Joist Hangers & Builders' Metalwork: A Site Guide to Correct Specification

A joist hanger is only as strong as its fixing. Fill every hole with 3.75 x 30mm square twist nails, match the hanger to the joist width, and seat it tight to the header or masonry. Do that and it carries its published load. Skip holes or improvise with odd screws and the load table no longer applies.

Builders' metalwork is cheap, standardised and unforgiving of shortcuts. This guide covers the hangers, straps, ties and brackets you'll actually order, and the specification details that building control will check.

Quick-reference spec table

Application	Metalwork	Fixing rule
Joist to timber (trimmer, beam, ledger)	Jiffy or standard-leg hanger sized to joist width	3.75 x 30mm square twist nails in every hole
Joist into masonry wall	Welded masonry hanger, built into bed joint	Build in as work rises; load only when mortar has cured
Heavier floors and long spans	Medium or heavy duty hanger	Full nailing plus any bolts the manufacturer specifies
Lateral restraint of walls	30 x 5mm restraint straps	Maximum 2m centres, notched over joists, packed solid at the wall
Stud and frame connections	Angle and corner brackets	Square twist nails or structural screws, every hole
New masonry to existing	Wall starter ties	Fix to existing wall, ties into every other bed joint

Hanger types and when to use each

• Standard-leg hangers (light and medium duty) - the everyday timber-to-timber hanger; the top flange nails over the supporting timber

• Long-leg hangers - same idea with an extended back leg, for when the supporting timber is deeper than the joist or you need the joist set lower

• Welded masonry hangers - a heavier welded body that builds into the mortar bed of a wall as the brickwork rises; the masonry above provides the anchorage

• Jiffy-type mini hangers - quick hangers for trimming light loads such as ceiling binders and loft openings, not a substitute for a sized floor hanger

• Restraint-type hangers - hangers that double as lateral restraint, tying the wall to the floor where the design calls for it

  
  

Size hangers by the joist, not by what's on the van: a 47mm joist wants a 47mm hanger, seated so the joist bears fully on the shoe with no gap at the back. The full range is under builders' metalwork .

The nailing rules that decide the load rating

Hangers are manufactured to BS EN 845-1, the standard covering ancillary components for masonry including joist hangers and straps, and every published load figure assumes the fixing schedule was followed exactly. In practice that means one thing above all: every hole gets a nail. The nail is the 3.75 x 30mm square twist, sherardised or galvanised - its twisted shank grips far harder than a round wire nail of the same size, and it's short enough not to burst through the far side of a trimmer. You'll find them under loose-nails.

What voids the load table: leaving holes empty because the hanger "feels solid", substituting drywall screws (brittle, and never rated for shear), and using bright round wire nails that work loose as the timber shrinks. On site inspections, a half-nailed hanger is the defect that turns up most, and it's also the cheapest one to avoid - the nails cost pennies.

Masonry hangers: bearing and build-in

Welded masonry hangers are built into the wall as it rises, bearing on the brick or block below with the flange trapped in the mortar bed. Two rules keep them right. First, don't hang load on them until the mortar has cured and there's enough masonry built above to anchor the flange - a hanger in green mortar rotates, and the floor dips. Second, seat the joist fully into the shoe and skew-nail it through the side holes so it can't back out.

Where joists sit directly on masonry instead of hangers, guidance such as the LABC upper floors technical manual looks for a minimum end bearing of 90mm. With hangers, the bearing is whatever the manufacturer specifies - another reason the paperwork that comes with the box matters.

Restraint straps: the 2-metre rule

Restraint straps tie floors and roofs to the walls so the wall can't bow away from the structure. Approved document A calls for 30 x 5mm straps at centres no wider than 2m where floors run parallel to a wall, and it's the detail building control measures with a tape. Light duty straps handle vertical restraint down walls; heavy duty straps take the horizontal, lateral-restraint job. Fit them across at least three joists, add noggins under the strap, notch it over the timber so it sits flat, and pack solidly between the wall and the first joist. A strap flapping over a void restrains nothing.

The supporting cast: brackets, ties and cramps

Angle and corner brackets turn butt joints into proper connections in stud work, decks and carcassing - same nailing logic as hangers, every hole filled. Wall and brick ties stitch cavity leaves together, with the tie type matched to cavity width and wall build-up. Wall starter systems let a new wall key into an existing one without toothing out brickwork, and frame cramps tie door and window frames back into rising masonry. None of it is glamorous, and all of it is what holds the structure together when the wind gets up.

Ordering right first time

• Measure the actual joist width - regularised timber is 47mm, older stock may be 50mm, and the hanger must match

• Count hangers per joist, then add the nails: a typical hanger swallows 15 to 20 square twist nails, so order by the kilo, not the handful

• Match the finish to the exposure - galvanised for internal and standard external work, stainless where it's coastal or permanently damp

• For masonry hangers, check the block strength the hanger is rated for; lightweight block often needs a different spec

FAQs

Can I use screws in a joist hanger instead of nails?

Only if they're the hanger manufacturer's specified structural screws. Ordinary woodscrews and drywall screws aren't rated for shear in this application - the standard fixing remains the 3.75 x 30mm square twist nail in every hole.

Do I really have to fill every hole?

Yes. The published safe working load assumes full nailing. A hanger with half its holes filled isn't carrying half the load safely; it's carrying an unknown load.

How far apart do restraint straps go?

No more than 2m apart where floors or roofs run parallel to the wall, per Approved Document A. Closer centres are fine; wider will be picked up at inspection.

What's the difference between light and heavy duty restraint straps?

Section thickness and job. Light duty straps (typically 2.5mm) handle vertical restraint; heavy duty straps (typically 5mm) provide horizontal lateral restraint at floors and roofs. If it's the 2m-centres job, it's the heavy duty strap.

Can a joist hanger replace proper bearing on a masonry wall?

Yes, that's exactly what welded masonry hangers are for - but they must be built in as the wall rises and loaded only once the mortar has cured. Retro-fitting a masonry hanger into a finished wall needs a face-fix hanger rated for that, fixed per its own schedule.