Joist Hangers: Types, Sizing and Correct Nailing

Summary

The joist hanger is a small piece of metalwork doing a critical structural job: transferring the entire end-load of a floor or ceiling joist into the supporting wall or beam. A 4m × 4m bedroom floor is around 200–400kg dead weight plus 1.5kN/m² imposed load on a typical residential design — that load passes through the joist hanger at each end of every joist. Get the hanger wrong (wrong size, wrong nail, wrong bearing, wrong masonry coursing) and the joist either deflects more than it should (squeaky floors, cracked plaster) or in extreme cases drops free.

The hanger industry has standardised around BS EN 845-1 for product specification, with the major UK suppliers publishing detailed load tables for each hanger in each application. The job on site is to: pick the hanger that matches the joist size, install it at the correct height for the bearing, build it into the masonry per the manufacturer's coursing detail (or nail it to the timber for face-fix types), and nail it off with the specified fasteners. Each of those steps has been wrong on enough sites for it to be one of the top defects spotted at Building Control inspection.

This article covers the main hanger types, sizing rules, the critical fastener requirements, bearing and coursing details for masonry-built-in hangers, alternatives for steel and timber-frame supporting structures, and the load tables you need to consult before specifying. The article assumes routine domestic construction; engineered scenarios (laminated joists, large openings, asymmetric loads) need engineer's calculations.

Key Facts

• Primary product standard — BS EN 845-1:2013 + A1:2016, ancillary components for masonry — Part 1: wall ties, tension straps, hangers and brackets
• Design code — PD 6697:2019 (UK guidance for masonry structures), and BS EN 1996-1-1:2005+A1:2012 (Eurocode 6) for non-routine design
• Building Regulations — Approved Document A (Structure); 100mm minimum bearing length for joists onto masonry
• Manufacturer specification — Simpson Strong-Tie, Cullen Building Products, BAT, ITW Industrial Holdings — each publishes EN 845-1 declared performance tables
• Fastener requirement — Sherardised square-twist nails to BS 1202 or the manufacturer's equivalent; substituting ordinary round-wire nails halves the declared load
• Standard nail size — 3.75mm or 5mm × 30–40mm depending on hanger type; one nail in every hole, no exceptions
• Hanger sizing rule — Match the hanger to the nominal joist size; do NOT use an undersized hanger for a deeper joist
• Built-in (BTBR) hanger — Built into the brickwork as the wall is built; flanges sit on a course of brick, the joist hangs in front
• Face-fix (FF) hanger — Nailed to a timber face (e.g. into a wall plate, ledger or trimmer); used in retrofit and timber-frame
• Top-flange (TF / top-mount) hanger — Used in steel-supporting-timber junctions; flanges sit over the top of a steel beam
• Bearing area requirement — 75–100mm of joist must sit within the hanger seat; overhang at the back is not acceptable
• Joist trimming — Joists must be cut square; any tapering or notching of the bearing end reduces the load capacity
• Headroom check — Some hanger designs reduce headroom by 25–50mm at the bearing; check before ordering for finished ceiling heights
• Galvanising / corrosion — Standard Sherardised finish for internal dry use; consider stainless or Z600+ for cellars, garages, semi-exposed

Quick Reference Table

Detailed Guidance

Selecting the Right Hanger

Hanger selection follows three steps:

1. Joist size — Match the hanger nominal opening to the joist (47 × 145mm joist → 47/150 hanger; never undersize). For deeper joists, do not "fold in" extra timber to fit an undersized hanger.
2. Support type — Masonry (built-in or face-fix to ledger), steel (top-flange), timber-frame (face-fix to nogged stud or ledger). The hanger range from each manufacturer covers all these; pick the one designed for the support.
3. Load — Calculate the design load on the joist end (manufacturer's load tables show declared capacity, typically with substantial safety factors); confirm it is below the hanger's published rating. For most domestic spans up to 4m with typical 1.5kN/m² imposed load, standard hangers are more than adequate. For longer spans, trimmer joists carrying multiple supported joists, or unusual loading, defer to engineer's calculations.

