Alleline
professor emeritus
Reged: 02/07/06
Posts: 517
Loc: Farmington, Maine
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I've decided to build a roll-off-roof observatory and would appreciate your friendly warnings. If you think I'm heading toward a problem, tell me now! Advice especially appreciated from those who have built a DIY roll-off-roof.
The observatory will house two mounts - my Meade DS-16 on original GEM and a CG-5 goto for my C-8 and refractor to alternate. I plan to use a green laser on the go-to so I can trace the beam with the DS-16 and find faint objects.
My yard is dark to very dark, with a little ambient light from town 2 miles away and my neighbor's annoying security floodlight to the NE. Great views in three directions, but trees block most of the east. I intend to roll the roof off to the NE, to block neighbor's light. I believe the opposite gable will block my other neighbor's driveway and occasional headlights coming up the road.
I plan to start very simple and rebuild in pieces as needed to get fancier. I am not 100% sure which site will be best. So I will put a 7'9"x11'6" shed on pressure-treated footers, with 4' side walls and gables/roof pitch of 3/4, so the peak will be at 7.' The floor will be 5-6" of crushed rock with three level pads for each mount - so I can adjust locations until I get two that work for all purposes.
I expect to paint the interior flat black before erecting the walls, and have only one wall opening - the door in the gable end opposite the rails.
Roof will be green metal on 2x4 trusses with cross-piece no lower than 5', on fixed 2" wheels from Home Depot. Triangular screens at the peaks to provide some vent. I will use stops to prevent the roof rolling all the way off the rails, and 1x8 side pieces to straddle the top of the walls and keep the wheels rolling on the rails. No motors - I think the roof will weigh about 200 pounds. I intend to build it on the ground and lift it into place.
Any immediate red flags pop up for you experienced builders?
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Tom
Meade DS-16 (F4.5), C-8, Synta 120mm F8.3 refractor.
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1965healey
Enginurse
Reged: 06/23/07
Posts: 2532
Loc: San Antonio, TX
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Only thing I can see may be the short sidewalls, leaves you a rather narrow track of usable space when you consider that the roof and trusses have to clear the scopes and mounts. Short walls work great for dobs since their "feet and body" are close to the ground. My CG5-GT with a pier extension on it and an 80mm short tube on it stands about 5'6"' tall when I park it with the OTA horizontal to the ground. Without the pier extension I'd be sitting on the floor to view objects at zenith. If you want to leave your mount polar aligned and not have to remove the OTA to close the roof a wall height of about 6' will be pretty good. Always build NOW for the future if you can, it'll be cheaper to do it once rather than to do it over. 
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1965Healey (Karen)
Woodlawn Lake Observatory
Celestron CPC 800/FT MIcro/APT Wedge
SV NHNG 80mm #0261/CG5-GT
Losmandy rails/rings
Starizona CWeight system
Celestron Neximage
Sony a100 DSLR/ZigView S2
Meade DS60's w/Autostar (2)
Meade LPI/Meade DSI-C/DSI ProII
750cc Honda Shadow Spirit (Thanks Dad!)
1965 Austin Healey 3000 MKIII
A little too much money and NO SELF CONTROL!
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Alleline
professor emeritus
Reged: 02/07/06
Posts: 517
Loc: Farmington, Maine
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The GEM on the DS-16 is low - when the scope points at zenith, the bottom is three inches off the ground. When the scope is level on the mount, it is just below 4'. I am going to have to figure out what a 5' wall would mean - I would hate to give up too much southern sky. I'll play with this. Thanks for your advice!
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Tom
Meade DS-16 (F4.5), C-8, Synta 120mm F8.3 refractor.
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1965healey
Enginurse
Reged: 06/23/07
Posts: 2532
Loc: San Antonio, TX
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Alot of folks opt for slightly higher sidewalls and a drop-down southern wall. 
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1965Healey (Karen)
Woodlawn Lake Observatory
Celestron CPC 800/FT MIcro/APT Wedge
SV NHNG 80mm #0261/CG5-GT
Losmandy rails/rings
Starizona CWeight system
Celestron Neximage
Sony a100 DSLR/ZigView S2
Meade DS60's w/Autostar (2)
Meade LPI/Meade DSI-C/DSI ProII
750cc Honda Shadow Spirit (Thanks Dad!)
1965 Austin Healey 3000 MKIII
A little too much money and NO SELF CONTROL!
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Snow dog
Carpal Tunnel
Reged: 07/17/05
Posts: 1614
Loc: Alberta Canada
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I might also opt for a lighter colored roof, maybe light grey or white. Green might make it get pretty hot inside and take longer to cool down at night with the heat waves.
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Marc
Someone get these crazy dogs off me
12" LX200 Classic
ETX-90PE
Meade DSI
Bushnell Astro 675 X 4.5" Reflector
Canon AE-1, T-80
My Home Page
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David Pavlich
Postmaster
Reged: 05/18/05
Posts: 6063
Loc: Mandeville, LA USA 30.38 X 90....
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Quote:
Alot of folks opt for slightly higher sidewalls and a drop-down southern wall.
