More to the point, how is it that those employed as architects seem blissfully ignorant of the latest UK(1995) Building Regulations?
Prior to 1995 a roof that was not pitched was classed as flat, regardless of its shape. After 1995 any roof that isn't flat is classed as pitched. So what?
The significance of this seemingly irrelevant bureaucratic nicety is that a building with a flat roof can be 3m tall before planning permission must be obtained, 4m if the roof is pitched. In other words, prior to 1995 you could erect a 4m tall domed observatory without planning consent, after 1995, anything taller than 3m needs consent. You won't find a single word about this in Moore's latest effusion. The inevitable result of not thoroughly researching the subject.
It is pointless following the advice given and trying to shoehorn your telescope and yourself (+A.N.OTHER visitor?) into a domette, deliberately made small enough to avoid the planning process. Contrary to what so called experts would have you believe, the planning process is a formality. If your proposed observatory complies with Building Regulations (even if it doesn't need to) you will receive consent. The process admittedly can take several months, but it only costs £80.
So there is no need to squeeze into a gnome-dome! The minimum workable size for any domed observatory is 12 feet. Make it smaller and you will soon yearn for something bigger, where you don't bang your head on the dome or catch your knee on the mounting. Remember you need floor space beyond the excursion limits of the telescope, at least two feet beyond, for a desk or table, and some chairs, an observing stool/steps &c &c. A 10 foot dome is far too small for even a medium aperture reflector. There simply isn't adequate floor space.
And what do you gain, post 1995, in sticking with this woefully undersized gnomette? Nothing - because unless you bury half the building below ground level, it will still be more than 3m (10feet) tall, and therefore still need planning consent.
That extra 2 feet in scaling up from a 10ft. to a 12ft. diameter produces an amazing amount of room. The increase in diameter may be a modest 20%, but the increase in floor area is 44%.
On the subject of sunken observatories, I know of only one that has worked without becoming a water storage tank. And that is my own because I took the trouble to build adequate C20P concrete foundations, properly reinforced and sealed - a process referred to in the construction trade as 'tanking'. If of course the pier footing is isolated from the rest of the foundation, inevitably water will be forced up between the foundation joints if and when the water table rises higher than the foundation floor level. It makes sense therefore to allow for this eventually by designing the pier footing to include a sump, and install a self priming submersible pump with a float switch, and an external drain into which ingress water may be pumped.
Over the past 25 years I have been privy to several society observatory projects, and many more individual projects. All followed the usual Heath Robinson approach advocated in Patrick Moore's book. Most of them are now in an unsatisfactory state. And the reason why is simple. If you build a dome using either GRP, polystyrene, hardboard, plywood or timber, it will degrade, in many cases rapidly. They easily succumb to wind damage, they are heavy and awkward to turn , their shutters don't work properly (if at all) and they need continual maintenance, including recladding and resealing. With the drive disconnected my 121/2ft. duralamin dome, which weighs only 283lbsf, glides round with an applied tangential force of only 8lbsf. I have never needed to do any maintenance on my duralamin dome other than to wash it down about twice a year! It has never needed resealing, and it has only needed repainting once in 15 years.
There's an old engineering maxim, "If it looks right it is right." Use the best materials for the job, not just the domestic materials you're familiar with. Innovate; don't blindly repeat other people's mistakes. And above all, don't listen to the advice of amateur astronomers, who almost to a man are office wallers, whose only contact with engineering is at the local garage or when the plumber arrives to fix their waste disposal unit.
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