Garage Construction Project

Lift Pad Location (Bay 3 PEX-Free Pads)

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Lift Pad Location — Bay 3 PEX-Free Pads

Why this document exists

When the 2-post lift is installed, the anchor bolts must land inside the two 4′×4′ PEX-free concrete pads poured in Bay 3. Drilling outside those zones risks puncturing the ½″ radiant-heat PEX embedded in the slab — an unrepairable failure of the in-floor heating. The original floor drawing from Marcus may not be available, so this document captures how to re-locate the pads from photo evidence + features still visible today, plus the open questions to resolve before drilling.

Created 2026-06-30. This is a living document — refine as measurements are gathered and the confirmation steps below are completed.

Key reframe: find the squares, not a single point

You don’t need one exact point. The pads were deliberately cut 4′×4′ so the lift’s baseplate/anchor template has room. The real goal is to re-establish the two 4′×4′ PEX-free squares on the slab and keep all 10 anchor bolts inside them, ideally with margin from the edges (PEX runs ~12″ outside each pad).

⚠️ The planning notes assumed ~10′6″–11′ column spacing, but the overhead photo shows the actual pad center-to-center spacing is closer to ~7.5–8 ft. Measure the real spacing — do not trust the planning figure. (Columns can still mount toward the outer edges of each pad to widen the drive-through.)

The embedded ruler (confirmed materials)

From [[Hydronic Heating Materials Delivery|Hershberger’s Invoice #97898]] (10/20/25) and Products Used:

  • 110 × “9x4 Creathrm” = Creatherm S45 under-slab panels: 2 ft × 4 ft (24″ × 48″), 2.8″ thick, with a staggered knob grid nominally on 3″ on-center spacing.
  • Coverage math confirms the panel size independently: 110 × 8 ft² = 880 ft² ≈ the interior slab area inside the 8″ rat wall (≈876 ft²).
  • Also delivered: 1 roll ½″ oxygen-barrier PEX, 3 EZ-Loop bend supports, manifold fittings.

This means every pre-pour photo contains two rulers cast into the floor: the panel seams (24″/48″) and the knob grid (~3″).

The photo evidence

The 2025-10-25 DJI top-down is the single most valuable artifact — a near-orthographic plan view showing, in one frame:

  • The form rectangle = the 24′×40′ building outline (= today’s walls)
  • The round floor drain (left-center) — still visible in the slab today
  • The two square PEX-free lift pads (cut-outs on the east/right third), PEX routed around them
  • The PEX manifold and the blue slab-sensor conduit as bonus landmarks

Other useful frames:

First-cut location estimate

Scaled from the DJI top-down to the 24′×40′ form. Treat as ±1 ft — the drone shot has some tilt. Refine on-site.

FeatureFrom west end (along 40′)From front/door wall (along 24′)
Floor drain (live datum)~12 ft~12 ft
Left/inner lift pad center~26 ft (≈14 ft from east wall)~11–12 ft
Right/outer lift pad center~33.5 ft (≈6.5 ft from east wall)~10–12 ft

Relative to the floor drain visible today: the pad centers are roughly ~14 ft and ~21 ft toward the east end, on about the same depth line as the drain. Pads are ~4′ squares, centers ~7.5–8 ft apart.

Method to make it definitive (in order)

1. Cheapest win — find a contractor sketch

The spec to Marcus explicitly requested “a sketch of the tubing layout and photos before pouring.” If the radiant installer or Terry (concrete sub) ever sent a dimensioned sketch or marked-up photo (text/email), that beats all reconstruction.

2. Photo reconstruction with a self-calibrating ruler

The “hex counting” method, made rigorous so it doesn’t depend on the published knob pitch:

  • Use the highest-resolution, most straight-down photos of the pad area.
  • Calibrate in-frame: count the knobs across one full panel (a known 48″ or 24″ edge) → true knob pitch = 48″ ÷ N. Self-correcting.
  • Count from a fixed datum to each pad edge: whole panel seams first (coarse, unambiguous — every 2′/4′), then knobs for the final inches. Zero from the floor drain and the form/wall edges (both exist today).
  • Output the four corners of each 4′×4′ square as distances from the east wall + front wall, cross-checked against the drain.

3. Confirm non-destructively before drilling

Do not drill on photo math alone

Reconstruction gives the chalk squares; a direct scan confirms the PEX is actually absent there.

  • Thermal imaging (best DIY confirmation): turn the radiant heat on, let the slab warm, scan Bay 3 with a thermal camera (FLIR One phone attachment ~$150, or borrow). PEX loops glow as warm serpentine lines; the PEX-free pads show as cold squares. Drill only in the cold square, clear of any warm line.
    • You don’t need the combi boiler fully commissioned to run this. The loops are already capped and pressure-tested, so any warm-water source pushed through the manifold creates the contrast. The installed combi boiler is just the clean, zero-effort way once it’s heating the slab normally.
    • Image during warm-up, not at steady state. Start cold (heat off overnight / a cool morning), run heat ~1–3 hours, and scan while it’s still warming. In that transient window the PEX is hot but the surrounding concrete hasn’t caught up, so the loops read as razor-sharp warm lines and the pad squares stand out as crisp cold blocks. At equilibrium the contrast washes out and the lines blur.
    • Bonus: the scan maps every loop run in Bay 3, so you can place each anchor for maximum clearance from the nearest tubing — not just “inside the square.”
  • Low-tech version: with heat on, lightly mist the floor — water flashes off warm tubing first, leaving the cold pad squares damp longer.
  • Gold standard: a concrete GPR scan (rent, or hire ~$300–500) maps both the PEX and the foam void under the pads.
  • ❌ A plain metal detector is useless here — the rebar is fiberglass and the PEX has no aluminum. GPR or thermal only.

4. Make it permanent

Once located and thermally confirmed: paint corner marks, photograph with a tape measure in frame, and record final dimensions here — especially before any floor coating goes down.

Open questions (to research, then update this doc)

  • Contractor sketch / measured photo? Did Marcus, Terry, or the radiant installer ever send a sketch or dimensioned photo of the pad/tubing layout (text/email)? Even an un-dimensioned marked-up photo helps.
  • Slab accessible? Are the walls up and the slab bare (no epoxy/coating yet), so we can measure from wall datums and the drain today?
  • Thermal camera available? Own / borrow / rent? This is the single most decisive confirmation.
  • More pre-pour photos? Beyond the ~25 October photos in the vault — any taken straight down over the pad cut-outs, or any with a tape measure in frame? These enable a precise knob-by-knob measurement pass.
  • Confirm actual pad center-to-center spacing (≈7.5–8 ft per photo, NOT the assumed 10′6″–11′).

Graph View

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