September 1, 2015

Builder Spotlight: Maria Klemperer-Johnson of the Hammerstone School and Hammerstone Builders

The builders, architects, and building owners we work with never cease to impress us.  Our customers bring a level of experience and deep commitment to high performance construction that is inspiring, with many committed to the same goals we share around foam-free construction and favoring the use of more natural building materials and techniques.  When we came across Maria Klemperer-Johnson, a builder and educator in the finger lakes region in upstate New York, we instantly knew we’d found another fascinating practitioner with a powerful story.  So we asked Maria to share a little about what brought her to 475, what projects she’s working on, and what’s important to her and to her clients, both in her school and in her professional practice.  She also writes quite well, so we’ll let her tell her story:

I (Maria) have been working as a builder in the Ithaca area since 2002.  I started in a cabinet shop, then worked for a conventional builder, and in 2005 started working as a “Natural Builder” when I built my own timber frame, straw bale home.  I worked for several years exclusively working on straw bale construction, but in recent years have been working on more conventional homes.  However, my background in straw and mud has always informed my approach to home construction.  My interest in good air sealing and weatherization was bolstered by experiences renovating several high end houses fewer than 15 years old that were suffering from severe rot (through to framing).

Hammerstone School's June class framing the tiny house

Hammerstone School’s June class framing the tiny house

In 2013, I started Hammerstone School: Carpentry for Women with the mission of increasing the number of women in the trades.  The school teaches short form, a-la-carte carpentry classes.  Our 2-day basic skills class is a favorite, but we also delve into more complex carpentry in rough framing classes and trim classes.  While our main focus is hands on skill building, we always seize the opportunity to discuss building science.  Since our inception, we have been organizing our longer classes around tiny house projects.  They offer all the elements of home construction in a scale that we are able to tackle in a week long course.  We try to offer a 5-day tiny house framing course and a 3 to 5-day tiny house trim course every summer.  Next year we hope to add a class on tiny house insulation and weatherization with our good friends and colleagues at Snug Planet (

In the fall of 2014 we started a contracting wing of Hammerstone School called Hammerstone Builders (my previous construction business was called Double Dog Timberworks  We do high end residential construction with a focus on high performance foam *free* methods.  In addition to timber frames, renovations, and new construction, we also do a lot of work on the tiny houses that are class projects for Hammerstone School.

The tiny house we are working on this year is the third we have been involved in.  All of the tiny homes we’ve worked on have been custom designed for the client, and each has a very different flavor.  The one we’re working on now is unique because the homeowner was interested in a foam free house.  The challenge with tiny houses (especially in our climate) is to squeeze enough insulation into the walls (which are constrained in their exterior dimensions) without losing too much interior space.  Because of that, and despite my aversion to foam, I usually recommend a spray foam wall system for both its high R value/inch as well as its low weight per R value.  I was thrilled, however, when Amy approached me with the challenge of a foam free wall assembly.

The first tiny house we built used salvaged polyiso foam boards in 2×4 wall cavities.  The biggest heat loss in my estimation in this house comes not from minimal R-value, but from inadequate air sealing.  In a house this small (165 sq ft), there is a very small volume of air inside.  Any air leakage can create significant heat loss.  The framing details around the wheel wells on the tiny house trailers present significant air sealing challenges.  So, when approaching Amy’s foam free house, I was adamant that a really well detailed air barrier was essential.

Interior: Amy had decided on Roxul insulation.  The comfort batts between the 2×4 studs provide R15.  To increase the amount of insulation, to reduce thermal bridging, and also to create a plane where we could incorporate a minimally penetrated air barrier, we put 2×2 strapping horizontally 16″ O.C.  We installed 1.5″ comfort board between the strapping for an additional R6.  In the ceiling we had 5.5″ of comfort batt with 1.5″ of comfort board.  Because the air barrier is 1.5″ behind the wall coverings, we are able to minimize penetrations through the air barrier to 2 – electrical wires (one feed for the house, and one exterior light), a water line, a gas line, a heater vent, an on demand hot water vent, and two HRV penetrations (more on that later).  We used INTELLO wrap for the air barrier because of its ability to let the wall system dry to the inside.  All seams, subfloor joints, and window openings were taped with TESCON VANA, and penetrations were (are being) sealed with ROFLEX gaskets.  This is the first time we have used many of these products, and we’ve been impressed with their quality.

