Scaffold Tie Calculator — TG20 Tie Pattern & Spacing

There is no single universal grid — the definitive tie pattern for a tube-and-fitting scaffold comes from the relevant TG20:21 compliance sheet for your bay length, lift height, height and exposure. As a common rule of thumb for an unsheeted scaffold, ties are placed roughly every 4m horizontally on alternate lifts, with the first tie near each end. This calculator simply divides your face by the grid spacing you choose (default 4m × 4m) and rounds up — it is an estimating aid, not a substitute for the compliance sheet or a bespoke design.

Sheeting and netting greatly increase wind load, so more ties are needed — but full monofilament sheeting and debris netting have very different wind-area factors and are NOT interchangeable. A sheeted or netted scaffold, especially against a permeable facade, must be specifically designed for wind load; it is outside standard TG20 compliance sheets. The 2.5m grid this tool applies when you tick 'sheeted' is only an indicative tightening to roughly double the tie count — always confirm against a TG20:21 design or an engineered calculation.

TG20 classifies ties by DUTY CLASS — the characteristic working load the tie must resist in pure tension — not by physical method: light 3.5 kN, standard 6.1 kN, heavy 12.2 kN. A given tie method can fall into more than one class depending on configuration. Through ties (tube through a window opening with an inside transom) are the preferred, most reliable method. Box ties loop around a return wall or column. Reveal ties (a tube jammed in a reveal with a reveal pin) are friction-dependent and the least secure: TG20 limits reveal ties to no more than 50% of the ties on any facade. Drilled anchor ties have NO universal SWL — their capacity is set by site testing (see below).

There is no default kN figure for an anchor tie. Per NASC TG4:19, the safe working load of a drilled-in anchor depends on the fixing and the base material and must be established on site: preliminary tests prove the allowable load of an anchor type in that material, and proof tests (carried out on every job) confirm correct installation. The proof test load is 1.25 × the working load — for example a 6.1 kN standard-duty tie is proof tested to about 7.6 kN, and a 12.2 kN heavy-duty tie to about 15.3 kN. A minimum of three anchors, or 5% of those installed (whichever is greater), are proof tested per scaffold. Use the tested safe working load, never an assumed value.

If ties cannot be placed at the TG20 pattern (e.g., due to building features, listed buildings), the scaffold becomes a 'design scaffold' requiring a specific design by a competent engineer. Additional measures may include: closer ties where possible, buttress bays, kentledge (weighted base), or raking tubes. Never omit ties without an engineered alternative.

Scaffold ties must be checked at every inspection (at least every 7 days): verify the tie is tight and secure, check it has not been removed or loosened by others, ensure the tie tube is properly coupled to the scaffold ledger or standard. Record the tie check on the scaffold inspection report (SG4 form). Any missing or defective tie must be replaced immediately.