Timber Connectors: Restraint Straps, Truss Clips, and Framing Anchors

A professional snagging inspector visits a newly built house, priced at over two hundred thousand pounds, and climbs into the roof space. Every single restraint strap in the entire roof, the galvanised steel straps meant to stop the gable walls blowing out in a storm, has zero fixings. Not one nail. Not one screw. The straps are draped over the timber like decorations. The inspector's verdict: "the potential of this carelessness and poor workmanship could be life changing."

That's not a freak case. It's documented. And it's the reason building control inspectors specifically check timber connectors at the pre-plaster stage. These are cheap fittings, a few pounds each, that prevent walls collapsing and roofs lifting off. Get them wrong and you have a structural failure. Get them right and nobody ever thinks about them again.

What timber connectors are

Timber connectors are galvanised steel straps, clips, and plates that tie structural timber elements to each other and to the masonry around them. Their job is resisting forces that nails alone can't handle, primarily wind uplift (which tries to peel the roof off the walls) and lateral movement (which pushes gable walls outwards).

Without these connectors, a masonry wall is just a stack of blocks sitting on top of each other with nothing stopping it from toppling sideways. A roof is just timber resting on a wall plate with nothing stopping the wind from lifting it. In normal weather, gravity and friction hold everything together. In a gale, they don't. UK storms routinely hit 70-80mph gusts. That's enough to lift an unrestrained roof structure clean off the walls.

One builder on a trade forum put it bluntly: "a grown man could push a gable wall out if it's not tied in." That's without wind. With it, the forces are vastly greater.

The connectors themselves are simple. Flat strips of galvanised steel with pre-punched holes for nails. Pressed steel clips that grip timber and wall plate simultaneously. Small folded brackets that join two or three timber members at angles. Nothing complicated to look at. But the specification, the nail count, the spacing, the way they're built into the blockwork, all of that is prescribed by Building Regulations and all of it gets inspected.

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Types of timber connector

Four types cover virtually every domestic extension and roof project. Each does a different job, gets installed at a different stage, and building control checks each one separately.

Heavy restraint straps

These are the ones that matter most and cause the most defects. A heavy restraint strap is a flat strip of galvanised steel, minimum 30mm wide and 5mm thick (that's the Building Regulations minimum section), with a 90-degree bend at one end. The bent end tucks down into the blockwork by at least 100mm. The flat section runs across the top of the inner leaf and nails to the roof timber, spanning at least three trusses or joists.

They come in various lengths: 600mm, 800mm, 1000mm, 1200mm, 1500mm. The length you need depends on truss spacing and how far the strap needs to reach. Most domestic roofs at 600mm truss centres use 1000mm or 1200mm straps.

Heavy straps resist horizontal forces. They stop walls being pushed outwards by the roof spreading, and they stop the roof being lifted by wind. Approved Document A requires them at no more than 2m centres along eaves level, at the base of every gable, and along roof slopes. For buildings up to three storeys (which covers every domestic extension), 2m spacing is the rule.

Light restraint straps

Lighter gauge steel, typically 27mm x 2mm section. These handle vertical loads only, holding the timber wall plate down onto the top of the blockwork wall. They run vertically down the inside face of the inner leaf and fix to both the wall plate (with nails) and the masonry (with screws into plugs or hardened masonry nails). Minimum 1m long.

Truss clips

Small pressed-steel clips, sized to match your timber width (38mm, 44mm, 47mm, or 50mm). They grip the bottom chord of each truss where it sits on the wall plate. One clip per truss, both sides. Without them, the trusses are just resting on the plate with nothing but gravity holding them in place.

Truss clips replaced the old method of skew-nailing (driving a nail diagonally through the truss into the wall plate). Skew-nailing risks splitting the timber, especially with modern kiln-dried softwood that's more brittle than the air-dried stock builders used decades ago.

Framing anchors

Versatile little brackets with bendable tabs. The Simpson Strong-Tie A35E is the standard. You bend the tabs on site to suit whatever angle you need: 90-degree joist-to-beam connections, trimmer joints around stairwells, any timber-to-timber joint that needs more than nails.

How to install them properly

This is the section that matters most if you're managing a build. Timber connectors are cheap and simple. The installation details are what building control actually inspects, and getting them wrong means failing the pre-plaster inspection.

Building Regulations: the non-negotiable requirements

Approved Document A (Structure) sets the baseline. For domestic extensions in England and Wales:

• Lateral restraint straps at maximum 2m centres at eaves level, gable base, and along roof slopes
• Straps must have a declared tensile strength of at least 8kN
• Straps must conform to BS EN 845-1
• Minimum strap section: 30mm x 5mm
• Minimum 100mm downturn into masonry at the bent end
• Straps must cross at least three trusses or joists

Scotland uses Section 1 of the Scottish Building Standards with equivalent requirements. The practical difference: Scotland specifies 2m maximum spacing for buildings up to two storeys (not three). For single-storey extensions, the rules are identical everywhere.

