Wednesday , 11, September 2013 Leave a comment

It has always been a dream of mine to have a small observatory. Well actually a big observatory with room for two mounts and a conditioned space for a desk, bed, and small kitchenette. The large observatory will have to wait but for now I am building a small observatory that has a pier for my mount and an area for the laptop and other accessories. Prior to making my decision I looked at several websites that converted metal or plastic prefabricated storage sheds. There were others that had domes but I wasn’t interested in that type. There were still others that were modular roll offs but were North of $10,000. I decided I would build a wood framed observatory with a roll off roof but spend a bit more on nicer exterior finishes.

There were two potential issues to deal with in my city. The first was city permits and the other was HOA compliance. Fortunately the city did not require permits for structures smaller than 120 square feet and I was at 64 square feet. The HOA did not require approval but any structure detached from the house had to be 3’ from a fence and not be seen from the street. This limited me in height to about 7’8”. Not ideal but easily workable and still have a functioning observatory.

I used Autocad to come up with a drawing that showed elevations. This gave me a visual feel for the material needed and also dimensions to work from. I am not an architect, carpenter, roofer, or painter by trade but I have seen enough construction projects to understand basic structural principles and construction methods. By putting the design on paper I could create a bill of material and assign costs to the project. I did throw a couple hundred dollars for “unexpected” costs due to my inexperience with building an observatory. Another note, I chose a foot print size that would minimize waste of material. The size I chose was an 8’x8’ box. Why 8’x8’? Well the most common and economical wood framing material sold at Home Depot, Lowes, etc. comes in 8’ length so an exterior size of 8’x8’ would allow me to use 8’ long 4”x4” for perimeter floor support, 8’ 2”x4” studs for floor framing, 8’ 2”x4” for wall framing, 4’x8’ OSB for shearing, 4’x8’ OSB panels for roofing, etc. with minimal waste. All dimensions smaller than 8’ were minimal and used only for blocking and the door framing. Minimal waste and using common size lumber keeps construction costs down!

I had someone make me a 10” diameter steel pier that was 44” high. This diameter is perfect for my AP900 and G11 mounts. The tubing is ½” thick and has a base plate that requires four  ¾” anchor bolts to secure it properly. I dug a 3’ deep x 2’ diameter hole for the concrete footing and used ¾” x 18” anchor bolts for the tie in to the pier. To keep the bolts aligned I used a template made from wood and double nutted the anchor bolts to the template. I mixed and poured the concrete and then pushed the anchor bolts down until I had the proper bolt projection elevation. I let it set for two days and then installed and leveled the pier.

I was now ready to build the floor assembly. The area I chose for the observatory currently has artificial turf installed and lays on top of 1” of compacted DG  + 2” of compacted road base on top of the native soil so it would pass any 90% soil compaction test. The floor assembly sits on 2” thick concrete blocks. I then formed a square frame using 4”x4”x8’ pressure treated wood. Next I used 2”x4” x8’ pressure treated wood for the floor joists and attached them to the perimeter framing using joist hangers. I took special care when framing around the pier so that no sub framing or flooring would be in contact with the pier or its anchor bolts. By doing this I can walk around without worry of vibration affecting my images. After the floor framing was complete, I used 4’x8’x3/4” plywood for the flooring. The underside of the floor sits about 6” above the artificial turf and it is unlikely any water would reach the underside but I treated it with a water and insect repellent.

Next was the wall framing and I chose 2”x4”x10’ Douglas Fir studs cut to 5’ length. With the height of the piers, floor framing, bottom plate, and double top plate this left me a rough wall height of 6’. I chose to build a custom door with final dimensions of 3’wx5’h. Next I wrapped the entire box with 7/16” OSB sheathing. I chose OSB because I wanted to use wood siding as a finish material and the OSB served  a couple of functions, one was to add rigidity to the framing and the other was to provide an attachment base for the 15lb roof felt for water proofing required for the siding. The 6’ tall rough wall height allowed me to use (1) 4’x8’ full sheet and (1) 4’x8’ sheet ripped down to 2’. This allowed me to utilize the remaining 2’x8’ piece for another side. No waste!

After the walls were wrapped I moved on to the roof structure. Okay, this is uncharted territory because I have never built a roof that had to roll away from the structure. There were many decisions to make here such as what track/castor system to use, how best to keep the weight down but still be rigid enough to roll off by hand, etc. I calculated the roof to weigh approximately 400 pounds when finished so I needed a track that would not get bent or warped with repeated use yet not be so heavy or large to be overkill. I chose 1”hx2”wx1/8”thick steel “C” channel. I called a local steel distributor who I’ve used before for car restoration and they were very helpful selecting this channel and some rigid castors to ride inside the channel. The castors were rated for 150 lbs. each but since I am using 8 total this extends the weight capacity quite a bit. The cost for 30’of steel channel and 8 castors was about $120.00. I mounted a 10’ section of track on top of two of the walls and let the extra 2’ hang over the edge. I chose to mount the channel by drilling holes in the bottom of the track and then using a larger drill bit to carefully create a countersunk hole so the heavier gauge galvanized wood screw head would sit flush with the track.

