Slip straw (straw/clay) stuffed between metal roofing and wire mesh.

Slip straw (straw/clay) stuffed between metal roofing and wire mesh.


Straw/clay roof insulation diagram

Straw/clay roof insulation diagram


Straw/clay roof insulation cross-section

Straw/clay roof insulation cross-section


Roofs present a number of challenges, including how to provide adequate, affordable insulation so the home remains comfortable. Straw/clay, also called straw slip clay is one low tech, low cost solution. The basic process involves making thin slurry of clay and water and then mixing this with straw.

The following information is quoted from An Insulation for San Pablo.

Goals
“Our goal is to create a new roofing system that will provide better insulation properties than that of corrugated steel. This material should be:
• inexpensive
• easy to construct
• fabricated from local materials
• supportive of the local economy
• light-weight
• environmentally friendly
• durable

Our Proposed Solution
We suggest that San Pablo improve the insulation of its houses by infilling its roofing system with slip straw. The slip straw would be stuffed between roof framing members, underneath the existing corrugated metal roof. Chicken Slip straw, is a natural building material that is made of loose straw coated minimally in clay slip, which is clay diluted with water to the consistency of a milkshake. Slip-straw is used as an infill panel built between framing members; it is tamped by hand or with a stick between “slip forms” and finished with plaster, which would act as a fire and moisture barrier.

Environmental and Cost-Benefit Analysis
As there is no environmental impact from our current insulation method, we compared the carbon footprint of the production of different insulation methods, including western methods, which include fiberglass insulation. There is no carbon footprint generated by using our insulation system.”


Comments

Straw/clay Roof Insulation — 13 Comments

  1. Would this also work with metal building walls? I know there can be an issue with moisture building up in strawbales if they cannot dissipate moisture. Is it the same with slipstraw if there is metal on one side? We want to build our home with metal but still have the benefits of straw and plaster walls.

    • If anything, it’s even more important that straw-clay be able to dry to both sides than it is for straw bale, because there is moisture in the mix and a higher likelihood of mold if that moisture can’t escape quickly. It may be possible to install some sort of vented airspace between the straw clay infill and the metal siding. I have never done this myself, but I’ve heard ideas on how to do so. I have been working lately with ‘ricecrete’, a combination of rice hulls and lime, that is extremely mold-resistant and also better insulation than straw-clay. If you live near where rice is grown and have access to rice hulls, this could be a good option. I would say, however, that ventilation in general is going to be a huge concern for any metal-sided building.

      good luck,
      Michael G. Smith

  2. thanks for the article

    I’m doing my bachelor research project entitled “Acoustic and thermal insulation of steel roofing sheets using straw. this article gave some hints about my research but I have some questions

    1. can we use slip straw without putting these wire mesh??
    2. are there any other chemicals used in binding?

    if anyone have some tips, papers which can be useful can please help me.

    Thanks

    • You need some way to support the slip straw in position. One way is with lath made with saplings, split bamboo, reeds, etc. Do one section at a time so it’s easy to add the slip straw. You could also use fishing net which is very low cost and durable. No chemicals are needed, although borax is a good natural additive to help deter insects. Clay is the only binder needed. Make sure it’s sticky enough. Also, make sure you leave space between the metal and the slip straw for proper ventilation. Improved acoustics is one of the main advantages of this system. Many school children in poor countries can’t hear the teacher when it starts to rain. In Nepal they’re using a drop grid ceiling using bamboo and slip straw. This provides space for extra insulation. And of course don’t use loose straw because it’s a fire hazard and attracts rodents.

      • Thanks Owen Geiger for your help, my supervisor suggested that we can use bitumen(by painting it or kinda of) on the metal sheet before laying on the straw on it, and he thinks that the straw will be attached on the sheet no need of supporting it!!

        any comment about it?
        can it really work?

        Thanks for your time

    • Hello I happen to be doing my bachelor research project in the same field , in case you got papers kindly share them to me.thanks

  3. What is the benefit of mixing clay slip with the straw versus plain straw? I would think that the clay slip would reduce the effectiveness of the insulation.

    • It does a little bit, yes. But this is a timeless technique that’s proven highly effective and can last hundreds of years. It was one of the standard building techniques in Germany at one point and is still very popular.

      The clay slip deters insects, reduces risk of fire, helps prevent mold…

  4. The rafters have to be strong enough so they don’t flex excessively under a load or the plaster will crack. Instead of plastering the ceiling, consider other materials such as reeds, bamboo mat, wood, etc.

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