I'm sure that I am one of the few that has the roof rolling off to the south. I face a phallanx of rather tall pines directly southand southwest. 
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A few scopes and mounts.
Proud Member; PAS NOLA,
Life expectancies would go WAY up if green vegetables smelled like bacon...
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Alleline
professor emeritus
Reged: 02/07/06
Posts: 517
Loc: Farmington, Maine
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Yeah, I hear you on the green. I saved $100 because they had some remaindered green. This is one of those decisions I may need to reverse as time goes on. But an 8x12 shed roof has many uses, so this one will get used here or elsewhere. I do take the point.
Going back to the sidewalls, I was thinking I could build trusses without cross-pieces. A friend of mine built a shed roof with small triangles of plywood holding the rafters in place, and no other bracing. It weathered this very snowy weather fine. This system would leave almost 6' of standing height down the center, and so the roof would roll leaving a good channel of clear space somewhat above the side walls. Does this change the view about the 4' walls, or have we got a consensus that they are a mistake?
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Tom
Meade DS-16 (F4.5), C-8, Synta 120mm F8.3 refractor.
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Spoonsize
Vendor/Clothing
Reged: 08/27/04
Posts: 1858
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Not much to say here...I feel the 4 foot wall height MIGHT work, if you somewhat follow what this fellow did....
http://www.cav-sfo.com/Me.html
Most metal roofing is a solid color on one side and white on the other...So, if this is the case with your material, put the roofing up inverted. What's it gonna hurt?
IF you decide to put crushed stone for a floor, purchase what is commonly known as "stone to dust", made up of crushed stone about bean size thru and including dust size. Pack it tight with a tamper and sprinkle calcium chloride on it to absorb moisture and keep the dust down. Eventually it will pack rock hard and then you'd be able to cover it with a heavy mill plastic with outdoor carpet over the top.
The above pieces of wisdom will self destruct/delete in a day or so........
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Steve Durham
www.margesmonograms.com
(Marge made me do it)
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John Fitzgerald
Pooh-Bah
Reged: 01/04/04
Posts: 1010
Loc: AR
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"No cross pieces" requires support from the side walls, which you will not have. Mistake, IMO.
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?
Observing since 1966
Messier Cert #898
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1965healey
Enginurse
Reged: 06/23/07
Posts: 2532
Loc: San Antonio, TX
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If your proposed roof design did well under a heavy snow load and it was the same size as you propose for your build then it may be sufficient. Remember though that yours will be a roll-off and may not possess the same compressive strength that being nailed to a side wall would give it. That can be countered by building the rails and rollers as sturdily as possible. Plans for the rails and rollers, as well as the structure itself, can be obtained from several sources. BYO and SkyShed both sell their plans and some of the components for rolling roofs as well. The plans are a good way of checking your build ideas against those of the pro's to make sure that you are not exceeding spans or loads for the type of structure you want to build. A four foot side wall design may suit you just fine for now and the forseeable future. My point in addressing the height was not to discourage you but rather to encourage you to think about where you want to be in a year or two. You may want to go with a permanent pier or a different scope/mount combo in the future and a bit more height now will leave those options a bit more open later. Also remember that you'll be in your obs with the roof open AND closed. Being able to move freely about the space without whacking your head can be a plus on a cold or rainy day when you want to commune with your astro toys. As for the roof color, it is what it is. In the winter you'll love it cause it'll absorb the suns rays and provide some passive heating. A big white canvas drop cloth and some bungee cords will help shed some of the suns rays in summer. There's always paint as well. Rv/trailer roofing paint is reflective and pretty good stuff since it's designed to live on a roof. Keep thinking and asking questions, it's the cheapest part of any plan.
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1965Healey (Karen)
Woodlawn Lake Observatory
Celestron CPC 800/FT MIcro/APT Wedge
SV NHNG 80mm #0261/CG5-GT
Losmandy rails/rings
Starizona CWeight system
Celestron Neximage
Sony a100 DSLR/ZigView S2
Meade DS60's w/Autostar (2)
Meade LPI/Meade DSI-C/DSI ProII
750cc Honda Shadow Spirit (Thanks Dad!)
1965 Austin Healey 3000 MKIII
A little too much money and NO SELF CONTROL!
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John Fitzgerald
Pooh-Bah
Reged: 01/04/04
Posts: 1010
Loc: AR
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The roof and walls should be thought of as independent objects. The roof of a roll off only rides on the walls, it gives the walls very little support, and the walls give the roof very little compressive support. If there are no cross pieces at the bottoms of the roof supports (trusses) the roof will want to splay outward. IMO vaulted type ceilings are a no-no for roll-offs, and only invite trouble. If the roof starts to splay outward at the bottom, the wheels will tend to climb up off the track and the roof may come off and be damaged or destroyed. The walls need to have horizontal bracing in the corners also. In a normal shed, the walls and roof mutually brace each other. Since in a normal shed each truss is firmly attached to the top of the wall, the wall cannot splay outward, and neither can the roof. Just my opinion, and that of the architect and the structural engineer who both helped me in the design and build.
