SSOT v3.7 · Contractor Detail Drawing · Acoustic Design Basis

Perimeter Gap Detail

The 10 mm perimeter isolation gap is the most critical element in the float-floor system. If the gap is bridged by grout, skirting, thresholds, or services, the room loses isolation performance completely [AC].

Standard Gap
10 mm [AC]
Column Gap
10 mm min [AC]
Backing Rod
13 mm PE (closed-cell)
Sealant
Tremco · 8 mm bead

Drawing 1 — Plan View at Room Corner

Gap must remain continuous [AC]

Top view of the float floor stopping short of the wall base. The continuous sealant line sits over a 13 mm closed-cell PE backing rod compressed into the 10 mm isolation gap (rod ≈25% oversize of the joint).

[AC] CRITICAL GAP 10 mm 10 mm Float floor edge Backing rod + Tremco sealant Wall base / slab line Plan note: gap is measured from finished wall face to float-floor edge, not to skirting.

Drawing 2 — Elevation Cross-Section at Wall

Structural slab to finish floor

The acoustic wall bears on the structural slab only. The float floor build-up rises beside it with the 10 mm perimeter gap packed and sealed at the finished-floor line.

[AC] DO NOT BRIDGE 10 mm 13 mm rod 8 mm bead 150 mm build-up Acoustic wall on structural slab Twin 18 mm T&G plywood Finish floor Structural slab Sylomer SR28 pads over slab

Drawing 3 — Column Clearance at COL_W / COL_E

10 mm min [AC]

Columns inside the Video/Podcast room use a reduced 10 mm isolation clearance. This is the minimum allowed gap, and it must still receive backing rod and acoustic sealant rather than rigid grout.

10 mm min [AC] 10 Float floor edge around column Backer rod + acoustic sealant on all 4 sides Applies to COL_W and COL_E

Drawing 4 — Wrong vs Right

Skirting must not bridge isolation

Wrong — Isolation Bridged

Baseboard fixed through the float floor and into the wall creates a rigid flanking path.

Rigid fixing bridges wall and floor Result: isolation failure

Right — Floating Baseboard

Baseboard sits on the floating floor only and clears the wall face so the isolation line remains intact.

Baseboard floats on floor only Gap remains free behind skirting Result: isolation maintained

Common Failure Modes

[HP] Inspect before closing finishes
  • 1. Grout or debris falling into the perimeter gap during construction.
  • 2. Skirting board fixed to both the float floor and the wall face.
  • 3. Door-frame threshold or metal saddle bridging the gap line.
  • 4. Electrical conduit crossing the gap without a flexible isolator.