A small "Roll off Roof" Observatory

A small "Roll off Roof" Observatory

In 1997 we acquired 2.000 m² of land close to La Coruña in the northwest of Spain where we live. It is located on top of a hill with unobstructed view to all sides and has still fairly dark sky. We will construct a small guesthouse, a main house and of course want to include a small observatory as well.
The observatory was finished in 1999 and is in use since then.

Construction diary

The observatory site

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• This picture is taken from the point where once the telescope will be. The view faces South-East and you can see that the observing site is situated fairly high and has almost no obstructions.

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• It is important to have some company while working. The neighbors goat soon discovered how interesting our observatory and future house is and ever since joins us while we are working. The result is that we have his eternal foot imprints in the concrete.

Excavation and foundation
June 1998

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• The observatory location was marked on the land in early June and excavation started on June 13. On the left picture you can see the concrete tube that will become the telescope pillar and on the right the excavation itself. The right picture gives an even clearer impression of the foundation form and shows also the central hole for the telescope pillar.

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• The foundation was prepared with steel reinforcement and the concrete was filled end of June.

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• The pier before being lowered in his hole. Observe the yellow insulation foam that will isolate it from the rest of the building to avoid vibrations.

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• The pier after being set in the hole. One can see the steel reinforcement bars. BTW using a prefabricated concrete tube greatly reduces the cost for a pillar like this as those parts are very cheap (at least in Spain).

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• The finished foundation with the pillar and the red iron brackets that will support the structure. The central part was filled with concrete a few weeks later. Between mud and concrete slab I layed plastic foil to keep moisture from rising through the floor.

Wood preparation
July 1998

As the house we are going to build, the observatory is a non toxic ecologically constructed building. For that reason the wood is not treated with toxic chemicals but with Borax salt which is much less harmful but equally efficient than other wood protectors. After three coats with Borax it the wood receives one finish of linseed oil and the parts that are exposed to the exterior receive three finishes of ecological varnish.

Support piers

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• The first wood ordered were the main support piers made of 10cm x 10cm red pine. They are mounted on iron brackets to avoid having to set them in the concrete itself. That way the observatory can be entirely dismantled one day and even the replacement of damaged wood won't be a problem. The photographs up show the bracket before being set in the concrete and after mounting the wood to it. Unfortunately we did not take enough care setting the brackets straight into the concrete and therefore had to shim several posts with small wood pieces afterwards. An awful work that can easily be avoided!

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• The pillars mounted before being levelled, cut to size and painted

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• The support piers after levelling and painting. You can also make out the black plasic foil previously mentioned.

Building the structure

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• The frame of the building is built up using 10x10cm, 5 meter long wood pieces as support for the rail and 10x5cm pieces to connect the sides. On the opposite side you can make out the place where the door will be.

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• The 5x10cm pieces are fitted in notches, cut out from the 10x10cm bars. The two 5 meter long 10x10cm pieces that make up one side meet in the middle and are supported by an extra piece of 5x10cm.

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• The sides will later be closed with tong and groove board screwed to vertical support pieces that will be fitted in notches like the one that can be seen on the photograph.

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• The building frame with the fitted support pieces.

Guide rails

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• The guide rail is made of 10 mm tube soldered to 5mm x 50mm straight pieces. I selected stainless steal for the rails to avoid future problems of corrosion. The 10mm tube fits exactly the groove in the drive wheels. The piece of wood in front of the rail is a stop-block.

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• A sideview of the rail, showing the spacing between roof beams and guide rail. The rails have a total length of 9.5 meters each and were soldered in two parts that had to be aligned accurately.

Roof support

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• I used Nylon wheels with a diameter of 100mm and a 10mm deep round groove. The wheels were then machined to a diameter of 97mm and a groove of 11 mm to let them ride more freely on the rails. The 5 wheel-housings in each roof support beam were cut with a hand router and a chisel. I installed 5 wheels in each beam. M12 screws are used as axis for the wheels. They are supported by rectangular metal pieces made of left over material from the rail construction.

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• This photo shows the mounted roof support beams.Using nylon wheels has the big advantage that opening and closing the roof does not make any noise.

The gable

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• One of three gables before assembly. One can see the cutouts for the tee halving joints.

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• Closeup of one Tee halving joint.

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• The assembled gable. The roof has an inclination of 25 degrees.

Building and roof frame

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• The pictures show the skeleton of the observatory with the supports for the roofing material. I used ONDULINE® roofing material which is made of a mixture of cardboard and asphalt. It is very light, resists the weather very well and is fairly easy to mount.

The entrance

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• This photgraph shows the door and window openings in the south-west wall of the building. In the meantime I have built the door and have mounted the window as can be ssen on the next photograph.

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• The wide overhang of the roof protects the sides of the observatory from wind and water.

The roof

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• The roof, once it is opened, can be secured in different positions. It can be opened completely, or for example can be left half open to provide some protection for electronic equipment.

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• The closed roof from outside and inside

Interior design

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• In the interior, I installed sockets on each side as well as white and red lights. The sockets and light switches are exterior quality.
  As flooring material I used carpeting made of coconut fibre. It insulates against the cold from the concrete slab, an provides a soft landing area for dropped eyepieces.

Protections

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• To protect the roof from opening during strong winds, I installed latches in each corner. We recently had storms with windspeeds up to 100 km/h which the roof withstood flawlessly.

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• I installed 3 iron-angle brackets on each side of the roof. They act like stormhooks against an angle-iron and prevent lift-off during storms.

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• As for the roof there are latches to avoid that the windows open during storms.

The finished observatory
April 1999

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• Here are a few photographs showing the completed observatory with the installed telescope. Total construction time was 11 months.