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Is exterior wood paneling on cob possible?

bp8963 | Posted in Green Building Techniques on

Hello,

My partner and I are located in France. I grew up in Maine and became found of farm houses. We are planning on building a cob house for cost efficiency; however, a few years down the line, I am curious if it is possible to add wood siding to the exterior of the cob later on? Again, I’m very found of the farm house look. Any suggestions or advice? Much appreciated. Merci beaucoup.

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Replies

  1. Expert Member
    Dana Dorsett | | #1

    The flatness of cob walls usually isn't super-planar, but I suppose you could make it fairly flat. One of the nice things about cob it the ability to make unusual shapes and curved surfaces, whereas most wood cladding tends to be fairly straight, which could be a practical/aesthetic issue if the underlying wall isn't very flat. As long as the wood cladding is back ventilated, with an air gap between the cob & cladding as a capillary break and drying path it should be OK from a moisture point of view.

    The topic has come up before on this forum:

    https://www.greenbuildingadvisor.com/community/forum/green-building-techniques/18345/exterior-siding-cob-walls

  2. GBA Editor
    Martin Holladay | | #2

    BP8963,
    The question hinges on fastening. If you know how to securely fasten vertical furring strips to a cob wall, then you should be all set.

    I think that the wall assembly would benefit from a WRB (perhaps housewrap), but you may have philosophical objections to the idea of a WRB. Whether or not you include a WRB between the furring strips and the cob wall, you need furring strips. Find a way to fasten the furring strips (long screws, perhaps?) to the cob, and you should be all set.

    The furring strips can be shimmed as necessary to get the furring strips co-planar.

  3. GBA Editor
    Martin Holladay | | #3

    BP8963,
    Some online research reveals that fastening furring strips to a cob wall won't be easy. I didn't come up with any great suggestions after reading these links:

    http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=2883

    https://forums.pigeonwatch.co.uk/forums/topic/290174-gun-cabinet-fixing-to-stonecob/

    https://community.screwfix.com/threads/cob-walls.4403/

  4. James Morgan | | #4

    I'll confess to being bewildered by this post - why on earth would you want to do this? First of all, if cob is an economical building material in your part of France the chances are it already 'is' the farmhouse look in your area. Farmers are generally pragmatic and economical people and the farmhouse 'look' in any given area generally reflects environmentally responsible local material options and construction technologies which local builders are thoroughly familiar with.

    But given that you do seem to have a hankering for a Maine farmhouse look, adding siding to cob is going to have some practical difficulties which are likely to have expensive solutions. As Martin has discovered, fastening nailing battens to cob is not going to be an easy matter and you’re likely to end up needing to build a full frame wall spaced off the exterior of the cob, maybe in pressure treated material and with the need for careful and complicated detailing at doors and footings and most especially at window openings. And then you will have a non-indigenous exterior cladding material which will require regular maintenance much in excess of the original cob. Sounds like a recipe for much trouble and expense.

  5. Expert Member
    Dana Dorsett | | #5

    James: The local "...farmhouse look..." in most of France is far more likely to be stone masonry than cob or wood cladding, and it's definitely more expensive than cob. Examples of homes of cob & stone in rural France can be found too.

    That said, there really isn't a resilience case for adding wood cladding to a cob structure. Decent roof overhangs and roof lines designed to protect from repeated torrential rain wetting are a good idea, but cob is pretty resilient on it's own. Insisting on wood cladding restricts the range of shapes that could otherwise provide a great deal of character and architectural spice that working with cob could otherwise offer. To my mind embracing the flexible nature of the material rather than covering it over to make it look like something else is more appropriate. YMMV.

  6. James Morgan | | #6

    Dana: certainly, stone is the common traditional building material in the parts of rural France that I’m familiar with, and brick or concrete masonry with stucco finish a more economical modern alternative. I wouldn’t consider cob a good choice if there were no local tradition of its use, there are many parts of France I have not visited and I was giving the OP the benefit of the doubt on that.

  7. Christopher Glasspool | | #7

    Interesting idea, and I have had an idea that is similar, but in reverse; build a rather traditional building that meets local codes, and jibes with what subcontractors are used to, to keep costs and complexity and harassment to a minimum, and then build your cob house inside the building. My day dream was to have it completely free of the sides and roof, and create a very organic shape. You are then not constrained by right angles, and boxed shapes, or a cob to roof connection, and protected from the worst of the elements. You could use the building as your form, to fill out, but I like the idea of a sculptural house inside a giant utility box, or enclosed porch.

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