Quite a few ICE members have home observatories of various types , so they will know the pros and cons of different observatory constructions and types , or at least their own from experience with it.
I am getting close to being ready to building my own observatory , so here we go.
Best is not the same as most cost-effective (Budget and SHMBO constraints may vary). Mine is timber base, due to budget. A slab would be far better, but beyond my DIY capabilities and budget. YMMV.
I'm leaning towards concrete but the price of slab is not nice. I'll still have to put decent concrete footings in for my steel pier no matter what.
May not be that much extra to lay a mechanically isolated slab about the footing at the same time - I've never done any concreting myself and don't have the gear for it so I'll have to get a concreter to do that for me.
An off ground platform may not be that much cheaper than a slab and my carpentry skill may not be up to it.
Best is not the same as most cost-effective (Budget and SHMBO constraints may vary). Mine is timber base, due to budget. A slab would be far better, but beyond my DIY capabilities and budget. YMMV.
How big is your base and how much (there abouts) did it cost you to do it ?
I made an off the ground timber base on 6 posts for my first obs. Cost was around $100 all up for the base.
I can imagine concrete would be better, but the timber base was very easy to do.
My slab was $300 for the concrete (half of that was the delivery charge) and about $50 for the reo. Easy, cheap and solid as. Wouldn't have it any other way!
That poll is confusing, a simple monolithic concrete slab with bolts set in it to take the pier (reo?, your kidding, why?) and an isolated Obs timber floor hovering above it is the simplest and easiest DIY, no subbies required, how hard is it to pour concrete into a hole and set bolts into it, sheesh?.
I voted other because you don't specify what equipment or purpose you have. An isolated pier on a big block of concrete is the best mount option in any scenario but after that the rest is price and comfort.
Sorry for the tardy reply. My obs is only 2.2x2.2m square with a treated pine pole at each corner, plus two more out the back to hold the wooden RO rails. I suspended the wood floor on pine joists attached to the poles, independant of the colourbond wall sheeting.
In retrospect, 2.2 is a bit too small, (it was more or less dictated by the dimensions of sheeting and my budget) and would be unsuitable for anything longer than a 1200mm newt. However, as I now do all my observing remotely from inside the adjacent house, the small size is not a problem.
My estimate of floor costs would be 2 x 2400 sheets of thick ply, plus about 6 treated pine 40x70? joists. It works well, but flexes slightly and creaks a bit, due to insufficient supports below the joists. (I'm a rotten carpenter, and built it all myself). But it works, carpeted, keeps the rain off, and I would estimate the total obs cost as $750 or so, including DIY bagged cement for the post ~50cm deep corner pole foundations and the 50x50x1m cement base for the I beam pier. Pier was a freebie from a friend and works well.
RO Roof is wood frame with polycarbonate sheet for daylighting, with judicious sarking to stop condensation and heat. Pics show.
Berry amachoor, but a solo job and I'm no spring chicken. It works just great in Brisbane west's rather benign climate. Will never win a spot in Grand Designs, though
Any observatory should have the minimum of thermal mass that can hold heat.
A large concrete slab is the worst option for a floor. It will equilibrate by dawn if you are lucky. This of course depends on climate.
I have a wood deck with gaps between the jarra slats. That way cool air comes from the ground and keeps the whole observatory about 7C below ambient during the day even in summer and full Sun!. It has a well insulated roof and IR reflecting paint on the outside.
At night with the ROR open it cools down to ambient in less than 30 minutes.
I originally planned to lay a 100mm concrete slab (2.5m x 2.5m).
However, after clearing/leveling an area of back lawn for a slab and casting a concrete pier (approx 1m deep and 30mm diam with 1/2" stainless threaded rods inserted), I changed my mind.
I elected to place the floor (frame of treated hardwood joists covered by yellow-tongue board) directly on the dirt.
Perfectly stable, and easy to shift when we eventually shift house in a few years.
I prefer a simpler solution and it has worked for me for the past decade. I use the tripod that came with my Meade 14". I have small peirs dug into the ground for each foot of the tripod. The observatory floor is wood and isolated from the piers. The piers comprise stacked 8" sqare cement tiles stacked like bricks with motar between them. The extend into the ground 12"-18". As long as you have a stable tripod (the meade supergiant tripod is very stable) then this solution works and is far, far, far cheaper than a pier.
Nice one higginsdj, and thinking about it, yep that would do the trick, as long as it is stable, go for it, and as you said, much cheaper, well done indeed.
The best base for an observatory depends on how much you need to spend to achieve your aim.
I built mine over a couple of weekends on a 2.3 metre by about 110mm thick reinforced concrete slab laid by my neighbour, a conctrete contractor fo $180. The rest of the the observatory was completed with the total cost under $4000 including the fibre glass dome.
I was only interested in a home for my 10" LX200, later 12" LX200 but it was polar aligned on a wedge accurately and was available 24hrs a day for observations.
If you are more interested in long exposure photography you will need better insulation and temperature control and a solid stable pier. The cost from here could be exponential.
Just a side thought/note. If you elect to lay a slab down as the base then you dont need a pier footing. You can simply lay concrete blocks on the slab (tied in with dyna bolts or cast in at time of pouring slab). Then you simply fill in the blocks with 15mpa block fill and can even cast the pier plate bolts in! This will help any differntial movement that subterranean footings can suffer with. It can also help with getting the correct height of your pier as you can elect to lay as many or few blocks as you require.
I did this as my pier was palced on an existing slab.
Note/Disclaimer: You should check the coeficient of linear expansion (temperature dependant) to ensure that the slab you lay (primarily surface dimension) has sufficent mass to a) support the above ground footing, and b) be of the same material to exapnd and contract in union.
Last edited by CoolhandJo; 21-08-2010 at 09:26 PM.
Reason: added CLE explaination
I have built 3 observatories to date. The first was a converted garden shed at home on a very thick 1 piece concrete floor. That worked fine.
Another was out in the country and that was an 8 inch steel tube, 5/6mm thick and 1.8 metres long set in a hole 800mm deep in the ground and set with rapid set concrete. Then pavers around the rest of the floor.
Worked fine and was easy to build.
The last was more sophisticated, a pier 800 x 800 x 800 deep. A 2nd slab 2m x 2m sitting on ground with building plastic and steel reo.
Then gravelly roadbase then finer paving roadbase and large pavers with a small gap at the slabs. Works fine, easy to lay looks good and is easy to maintain. No vibration issues.
The structure around it is not in contact with the floor so no wind induced vibrations.
I had read stories of one slab observatories where merely walking on the slab caused vibrations that wrecked images.
Frame is treated pine and L brackets and roofing screws. Cladding is Aircell insulbreak everywhere and colorbond Trimdek. Roof rolls off on 2 100x 50 x 4mm steel section and 8 wheels on top of the frame. Several trusses and light metal roof battens with the Insulbreak underneath.
Before summer I intend to install a solar powered fan to circulate air and maybe a whirlybird on the roof.
You need insulation and air circulation as you don't want your gear to fry in summer but you want rapid cooldown at nights.
first put in the pier, with footings, then surround with an elevated floor, that was mine as well. 
H took it all. 
with you response. 
