Dos & Don'ts

Balconies & Raised Decks

A balcony is the one DIY project where a mistake doesn't mean redoing the work — it can mean someone falls. These are the rules that keep the structure on the house and the people on the balcony, in plain language.

Ledger attachmentJoist hangersGuard railsFlashingWhen to call a pro
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Read this first. An elevated balcony is safety-critical construction, and in most countries it needs a building permit. Plan it yourself, price it yourself — but have a qualified builder or structural engineer verify the house attachment and the guard rail before anyone stands on it. Nearly every deck collapse in the accident statistics is a ledger that let go of the house.

The Structure

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Bolt the ledger through the house structure

Fix the ledger board with through-bolts or structural screws into the floor structure or a concrete wall — roughly every 600 mm, in a zig-zag pattern. The ledger carries half the balcony.
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Never nail-only, never into cladding

Nails and decking screws into siding or insulation hold… until they don't. The ledger must reach the actual structure behind the facade. If you can't confirm what's behind, stop and get a professional to open it up.
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Hang joists in joist hangers

Every joist sits in a galvanised joist hanger at the ledger, nailed/screwed through every hole with the fixings the hanger maker specifies. Two hangers per joist (ledger end + bearer end) is the pattern our balcony calculator counts.
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Don't toe-nail joists

Screws driven at an angle through the joist end have a fraction of the strength and split the wood. Hangers cost a couple of euros each — this is not the place to save.
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Flash the ledger properly

Water running down the wall must be led OVER the ledger and out — a metal or membrane flashing tucked under the cladding above and over the ledger face. Slow rot at the ledger is invisible until it's critical.
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Don't trust sealant

A bead of silicone against the wall fails within a few seasons. If water can sit between the ledger and the wall, the strongest bolts in the world are anchored in rotting wood.
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Set posts on proper footings

Posts stand on concrete footings below local frost depth (Ø300 mm, typically 900 mm deep in frost climates) with a post shoe that lifts the timber off the concrete. Use ground-contact (UC4) treated timber.
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Don't stand posts on slabs or soil

Paving slabs tip and sink under point loads, and timber straight into soil or concrete wicks water and rots from the bottom. Both mean a sagging corner within a few winters.

The Guard Rail

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Build the rail ~1.0 m high with tight gaps

Common EU/US practice: guard height at least ~900 mm for low decks and ~1,000–1,100 mm for balconies, with no opening a 100 mm sphere can pass through (that's a small child's head). Check the exact figures for your country.
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Don't build a ladder

Horizontal rails, cables or decorative cut-outs that give a foothold are climbable — many building codes reject them where children are expected. Vertical balusters or certified glass are the safe defaults.
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Anchor rail posts to the frame

Rail posts bolt through the rim joist or frame with carriage bolts — a guard must take a heavy adult falling against it. Test with a hard shove (not your full body weight over the edge).
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Don't fix posts to decking only

Screws into deck boards pull straight out under load. The boards are a floor, not a structure.
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Using glass? It must be certified laminated safety glass in the maker's clamps — never window glass, never improvised fixings. Our fence & railing calculators count panels and clamps for standard 1.5 m bays.

When to Call a Professional

Call in a qualified builder or engineer — not as a formality, but because these are the failure points that hurt people:

  • Always: verifying the ledger attachment on any elevated balcony (above ~500 mm fall height)
  • Always: sign-off on the guard rail where a fall could cause injury
  • The house wall is timber-frame and you can't confirm what the bolts will bite into
  • The balcony is on the 2nd floor or higher — fall energy and permit requirements both rise
  • Anything cantilevered (no posts) — that is engineered construction, full stop
  • Your local rules require a permit — most do, for any elevated balcony

Plan Your Balcony

Draw the balcony on your floor plan — ledger, joists, hangers, posts, concrete and railing are counted automatically, floor by floor.

Open the Home Planner

Frequently asked questions

How high must a balcony railing be?

Common practice is at least ~900 mm (36") for low decks and ~1000–1100 mm (42") for balconies, with no opening a 100 mm (4") sphere can pass through. Exact figures vary by country — check your local building code.

Can I attach a balcony ledger with screws?

Only with structural screws or through-bolts into the building’s structure (floor rim or concrete), roughly every 600 mm. Never nails, and never fixings that only reach cladding or insulation. Have the attachment verified by a professional.

Do I need a permit for a balcony?

In most countries, yes — an elevated balcony is structural, fall-protection construction and usually requires a permit and often professional sign-off. Check with your local building authority before starting.

Why are horizontal railings a problem?

Horizontal rails and cables are climbable — a ladder for small children right at the drop. Many building codes reject them as fall protection; vertical balusters or certified laminated glass are the safe defaults.

Guard heights, gap limits and permit thresholds vary by country — the figures here are common EU/US practice, not your local code. A balcony is fall-protection construction: have the attachment and guard verified by a qualified professional before use.Last reviewed: July 2026