Built-in Hangers (Masonry New Build)

The built-in hanger is built into the brickwork or blockwork as the wall is built. The hanger's top flange sits on a course of brick at the correct height for the joist top to align with the floor finish; the brick is laid over the flange in the next course, locking it in place.

Critical points:

• Coursing alignment — Plan the brick coursing so a course junction falls at the joist bearing height; trim/sit the hanger so its flange sits on full bricks (not over-cut)
• Mortar bedding — A full bed of mortar over the flange transfers load into the wall above; gaps under the flange concentrate load and may crack the brick over time
• Joist install timing — Joists can be slotted into the hangers once the masonry is up to floor-plate height; do NOT install joists into hangers before the wall above has cured (the load over the hanger flange must be in place before vertical loading)
• Cavity sealing — The hanger creates a cavity-bridging route from outer to inner leaf at the bearing; seal with appropriate flashing or cavity barrier per manufacturer

Face-Fix Hangers (Retrofit, Ledger, Timber-Frame)

A face-fix hanger is nailed (or screwed in some designs) to a timber face — typically a wall plate, ledger board, or trimmer joist. Used routinely in:

• Loft conversions where a ledger is bolted to an existing wall to carry new joists
• Timber-frame new build where joists hang from the trimmer at the inner-leaf face
• Extension work where a ledger is bolted to the existing house to support new floor joists

The hanger sits flat against the timber face, the nail holes are populated with the specified fastener, and the joist drops into the seat. The supporting timber (ledger, trimmer) must itself be adequately fixed — a face-fix hanger transfers load through the ledger into whatever the ledger is fixed to. A ledger bolted with four M12 resin anchors at 600mm centres can carry a substantial floor; a ledger nailed to the existing wall is not load-bearing.

Nail Specification — The Most Common Failure

The single most common joist-hanger defect found at Building Control or party-wall surveyor inspection is the wrong nail in the hanger. Sherardised square-twist nails to BS 1202 (or the manufacturer's specific product, e.g. Simpson SDS) are designed to withstand the shear loading from the joist; ordinary round-wire nails work loose under cyclic loading and the published load capacity is halved or worse.

Every hole in the hanger must be filled with the correct nail (or screw for some designs). "Some holes are enough" is wrong — the manufacturer's load table assumes full nailing. Reuse of recovered nails from demolition: not acceptable.

Avoid:

• Nail guns loaded with collated round-wire framing nails — wrong nail entirely
• Drywall screws or other quick-fix substitutes — not rated for shear
• Galvanised round-wire nails (slightly better than plain but still not square-twist)

A 50p saving per hanger on cheap nails creates a 50% reduction in the hanger's structural capacity. Always insist on the manufacturer-specified fastener.

Bearing and Trimming

The joist must:

• Sit fully in the hanger seat (not overhanging at the back)
• Be cut square at the bearing end (a sloped cut concentrates load on a small bearing area)
• Not be notched at the bearing — any notching for plumbing or wiring must be at least 200mm from the bearing
• Have a minimum of 75mm of joist seated in the hanger; manufacturer's product datasheet will specify exact

For deeper joists (195mm+), check the manufacturer's "bearing length" requirement — some hangers require the joist to bear on a longer seat with additional packing or filler.

Trimmers Around Openings

Where joists are trimmed around openings (stairs, hatches, chimney breasts), the trimmer joist carries the load of all the supported joists into the trimming joist at each end. Use:

• A double or triple thickness trimmer joist (depending on opening width and supported load)
• Heavy-duty hangers at the trimmer-to-trimming connections
• Hangers sized for the doubled or tripled joist (don't use a single-joist hanger on a doubled trimmer)

For openings >1.2m wide or carrying >3 supported joists, an engineer's calculation is normally required to size the trimmer and hangers.

Top-Flange Hangers (Steel Beam Support)

When a steel beam (RSJ, UB, UC) supports timber joists, the top-flange hanger hooks over the top of the steel beam, with the joist hanging from the hanger seat at the underside of the beam. The hanger transfers load directly into the steel through its top flange; no fixing to the steel is normally required, though some designs include bolt holes for additional restraint.

