By April 2019 the observatory roof was becoming increasingly difficult to open.

The wheel bearings on the roof has started to rust and were binding and with all the terrible weather, the bitumen corrugated roof was starting move and was leaking. The roof seemed to have gained quite a few kilos and in the end, I needed a second pair of hands to open up.

Having heard good things about EPDM, which is a rubberized material, which is totally impervious to UV degradation and as long as it never punctures is 100% leakproof. I decided to give this a try.

I decided to completely rebuild the roof assembly, with a new galvanised runner, new wheels and an 8mm OSB sheet overlaid on the framework in order to support the rubber membrane.

The old wheel runners come off to be replaced with new ones which are now easily greased.

The I needed to remove the rusted old runners.

To stop binding, I decided to mount a couple of lengths of galvanised ‘L’ section steel and mount these only on just side of the observatory. This would keep everything running true fore and aft. The wheels on the other side would just run on top of the wooden top rail.

Once the frame was complete, the 8mm OSB was screwed in top of the framework and ready to accept the EPPDM membrane.

The membrane is glued onto the ply with two kind of adhesive. One is like Copydex contact, and this is used everywhere except a 200mm surround at the edges, where a stronger adhesive more like a traditional brown smelly Evostick contact adhesive.

All the edges then fold down over a 75mm wooden vertical edge which stands outside the sides and allows the water to drip off the roof.

Wooden capping was overlaid over all the edges. At the Southern end a 150mm wide strip of EPDM was made into a flap that keeps the water from entering the gap between the roof and the observatory base, as well as allowing the roof to open, without having any kind of hard mechanical flap that has to be opened first.

The whole exercise was a complete success. The roof is lighter. I can open it with one hand now and is completely waterproof. Another plus is I no longer get condensation dripping off the roof inside. The plywood acts as an insulator, so now I don’t need to cover the scope and mount with any kind of cover.