Hammerstone crew working on the air sealing details at the windows

Hammerstone crew working on the air sealing details at the windows

Comfort batts in stud bays, continuous Intello air barrier, horizontal 2x2 furring strips creating utility chase, 1.5" comfort batt

Comfort batts in stud bays, continuous Intello air barrier, horizontal 2×2 furring strips creating utility chase, 1.5″ comfort batt


Sealing penetrations to the air barrier with ROFLEX gaskets

Sealing penetrations to the air barrier with ROFLEX gaskets

Exterior: Amy (like many prospective tiny house owners) has a tight budget, and we spent a lot of that on the high quality products for the interior.  The exterior weatherization is also a critical part of the entire home system, especially since we minimized overhangs to increase usable interior space.  We chose to go with a lower price weather resistive barrier (Tyvek), but to use high quality products in critical locations: We used SOLITEX UM [a vapor open, waterproof roof underlayment with integrated 3D mesh] on the roof under her metal roofing to create a drainage plane that allowed drying to the exterior (critical in a cathedral roof); and we used EXTOSEAL ENCORS tape for site built sill pans in the windows and door.  We were thrilled with the ease of use and quality (stickyness) of the Extoseal.  To be sure that the Tyvek drainage plane performs, we installed a 1/2″ vented rainscreen, and sealed all penetrations with ROFLEX gaskets.

Sealing penetrations to the WRB to prevent water and air intrusion

Sealing penetrations to the WRB to prevent water and air intrusion

Tiny House being raised and sheathed

Tiny House being raised and sheathed

Exterior of tiny house showing WRB and rain screen furring strips

Exterior of tiny house showing WRB and rain screen furring strips

Air quality:  Because a tiny house has such a small volume of air, it is critical that with well detailed air sealing (as we are aiming for) that there is mechanical ventilation.  We decided to use a pair of LUNOS e² HRVs.  They are small enough to fit in a house this size.  We also are using direct vent propane appliances (Rinnai space heater and EccoTemp hot water heater).

endquoteWe’re excited for the opportunity to take our air sealing and weatherization details to this level on this tiny house.  We are working on scheduling a blower door test to see how well we did.  And the real test will be this winter as Amy lives in her new tiny house.

We’re excited for her, too.  From using a service cavity to limit penetrations to the air barrier to thinking about moisture control and adequate ventilation with airtight construction, Maria pays attention to details and guides her client through a project that will help her accomplish her goals of comfort, health, indoor air quality, and energy efficiency.  Big ups to Amy on her willingness to acknowledge that there are alternatives to foam.  We hope to check in with Maria as she gets her blower door results back, and with her school to see all of the great leadership she is providing to women in the trades.


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3 Responses to Builder Spotlight: Maria Klemperer-Johnson of the Hammerstone School and Hammerstone Builders

  1. zpetruso March 11, 2016 at 2:08 pm #

    I was just given a link to this page from a support member at Great read, curious to see the results of the blower door test. Does it live up to the PHPP specifications? I will be building a similar tiny house in the near future similar to this one. How did the LUNOS work out!? I would love to see the finished product!

    In my opinion, the lack of code(s) for the construction of tiny houses on wheels could take a page from the PHPP guidelines, especially considering efficiency plays such a key role in their sustainability, low energy usage and flexibility.

    It’s good to see construction held to such a high standard, even in tiny homes!

    • John March 11, 2016 at 2:18 pm #

      Good question. We’ll have to check back in to see the results, and let you know. I can tell you the LUNOS has been a big seller for tiny house enthusiasts. In our experience we’ve found that one pair of e2 work best, as opposed to trying to run the house on one eGO unit.

      Keep in touch with the Monthly Newsletter – we’ll post updates to blog posts there.

    • Craig January 9, 2017 at 6:40 pm #


      Long delayed response! We just checked in with Maria and her blower door number on the tiny house was 34 CFM50, which came out to 1.34ACH50. Will let you know if we get more direct feedback from Maria or Amy about Lunos in a tiny house, but as John said, they are fairly popular in the tiny house community and I’m sure you could find some feedback somewhere online. I hope you’ve had a chance to make some progress on your project – if you need any advice, let us know.

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