The dome's wall ring is 88″ across. Everything else is a question of how much deck you want around it, and what you intend to do with that margin.
Three footprints got modeled in full — 12′ × 10′, 8′ × 10′, and 10′ × 10′ — each with its own framing plan and parts list. The deciding factor was not floor area. It was whether a storage bay would fit later.
The bay is what decides it
NexDome's bay is a 36″ × 22″ bump-out that bolts to a wall panel. It is optional and it was hypothetical. But retrofitting one onto a finished deck means cutting the skirtboard and sistering in joists, so it was worth knowing in advance.
Source NexDome — NexDome 2.2m (8') Complete Observatory, product page — https://www.nexdome.com/nexdome-2-2m-8-complete-observatory
| Footprint | Area | Clearance | Bay fits inside? |
|---|---|---|---|
| 8′ × 10′ | 80 sq ft | 4″ / 16″ | No — overhangs by 4.6″ at best |
| 10′ × 10′ | 100 sq ft | 16″ all around | At 45° only, with 0.6″ to spare |
| 12′ × 10′ | 120 sq ft | 28″ / 16″ | Yes, at 35°, with ~7.5″ spare |
Those numbers come from sweeping the bay through every angle from 0 to 90° and measuring the slack to the nearest deck edge. The 10 × 10 result is the interesting one: it technically fits, at exactly one angle, by less than the width of a pencil line. That is not a margin you can build to.
Why the square footprint is the problem
On a square deck the only spare room is on the diagonal. So the bay gets forced into a corner with no freedom to rotate — one workable angle instead of a range.
The 12 × 10 has a range. The 10 × 10 has a coincidence.
The fix: stop centering the dome
The pier must be at the dome's center. The dome does not have to be at the deck's center. That distinction was sitting unexamined behind the whole exercise.
This deck exists only to carry the observatory. There is no reason to walk all the way around it. So the dome moved to (52, 52) — 8″ off the deck's midpoint on both axes — and the space budget across each axis became:
8″ behind the dome · 88″ of dome · 24″ of clear deck
| Centered | Off-center | |
|---|---|---|
| Dome to near edge | 16″ | 8″ |
| Bay orientation | 45° only | square to the deck |
| Bay clearance | 0.6″ | 2″, and it fits |
| Door access | none planned | 24″ apron |
The off-center layout bought two things at once: a 24″ apron to step onto, open the door, and step in; and a 22″ strip where the bay fits square to the deck rather than skewed.
What it costs
The layout now commits to a direction. A second bay directly opposite has nowhere to go — there is 8″ there. A bay at 90° still has room.
That is a real constraint, and it should be a deliberate choice rather than a surprise. If two opposed bays were likely, this would be the wrong footprint.
A correction worth recording
Early drafts of this plan said to "pick the dome rotation that puts a wall panel seam nearest X°," as though the bay's compass direction were constrained by the panel layout.
It is not. The wall ring is circular and bolts down wherever you drill it, so the whole assembly can rotate freely and the bay can face any direction. What the panel layout actually fixes is the angle between the bay and the door.
So the question to ask the assembly instructions is not "can a seam land at 0°" but "where does the door end up once the bay faces where I want it."