What are the most comfortable dimensions for a 200 sq/ft ROR Observatory for two Rigs?

I have 2×4 sqm observatory with two piers next to each other on an east-west line. The observatory houses 2 8” (1 m focal length) telescopes. The roof is divided in two sections, so that I can operate each telescope without having the other one exposed to the elements. This solution requires a roof supporting beam between the two halves.

When you design your observatory, make sure that each scope can swing freely with you standing between them. With a 10×20 ft floor plan that isn’t going to be a problem, unless you have very large telescopes. Having a square observatory that houses two telescopes seems to be an inefficient use of area to me.

Wim

Here’s more info on the design and building process

observatory build

Wim

Tommy Mastro:
Hi guys!

Im looking for feedback. IYHO, what are the most comfortable dimensions for a 200 sq/ft ROR Observatory?

Should I go with long and narrow, like 8ft X 25ft. With these dimensions I can place the 1st pier 5ft off the narrow wall, another pier 10ft from the 1st. Now, with a pier at the 5ft mark and another at the 15ft mark, I have another 5ft for the second pier to move, leaving the last 5ft for me to have a chair.

Or do I do a 14ft X 14ft Square with the two scopes offset from each other and I sit in one of the open corners?

Or something in-between, say 12 X16?

My two mounts are the Astro Physics 1600GTO-AE and 1100GTO-AE. My largest scopes are two C11s with dew shields. Currently, one of them sits inside my 8X8 observatory on top of the 1600GTO perfectly (with room for me to sit in the corner but it’s tight).

The plan is to replace this 8X8 with something that can fit both mounts and scopes, with enough room for me to fit an office chair. My max footprint is 200 sq ft. I should add this is for astrophotography only, no observing. Also, I don’t need a “warm” room. I live in AZ.

Thanks!

Tommy

Martin Curran · Nov 1, 2025 at 04:16 PM

I went 12’ x 16’ with the piers East and West, so the roll off roof is wider than long. Piers are 5’ apart (center to center) and just under 5 feet from the walls (due to wall thickness). At the time, I had a 91mm refractor and an 8” SCT. Recently I replaced the 8” SCT with a 156mm refractor, so space has gotten pretty tight. I had to push the big refractor way up the saddle to get it away from the other refractor in it’s park position and then counterweight the hell out of it. All working good but a little scary the first time I exercised the mount with the big refractor on it and watched the camera swing under the small refractor.

📷

That makes sense. My C11 with Dew Shield brushes the wall when level. That’s centered in a 7.5ft X 7.5ft (ID) observatory. That’s why I’m favoring the 10 X 20. It gives me 5ft OC from each wall and 10ft OC from pier to the pier. That should suffice for any scope I install in the future.

Right now, I’m mostly concerned with how to get this idea past the city and the HOA. 🤔

Tommy Mastro · Oct 29, 2025, 11:58 PM

Hi guys!

Im looking for feedback. IYHO, what are the most comfortable dimensions for a 200 sq/ft ROR Observatory?

Should I go with long and narrow, like 8ft X 25ft. With these dimensions I can place the 1st pier 5ft off the narrow wall, another pier 10ft from the 1st. Now, with a pier at the 5ft mark and another at the 15ft mark, I have another 5ft for the second pier to move, leaving the last 5ft for me to have a chair.

Or do I do a 14ft X 14ft Square with the two scopes offset from each other and I sit in one of the open corners?

Or something in-between, say 12 X16?

My two mounts are the Astro Physics 1600GTO-AE and 1100GTO-AE. My largest scopes are two C11s with dew shields. Currently, one of them sits inside my 8X8 observatory on top of the 1600GTO perfectly (with room for me to sit in the corner but it’s tight).

The plan is to replace this 8X8 with something that can fit both mounts and scopes, with enough room for me to fit an office chair. My max footprint is 200 sq ft. I should add this is for astrophotography only, no observing. Also, I don’t need a “warm” room. I live in AZ.

Thanks!

Tommy

Hi Tommy,

I’ve gone through a similar setup planning for a dual-pier roll-off roof observatory, so here’s what I’ve learned.

If your goal is strictly astrophotography without a warm room, an 8 × 24 ft layout works very efficiently. You can align both piers along the long axis with around 5-6 ft of spacing between them, and still keep a comfortable passage for movement or a chair. This shape makes cable routing and roof travel much simpler.

However, if you prefer easier access around both mounts for maintenance, cabling, or guiding adjustments, a more balanced footprint like 12 × 16 ft or 14 × 14 ft will feel far more comfortable. The square layout lets you move around freely, and one corner can easily fit a small desk or an office chair without blocking anything.

Considering your two C11s on the 1600GTO-AE and 1100GTO-AE, the 14 × 14 ft option is likely the best compromise. It provides enough space to work around each pier, keeps the roof structurally balanced, and offers a better workflow for dual setups. Since you’re in Arizona, insulation isn’t critical, but I’d still include good airflow and dust protection, especially at floor level.

If you can, visualize both designs in SketchUp or any simple CAD tool to check clearances when the telescopes slew near the horizon. It helps a lot before committing to construction.

In short, go with the rectangle if you want simplicity and tight space efficiency, or the 14 × 14 ft square if you value comfort and flexibility during imaging nights.

Makrem

Makrem Larnaout · Nov 4, 2025, 07:56 PM

Tommy Mastro · Oct 29, 2025, 11:58 PM

Since you’re in Arizona, insulation isn’t critical, but I’d still include good airflow and dust protection, especially at floor level.

Actually, because I am in AZ, the insulation is critical. My current observatory is insulated with R13 under 1” foam board. The AC unit is on a thermostat that kicks in at 95-degrees. Otherwise it can easily reach 130-degrees on a hot summer day.

The 14 X 14 has another advantage . . . it doesn’t matter which way I roll the roof off! This might be the solution to my property layout issue. If I go with 14X14 should the scopes be offset maybe?

That’s my fear.

My other fear is they won’t understand what it is and just deem it unsafe and deny me a permit altogether.

I wonder if the code would allow me to have two separate structures that fall under the 200 sq ft rule? Then I would just build another 8X8 and have two separate observatories.

It’s not ideal, but it would save me a lot of work and a little bit of money. Hmmmm . . .

Scott Lockwood · Nov 6, 2025, 08:48 PM

"A work shed with a machine stand and an operable skylight."

That is fantastic … !!!