Nail specification

This is where builds fail inspection. The strap is only as strong as its fixings. An unfixed strap is decoration.

For Simpson Strong-Tie heavy restraint straps (the market leader), the manufacturer specification is: minimum 8 no. 3.75 x 30mm galvanised square twist nails, evenly distributed along the strap length.

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NHBC-warrantied buildings have an alternative fixing specification: 4 no. 50mm minimum x 4mm steel screws, or 4 no. 75mm x 4mm round wire nails, with one fixing into the third rafter. Both approaches are correct in their context. Use whichever your warranty provider or building control officer specifies.

For light restraint straps, the timber fixings are: 3 no. 3.75 x 30mm square twist nails into the wall plate. The masonry fixings are: 4mm x 75mm hardened masonry nails or 5.5mm x 50mm screws in plugs.

Truss clips take short nails through their pre-punched holes into both the truss and the wall plate. Follow the manufacturer's stamped instructions on the clip. It's usually 4-6 nails per clip.

The installation sequence that matters

Heavy restraint straps must be built into the blockwork as the walls go up. The bent end gets bedded into a mortar joint between block courses. You cannot properly retrofit this afterwards.

1. Build the strap into the blockwork

   As the inner leaf reaches the correct course height (typically two or three courses below wall plate level), bed the bent downturn of the strap into the mortar joint. The strap must sit tight against the face of the blockwork. No gaps, no kinks, no bends. The flat section of the strap lays across the top of the wall, ready for the timber.

2. Install the wall plate and trusses

   The wall plate goes on, the trusses go up. The flat section of the strap now lays across the top of the truss bottom chords (or across noggings fitted between trusses).

3. Fix with the correct nails

   Drive 8 no. 3.75 x 30mm galvanised square twist nails through the pre-punched holes, evenly distributed along the strap length. The strap must span at least three trusses. Do not fix to longitudinal bracing, that's a common builder shortcut that doesn't comply with NHBC Standards or Building Regulations guidance.

4. Install truss clips at every junction

   Fit a truss clip at every point where a truss bottom chord meets the wall plate. Both sides if accessible. Nail through every pre-punched hole.

The critical thing about this sequence: step one happens during wall construction, possibly weeks before the roof goes on. If the bricklayer forgets to build the straps in, you have a serious problem that's expensive to fix later.

What building control inspects

Building control checks timber connectors at two stages. First, at the roof structure inspection (truss clips, strap positions relative to trusses). Second, at the pre-plaster inspection (everything visible in the roof space before it gets boarded over or insulated).

They check:

• Strap positions at correct centres (2m maximum)
• Correct nail count in every strap (they will count them)
• Straps tight against the masonry face with no gaps
• Straps not kinked, bent, or twisted
• 100mm minimum downturn built into blockwork
• Straps spanning at least three trusses
• Truss clips on every truss-to-wall-plate junction
• Correct nail type (square twist, not round wire for the main strap fixings)

Fail any of these and you'll be asked to rectify before sign-off. Retrofitting straps that should have been built in means drilling, plugging, and screwing into the masonry face, which is never as strong as a properly bedded strap.

How much you need

For a typical single-storey rear extension with a pitched roof:

Restraint straps (heavy duty): Count the total run of wall at eaves level and divide by 2m. A 6m-wide extension needs a minimum of 4 straps along the eaves (one at each end, two in between at 2m centres). Add straps at the base of any gable (2 per gable, one each side). Add straps along the roof slope at gables (2m centres up the slope). For a straightforward 6m x 4m rear extension with one gable, that's roughly 8-12 heavy straps.

Restraint straps (light duty): One per wall plate anchor point, typically at 2m centres along the wall plate. Same 6m extension: 4-6 light straps.

Truss clips: One per truss, per bearing point. Trusses at 600mm centres across a 6m span means 11 trusses, each with clips at both ends. That's 22 truss clips. Buy a 20-pack and a spare pack. They're cheap enough to over-order.

Framing anchors: Depends on your roof design. Valley junctions, trimmer details, any non-standard timber joint. A simple roof might need 6-8. A cut roof with valleys could need 15-20. Your structural engineer's drawings will show every connection.

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Cost and where to buy

Timber connectors are among the cheapest structural components on any build. The total connector cost for a single-storey extension is roughly TBC, plus nails. The nails themselves will cost more than some of the connectors.

