Restraint Straps (Domestic Floors)
Restraint Straps (Domestic Roofs)
Perpendicular Restraint
Lateral restraint of the walls can be provided by the roof, the restraint must be provided perpendicular to the roof trusses.
Floor Level
Detail
Region
Vertical restraint straps counteract uplift forces on roof elements i.e. wall plates and trusses. Horizontal restraint straps provide lateral stability, securing the roof to walls and preventing sideways movement. The information we provide has been compiled using the minimum requirement from Building Regulations 2010 approved document A, Scottish Building regulation domestic, NHBC standards and British Standard BS 5628–1;2005 Annex D.
ROOF
Ground Floor
1st Floor
2nd Floor
England & Wales
PFS required at 2m max centres
3RD STOREY
Perpendicular
PFS required at 1.25m max centres
Scotland
PFS required at 2m max centres
2ND FLOOR
Please refer to page 4 for further information on PFS straps For all applications strap must extend over a minimum 3No Joists PFS surface fixed to I–Joist
2ND STOREY
1ST FLOOR
These have been issued as guidance only, the overall responsibility lies with the Building Designer.
— Noggins to be installed between the I-Joists or Metal Web Joists using 2No UZ-Clips and 2No. skew nails staggered either side — After fitting all noggins the PFS strap can then be located tight to the block work and centred on the noggins — The strap should be nailed with a minimum of 8No 3.4 x 35mm square twist nails evenly spaced and into at least every joist
— Only suitable when joists line through with top of block work
1ST STOREY
GROUND FLOOR
3 STOREY HOUSE
Vertical Restraint Bent Strap To Wall Plate
Noggins - NHBC Requirements — Width: min. ½ I-Joist depth, max. 150mm — Depth: min. 38mm — Timber: min. C16 grade
Twisted Strap To Truss
RST strap to be nailed to truss with 3.4 x 35mm square twist nails. Nail quantity dependant on uplift value. Fixings into masonry to be specified by building designer. Please refer to page 6 for further information on RST straps
Fix VRS to the wall plate with 2No 3.4 x 35mm square twist nails. Fixings into masonry to be specified by building designer. Please refer to page 7 for further information on VRS straps
PFS through web of I–Joist
— Cut a small slot in the I–Joist web, just under the top flange — Slide the PFS through the slots and position tight against the block work — To provide a fixing for the PFS, noggins must be nailed in place between the I-Joists through the I-Joist web — The strap should be nailed with a minimum of 8No 3.4 x 35mm square twist nails evenly spaced into the noggins
— Not suitable when joists line through with top of block work
Noggins - NHBC Requirements — Width: min. 38mm — Depth: min. ½ I-Joist depth, max. 150mm — Timber: min. C16 grade
Horizontal Restraint (Masonry Gables)
Floor Level
Detail
Region
Up to and including 2 storeys
3 storeys
4 storeys
PFS required at 2m max centres
PFS required at 1.25m max centres
England & Wales
PFS through web of Open Web Joist
Perpendicular
PFS required at 2m max centres
PFS required at 1.25m max centres
Scotland
— Strongback/Additional Noggins to be installed as per manufacturer’s guidelines — Position PFS tight to block work and centred on block — The strap should be nailed with a minimum of 8No 3.4 x 35mm square twist nails evenly spaced into the noggins
— Straps to be installed at not more than 2m centres (or 1.25m where appropriate) along gable end. — Strap to be of sufficient length to be fixed to a minimum of 3no. Trusses. — Blockwork to be built up to suit strap location — Longitudinal bracing to be fixed to each truss with 2no. 3.35 x 65mm round wire nails (in all details 3.1 x 90mm long mechanically driven nails may be substituted for 3.35 x 65mm long wire nails). — Where the position of the strap does not coincide with an existing longitudinal truss brace, then the strap may be fixed to an additional 25 x 100mm longitudinal binder (as shown in following details ). The binder to be fixed over a minimum of four trusses and fixed to each truss with 2no. 3.35 x 65mm round wire nails. — Fix straps to longitudinal bracing with 8no. 3.4 x 35mm square twist nails, evenly spaced along the length of the strap (for NHBC warrantied buildings, in accordance with NHBC Standards 2017 section 7.2.8, 8no. 25 x 4mm steel screws shall be used instead of square twist nails). — Parallel restraint straps are not required to roof trusses unless specified by building designer.
The latest version of the technical guide will always be the digital format on our website.
The latest version of the technical guide will always be the digital format on our website.
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Technical support: 01592 771132 / technical@itwcp.com / https://www.itwcp-offsite.co.uk 11
Technical support: 01592 771132 / technical@itwcp.com / https://www.itwcp-offsite.co.uk
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