How close to the edge a balustrade can sit depends on both its fall-protection function and the construction beneath it. It should not leave a usable ledge outside the protective barrier, but the fixings must also be far enough from the edge for the supporting material to carry the load.
The minimum feasible distance depends on the structure, mounting method and the edge-distance requirements of the selected fixings. Check both the balustrade position and the technical conditions for securing it at the particular location.
In this guide, we’ll go over how fall protection, the substrate, concrete anchoring, top mounting, and side mounting affect where the railing can be installed.
What determines how close to an edge a balustrade can be fitted?
Two factors matter: the balustrade should not leave a usable ledge outside the protective barrier, but it must not be positioned so close to the edge that its fixings or the supporting material are compromised.
A ledge may remain outside the balustrade
If the balustrade is set well back from the outer edge, it may leave an area outside the protective barrier. If someone can step onto that area, they would be on the unprotected side.
The railing should therefore be placed close enough to the edge so that the area outside it does not become a usable ledge.
Fixings too close to the edge can weaken it
An anchor near a concrete edge can affect the material when the railing is subjected to lateral forces. On a timber decking, it is also not sufficient to attach the post to the outermost part of a deck board.
Check the minimum edge distances for the fixings and the condition of the supporting structure before deciding where to position the balustrade.
The right position balances the protective function of the balustrade against the minimum distances and structural requirements for its fixings.
What clearances below a balustrade need checking?
Permitted openings beneath balustrades depend on where they are installed and how the space is used. Additional safeguards may be needed where young children are present. Check the applicable clearance requirements for the specific location.
From the underside of the balustrade
- To the balcony floor beneath the balustrade.
- To the nosing of the stair tread below the stair balustrade.
Clear vertical opening
Check the permitted clearance between the underside of the stair balustrade and the landing, tread or floor at the installation location.
Measure vertically towards the floor, not inwards from the edge
Clearance requirements beneath a balustrade relate to the vertical gap. They do not tell you how far the balustrade or its posts must be set back from the outer edge; the fixing edge distance must be checked separately.
How does the substrate affect the position of a balustrade near an edge?
The supporting substrate determines where the fixings can carry the load and what edge distances are achievable. A balustrade must be fixed to suitable structural material, not merely to the visible surface closest to its posts.
| Supporting structure | What matters is | Common mistake |
|---|---|---|
| Timber decking | Load-bearing joist or edge beam | Fixing only in the deck boards |
| Concrete slab | Fixing edge distances and concrete conditions | The anchor is mounted too close to the edge |
| Balcony slab | Slab thickness, reinforcement, and selected fixing | Drilling without checking the reinforcement and structure |
| Masonry edge | Load-bearing capacity of the masonry and mortar | Fixing directly into a weak joint |
| Raised roof upstand | Load-bearing capacity of the upstand and waterproofing details | Penetration without a properly designed seal |
What determines the minimum edge clearance for a concrete fixing?
The minimum edge clearance is determined by the selected fixing and the properties of the concrete, not by a general rule of thumb. Mechanical and chemical anchors transfer the load in different ways and may therefore have different requirements regarding the distance to the edge.
Mechanical fixing
Expansion bolt
An expanding fixing transfers force to the walls of the drill hole. If the anchor is installed too close to the edge, the load may increase the risk of damage to the concrete.
Therefore, the minimum edge clearance for the specific fixing selected must be verified before drilling.
Bonded anchorage
Chemical anchor
A chemical anchor bonds the fixing into the drilled hole with a resin or similar compound; it does not create the same expansion forces as a mechanical expansion anchor.
Some chemical anchor systems may permit a smaller edge distance, but the technical documentation for the selected system must always be checked.
The type of fastening can therefore affect how close to the edge of the concrete the post can be placed. It is therefore not possible to specify a single edge distance for all anchors.
How are balustrade dimensions calculated when you order?
For a custom-sized balustrade system, enter the actual outer edge dimensions of the substrate. Based on those dimensions, the railing’s system dimensions are calculated, taking into account posts and the margins associated with the selected balustrade system.
The edge clearance of the fixing must still be verified separately based on the substrate, the installation method, and the technical documentation for the selected fixing.
Your substrate
Enter the outer edge dimensions
Measure corner to corner or edge to edge across the surface where the balustrade will be installed. Enter the full substrate dimensions without making your own deductions.
