Loading ...
Sorry, an error occurred while loading the content.

Re: Rammed Straw

Expand Messages
  • Ruth Andrade
    Hi Everyone, I have a few comments, first being based in Brazil, TIBA promotes the use of earth buildings a lot: adobe, rammed earth, super adobe, wattle and
    Message 1 of 19 , Sep 21, 2012
    • 0 Attachment
      Hi Everyone,

      I have a few comments, first being based in Brazil, TIBA promotes the use
      of earth buildings a lot: adobe, rammed earth, super adobe, wattle and
      daub, etc. So strawclay would already offer more thermal insulation than
      say just adobe. It's also quite appropriate for the climate. We really
      don't need a lot of thermal insulation in Brazil.
      Also, while living in Portugal last year, I was involved (mainly doing the
      cooking and organising volunteers rather than actually building :-/ ) in
      the restoration of an old stone ruin which was rebuilt as lovely cottage.
      The ruin has 2 walls standing, one next to an immense boulder that served
      as the third wall and the fourth was rebuilt in strawclay.
      The strawclay worked quite well and again, because of the climate, high
      insulation values are good but not essential. The wall was made too thick
      at 400mm, so it took a very long time to build. In hindsight, we could have
      been made a lot thinner, 200mm-250mm. The thick version took a long time to
      dry.
      Anyway, for Brazil strawclay is a very good option, better than strawbale
      in my opinion.
      Regarding the muddy waters... that's probably the Brazilian-English version
      of clayslip ;-)

      Regards,

      Ruth


      [Non-text portions of this message have been removed]
    • Chris Green
      ________________________________ From: Derek Roff ... I agree that this would be a much better approach for framed construction,
      Message 2 of 19 , Oct 5, 2012
      • 0 Attachment
        ________________________________
        From: Derek Roff <derek@...>
        <..clip....>


        > I'm favouring an 18" Larsen Truss wall system (for frame buildings) these days. R-56+, with R-80 to 100 in the ceiling. :-)

        I agree that this would be a much better approach for framed construction, although very careful detailing would be needed to get to the R-56 rating. Dr. John Straube of BuildingScience.com and the University of Waterloo, Canada, endorsed high levels of insulation, saying at the International Straw Builders' Conference that going to R-100 in the ceiling causes an increase in comfort that occupants notice, in addition to the energy savings. <.....>

        I have studied the Larsen Truss illustrations at BuildingScience.com and other sources (Fine Homebuilding) carefully, and intend to build some kind of portable jig to be able to build the truss assemblies in a consistent manner. I have chosen to go for the 18" depth rather than the 12" shown in the various designs. 3 layers of mineral wool = 16.5", plus a layer of spray foam about 2" will actually give something link R-67.5 for the mineral wool+ 2x R-4.75 or so = oh, a heck of a lot. R-77 or so, minus whatever is subtracted because of the doors and windows.
         A bit more than the R-56 I said.
        Expensive, but cheap in the long run.

        This version is for stick-built projects, obviously.

        The Larsen truss set up I am working on is a 2x4 load-bearing inner stud with a 2x3 outer stud part, with spacers and gussets. The last time I estimated the price, the L-Trusses would cost around $7-8 each, which isn't too bad, considering they should be able to be set 24" O/C,  but prices have gone up a bit in the past while.

        I haven't priced out the insulation yet, but that will come.

        The truss assembly will be cantilevered out from the floor assembly, umm, 14.5" or so, to allow the 2x4 sill plate to run along the edge of the flooring,  and the system will run down the wall a bit to the foundation. Maybe lower.

        As Dr. Straube says, careful detailing is important, but that's true in any system.  In B.C., code calls for a smoke barrier at the top of stud cavities where double wall systems are used, a detail which currently isn't shown in a some of the L-Truss systems varieties.

        I've drawn up a first iteration of this idea using SketchUp, but I'm not quite happy with some details, so I'll be redoing the work to make changes.  Once I get that done, I can then build the truss jig.

        And then go look for an opportunity to build something... :-)

        Cheers,

        Chris Green.

        <......>

        He also stated that a straw bale has an R-value of 3-3.5 per inch, and that the earlier, lower numbers that have been widely reported have been contradicted by more recent and more precise testing. Of course, the R-value for a whole wall will be less than the R-value for a single unit of insulation (such as a batt or bale), and careful construction is important to achieve maximum insulation.

        Humorist Dave Barry reached a similar conclusion, when he described insulating his house. He concluded that it was impossible to install batt insulation properly, and in the end, suggested just dropping the rolled up batts into the crawl space, smearing some caulk on the spiders, and calling it done.

        Derelict

        Derek Roff
        derek@...

        [Non-text portions of this message have been removed]
      • Chris Green
        ________________________________ From: Ruth Andrade To: SB-r-us@yahoogroups.com Sent: Friday, September 21, 2012 10:35:00 AM Subject:
        Message 3 of 19 , Oct 5, 2012
        • 0 Attachment
          ________________________________
          From: Ruth Andrade <ruth.andrade@...>
          To: SB-r-us@yahoogroups.com
          Sent: Friday, September 21, 2012 10:35:00 AM
          Subject: [SB-r-us] Re: Rammed Straw


           
          Hi Everyone,

          I have a few comments, first being based in Brazil, TIBA promotes the use
          of earth buildings a lot: adobe, rammed earth, super adobe, wattle and
          daub, etc. So strawclay would already offer more thermal insulation than
          say just adobe. It's also quite appropriate for the climate. We really
          don't need a lot of thermal insulation in Brazil.
          <....>
          I downloaded a replacelment copy of Gernot Minke's book, Building With Earth, and in it I noticed he advises us that the use of straw in warm, humid climates can allow for certain insects to inhabit the walls. The insect to worry about in South and parts of Central America is a family called 'kissing bugs'. These are carriers of Chagas disease, which can cause blindness and other health problems in humans. 
          This parasitical disease is endemic in those regions.   (See the map at the Chagas Disease wiki page)

          So, given this, the use of rammed straw in the infected regions should be approached carefully. Adding Borax to the clay slip might help keep the insects away, but that has to be tested by competent researchers and compared to un-boraxed wall assemblies.

          Until then, maybe pass  on  using this method in Brazil, Florida, etc.  
          http://en.wikipedia.org/wiki/Chagas_disease

          Elsewhere, the insect which is the host for this can't survive the cold winters, or (as in Africa) isn't present.


          <...>
          Anyway, for Brazil strawclay is a very good option, better than strawbale
          in my opinion. <

          And I'm now thinking that a bit more thought be put into this, as I've explained.

          To download a pdf copy of  Gernot Minke's book, Building With Earth,  go here:

          http://archive.org/details/Gernot_Minke-Building_With_Earth

          Cheers,

          Chris Green.

          [Non-text portions of this message have been removed]
        Your message has been successfully submitted and would be delivered to recipients shortly.