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?
Observing since 1966
Messier Cert #898
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Alleline
professor emeritus
Reged: 02/07/06
Posts: 517
Loc: Farmington, Maine
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Okay, cross-pieces it is. I am going to mull over whether I lose more to walls that are too high or too low. I will take a look at fold-down issue when I get home tonight.
Edited to add that spoonsize's link re-opens an option i had mulled over - a roll-off top half.
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Tom
Meade DS-16 (F4.5), C-8, Synta 120mm F8.3 refractor.
Edited by Alleline (07/03/08 01:09 PM)
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Kinsale
journeyman
Reged: 02/28/08
Posts: 5
Loc: Altair 4
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Making walls square and plumb, and keeping surfaces staight and level is harder than it seems. Extremes of weather will cause buildings to settle and shift. So allow for the ability to adjust the roof rolling mechanism a few months after it has been installed.
Also, even in Maine a building can get pretty hot on a sunny Summer day, so consider insulation in the roof and maybe an electric fan for active cooling.
There's actually no advantage to black walls (IMHO), and they look bad once they get scuffed up a bit. If you really feel the need to paint the interior you might want to use a flat neutral gray. I actually think the time and money would be better spent putting in a red LED lighting system so you can see in the dark. At night the walls will look black anyway. They do in my Obs.
If you don't put in permanent piers, at least put in tie-downs to lock-down the portable piers you have, so you don't have to re-align on the NCP every time you bump a scope.
Edited by Kinsale (07/03/08 01:44 PM)
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HUsher
member
Reged: 04/14/06
Posts: 92
Loc: South Wales, UK
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We made the mistake of trusting the shed manufacturer that a vaulted roof would be OK! We've had to reinforce front and back and put in 3 triangular braces too.
Helen
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DeanS
sage
Reged: 07/12/05
Posts: 394
Loc: Nicholasville, Kentucky
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I painted my interior walls black and all it seems to do is make my sky look even worse than it is 
I would not go with the darker roofing unless you insulate the underside very well as it will transfer a lot of heat. Mine is light beige and it was noticable even with a thin foil faced insulation under the sheets. I ended up using 1" think foam to make a ceiling which helped 100%. I also use a small AC unit on a timer to keep it cooler during the hot days.
Taller walls are not as big of a deal as most worry about, at least if you are mainly imaging. The quality of the sky is not good for imaging very low anyways, and a taller wall has meant I can image on breezy nights that otherwise I couldn't. And I like to tinker in mine a lot so headroom is nice too.
I have some pics of mine under construction on my website that may give you some ideas. I did the solid concrete floor for a couple reasons, to give me added flexiblity if I want to move my piers around, which I have several times, and if I want to turn this into a garden shed it can hold about anything.
Good luck,
Dean
Edited by DeanS (07/08/08 08:54 AM)
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Alleline
professor emeritus
Reged: 02/07/06
Posts: 517
Loc: Farmington, Maine
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Thanks - I am planning on foregoing any interior paint. I will also build a 2' high box on the rails before attaching the roof so that I can walk down the center. I'm stuck with a dark green roof, but will put hard foam insulation in as a ceiling.
The hole is dug and leveled - now I'm waiting for two yards of "crusher dust" for the floor. I expect to spend the weekend building a pressure-treated foundation and shoveling dust.
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Tom
Meade DS-16 (F4.5), C-8, Synta 120mm F8.3 refractor.
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csa/montana
Astro Ambassador
Reged: 05/14/05
Posts: 25259
Loc: montana
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Tom, we are excited for you! Don't forget lots of photos 
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Carol
AstroTech 16" Dob (Thanks ASTRONOMICS!)
AstroTech 66ED / Vixen 80MF/AstroTech Voyager
Masuyama's 7.5, 15, 25W, 35mm,
Tak LE 5mm
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John Fitzgerald
Pooh-Bah
Reged: 01/04/04
Posts: 1010
Loc: AR
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If you want advice, crusher dust will get into everything. I would keep optics well away from it. I have seen it used as a base for concrete, because it packs well, but it will make a very undesirable floor by itself.
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?
Observing since 1966
Messier Cert #898
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Alleline
professor emeritus
Reged: 02/07/06
Posts: 517
Loc: Farmington, Maine
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Sheet of vinyl on top of it?
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Tom
Meade DS-16 (F4.5), C-8, Synta 120mm F8.3 refractor.
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mikey cee
Carpal Tunnel
Reged: 01/18/07
Posts: 2044
Loc: bellevue ne.
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What?.....and slip on your butt? Go a more conventional route please.  Mike
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Mike 10x50 sears tower binocs, 3" f/10 edmunds reflector, 2.4" f/11.7 manon refractor, 6" f/8 jaegers refractor, "The 8 Ball" 8" f/13.3 brandt refractor, 3" f/15.8 sans&streiffe refractor, 3.1" f/15 selsi refractor(towa 339), 2.4" f/15 sears refractor, selsi 30x30mm spyglass, criterion 5-draw 25x45x75x spyglass(1957).
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