Roofs and ceilings are where most of the heat in your home escapes and thus is where you want to install the most insulation. Properly detailing the roof to prevent losing valuable winter heat in the greenhouse we are currently building was a major priority. You can certainly use the typical fiberglass insulation you find down at the home improvement box store but there is a natural way to insulate.
Using slip-straw also known as light straw clay we accomplish the same effect of fiberglass insulation without nearly the same manufacturing process. Slip-straw is also much more pleasant to work with than fiberglass insulation.
Slip-straw is the simple combination of a paint-like consistency of clay (slip) and straw. The clay inhibits mold growth, allows the mixture to be compacted and stay together, and also is a fire retardant.
In this application, we did a 3.5″ layer of slip-straw installed between rafter bays of the greenhouse roof. To prevent the slip-straw from eventually failing due to gravity, we used both milled lumber lathe as well as willow lathe nailed to the bottom of the rafters. One of the major advantages to slip-straw over say strawbale is that it can be used to retrofit existing structures very quickly and easily. With a small crew of five we were able to install slip straw along the roof, the top of the bales, and in several other details all in one day.
The next steps after the slip-straw has dried will be to install the first layer of plaster. A slideshow from the workday is below.
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