Scaffold Technical Guide • Tube-and-Fitting • TG20:21
What Is TG20:21?
TG20:21 is NASC good-practice guidance for many standard tube-and-fitting scaffold arrangements. It helps scaffolders, supervisors, contractors and temporary works teams understand when a scaffold can be built to a recognised standard configuration and when specific design input may be needed.
TG20:21 decision route
Definition
What is TG20:21?
TG20:21 is technical guidance published by NASC for tube-and-fitting scaffolding and is commonly used alongside BS EN 12811-1 working scaffold principles. It is used to help determine whether a scaffold arrangement fits recognised standard guidance or whether the scaffold needs project-specific design input.
In practical terms, TG20:21 is used to assess scaffold type, geometry, height, bay length, lift height, platform loading, tie pattern, wind exposure, bracing and other limits that affect whether a standard tube-and-fitting scaffold arrangement is suitable.
TG20:21 Suite
The main parts of TG20:21
TG20:21 is not just one simple checklist. It is a set of guidance documents and digital tools used together. The exact document or output used depends on the scaffold arrangement and the level of technical detail required.
Used by scaffolding contractors, supervisors and site teams to understand common tube-and-fitting scaffold arrangements.
Helps scaffolders and supervisors interpret TG20:21 requirements and compliance sheet information.
Provides technical information for design engineers where the scaffold is outside the eGuide scope.
The digital route used to generate a TG20 compliance sheet for scaffold arrangements that meet the relevant standard criteria.
Compliance Sheets
What is a TG20 compliance sheet?
A TG20 compliance sheet is the project-specific output generated when the scaffold arrangement has been checked against the TG20 criteria. It records the scaffold type and main parameters that have been selected, then sets out the relevant limits and requirements for that standard arrangement.
- Scaffold type: the arrangement being checked, such as independent access, birdcage, tower or another tube-and-fitting arrangement within the TG20 scope.
- Dimensions: height, bay length, lift height, platform width and overall scaffold geometry.
- Loading: duty class, platform loading and intended working platform use.
- Ties and stability: tie pattern, bracing, returns, buttressing or other stability requirements where relevant.
- Foundation details: base plates, sole boards, support surface and bearing assumptions.
- Sheeted or unsheeted condition: whether cladding, sheeting or debris netting affects the scaffold configuration.
Technical Terminology
Key TG20:21 scaffold terms
TG20:21 uses scaffold terminology that should match the actual scaffold arrangement. The guidance is only useful when the scaffold type, dimensions and loading are described accurately.
A scaffold arrangement that fits the relevant TG20 criteria and can be supported by a compliance sheet.
A scaffold arrangement that exceeds or falls outside the standard TG20 limits.
The intended load category for people, tools and materials on the scaffold platform.
The spacing between standards along the scaffold length, affecting load capacity and layout.
The vertical distance between scaffold lifts, affecting stability, access and working height.
The arrangement of scaffold ties to the supporting structure where ties are required.
Scope
What TG20:21 is used for
TG20:21 is used for tube-and-fitting scaffolds that fall within recognised standard arrangements. It is commonly used to support straightforward scaffold planning where the scaffold type, loading, height, ties, bracing and site conditions remain inside the guidance limits.
- Independent tied access scaffolds where the arrangement fits TG20 criteria.
- Birdcage scaffolds and internal access arrangements where they fit standard guidance.
- Putlog, tower, loading bay and chimney scaffold arrangements where the selected type is within TG20 scope.
- Scaffolds where platform loading, bay size, lift height, tie pattern and bracing can be matched to a recognised compliance sheet.
Limits
What TG20:21 does not mean
TG20:21 does not mean every scaffold is automatically covered by a standard arrangement. The scaffold still has to match the relevant TG20 criteria. Outside recognised standard configurations, bespoke calculations by a competent designer are required.
- Not for every scaffold: unusual height, loading, geometry, support condition or site exposure can place the scaffold outside standard guidance.
- Not system scaffold guidance: system scaffolding has different manufacturer and guidance requirements, with TG30 relevant to system scaffold standard configurations.
- Not a substitute for competence: the scaffold still needs competent planning, erection and alteration by appropriate personnel.
- Not a design where design is required: if the arrangement is outside the standard scope, a TG20 sheet should not be treated as a project-specific design.
Design Boundary
When might design input be needed?
Outside recognised standard configurations, bespoke design is required. That can happen because of height, loading, tie availability, sheeted condition, unusual geometry, bridging, cantilevered sections, poor support conditions or site-specific restrictions.
- Scaffolds that exceed TG20 height, lift, bay, loading or tie limits.
- Complex geometry, returns, bridges, cantilever sections or unusual plan layouts.
- Scaffolds affected by sheeting, cladding, debris netting or wind loading beyond standard assumptions.
- Restricted tie locations, weak supporting structures or unusual base support conditions.
- Temporary works situations where the principal contractor or temporary works team requires a design check.
FAQ
TG20:21 questions
Is TG20:21 the same as a scaffold design?
No. TG20:21 can support a standard scaffold arrangement using a compliance sheet. Outside the standard criteria, competent design and calculations are required.
Does TG20:21 apply to system scaffolding?
TG20:21 is for tube-and-fitting scaffolding. System scaffolding relies on manufacturer information and system scaffold guidance, with TG30 relevant to standard system scaffold configurations.
What does a TG20 compliance sheet show?
It records the selected scaffold arrangement and the key criteria that apply, such as dimensions, loading, tie pattern, bracing and other standard configuration requirements.
Why does TG20:21 matter?
It gives a recognised technical route for many standard tube-and-fitting scaffolds and helps identify when the scaffold needs a different level of technical input.
Need a TG20:21 scaffold arrangement checked?
BlackFox Scaffolding can assess whether a planned tube-and-fitting scaffold appears to suit a standard TG20:21 route or whether the arrangement should be treated as requiring specific design input.