In the first part of this article I discussed some of the ideas that go into the construction of a roll-off roof observatory and some of the considerations you might overlook in building such a structure. In this half of the article I will show you how I took such principles into account when I built my own observatory. Once again, I hope that you gain a great amount of insight into how you might take the best of what I have already done while leaving all the mistakes to me.
You'll have to give consideration, first and foremost, to the foundation(s) of the structure. The critical choice in your decision has to be the method by which you anchor your observing pier to the ground. Secondly, and equally as important, you need to consider how your building structure will relate to that pier.
I expressed my thought on the principles of good pier design in the first article. By now you should know that I believe that the project should use two separate systems, where the
observing pier has absolutely no connection to the surrounding structure. Some may argue that putting everything on a single concrete slab would be sufficient and perhaps it might be if visual observing is your only intent. But when doing photography, why take the chance? Two separate systems will allow your scope and cameras to do their work while you are not bound by tippy-toeing around.
Therefore, the Ballauer Observatory utilizes this two foundation system, one of which is the concrete pier support and the other is the wooden pier and beam structure of the building itself.
I knew I would use a pier design that would bolt onto concrete slab. In this way, if I ever needed to change or modify the pier then I could simply unbolt it from the slab and place the new or modified pier over the same anchor bolts. Of course this requires planning on how you might setup the anchor bolts in the concrete as it drys. For this purpose a wooden template can be made to hold the anchor bolts in place while you allow the concrete to completely cure.
As the concrete dries you can begin your work on the floor structure of the observatory. But if you simply have to slap your pier on it for a first test, then I'd suggest allowing the concrete to cure for at least a day before doing so. It takes a while for the concrete to pack around the anchor bolts. Once the concrete has dried, then the forms and template can be safely removed.
One other point that I may or may not have mentioned in the first article. A good rule of thumb for the size of an all-concrete pier, which once again I opted NOT to do, is 1" diameter per 1" of scope aperture. This makes for a pretty solid pier. When using pipe for your pier, the diameter is not as important as the thickness of the pipe's walls. I used 3/8 inch walled pipe which proved to be very solid indeed. Because of this I could go with a 6" diameter pipe for a 10" scope. Again, the beauty of this pier design is that should I ever upgrade to a much larger scope then I can redesign a new pier to accommodate it. If you have opted for the concrete pier design then I would suggest using a larger diameter than needed in anticipation of future scopes, since your pier would then be truly PERMANENT.
After pier construction finished then work begins on the foundation of your observatory floor. Since I used a pier and beam technique, with cinder blocks and 4x4s underneath 2x6 treated floor joists, it was not necessary to assure that the ground surrounding the pier was completely level. In this way I could use any number of cinder blocks necessary at each footing in order to get close to the height I need. This way, only a minimum of digging is required to provide a level beam structure. Because my structure is a rather lengthy 10x20 feet, I used a transom to level my corner supports first. I then found the level of the center supports with a normal carpenter's level. 4x4 piers are then laid on top of the supports according to plan and the floor grid is constructed over the top.
Because the flooring and concrete pier support are two separate systems, care must be made to assured that the floor joists clear the concrete. In this way, any vibrations made to the observatory floor do not translate to the pier itself, and consequently to the eyepiece or camera on your telescope. The floor is reinforced over the pier to provide utility access to the pier itself while giving additional support to this most walked-on area. Treated floor joists are nailed down to the 4x4 beams where possible. This is really the only place where treated wood is required over the entire project, the exception being the 4x4 roof piers that are constructed later.
Once the floor grid is complete, I used a layer of OSB followed by another layer of plywood as decking. I simply did not want a whole lot of flexure in my floor. As a result, this floor is indeed pretty solid. The foundation is then finished off by the base plate for the walls, unless you decide to fabricate the entire wall first. For me, I wanted to construct the walls from ground up in the event that my measurements were not precise. Better to replace a board at a time instead of a whole wall in the event of a mis-measurement.
