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Observatory build Reference

Parts list

Everything purchased, by category, with the reasoning where a choice was contested.

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This is one person’s build, not engineering guidance. Local codes, soils and loads vary.

On this page
  1. Foundation
  2. Framing lumber
  3. Deck hardware
  4. Pier — concrete and form
  5. Pier adapter
  6. Conduit and trench
  7. Isolation
  8. Wind anchoring
  9. Tools
  10. Four choices worth explaining

Quantities are what to buy. Where the installed count differs, both are shown.

Foundation

QtyItemSpecNotes
8 eachCAMO Block deck block15.75" x 15.75" x 3.5" polyolefin, 1800 lb ratedAccepts a 4x4 post directly. Six passes but sits at 85% of rating — eight halves it.Source: https://www.homedepot.com/p/CAMO-2-2-lb-Deck-Block-for-Joist-and-Post-Foundation-0420001/319396055
0.5 cu yd3/4-minus crushed gravel4" compacted under each blockNot sand. Not pea gravel. Tamp in two lifts.

Framing lumber

QtyItemSpecNotes
1 8' stick4x4 PTground contact UC4AYields all 8 short posts. Cut individually AFTER blocks are leveled.
4 10' stick2x10 PTground contact UC4ASkirtboard, all four sides
11 10' stick2x8 PT—9 joists at 117" + 2 spare
4 8' stick2x8 PT—Pier blocking, ring blocking, bay blocking
24 10' board (installs 21)5/4 x 6 PT deckingactual 1" x 5.5"Rated for 16" o.c. Extra covers hatch sub-frame and culls.
4 10' board1x or 5/4 fascia—Skirt. Stop 2" above grade for ventilation.

Deck hardware

QtyItemSpecNotes
20 each2x8 face-mount joist hangerhot-dip galvanized or stainless9 joists x 2 ends + spares. No ledger — fastens to the 2x10 rim.
1 1 lb boxJoist hanger nails 1-1/2"HDGHangers need hanger nails, not deck screws
16 set3/8" x 6" carriage bolt + washer + nutHDG or stainless2 per post into the skirtboard
500 screwGRK Deck Elite #9 x 2-1/2"type-17 point, bugle head, Climatek coatingThe type-17 point is what prevents splitting — not the gauge. No pre-drilling needed in 5/4.
1 canEnd-cut preservative—Every PT cut

Pier — concrete and form

QtyItemSpecNotes
12 bag60 lb high-strength concrete mix—~5.4 cu ft for a 12" form to this height
1 eachConcrete form tube12" diameter x 48"Cut to length IN PLACE so the rim is the screed line. Set from grade up — it is a form, not structure.
4 10' bar#4 rebar1/2"Cut to 70" for verticals. 50" offcuts become footing cross ties.
1 4' bar#3 rebar3/8"Twelve 5" tie pieces need 60" of bar plus kerf, 12" more than one 4' bar holds. No bending required.
1 rollTie wire—Ties, and hanging the cage from the rim stick
4 eachDobie blocks3"Or place a 4" base lift and set the cage into it. Never wood, brick or rock.

Pier adapter

QtyItemSpecNotes
2 eachBrake rotor, solid2012 Chevy Malibu — center bore fits the EQ6-RDegrease thoroughly. Leave embedded faces bare.
4 each1/2"-13 x 36" all-thread304 stainlessCan never be replaced without destroying the pier. Hot-dip galvanized is equally correct.
20 each1/2" hex nutmatch rod material5 per rod
8 each1/2" fender washermatch rod material2 per rod — top (spans 5/8" holes) and buried anchor
16 each1/2" flat washermatch rod material1 per rod used, rest spare
1 bottleNickel anti-seizenickel-based, NOT PTFE or food-gradeStainless galls. Exposed threads only — never on anything concrete touches.
4 eachSteel tube spacer2" OD x 0.25" wall, cut to the chosen gapEnds must be faced square and flat
1 assortmentStainless shim stock—Leveling under the spacers
1 each5/8" drill bit for cast iron—Top rotor only. Drill dry, 300-400 rpm, clamp the work.

Conduit and trench

QtyItemSpecNotes
measure (10' stick)1" PVC sch 40 conduit (gray electrical)gray electrical, NOT white plumbingTwo runs. Quantity = run length + 20%, rounded to whole sticks, x2. Measure your distance to the house.
6 each1" PVC sweep 90long sweepNEVER hard elbows — you will not pull Cat6 through one
1 setPVC conduit cement + couplings—
2 rollPull string / mule tape—Run before backfilling. Non-negotiable.
4 eachConduit caps—Concrete inside a conduit ends that conduit permanently

Isolation

QtyItemSpecNotes
1 eachFlexible pier collar / boot / loose trim ring⚑ Critical to isolation—Closes the 1-1/4" gap. Fastened to the DECK side only. Never caulk solid.

Wind anchoring

QtyItemSpecNotes
4 eachEarth/auger anchor + cable or strap⚠ Unresolved — ask the manufacturer—UNRESOLVED — this is a floor, not a manufacturer spec. Ask NexDome about anchoring on a non-monolithic base.

Tools

ToolWhy
Rotary laser level or long straightedge + levelEight blocks to a single plane
Post-hole digger or rented 12" auger36" pier hole
Trenching shovel18" conduit trench
Wheelbarrow or mixing tub + hoe12 bags of concrete
25' steel tape, chalk line, speed squareDiagonals must read 169-11/16"
4' levelForm plumb in two directions
Torpedo levelRotor at 0/45/90/135 degrees
Circular saw—
Impact driver + socket setCarriage bolts
Rebar cutter or angle grinderCutting bars to length
Hand tamperGravel pads in two lifts
Respirator + eye protectionCast iron dust is fine and dark; wet concrete is caustic

Four choices worth explaining

Ground-contact PT (UC4A), not above-ground (UC3B) for posts, skirtboard, and anything within 6" of soil. Small price difference, and it is the wet-climate failure mode.

Hot-dip galvanized or stainless fasteners only. Modern PT chemistry destroys electroplated fasteners — hangers, bolts, screws and nails alike.

304 stainless rods over cheaper options. Not for strength; the static load is under 100 lb and any rod is overbuilt. These four rods can never be replaced without destroying the pier, and the 6-1/4" bolt square leaves only 1.33" of cover. Hot-dip galvanized would be equally correct — electroplated zinc would not.

GRK Deck Elite screws after three wrong answers. What prevents splitting in 5/4 decking is a type-17 auger point, not the gauge. A #10 stainless splits without pre-drilling, a #7 stainless snaps heads in dense PT, and a trim head pulls straight through decking.