Next was the actual roof frame and for convenience and expedience I built the roof on the ground.  I used 4”x4”x8’ Douglas Fir for the perimeter frame and then mounted the castors to the frame using ¼”lag bolts. I then used some 2”x4” Douglas Fir for the vertical riser to support the 2”x4” roof ridge. I then used 2”x3” material for the roof rafters and attached them using roof rafter hangers. Now I had a complete roof structure minus the sheathing so now was the time to lift this on to the track. Once on the track I sheathed the framing using 4’x8’x7/16” OSB. I should mention here that when I mounted the 10’ sections of track they weren’t exactly parallel and I discovered this when I tried to roll the roof. I had to jack up the roof on one side so I could unscrew and shift the track a wee bit. I secured the track in two places and tested the roof and this time I could roll it with one hand. I then jacked it up again and secured the track using all screw holes. Well now I have a rough framed roof structure fitted properly on to the track system so now I needed to continue the steel channel outside of the observatory on to the 4”x4”x8’ supports I chose to use.

Next was building the support for the roof when it is open. Installing the 4”x4”x8’ beams from the exterior OSB siding of the observatory out to the concrete piers for the vertical columns went surprisingly well. At the observatory exterior wall I attached a 2”x4” stud to the exterior wall for the 4”x4” beam to rest on. I then plopped an 8”x8”x8” concrete pier in place and nailed a 4”x4” column to the pier strap and rested the beam on top of the column. I used Simpson Ties for the connections at the column/beam. After a bit of leveling I nailed everything in place and repeated this on the other side. Next was installing the steel channel to the 4”x4” beam and this time I only used two screws on each side to temporarily hold the channel in place while I tested the full movement of the roof. I nailed it on the first try this time so I properly secured the channel and retested to be sure. I did notice that the 4”x4” column and beam system was not as rigid as I would like so I cut some diagonal bracing to lock everything in place.

Okay, now it is time for some finish work to complete the exterior of the wall structure. We recently upgraded our entire backyard with pavers, seat walls, bbq structure, etc. so I had to make this observatory fit in architecturally. First I decide to create a fake window to break up the appearance of the front wall.  I then decided to use tongue and groove siding with vertical trim pieces on the corner. I have never used tongue and groove siding before but it was very easy to install and I face nailed it to minimize any cupping. I chose a light stain for the finish to preserve the natural look of the wood.

By now I had a solid floor, walls, and roof structure. But what to do about those gaps between the top of the wall and the underside of the roof support structure created by the height of the castors? I knew from my initial drawing that the front of the roof assembly was the piece that I had no idea how to address. The sides and rear can be concealed using a simple side board attached to the roof support structure using some blocking to hold it away from the siding. But what about that front piece? It has to travel over the top of the wall and can’t hang down like the other sides. I decide to rig up a hinged board that lifts up to allow the front wall of the roof to slide over the observatory. The board is held open by a hook and eye assembly that is easily opened and closed. I also added two draw type latches on both side walls to hold the front board secure when it is closed. So when closed the gap is concealed and water tight.

Last but not least was the roof tile and I chose an asphalt tile roof product to keep the weight down. It calculated to about 3lbs per square foot and this method was by far the lightest of my desired options. There were several styles and colors of asphalt tiles to choose from but I chose a lighter color to reduce heat absorption. I know metal or aluminum are the lightest roof types but custom cut panels are expensive and I didn’t like the finish look. Concrete or clay tiles fit in architecturally but can weigh around 10lbs per square foot installed!

I added a switch for a light and several quad receptacle outlets inside for any power needs. I was not sure where I wanted the work top so I installed outlets on each wall. I can figure out the location once I get my equipment set up.

Next was the most exciting part of the entire build. I was stoked to get the gear installed and ready for the night. The weather report called for clear skies and they nailed it. I decided to start collecting some narrowband of the Bubble Nebula so I set up some 15 minute images and let ‘er rip. I will post the results when I collect enough data.

After all of the construction was finished I added some large 10 gallon flower pots next to the corners of the observatory to brighten up the most exposed sides. I even added some screw hooks for hanging plants to the underside of the 4”x4” roof track supports.

I have to say I was a little overwhelmed when I planned this project and I even called a General Contractor for a quote.  But after putting my ideas on paper and thinking the whole project through I decided it wasn’t as complicated as I first thought. I do have some construction knowledge and I am also good with my hands and this helped a lot. Planning is everything!

Total cost of the build: $2,276.32







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