CONCRETE BASE - ADVICE GRATEFULLY RECEIVED

I'm getting one of these,

Two inches of Sand laid over the hard core seems to be the standard thing, Sheal, possibly to stop the damp proof membrane being punctured by th weight of the concrete on top of that.
The Mesh or Rebar as recommended in several Astronomy Forums is to help stop the concrete from cracking should it move. But there were several recommendations to use the fibre additive which really strengthens the concrete one or two fold.
As you can see in the pic the Dome is on a raised base and that's how I want mine to be but higher to around "two bricks" high or about 8 inches. The 12 inches of depth for the concrete might be a bit of over kill but the minimum depth would be 9 inches.
It's the weight/load of the concrete on the soil that is the issue regarding footings which is why I'm asking about depth of them. I will need approximately 2.5 cubic yards or 2 cubic meters of concrete for the base which, I think will weigh around the 3 and half ton mark. So having good deep footings will probably be needed.

 

Will it pivot?

 

Yep, Shiney, the roof turns 360 degrees and I'll probably have it motorised to make things easier. You can see the sliding shutter on the roof which is what I like about it. I did initially look at "Roll on Roll" types but [a] they look like Sheds, they take up too much room with the design, [c] the local wildlife would probably treat it as Hotel Astronomical and there'd be no room for me!!

It's actually only about 8 feet 2 inches tall, Sheal, but with a concrete base of 8 inches above ground level that will take it towards the 9 feet mark.

"Armandii's Folly"????

 

Will you need Planning permission? If it's classified as a 'shed' you should get away with it as long as it's 5m from the house. Even without being a shed it should be OK as it looks as though it's just a simple metal construction.

How will you run electricity to it? Will it be buried in a channel and brought up through the base? You'll still need Part P on it. If you run the channel you can also run a water pipe in the channel. Then you'll have a fridge, kettle and sink.

I don't know about these things but would the hot nights we've been having cause a problem with air distortion between the inside and outside of the dome? Even with the open section you may get the hotter inside air rising past the lens

 

Hi Shiney, no, it doesn't need planning permission [although I made enquiries] as the Observatory is classified as a "temporary" building and the local Council is happy with that.

It's actually a very strong and thick fibreglass/resin construction.......which will not attract any lightning strikes in itself.

Power will come from the Garage RCD power source, laid in a trench via a plastic conduit. That enable me to install 3 weatherproof RCD double socket units. The number of power sockets is a bit of an over kill again as I will only need power for the drive to the Telescope mount and internal lighting of red LED Strngs about mid way around the circumference of the Observatory...but you can never have enough power sockets!!

Don't forget the bed!!

Actually, the concrete base can be a problem in itself, absorbing heat during the day and releasing it at night causing a updraft of warm air around the Observatory. I might paint the base white to help reflect the heat but I haven't come to a concrete [] decision about that yet. Also, I believe the construction of the Dome and the fact that it's white helps partially to reflect heat. Warm air inside the Observatory can initially be a problem but most experienced Astronomers recommend using a Fan inside to push the air out and usually within 15 minutes you can get a comparable temperature to outside.

Another problem is the Newtonian type telescope itself as it can hold warm air inside the tube causing air turbulence inside it and marring the light from the primary mirror to the secondary mirror. That could cause a blurring of the image so a small fan might be needed to solve that problem, makes Life interesting though

 

I'll just clean the outside of the Dome with a pressure spray after the birds have "visited"!!

 

No, Pete, you haven't read it wrong. What I've tried to make obvious is that I'm no builder and that I would have trouble putting a Leggo kit together so I'm just asking for opinions and advise from people with more knowledge and intelligence than me.
One of the listed components of the footings is the dpm.........now where it will go is something I guess I will leave the Builder. But it does raise the question in my mind that should the dpm go above the ground that would mean the concrete would be lying on a plastic sheet with only the weight holding it from moving. So, in theory, because the plastic dpm would be slippery you would be able to push the base over the dpm....or could you??

 

It's not that strange, Pete, it's just a circular building on top of a concrete slab!!!

I agree and that's what I will do. The Visqueen will go inside the building with rubber tiles on top. But what was causing confusion [to me] was that on a lot of the Astronomy Forums where people had built bases [mostly American] and used a dpm in the base itself. I would rather use just a concrete base with ordinary footings. But one of the questions I was asking is how deep would the footings have to be for a 12 inch depth cement base.??