Once the floor is constructed, work can begin on the wall frames. Since I nailed down my base plate first, wall construction would have to be done from bottom to top. This would require toenailing wall studs into the floor plate. This can be avoided if you construct the entire wall individually but I find this method is no easier than the way I did it. And as I said, by working one stud at a time over the afixed plate I can better compensate for mistakes I might have made in pre-planning. In actuality, there really is no right and wrong when doing the framing. The biggest concern is stud placement so as to give yourself something to nail into when you put on your outer siding. Likewise, a properly planned wall frame will give you something to nail into if you decide on using interior siding or sheet rock. Of course that's why we take such care to set our studs on 16" or 24" centers in the first place.
Walls are constructed and tested for squareness as they rise by measuring from corner to corner of each room. Equal measurement suggest that the walls are indeed square. Diagonal braces are notched into the walls to retain squareness and provide rigid support. This is a critical step, in my opinion. A before and after push on the wall frames suggests that without the diagonal braces the walls have entirely too much flexure. Though the exterior siding helps to maintain trueness and to give it strength, reinforcing the wall frames with diagonal braces help to provide additional support and peace of mind.
Walls are topped off with a top plate of 2x4s according to plan. Care must be taken to assure than you have provided a way for the external roof rails to be incorporated into the structure. In my case, I had to make sure that the top plates are left a bit short at the west wall, where the roof rails will extend from the structure.
Upon completion of framing, preparations can be made for exterior siding.
Using tar paper as a vapor barrier is the first step to provide protection from moisture. It's not a critical step unless you are planning to put on interior siding, but its still a good idea if for no other reason that it will make the interiors of your observatory black, something you'll probably want anyway.
Because I have windows, this is a good time to frame them into the walls. Likewise, because my control room will have climate control, siding must be placed on the interior wall facing the observing room. This control room will be insulated and entirely enclosed. A window unit air conditioner is also framed into the control room wall, not shown here. These modifications should be made prior to the placement of exterior siding on your structure. In this way the siding can be perfectly cut to size and nailed into place, providing support and squareness all the way to the window frames. Once the siding is in place you will discover that the walls won't budge a whole lot. It really solidifies the structure and the better quality siding you use the more stability you will get.
Essentially, I have incorporated two independent roofs structures into my design as you will see. For those of you building single room observatories with a single rolling roof, you should be able to focus only on the rolling roof portion of these construction notes. My concepts on this portion of the roof can be taken pretty directly into your own design, though you may have to device a practical way of enclosing the eaves on the gable ends, when closed, while still allowing a freely rolling roof. That shouldn't pose too big of a problem for you anyway, plus my design can easily be modified in a way specific to your needs.
Because of the difference in height of my walls between the control room and the observing room, a consideration which was pre-planned, I knew that I could construct my fixed roof prior to the rolling roof. So that is exactly what I did. The fixed roof portion was constructed with 2x6 rafters and 2x6 ceiling joists, because I planned to put a ceiling in my control room. Both the rafters and ceiling joists were placed on 24" centers. Rafters are nailed at the top into a peak board, another 2x6 in this case, and then notched at the bottom and nailed into the top plate of the walls. This leaves a gap of ~2.5" between roof coverings and top of wall plate, which will be covered by a "bird board" later in construction.
Once the trusses are in place, I needed to trim a bit off the ends of the ceiling joists since they protruded beyond the top of the rafters. This is easily done with either a reciprocating saw or a hatchet.
Because I was concerned about heat build-up in the attic area of the control room, I framed an attic fan into the East wall. This fan will serve to direct heat exhaust from the attic to the outside. Since the fan is rated for a greater square footage than this attic area, I put intake holes in the opposite gable, opening into the observing area of the structure. In this way, any hot air that accumulates near the scope will be pulled into the attic of the control room and circulated out through the fan. The fan itself is thermostatically controlled, coming on when attic heat reaches a fixed temperature.
