MCA which is far less corrosive to fasteners than previous generations of treated wood. See their site for details but Hot Dipped or equiv is approved.
      Best, Matt

  • Sir,
    I am really looking forward to your series on the perfect environment separator. I hope you will give your usual treatment of closely detailing subjects such as: insect screen at the top and bottom of the rain screen vents, external sheathing tie in to window bucks, external insulation connection to foundation, and roof to wall detail. Are you planning to “clip on” a roof overhang on this house or leave as is (or should I exercise a little patience)? I like the idea of attaching a roof overhang in order to minimize risks with having holes in the water/vapor barrier but unsure on how to execute the idea. Again thank you for your work and I look forward to closely following your progress.



    • Trent, I plan to blog the heck out of this project! I’ve been taking TONS of pictures and I’ll be doing many posts on this one.
      Just to answer a few of your questions now:
      -Roof overhangs. With the “Perfect Wall” we want want a 100% continuous water/air/vapor barrier. Overhangs interrupt that continuity, so we wrap the house in an upside down U shape with the barrier then add overhangs as necessary. In this house’s case, we are using porch roofs and awnings over most of the doors/windows. The house will have a big 10″ box gutter but no over hang – per se.
      I’ll be posting pics of this soon.

  • kerrywebster

    Are there any written materials on building with this technique? I am looking to build a small cabin in the North Texas/Southern OK area and would like some technical information.

    • Look at for more info. I’m just finishing this house and should have some future blog posts and hopefully an article in Fine Homebuilding coming soon too. Best, Matt

  • noah jensen

    Matt, How do you deal with roof overhangs and window/door installations on this system?

  • Michael Bender

    Matt, I’m in NC doing a remodel and am wondering about running this system all the way down over the foundation. Do you think the carlisle product would seal to brick/masonry foundation? I’m thinking if I dig out around the house to add a perimeter drain along the footer that I can run this assembly, primarily the foam all the way down to the top of the aggregate for the drain so any water that does get behind the system can drain into the perimeter drain. Then I get my closed crawl space as well. What details did you use at the foundation of this system?

    • Matt Risinger

      Michael, I wouldn’t do that as you’ll have some termite and ant tunnels ready made in that install. Do a break in the foam before you hit the ground, then pick it up sub-grade with a Borate treated foam like Nissus Bora-Foam. OR, go into your crawl and insulate from the inside. Best, Matt

    • J Webber

      I realize this is 5 months ago. However, as a former pest control guy, if you run foam down to grade you WILL have termite/bug problems.

      • Michael Bender

        Thanks. I haven’t started this project yet so still very relevant. I wonder how or if it is possible then to fully insulate a crawlspace down here in the south on a retrofit.

  • GapUp

    Why not use 45 mil EPDM?