While we were planning to build a new house, it was quite obvious that an observatory was required due to the very pleasurable experiences with its predecessor. There are a number of possible options when it comes to observatories. Probably the first question you need to ask is: build or buy? The buy part has several options ranging from domes to pods and even wooden garden sheds that are being constructed for you. However domes have serious disadvantages: you need a building permit for construction and you can only put one telescope in a dome. In Flanders, the average piece of property varies between 300-500m² for newly constructed houses. Due to that, zoning regulations concerning garden sheds are quite strict. I wanted to have 2 permanent mounts so getting a permit that would allow me building two domes is a sheer mission impossible. Domes are not very cheap as well, the smallest model with walls will easily set you back 6500 EUR, so buying 2 of those would have cut the building budget of our house considerably. A lower-cost alternative for a dome is a Skyshed Pod but these still cost around 3500 EUR a piece. So far for the buying part... our money is probably better invested in the new house.
Building a roll-off observatory has several advantages. First of all, roll-off observatories are easy to construct. You do not need a building permit for observatories in size under 12m², so the neighbors cannot object to building one. Additionally, these types of observatories are inconspicuous for a burglar which is exactly what we want. The garden shed I bought is made of evergreen timber. The walls are 3 cm thick to ensure durability. The measurements are 4 by 3m, being exactly 12 m² as regulations prescribe. This leaves me with enough room to install 2 mounts or one really big scope (0.5m range). edit: now having a 0.4m telescope on a Paramount MEII and an 11" smaller Cassegrain with room to spare
Modifying the shed to become a roll-off observatory was rather easy, as the design had a roof-part being placed on top of the walls. Normally long screws would secure the connection between roof and walls, so all I had to was reinforce the walls and put wheels under the roof.
So in November 2009, the observatory build was started! In the planning phase of the house, a conduit between the front of the house and the shed (about 40 meters) was dug in. This conduit has a diameter of 8 cm and is used to provide electricity, network cabling, and alarm cabling. The second phase consisted of pouring a concrete slab. The slab is 15 cm thick, but in the middle, a solid block of concrete of 3x1x1 meter was poured to support the piers. This block does not touch the slab anywhere, to reduce vibrations. In the block of concrete, 6 metal rods of 1 meter length were inserted to hold one of the piers. The red tube that can be seen is the conduit. About 8 cubic meters of concrete were needed: rock solid!
The observatory wasn't the only thing being poured that day. In total some 5 trucks of concrete poured the foundation slab of our house as well.
When the shed was delivered it was pouring rain. As you can see on the images some elements were prefabricated, but most still had to be done. Construction of the wooden skeleton was the first step. Did I already mention the observatory was finished before the house was?
In reality I needed the room for construction materials for the house, but in all truth: the first telescope was installed half a year before construction of the house ended!
After a full day of work, most of the walls were erected. On top of the wooden skeleton, another layer of wooden beams was added to ensure extra support. The roof is made of metal and weighs quite a lot. Without the extra support, the original beams would probably bend while the roof is riding over them. The roof is riding towards the north. To ensure smooth riding, aluminum L-profiles were used, with the open side towards pointing outwards. Six roller bearing wheels were used, each capable of carrying over 250 kg. Due to the heavy construction, the roof was constructed when already on the observatory. Otherwise a lifting tool would have been required to get it on the right position. Nevertheless, lifting the roof frame with 2 persons proved to be a daunting exercise.
Four extra concrete blocks were poured to support the poles the roof rides on. Aligning both aluminium tracks was quite hard as the total distance is about 8 meters and tolerances are small. The support is very rigid and can hold the roof easily. The poles are adjustable by means of 4 bolts if they would ever require adjustment. The next step was closing the gaps between the roof and the walls. As the wheels are lifting up the roof, a gap between the skeleton and roof was created. To prevent any rain or snow to enter the observatory, vertical boards were fitted. They are very effective in keep rain/snow out, but enough air is flowing to cool the observatory.
The roof is made of metal plates. To prevent condensation, the manufacturer provided a wooden under roof. Normally this under roof is fitted directly on top of the beams, above the metal roof. (edit: to install a roof motor, the under roof was removed to save weight) In my previous observatory I suffered in summer from high temperatures in the observatory. The roof was heating too fast, so temperatures quickly rose to 30-40°C on the hottest days. You can imagine it took ages to cool the scope, situated directly under the roof. This is something I absolutely wanted to prevent. The goal was to achieve that the observatory would not heat at all in summer, so insulation became crucial. To achieve this I placed 12 cm of Rockwool between the metal roof and the wooden under roof. On top of that the walls were insulated with 5 cm of Rockwool and 18 mm of OSB-plating was added. The combination of both measures really pays off. On the hottest day this summer, the inside temperature of the observatory barely rises above ambient temperature outside. My neighbors who have exactly the same garden shed will often temperatures of over 45°C. To be able to keep the observatory closed and still actively cool, a large fan was installed. This fan will blow in 800m³ of air per hour. The fan is pointed towards the floor, effectively pushing out hot air through the venting gaps in the roof structure. This allowed for example to observe Jupiter at 4am with a cooled down telescope, despite the fact the observatory was closed the entire night.
In my previous observatory I used to have a switch-on and switch-off sequence for all the equipment, with the ever present danger of leaving the mount switched on. It wouldn’t be the first person to find stripped gears or torn cables due to such stupidity. In the current observatory every telescope has a circuit. This is quite handy. To switch off all the equipment only one fuse needs to be switched off. Below the wooden floor, I installed some conduits that allow easy cabling to the telescope under the floor.
When the roof is closed, the telescopes are positioned horizontally. Another advantage of the roll-off is that I can position the roof halfway. This is perfect when doing photometry with the Newton while not using the other telescope. Meanwhile all the equipment under the roof stays dry. Construction the base structure of the observatory took about 3 full days of work with 2 people. Finishing everything such as plating, under roof, insulation took another 5 days. Total costs exceeded a little over 4000 EUR.