Cedar Cladding – Rainscreen Method

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I am in the process of putting up the cedar cladding on the front and left-hand-side of the building. The cladding will be installed vertically.

Now I’ve got the hang of it, I probably need a day to finish it. It actually goes up quite quickly, but there is a fair bit of fiddly cutting to do.

There are several ways of doing this – the quickest (and worst) is to nail it directly to the breathable membrane – this punctures the membrane and creates a route for rain to be driven in by wind or pulled in by capillary action. Furthermore, there is no easy way for the water to drain out and no ventilation to let it evaporate. NOT GOOD.

The next quickest way is to install horizontal battens – not ideal since any water driven in will sit atop the battens and – depending on where it ends up – may pool against the building or the cladding, also NOT GOOD.

So I am doing mine using the ‘rainscreen’ method, as used by the Scandinavians for centuries and as recommended by our friends in the Scottish Executive:

This document contains a good overview of this method, and other cladding related info.

rainscreen method

The trick with this method is to see the cladding as a barrier that will shed most of the rain but will let in water at some point. Because of this you need to create a route for the water to escape and also permit any residual moisture to evaporate – you do this by creating a cavity behind the cladding. This is how I did mine:

Step 1 affix vertical counter battens at 400mm centres
Step 2 affix horizontal battens, also at 400mm centres, with a bevel of 5 degrees cut on the top face (another job for the plunge saw)

.. the purpose of the bevel is to allow water to run of and be taken by away from the building by gravity. The cladding overhangs the barge boards at the bottom by 50mm, leaving a 200mm gap to the floor so the amount of water splashing on to the cedar minimised.

Finally, don’t forget to treat any cut surfaces with a suitable wood preserver: although the battens are pressure treated with preservatives, this only penetrates a couple of mm into the timber.

nails

then you can nail up your cladding – I am using a tongue and groove profile that is ‘secret nailed’ through the tongue such that the nail is hidden by the next board.

cedar cladding going on

Don’t be tempted to use galvanized steel nails as apparently they will stain the cladding after they get wet. What you want is stainless steel annular ring nails of the “lost head” variety – as a rule of thumb the nails should penetrate solid wood by about 30 mm. My cladding is 19mm so I got 50 mm nails.

2 thoughts on “Cedar Cladding – Rainscreen Method”

  1. This is so helpful thank you.

    I would be grateful for some advice if possible?

    My carpenters are placing the cladding, so it goes directly on the floor. Think there has to be a gap surely at the bottom to stop capillary action i.e. water running up the cedar cladding.

    Thety are using horizontal battens only and putting the breathable membrane over top of battens not underneath it …you say should not nail through battens?

    Also a lot of the cladding is vastly different so doesn’t look to match – i realise they wont match exactly but do look like a patch work i.e. very light and very dark, is this avoidable.
    can you advise.

    Reply
    • hi Chris , keeping in mind that I’m am just a random person on the internet :), you should discuss specifics with your builders, but I can give you a quick overview of some of the problems and standard solutions for shed building and water.

      Any timber that is in contact with the ground will eventually rot, regardless of what type of wood it is or if it has been treated (treating wood to prevent rot only defers the inevitable).

      Cladding can also rot, become discoloured etc, because it gets continually wetted from rain splashing back from the ground. Ideally it is raised several inches above ground level to prevent this, but the design has to allow for this. For instance, If you raise the cladding off the ground and water splashes back onto the internal structure instead this would be a significantly worse (more expensive) problem.

      The purpose of the breather membrane is to stop water blown in through the cladding wetting the timber structure of the building and to allow any water that get behind it to evaporate. It will inevitably be punctured during construction since it has to be affixed to the substructure, and therefore will never be 100% watertight. The normal solution is to construct timber sheds – at least sheds that are expected to last – as follows (from outside in):

      Cladding, air gap, battens, breather membrane, frame, vapour barrier

      The air gap helps evaporate any water that enters through the cladding but does not drip to the floor.

      A disadvantage of vertical battens attached directly to the membrane is that water running down the membrane can puddle on top of the battens. Ideally it is counter battened with verticals to allow the water to drip unimpeded to the ground.

      hope that helps!

      PS not sure what you are using for cladding so hard to comment – it is normal for cedar to have some variation in colour though (and the colour will change when it is exposed to sunlight, according to what treatment you use to protect it etc etc.)

      Reply

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