Cladding The Walls

I almost forgot!  I know I ended the last post saying it was time to build the dome... but patience, we are not quite finished with the walls yet!

With the ring finally fixed in place the walls were now strong enough to clad with their outer skin.  Up until now I had worried that adding the outer skin would put the walls at considerable risk of getting blown flat by the strong winds that frequently whip up the valley here so I had left the structure open.   Now it is time to start making the observatory weather tight.

An often overlooked feature of observatories is that the atmosphere inside is going to pretty closely match that outside, this means that we need to mange humidity as the temperature rises and falls through the day, we don't want rivers of condensation running down the walls or dripping off the roof!  So the first step in cladding out is to fit a breathable membrane around the outside of the framework, rolls of membrane can be found inexpensively at any builders merchant and is happily very easy to fix in place with staples.  One word of caution here: the membrane isn't very strong but it does make a very good sail... only fix as much membrane as you can clad over in the time available otherwise you will end up decorating your surroundings with shredded membrane and having to fit it all over again!

The next step is to cover the membrane with the outer skin of the observatory, for this job I am going to use more pallet planks, fixed vertically (one screw at the top, one in the middle and one at the bottom) and overlapping to provide a water tight and wind tight outer skin.  I built this up in two layers, the first layer had alternating planks then a gap, then another plank:

On the left both layers of cladding are in place, on the right only the first layer has been fixed.  The breathable membrane is the grey fabric that can be seen through the gaps

The second layer of planks were fixed to overlap the gaps in the first layer.  You could do some joinery at the angles of the wall but I found that a perfectly satisfactory weather seal can be achieved by simply butting the planks in the first layer then overlapping the joint with a plank on the second layer.  The cladding does not have to be 100% water proof, the breathable membrane will stop any water that manages to work its way through the joints, we are just aiming to prevent the wind driving water inside.  As long as you leave an air gap between the cladding and the membrane the walls should be weather tight.

Working in this way I was able to completely clad the outer walls with just a couple of days work using about 320 planks of wood recovered from pallets which I got for free from the local builders merchants and various building sites nearby *. If you want to be really hardcore about your upcycling you could straighten out all the nails you pull out of the pallets and use those to fix the planks... I drew the line at this and fired in about 1100 screws to hold the planks in place.  It is advisable to drill pilot holes in the pallet planks before putting the screws in, the planks are often quite brittle and easily split if you don't.

Now the walls are finished we really can move onto building the dome :)

* Always ask before taking anything, even if it looks like scrap.   If for no other reason than you will often find that you get offered other materials to take away too!