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Diagonal lumber sheathing info?

OffGridForever | Posted in General Questions on


I am interested in diagonal lumber sheathing. I am trying to find specifics about what can be used for material?

I live in BC, Can. Walls are 24 oc exterior walls and from what I gather the code says 17mm lumber is specified and unless I am mistaken, I can use upward of 12″ wide boards. (11.25″ actual). What I can’t seem to find is if the diagonal lumber must be tongue and groove? I can find standard 1×12 pine locally with a square cut edge, is this acceptable? All the guides I’ve seen used tongue and groove but I don’t see it mentioned when I look up the code, not that I am an expert.

For reference, the reason for the diagonal lumber is severe allergy (sensitization) to isocyanate chemicals. Osb, plywood, polyurethane/polyiso and many, many other building materials contain isocyanates and I cannot go remotely close to that stuff, even the residual off gassing.

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  1. walta100 | | #1

    You may find this article interesting.

    Back in the days before ply wood this was common with no tongue and grove joints but they also allowed lots of air movement inside the wall.

    If you are as sensitive as you say life must be very difficult since every building would be off limits.

  2. Expert Member


    Are you in the coastal seismic zone? If not then yes you can use board sheathing, and no it doesn't have to be T+G.

    Are you getting this inspected? I don't think the roof assembly we talked about meets code.

  3. OffGridForever | | #3

    Yes on the difficulty with many buildings. Unfortunately a work related accident from overexposure in the manufacturing industry. As per workers comp now even 1 or 2 molecules breathed in the air can be enough to exacerbate asthma symptoms. I spend a lot of time in the outdoors! But one must have a place to sleep comfortably at the least.

    This will not be getting inspected currently. It is an off grid cabin in an off grid location. It is however in the seismic zone. I guess that would disqualify diagonal sheathing?

    As far as the ceiling meeting code, is it just the R value that wouldn't pass or is there some other consideration? It is a small building 320 sq ft.

    1. Expert Member
      MALCOLM TAYLOR | | #4


      Unfortunately the code doesn't distinguish between big and small houses. It's worth deciding if you will ever choose to get the building approved, because that will certainly affect what you need to do now.

      The roof insulation is too low, but also the BCBC now requires all Part Nine buildings to meet Part Three of the Energy Step Code. To do that you need an energy consultant.

      Off-grid houses are particularly difficult to make meet code because of the requirement for full time mechanical ventilation. Because of that the code now says that if grid power is available, the building must be connected to it. Some commentators have called it the death of legal off-grid buildings in BC.

      In the coastal seismic zone, it's not just the type of sheathing, but where it is located. There are rules around the percentage of each exterior wall which have to be Braced Wall Panels. They also affect where your anchor bolts must be, and the nailing schedules you have to use.

      Although this doesn't deal with requirements specific to BC, it is a good guide to code compliance for small dwellings:

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