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Short answer

How close to the wall must a scaffold deck be?

The inside edge is the one side of a scaffold that often has no rail. Whether it may stay open depends on one measurement: the gap between the deck and the face of the building.

By Ole Emil Frikstad Urstad · How the numbers are computed ·

Close-up of the top HAKI Universal lift below the eaves, with guardrails and toe boards, in the ScaFix 3D model
The top lift below the eaves, with guardrails and toe boards.

How close to the wall must a scaffold deck be?

Under OSHA 1926.451(b)(3) a platform's front edge may be at most 14 in (36 cm) from the face of the work, 18 in for plastering and lathing and 3 in on outrigger scaffolds, unless a guardrail or personal fall arrest protects it. British law sets no figure; guidance based on NASC SG29:17 works from 225 mm, one board's width.

What exactly does OSHA 1926.451(b)(3) allow?

29 CFR 1926.451(b)(3) measures from the front edge of the platform to the face of the work:

  • 14 in (36 cm) for most supported scaffolds;
  • 3 in (8 cm) for outrigger scaffolds, (b)(3)(i);
  • 18 in (46 cm) for plastering and lathing, (b)(3)(ii);
  • beyond those, a guardrail system along the front edge, personal fall arrest under paragraph (g), or both.

The face moves with the job: strip old cladding and the gap grows, so check it at the worst stage. Rail heights are on the guardrail height page.

What does British law say about the inside gap?

No number. Schedule 3, paragraph 5 bans platform gaps a person could fall through and, so far as reasonably practicable, anyone being caught between platform and structure.

The detail is in NASC's SG29:17 on internal edge protection. Jersey's inspectorate summarises it (pdf):

  1. Under 225 mm, with no opening to fall through: inner protection not normally required.
  2. 225 mm or more, injury risk but no fall-through: at least a single guardrail.
  3. 225 mm or more and a person could fall through: double guardrails.
  4. Where rails would block the work: a safe system of work, such as a harness and restraint lanyard.

Treat 225 mm as guidance, not law. Fitted inside rails must meet Schedule 2: 950 mm, no gap over 470 mm.

Close-up of the corner where the long wall and the gable wall meet, with Layher Allround standards, decks, guardrails and toe boards in the ScaFix 3D model
The corner: the bays of the two walls meet, with deck, guardrail and toe board on each lift.

How do other countries set the limit?

CountryGap allowed without inside protectionClause
United States14 in; 18 in plastering and lathing; 3 in outrigger29 CFR 1926.451(b)(3)
Great BritainNo figure in law; 225 mm in SG29-based guidanceWAHR Sch. 3 para. 5
Norway0.30 m§ 17-14
Germany0.30 mTRBS 2121-1, 4.2.1 and 4.3.1
Denmark0.3 m; 10–15 cm advised for windows and renderingBEK 428 § 94, AT fact sheet
Netherlands15 cm, item 15 of the handover checklistA-blad Steigerbouwen, bijlage 5
Poland0.2 m, then a balustrade on the wall side§ 115 ust. 4

Why do insulation and balcony jobs break the limit?

External insulation (ETICS) needs room behind the deck. The German trade associations' 2020 guidance (pdf) plans the gap as the system thickness plus at most 30 cm of working space, notes boards of 14 to 30 cm today, and leaves about 23 cm of working space at the frame lines. Any stage over the limit gets an inside two-rail guard or bracket.

Balconies and bay windows push the scaffold out for whole bays. DGUV Information 201-011 (4.7.1) names balconies and oriels as features that can rule out even the single assembly rail on the top lift during erection, leaving personal fall protection. Corners are covered in scaffold corners and returns.

When does an inside bracket close the gap?

When the work must be close to the wall. A bracket, a "hop-up" on UK sites, carries boards inboard of the frame. Which brackets a system allows, and how they are tied, is set by its manufacturer. In the Norwegian Jamax system, for example, the manual offers 0.3 and 0.6 m brackets and requires one extra wall tie per bracket, fitted before the decks (Alutec); see scaffold ties.

ScaFix plans scaffolds in 3D with a parts list; it does not check the inside gap against these rules.

Planning information, not structural approval. The clauses above and the manufacturer's instructions decide the gap, the brackets and the ties, and a competent person must inspect the scaffold before use.

Frequently asked questions

What is the maximum gap between a scaffold and a wall?

14 in under OSHA; 0.30 m in Norway, Germany and Denmark; 0.2 m in Poland. Great Britain has no figure in law.

Can a harness replace an inside guardrail?

Under OSHA, yes. The SG29-based guidance allows harness and restraint only where rails would stop the work.

How far from the wall should a scaffold be for rendering?

OSHA allows 18 in for plastering and lathing. Denmark's Arbejdstilsynet advises 10 to 15 cm for window fitting and rendering.

What is a hop-up bracket?

A short inside bracket carrying one or two boards closer to the wall. Manufacturers set the tie rule; Jamax, for one, requires an extra tie per bracket.

Does insulation change the allowed gap?

It moves the face you measure to. German guidance plans the insulation thickness plus at most 30 cm.

Sources

Primary sources used for this article, with the date each was read.