Observatory Build [Archived from astronomyshed.co.uk]

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Observatory Build [Archived from astronomyshed.co.uk]

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Back when I built my roll-off-roof observatory, I wrote up the procedure on the astronomyshed.co.uk forums. Unfortunately those forums are likely to be shut down in the not too distant future, so to preserve the information I am reposting it here.

Note that this is not a new build project - everything below happened in 2013-2014.

The original thread can still be found here (for the moment, anyway) : http://www.astronomyshed.co.uk/forum/vi ... 35&t=19209

cheers,

Robin
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Re: Observatory Build [Archived from astronomyshed.co.uk]

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I've posted odds and ends about my Observatory build here on the shed over the last year or so, but seeing as how I've made some good progress recently I thought it would be worth bringing it all together in its own thread...

Here's the site as it was in July 2012 - some rather manky shrubs that have really been allowed to grow too large and were really doing nothing for the garden

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By August, the shrubs are on the half gone and after some in depth negotiations with SWMBO, the location for the pier has been agreed :)

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more to follow...
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Re: Observatory Build [Archived from astronomyshed.co.uk]

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Fortunately the garden is on the site of an old Orchard, so the soil is pretty easy to dig - about 2 feet of topsoil before hitting the clay. I dug out the footing for the pier to about 75 x 75 cm x 60 cm deep, with an extra foot of depth in the center to allow the pipe to go deeper.

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I borrowed a mixer from the father-in-law, which made the concrete mixing easy, although I had to barrow all the ballast (~600kg) from the front of the house and up two steps before shoveling it into the mixer. Certainly kept me warm :)

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The 6" drainpipe was only £25 from Toolstation with free delivery. The pier topping plate was made by Astrotec and is very sturdy.

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Re: Observatory Build [Archived from astronomyshed.co.uk]

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After building the pier in October 2012, there was a long period when I had no chance to progress any further. Winter didn't help, but there were also lots of things that needed doing round the house that took up an awful lot of my spare time. When I did have some free time in the evenings I worked on the plans for the observatory, which I drew up using 'SketchUp'

SketchUp is a free 3D drawing program - formerly owned by Google - http://www.sketchup.com/. I found it was excellent for refining the design from a rough idea through to a full construction plan. It certainly helped me by allowing me to catch potential problems at the design phase, rather than when you've cut a bit of wood and discovered it won't fit.

Here's a view of one of the early plans - I'll include the up-to-date plan in a later post

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Re: Observatory Build [Archived from astronomyshed.co.uk]

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The Observatory plan was for a roll off roof observatory about 7 feet square (I failed to get the 8 foot square plan past SWMBO). The position of the observatory near the back of the garage means that I can have the rails for the roof to run off onto attached to the garage wall - meaning that I didn't need support posts.

The observatory will have two fold down flaps - on the south-east and south-west sides, giving the best possible view of the southern horizon. The fold down flaps allow me to deliberately offset the pier towards the southern corner of the observatory (in the picture above, south is in the far corner, away from the viewpoint). By offsetting the pier, I get more space on one side of the observatory, to allow some storage space.

For those who are interested... Spend so far :

Drainpipe : £25
Building materials - Ballast, Cement, Breeze Blocks : £100
Pier top plate : £90
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Re: Observatory Build [Archived from astronomyshed.co.uk]

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I didn't get much done in the early part of 2013 until the beginning of June, when I decided that even though I wasn't ready to build the actual observatory, it was time to make some progress. The plan was to build a deck around the pier, which would be fairly easy, tidy the site up and in due course be the foundation for the observatory shed.

Decking bearers (2"x4" treated) and deck boards came to about £150. I've previously had good results for decks and sheds by setting breeze blocks into the ground on pads of concrete (to get a good level) and then laying the bearers on the breeze blocks, so I decided to use the same approach here. I already had the breeze blocks and some left over cement and ballast from the pier build.

Here are the breeze blocks already in place with the bearers sitting on top having their cut ends treated

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The subframe is simple to assemble, held together with decking screws. The breeze blocks are placed so that they aren't in direct contact with the pier footing to minimize vibration transfer from the deck to the pier. There's a longer span than the normal 15-18" gap involved in bridging the pier, so I've doubled the bearers over that gap.

