What is the maximum height-to-base ratio for a mobile tower?

Per PASMA (Prefabricated Access Suppliers' and Manufacturers' Association) and BS EN 1004: maximum height-to-base ratio is 3.5:1 for indoor use and 3:1 for outdoor use. So a tower with a 1.4m wide base can reach 4.9m indoor or 4.2m outdoor. With stabilisers/outriggers, the effective base is enlarged, allowing greater height.

When do I need stabilisers or outriggers?

Stabilisers are needed when the required working height exceeds the base-only height limit. They extend the effective base footprint, increasing the permissible height. Some manufacturer instructions require stabilisers at all heights above a certain point. Outriggers must be set on firm, level ground and all four must be deployed — never use only two.

Can I use a tower scaffold on uneven ground?

Towers must be set on firm, level ground. Adjustable leg jacks allow levelling on slightly uneven surfaces — the tower should be level to within 2°. Never use loose bricks, blocks, or timber to level a tower. On sloping ground, use a larger base tower or erect a birdcage scaffold instead. Castor wheels must be locked before climbing.

What training do I need to use a tower scaffold?

Anyone erecting, modifying, or dismantling a tower scaffold should hold a PASMA tower qualification. This covers safe assembly sequences (3T or AGR method), inspection, use, and dismantling. The course typically takes one day. PASMA training is strongly recommended and increasingly required by principal contractors and CDM regulations.

What height can common tower bases achieve?

Standard tower heights: 0.8m wide (narrow) — max 2.8m outdoor / 3.2m indoor. 1.4m wide (standard) — max 4.2m outdoor / 4.9m indoor. 1.8m wide (large) — max 5.4m outdoor / 6.3m indoor. With stabilisers: heights increase to 8-12m depending on the manufacturer's instructions. Always follow the specific manufacturer's assembly guide.

TradeCalculator

Tower Scaffold Height Calculator — Max Height from Base Size

Calculate the maximum safe height for a mobile tower scaffold from base dimensions. Checks the height-to-base ratio per PASMA guidance and BS EN 1004.

Base Length

Longer dimension of tower base

Base Width

Narrower dimension of tower base

Location

Outdoor is more restrictive due to wind

Required Working Height

Platform height needed

How We Calculate This

This calculator determines the maximum permissible height for a mobile tower scaffold based on the base dimensions and location, following PASMA guidance and BS EN 1004.

Height-to-base ratio

Indoor: Maximum 3.5:1 (height ÷ smallest base dimension)
Outdoor: Maximum 3:1 (more restrictive due to wind)
With stabilisers: Effective base enlarged by stabiliser reach

Frequently Asked Questions

Related Calculators

Scaffold Hire Cost Calculator

Calculate scaffold hire cost from building perimeter, height and hire period.

Scaffold Load Class Calculator

Determine scaffold load class by trade use with platform loading check.

Scaffold Tie Calculator

Calculate scaffold tie pattern per TG20 with tie type selection.

Scaffold Board Calculator

Calculate scaffold platform boards, toe boards and ladder access per bay.

MEWP Selection Calculator

Select MEWP type from working height with ground bearing pressure check.

Last updated: March 2026

All calculations are estimates. Verify with your supplier.