What is the 100mm rule for balustrades?

UK Building Regulations (Approved Document K) state that the gap between spindles must not be large enough for a 100mm sphere to pass through. This is a safety measure to prevent small children from falling through or getting their heads stuck. In practice, gaps are usually set to 95mm or 99mm.

How high should a decking handrail be?

For domestic decks that are more than 600mm above ground level, the handrail must be a minimum of 900mm high. If the deck is for a commercial property or accessible to the public, the requirement increases to 1100mm.

How many spindles do I need per linear metre?

For standard 41mm square spindles with a 99mm gap, you need approximately 7.1 spindles per metre. Our calculator provides the exact count based on your total run length to ensure even spacing.

Can I use horizontal wires for a balustrade?

While popular for a modern look, horizontal wire balustrades are often discouraged by building inspectors because they create a 'ladder effect' that children can climb. Vertical spindles or glass panels are the safest and most compliant options.

What is the 100mm rule for balustrades?

UK Building Regulations (Approved Document K) state that the gap between spindles must not be large enough for a 100mm sphere to pass through. This is a safety measure to prevent small children from falling through or getting their heads stuck. In practice, gaps are usually set to 95mm or 99mm.

How high should a decking handrail be?

For domestic decks that are more than 600mm above ground level, the handrail must be a minimum of 900mm high. If the deck is for a commercial property or accessible to the public, the requirement increases to 1100mm.

How many spindles do I need per linear metre?

For standard 41mm square spindles with a 99mm gap, you need approximately 7.1 spindles per metre. Our calculator provides the exact count based on your total run length to ensure even spacing.

Can I use horizontal wires for a balustrade?

While popular for a modern look, horizontal wire balustrades are often discouraged by building inspectors because they create a 'ladder effect' that children can climb. Vertical spindles or glass panels are the safest and most compliant options.

Balustrade Calculator

Safety-compliant material takeoff for decks and stairs.

Total Balustrade Length (m)

Spindle Width (mm)

Desired Gap (mm)

UK Regs: Max 99mm

Handrail Section Length (m)

Material Summary

Building Regs Note: For any deck higher than 600mm off the ground, a balustrade is **mandatory**. The height of the handrail must be at least 900mm (or 1100mm for commercial projects).

Safety First: The Art of the Balustrade

Regulatory Compliance

A balustrade is more than a decorative finish; it is a critical safety barrier. In the UK, strict building regulations govern the height and spacing of balustrades to protect users, especially children.

Our **balustrade calculator** is programmed to enforce the 100mm sphere rule, ensuring your project meets local building standards from the very first measurement.

Safety Standards

Max Gap99mm

Min Height (Domestic)900mm

Min Height (Public)1100mm

Structural Newel Posts

The strength of your balustrade comes from the **Newel Posts**. These should be securely bolted to the deck's sub-frame (joists) using heavy-duty carriage bolts or timber screws.

Never rely on simply nailing a post to the surface of the decking boards; it will not have the lateral strength required to stop someone from falling if they lean against the rail.

Equal Spacing

To achieve a professional look, you must ensure the gap at the start and end of a run is equal. Our calculator helps you find the total number of spindles; once you have this, divide the remaining space by the number of gaps to find your perfect custom spacing.

Baserails

A baserail sits on top of the deck and holds the bottom of the spindles. This is superior to screwing spindles directly into the deck as it prevents water from pooling in the bottom screw holes, which causes rot.

Pro Tip: Spindle Infill

If you are using a handrail with a 'plow' (a groove in the bottom), you will need **infill strips** (also called spacers). These are small pieces of wood that fit between the spindles in the groove, hiding the nails and creating a clean, professional finish.

Balustrade & Safety FAQ

Technical Disclaimer

This tool calculates quantities for standard vertical spindle balustrades. For glass panels, metal railings, or unique geometric designs, consult the specific manufacturer's installation guide to ensure compliance with UK safety standards.