Critical: the joist must be the correct depth relative to the beam — too deep and the joist hits the underside of the beam; too shallow and the joist top is below the beam top, creating an awkward floor build-up. Plan the joist depth, beam depth, and finished floor in coordination.

Corrosion Class

Standard joist hangers are Sherardised (zinc-coated by mechanical adhesion). This is suitable for normal dry internal use. For:

• Damp internal environments (cellars, bathrooms in some constructions) — Z600 (heavy zinc) finish
• External or partial external exposure (covered porches, garages) — stainless steel or Z600
• Coastal locations within 1km — stainless steel grade 304 minimum

A hanger that corrodes loses cross-sectional area and ultimately fails. The lifetime of the building is 60+ years; a £2 saving on a hanger upgrade is meaningless against the cost of a failure inspection 30 years on.

Frequently Asked Questions

What nails should I use in a joist hanger?

Sherardised square-twist nails to BS 1202, or the manufacturer's specific connector nail (e.g. Simpson SD Connector). Every hole in the hanger must be filled with the specified nail. Substituting plain round-wire nails halves the published load capacity and is the most common defect found at structural inspection.

Can I use joist hangers to attach a new floor to an existing wall?

Yes, but the load path needs thought. Face-fix hangers attached to a wall plate that is itself bolted to the existing wall is the routine method. The wall plate (typically 47 × 100mm) is bolted to the wall with M12 chemical anchors at 600mm centres, and the hangers nail to the wall plate. The existing wall must be sound and able to take the load — a 1930s cavity wall is fine; a single-skin 100mm wall may not be.

What's the minimum bearing length for a timber joist on masonry?

100mm minimum per Approved Document A, with the joist seating directly in the hanger and the hanger's flange built into the masonry coursing. The joist itself does NOT need to extend further into the wall; the bearing is via the hanger seat, not direct timber-to-masonry contact.

How do I install a joist hanger when one already exists in the wrong position?

Carefully remove the old hanger (it may need a brick to be cut out around it), install a new hanger at the correct position, and rebuild the masonry around it. This is a structural alteration — get the work signed off by Building Control on completion. Do NOT just bolt or face-fix a new hanger over a position where one already failed — the substrate is compromised.

Can I cut the hanger to fit?

No. Cutting the steel of a joist hanger reduces its structural capacity in unpredictable ways and voids the manufacturer's declared performance. If no off-the-shelf hanger fits, order a custom hanger from the manufacturer (most produce non-standard sizes on a 1–2 week lead time) or change the joist size to suit a standard hanger.

Regulations & Standards

• BS EN 845-1:2013 + A1:2016 — Ancillary components for masonry, Part 1: wall ties, tension straps, hangers and brackets (the product standard)

• PD 6697:2019 — Recommendations for the design of masonry structures

• BS EN 1996-1-1:2005+A1:2012 — Eurocode 6: design of masonry structures

• Approved Document A — Building Regulations Part A: Structure (notifiable; Building Control inspection at first-fix structural stage)

• BS 8103-3:2009 — Structural design of low-rise buildings — code of practice for timber floors and roofs

• BS 1202-1 — Specification for steel nails (the standard for the recommended square-twist nails)

• BS EN 14080:2013 — Timber structures — glued laminated timber (where engineered joists are used)

• NHBC Standards Chapter 6.4 — Timber and joist hanger installation guidance (warranty-provider requirements)

• Simpson Strong-Tie UK technical guide — UK market leader; load tables and installation guides

• Cullen Building Products — UK manufacturer; full product range

• BAT structural fixings — Alternative UK supplier

• NHBC Standards Chapter 6.4 — Joist hanger warranty requirements

• joist installation — Floor joist installation procedure

• timber spans — Joist size selection from span tables

• roof truss types — Roof structure connection design

• wall ties types and spacing — Related BS EN 845 ancillary components