Restraint straps (heavy duty):

• Simpson Strong-Tie 1000mm bent, 10-pack: TBC (about TBC each)
• BPC Fixings 1000mm bent (Toolstation): TBC each
• Simpson Strong-Tie 600mm flat, 10-pack: TBC (about TBC each)

Restraint straps (light duty):

• Simpson Strong-Tie 1000mm bent, 10-pack: TBC (about TBC each)
• BPC Fixings 1200mm bent (Toolstation): TBC each

Truss clips:

• Simpson Strong-Tie 47mm, 20-pack: TBC (about TBC each)
• Simpson Strong-Tie 38mm, 20-pack: TBC (about TBC each)
• Sabrefix 44mm, 20-pack: TBC

Framing anchors:

• Simpson Strong-Tie A35E, 10-pack: TBC (about TBC each)

Match your truss clip width to your timber. Measure the actual truss bottom chord. Most modern trusses use 35mm or 47mm C16/C24 timber, but check. A 47mm clip on 35mm timber won't grip properly.

Simpson Strong-Tie dominates the UK market. Sabrefix is the main alternative at similar pricing with DX275 galvanising. BPC Fixings offers a slightly cheaper range, widely stocked at Toolstation. Expamet covers the basics but has a smaller product range. All are adequate for domestic work. Pick whichever your merchant stocks.

Alternatives

Before timber connectors became standard (the requirements only became stringent from around 1989), builders used traditional built-in ties: strips of hoop iron or bent steel flats bedded into mortar joints and nailed to timber. Some pre-war houses have nothing at all, relying entirely on the weight of the roof and the friction between wall plate and blockwork.

Traditional ties work, in the sense that millions of older houses haven't blown apart. But they're slower to install, less consistent, and harder for building control to verify. Modern pressed-steel connectors are engineered to a declared load capacity, CE marked, and designed to be inspected. There's no reason to use anything else on new work.

Angle brackets can substitute for framing anchors in some non-structural timber-to-timber joints. But they're not a replacement for restraint straps or truss clips. Those do a job that nothing else does as well.

Where you'll need this

Timber connectors appear at two stages of your build and one inspection point:

• Walls and blockwork - restraint straps must be built into the inner leaf as the walls go up. This is a hold point. If the bricklayer gets past the strap courses without building them in, you're looking at a retrofit that's weaker and more expensive. Watch this stage closely, or have your project manager watch it.
• Roof structure - truss clips go on as each truss is placed. Heavy straps get their nail fixings once the trusses are in position. Light straps get their timber fixings to the wall plate. Framing anchors go in wherever the structural engineer has specified timber-to-timber connections.
• Building control inspection - the BCO inspects at roof structure stage and again at pre-plaster. They check positions, nail counts, strap condition. This is one of the items they always check. Not sometimes. Always.

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Common mistakes

Forgetting to build straps into the blockwork. The most expensive mistake because it's the hardest to fix. Once the walls are up and the roof is on, you can't go back and bed a strap into a mortar joint. The retrofit option (screw-fixing straps to the masonry face with plugs and masonry screws) works, but it's weaker than a built-in strap, costs more in labour, and some BCOs will push back on it. Tell your bricklayer before work starts: straps go in at the specified courses, no exceptions.

Insufficient nails. The snagging report that opened this page found zero nails. That's the extreme case. More commonly, builders put in two or three nails instead of eight because the strap "looks secure enough." It isn't. Wind loads are intermittent and cumulative. A strap with three nails will hold the timber down on a calm day. In an 80mph gust, it won't. Count the nails yourself.

Kinked or bent straps. A strap that's been bent, kinked, or twisted during handling has reduced tensile strength. The kink creates a stress concentration point that can fail under load. Straps should be straight along their length with only the manufactured bends (the downturn into masonry). If a strap gets damaged, replace it. They cost a few pounds.

Wrong strap type. Heavy duty for horizontal restraint (roof-to-wall, floor-to-wall). Light duty for vertical loads (wall plate to masonry). Using a light strap where a heavy strap should go means half the tensile capacity and a potential inspection failure.

Fixing to bracing instead of noggings. Longitudinal diagonal bracing runs across the top of truss webs to stabilise the roof structure. It's tempting to nail the restraint strap to this bracing because it's already there and runs in the right direction. Don't. The strap must fix to noggings fitted between trusses, or to the truss members themselves, not to bracing. Fixing to bracing doesn't transfer the restraint load into the truss structure correctly.

Skipping truss clips and relying on skew-nailing. Skew-nailing a truss to a wall plate risks splitting the timber and doesn't provide the same restraint as a properly fitted clip. Truss clips cost under 50p each. There's no reason to skip them.

These are not cosmetic issues. Every one of these mistakes reduces the ability of your roof and walls to resist wind forces. The UK doesn't get hurricanes, but it gets plenty of storms that will test every connection in a roof structure. Timber connectors are the cheapest structural insurance on any build. Get them right.