Technical Requirements for Engineered Horizontal Restraint Straps in Timber-to-Masonry Applications
In traditional masonry construction (brick and block), lateral restraint straps tie the masonry outer walls back to the floor or roof diaphragm. This provides structural stability to the masonry and enables it to resist wind forces in tension. These straps were traditionally 30 × 5 mm with a 90° bend. However, with the introduction of BS EN 845‑1, specific performance criteria were established:
“To provide an equivalent performance to the prescriptive 30 mm × 5 mm lateral restraint straps commonly used in the UK, tension straps should have a declared tensile load capacity of no less than 8 kN and a displacement of no more than 2 mm.”
These restraint straps are detailed within Building Regulations Approved Document A (Structure), Scottish Building Standards, and PD 6697 (Recommendations for the design of masonry structures to BS EN 1996‑1‑1 and BS EN 1996‑2).
Typically, these straps are installed at a maximum of 2 m centres, although this varies depending on building height and regional requirements within the UK.
Where the traditional 30 × 5 mm strap required floor joists to be notched when installed perpendicular to the joist, the introduction of engineered joists meant notching was no longer an option. With the introduction of a minimum performance requirement, thinner engineered straps that could be installed over the top of joists became the industry standard.
Introduced in early 2024, BPC Fixings’ HX Horizontal Engineered Restraint Strap meets these requirements while reducing material thickness and delivering characteristic capacities equivalent to traditional 30 × 5 mm restraint straps. This is achieved through a patent‑pending, unique ‘X’ reinforcement in the 90° bend, enhancing performance at this critical location while allowing a reduction in material thickness.
Horizontal Engineered Restraint Strap
Provides horizontal lateral restraint by connecting masonry walls perpendicular to timber roofs, trusses/rafters*, or floor joists*.
Can also be used to connect timber gable panels perpendicular to timber roof trusses/rafters*.
*Roof trusses/rafters must be suitably braced, and floor joists must have suitably connected decking to transfer horizontal wind forces into the diaphragm.
The products are independently tested to the requirements of BS EN 846‑4 and assessed in accordance with BS EN 845‑1, allowing CE and UKCA marking. They are manufactured from galvanised mild steel compliant with BS EN 10346:2015 (Z600 coating), meeting the requirements of Table A1 of BS EN 845‑1 (materials and corrosion protection systems).
HX Horizontal
Material:
1.5 mm S250GD + Z600, with pre‑punched 4 mm and 6 mm holes for fixing to timber or plugging and screwing to masonry.
Characteristic capacities:
- Bent versions (e.g., 100 mm bend): 8.0 kN (timber‑to‑masonry)
- Flat tensile: 10.8 kN
Standard bent lengths (examples):
- 600 mm (500+100), 800 mm, 1000 mm, 1200 mm, 1500 mm total
(Custom lengths available)
Fixing requirements:
- Timber: 8 No. 3.75 × 30 mm sherardised square twist nails (Type A loose or Type B collated)
At least one fixing must penetrate into the third joist or truss.
For further information, please contact Technical Support: 01924 364 794.
Scott McAndrew MSc. MIMMM
Technical Director