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Here's the complete AstroDeck (sounds like something off of Star Trek :) )

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Re: Observatory Build [Archived from astronomyshed.co.uk]

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The AstroDeck was as far as I got for the summer - more indoor DIY needed attention, but I did manage to pick up some useful hardware at car boot sales over the summer. I found in particular that the sort of stall selling random DIY hardware was worth checking out and picked up some good quality stainless steel hinges for the fold down flaps for £1 each along with some other bits and bobs.

Finally, come September, it was time to actually get on with the building. I drew up a shopping list for the timber merchants based on my hi-tec plans, added a good 10-20% for luck and ended up with an enormous mound of timber being delivered.

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What I've got there is a big pile of 125mm by 16mm shiplap for cladding, a big pile of treated 63x36mm CLS cladding for the main framework, lots of treated tiling battens (50x25 and 38x19) for smaller parts of the framework and finally a couple of 4.8m long 100mmx50mm beams for the run off rails.

Having the detailed plans drawn up meant that I was able to build the framework for each of the four sides separately and relatively quickly

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and then simply join them together to get the basic framework built up

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Re: Observatory Build [Archived from astronomyshed.co.uk]

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The next phase was to get the beams across to the back wall of the garage - not only do they provide the support for the run off roof, but they also help keep the framework from flexing.

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There are also some diagonal braces to stop flexing in the other direction. In a normal shed, the roof would help limit flexing, which obviously doesn't work with a roll-off roof, so some extra reinforcement is needed. I'm fairly sure that the flex will completely vanish once the shiplap cladding is on.
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Re: Observatory Build [Archived from astronomyshed.co.uk]

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Right... now the tricky bits... particularly the roof.

A pitched roof pushes out sideways - in a standard shed the walls form a square with enough strength to resist this, with a roll off roof, there needs to be a rolling frame with enough strength to keep the roof in shape. I built the outer frame from 63x36mm CLS studding.

My original plan for the rolling off bit was to use rubber wheels and have them run directly on the wooden beams, with a couple of rails to stop the wheels from going off the edge. However, during the planning phase I saw a lot of people talking about using sliding gate hardware for roll-off roofs and in the end decided to go with that approach in spite of the additional cost.

I bought 3*3m lengths of sliding gate track from FH Brundle for about £75, and 4 matching wheels off of ebay for £14 each (from an excellent seller 'quality_handling' - highly recommended). The wheels are mounted in a bracket that makes them very easy to mount into the frame (http://www.ebay.co.uk/itm/Gate-wheel-pu ... 3382caf1ee).

I'm really glad that I went with the gate track approach - the whole roof can be moved with one finger and glides beautifully smoothly.

Anyway, here's the beginning of the roof - just a square outer frame with the wheels mounted and a couple of uprights that will define the peak of the pitch. The fold down flaps are also in place now, but for the moment they are just screwed into place. I'm holding off mounting them on hinges until I have the cladding on, since I want to make sure that the flap fold down doesn't get fouled by the depth of the cladding timber putting it forward of the hinge fold line.

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Here's a closer view of how the wheel is set into the outer frame of the roof - basically I just cut 4 holes through the beams with the old 'drill lots them chisel out the rest' technique and then screwed the wheel brackets into place

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Finally, a longer view of roof frame and track (don't worry - it will go all he way across to the garage wall, it's just not all in place yet in this photo)

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Re: Observatory Build [Archived from astronomyshed.co.uk]

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And now I'm nearly up to date... Today I've been working on the roof, getting the supporting framework in place so that I can put the board on and felt it the next time I have some good weather and a free day coincide...

My original plan for the roof called for just a couple of cross beams on each side of the pitch, but it didn't look like it was going to be sturdy enough, so I increased that to 3 on each side with an extra 36x63mm beam running across the peak of the roof (I can swing from the middle of this beam and the whole structure takes my weight, which is promising). I've also built a 3rd A-frame structure to go in the middle of the roof, so that the cross beams will be supported by each gable end and a central A-frame, meaning they will flex much less.

Here's the roof with the cross supports in place, but no central A-frame yet

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When I get to the end of this project I will update my sketch up model to reflect how I actually built the observatory (or perhaps how I wish I'd built it with the benefit of hindsight ;) ) and share a link to it. Might come in handy for others looking to solve the same sort of problems when building their own obsy.
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