System calculations
The balustrade dimensions are calculated
Based on the outer edge dimensions, deductions are calculated for the posts and the railing system's own margins.
Before installation
The measuring template shows the positioning
The template supplied with the order shows where the balustrade and posts will sit in relation to the outer-edge dimensions you entered.
What are the options for fixing a balustrade near an edge?
The mounting method affects both how close the balustrade can sit to the outer edge and which part of the structure carries the load. Top-mounted and side-mounted posts have different positions, while through-bolting or fixing to a suitable structural upstand may be possible depending on the construction.
- Top mounting
- The post is mounted on top of a deck, slab, or other load-bearing surface. The placement requires space inside the outer edge for both the post’s base and the fixing used.
- Side mounting
- The post is mounted to the side of a load-bearing edge beam or slab edge. This can free up floor space and make it easier to position the balustrade along the outer edge.
- Through-bolting
- A bolt passes through a load-bearing structural member and is secured with a washer and nut on the opposite side. The construction must be suitable for through-bolting, with access to the reverse side.
- Fixing to a structural upstand
- In some constructions, the balustrade can be fixed to a raised structural upstand rather than through the horizontal surface. The upstand must be load-bearing and capable of carrying the relevant balustrade loads.
How do you check that the distance to the edge is correct before installation?
Check the supporting structure, fixing requirements and proposed balustrade position before drilling or screwing. You can then determine whether the mounting method needs changing before installation.
Checks before installation
Check these points before positioning the posts
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Identify the load-bearing structure
Find out what will actually support the railing. In a timber decking, it might be a joist or a perimeter beam, while a concrete structure needs to be evaluated based on the conditions of the slab or the perimeter.
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Choose the balustrade mounting method
Check whether top mounting, side mounting, or another mounting solution is best suited for the design. The mounting method affects how much space is needed at the edge.
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Check the minimum edge distance for the fixings
Read the technical documentation for the anchor, screw or fixing system. Check the edge distances specified for the particular substrate, load and application.
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Check the area outside the balustrade
Avoid a usable ledge outside the balustrade where it is intended to provide fall protection. Its position must be considered in relation to the actual outer edge.
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Check the clearance beneath the balustrade
In areas where young children are likely to be present, current requirements regarding openings must be taken into account. Therefore, check the distance between the bottom of the railing and the floor, the top of the step, or the landing, as applicable.
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Check for reinforcement before drilling into concrete
The placement of the drill holes must be adapted to the structure. Do not assume that you can drill freely just because the base of the post fits on the surface.
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Verify the placement before continuing with installation
Check the first post’s position against the outer edge, supporting structure and balustrade dimensions before applying the same layout to the remaining posts.
Brief summary
There is no single edge distance that works for every balustrade. Positioning must satisfy the function of any required fall protection while allowing secure fixings into the supporting structure.
Next step
Not sure how to fix a balustrade near the edge?
The substrate, mounting method and fixings must work together. Choose the balustrade type, then assess the structural conditions before deciding where to position it.
What are common questions about balustrade edge distances and fixings?
Common questions include what the balustrade can be fixed to, how to assess a concrete anchor and what to check before measuring and installation.
Can I fix a balustrade to a decking board if the screw is long enough?
No, not if the decking board alone would carry the load. The fixings must reach a suitable load-bearing part of the structure, such as a joist or edge beam, capable of supporting the balustrade.
How do I know what edge clearance a concrete anchor requires?
Check the technical documentation for the fixing to be used. The requirement may be affected by factors such as anchor type, dimensions, anchorage depth, load, and concrete properties.
What should I do if the post base fits but the anchor ends up too close to the edge?
Do not move a drilled hole without checking the full fixing arrangement. You may need to change the post position or mounting method so that both the post base and its fixings are supported by suitable load-bearing material.
Can " side mounting " provide more space on the deck?
Yes. Side mounting keeps the post base off the top surface of the deck, which can free up usable space. The edge beam or slab edge must still be suitable for load-bearing fixings.
Should I deduct the edge margin when taking measurements for an order?
No. Enter the actual outer-edge dimensions of the supporting surface without making any deductions. The balustrade system dimensions are calculated from these measurements; the fixing edge distances must be checked separately.
Do I need to check the rebar before drilling into a concrete slab?
The location of the drill holes must be adapted to the specific structure. When drilling into a reinforced concrete slab (fixing), you therefore need to know the conditions at the location where the holes will be drilled before you begin drilling.
