Thursday, June 8th, 2006 | Popularity: 6%
If you want a super insulated roof, add a layer of rigid insulation on top of the roof assembly or add an extra framing member to deepen the joist cavity and add more insulation. There are environmentally sound insulations out there and ultimately, the roof will have less embodied energy and will be more environmental if done in a standard frame. Consider engineered lumber uses smaller trees, cotton insulation uses a renewable resource. Now compare that with ferro cement, poles big enough to handle the weight of the bales and the cement, 1×4 nailers, a heavy moisture barrier, chicken wire, and all his is experimental and may fail. To me this is another example of trying to place bales in a section of a building where they do not belong. My two cents.
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I simply must ask: WHY? Why use bales as a roof insulation? The amount of time, effort, cost, and embodied energy in such a task seems to me to heavily outweigh the benefits. If two string bales yield an R-value of R-40 (debated by the way) across the 18″ direction, then one would only achieve an R-40 roof at best (perhaps a bit more with the inclusion of the other construction materials. A standard roof assembly provides R-38 so what on Earth is the point?
If you want a super insulated roof, add a layer of rigid insulation on top of the roof assembly or add an extra framing member to deepen the joist cavity and add more insulation. There are environmentally sound insulations out there and ultimately, the roof will have less embodied energy and will be more environmental if done in a standard frame. Consider engineered lumber uses smaller trees, cotton insulation uses a renewable resource. Now compare that with ferro cement, poles big enough to handle the weight of the bales and the cement, 1×4 nailers, a heavy moisture barrier, chicken wire, and all his is experimental and may fail. To me this is another example of trying to place bales in a section of a building where they do not belong. My two cents.
Popularity: 6%
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Andrew Morison is a licensed contractor specializing in straw bale and green construction. He has shown thousands of people how to build their own straw bale projects through his comprehensive series of instructional straw bale, concrete foundation, and plastering DVDs. You can check these out at http://www.LearnStrawBale.com.
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September 6th, 2007 at 12:18 pm
Jan Verstricht from Mol said…
My roof is straw bale insulated. Designed with engineered lumber et. I did not use ferro cement or chicken wire for my roof. In any case, so mass should be incorporated in the roof: thermal mass (heat in summer), a heavier roof won’t blow away with the heavier storms that we should anticipate, etc. And it can also carry a green (extensive) roof system…
Maybe your reaction is based on some non-ecological design you have seen (btw, I hope no pesticides have been used for the cotton - I would rather suggest Isofloc or equivalent cellulose or wood fibre insulation).
In any case, bales are usefull also in the roof (and in my floor !).
Best regards from Belgium,
Jan.
jan_1965@yahoo.com
September 6th, 2007 at 12:21 pm
Andrew Morrison said…
Jan,
Thanks for your comments. I have seen bales used in living roofs and in other applications. In the case of a living roof, the design is going to call for the added structural elements to handle the weight of the load anyway, so I can see no problem with that. What I am commenting on is using bales simply as roof insulation in place of other insulation. There is no need for it. Again, R-40 versus R-38 does not justify the added materials and labor required to add the bales to the roof. I do not think that bales should not be considered if a living roof is in the design, but to simply replace insulation with bales above the walls is a waste of time and materials. Also, keep in mind that the more weight you have up high, the more risk you have in your walls. Engineers can explain it better than I can, but the idea is that the more weight you have up high, the more risk you have of your walls toppling over. It is always a good practice to minimize weight up high on any building, so adding bales to the ceiling not only requires more framing up high, but more framing and engineering in the walls. Again, it is a waste in my opinion.
9:16 AM