The permanent portion of the roof is completed by constructing the eaves, enclosing the gable ends, and applying the plywood (OSB) roof deck. The ventilation slot is made into the opposite gable end of the fan. Roof is then tar papered and covered with composition roofing shingles. I used white shingles to reflect as much sunlight as possible during the day. Remember, this is Texas. It gets awfully hot here in the summer time. Any method that will reduce the amount of heat collected within the observatory will benefit both the safety of the equipment as well as the amount of time required for cooldown at night. Providing good air circulation, bright reflective exterior surfaces and insulation around your control room are excellent ways to battle the summer heat. If cold weather is a concern where you are located then the same principles apply, only you'll want to retain heat instead of exhausting it. Heat absorbing colors and space heaters will work well to retain and circulate warm air through cold environment observatories.
Once the main roof is constructed, the rolling roof portion of construction can start. Framing of this 10 x 12 foot roof is accomplished on the ground using 2x4s for trusses placed 24" on center. The same construction techniques are used as on the main, fixed roof. Rafters are nailed into a peak board and notched at the bottom around rails where the 4 inch 'V' grooved coasters are placed. Ceiling joists are not used because scope clearance is a concern. 1x4 braces are nailed into each truss to provide support.
Once the rolling roof is framed it can be lifted into place atop the observing room. 1x4s are nailed to the interior of the top plate to prevent roof from falling off. The wheels will ride atop angle iron affixed to the top plate. Of course the angle iron cannot be placed until the roof rails and posted are in place, which is the next phase of construction. But first, aluminum roofing material is then put into place, used because of its light weight.
Before the roof can be rolled off the structure, you have to build a rail and column system to hold the roof when the observatory is in use. I sunk four treated 4x4 posts into the ground, two on each side, and set them with concrete. I placed 4x4 rails atop these posts from North to South and set the rails from the observatory atop these. Careful measuring is required to assure that the height of your posts is level with the top plate of your observing room wall. This allows for the roof to roll smoothly from its closed position. I actually made the connections of the 4x4s by drilling holes and bolting them together. At this time the angle iron can be placed atop your rails. Roof should be tested before nailing angle iron in place in order to find the rail position of least resistance. Wooden "stops" are placed at the end on the rails so that the roof can't be accidentally rolled completely off the rails.
At this point, you've actually come to the point where your observatory is complete functionally. Additional touches can be added at money and time allows. But I'd take a little bit of time to set up your scope and see how well you did. Such a "first light" use of your observatory will give you some ideas about what you want to do during the finishing stage.
The amount of work you put in here really depends on your own personal tastes. The door(s) is obviously the next step in order to prevent possible theft of your equipment and tools. Exterior trim can be done during this time. Interior electrical work, insulation, network cabling, and interior siding/trim can be accomplished if necessary. Weatherproofing can be completed. A locking method for the roof can be put in place (I used hooks and turnbuckles). Painting of exteriors and enclosure around the rails can now be done.
I left the space underneath the roof wheels open. I figured that it would greatly assist in air circulation. Plus, I found that complete enclosure of this area, while maintaining full functionality of the rolling roof, is a tall order. Perhaps some type of rubberized flap can be put into place to keep the insects or birds out of the observing room, but I didn't see that as a critical need. If critters get in I'll just use bug spray. Because the aluminum roof extends out a foot over the rails, rain cannot directly enter the room. Some moisture can still enter but I keep my observing room equipment covered anyway. I can live with a little moisture here as a fair trade for the extra air circulation. Because the footprint of the observatory is increased by the external rail system, I enclosed this area with some corrigated roofing/siding to make a lean-to storage area. It's a good place to keep your lawn equipment and a good use of otherwise useless space. Alternatively, those with kids might be able to mount swings to the underside of the sturdy 4x4 rails. This way you'll have a true multi-function facility.
I've tried to show you the more common areas of observatory construction techniques that are applicable to most all roll-off roof designs. For example, finish work is highly individual in practice, specific to your needs and requirements. Electrical considerations go beyond the scope of this article since I am no Electrician. I would hate to have any of my advice be the cause of a fire at your observatory! I hope you consider these articles a great help to you. For any extra advice please feel free to email me personally at firstname.lastname@example.org. Or just drop me a line to let me know if these articles have been any help to you.
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