Seal party-wall cavities in one push-fit move
ARC Party-Wall Cavity Socks are vertical fire, smoke and sound barriers that friction-fit the full height of a party wall. Made from Euroclass A1 rock-fibre wrapped in a red polythene sleeve, each 1.2 m length expands to close the void, delivering up to 4 hours fire integrity and 15 minutes insulation when tested to EN 1366-4 and certified under IFCC 1728. The mineral wool’s λ 0.037 W/m·K slashes cold bridging, helping you chase that elusive zero U-value at party-wall junctions.
Order before 12:00 and spend £200 ex-VAT for free next-working-day delivery. Our technical desk (0118 922 7941) will size and schedule the socks straight from your drawings.
Pick the right sock in seconds
| Clear cavity | Product link* | Dimensions (mm) | Pack qty |
|---|---|---|---|
| 50 mm | PWCSS 50 | 55 × 250 × 1200 | 12 |
| 75 mm | PWCSS 75 | 80 × 250 × 1200 | 10 |
| 100 mm | PWCSS 100 | 105 × 250 × 1200 | 8 |
| 125 mm | PWCSS 125 | 130 × 250 × 1200 | 6 |
| 150 mm | PWCSS 150 | 155 × 250 × 1200 | 6 |
*Links take you straight to the individual bagged sizes on Spechunter.
Need a wider barrier? Step up to our ARC T-Barrier Masonry, available to 300 mm.
Three-step installation
Measure & cut – trim socks with a sharp knife so all joints land tight to floor slabs or gable returns.
Compress & insert – squeeze the mineral wool and push into the cavity until the sleeve sits flush with the brick face of the party wall.
Seal junctions – butt successive pieces firmly; seal gaps > 5 mm with intumescent acrylic or mineral-wool offcuts.
That’s it—no mechanical fixings, ties or DPCs required.
Compliance snapshot
| Requirement | ARC Party-Wall Sock performance |
|---|---|
| Fire safety (ADB & BS 9991) | Up to 4 h fire integrity / 2 h insulation |
| Acoustics (Part E) | Mineral wool core damps flanking sound; supports +5 dB targets. |
| Thermal (SAP / Part L) | λ 0.037 W/m·K; helps achieve zero U-value at party wall. |
| Third-party certification | IFC Certificate IFCC 1728 – ongoing factory audits. |
Frequently asked questions
Do I need a separate DPC at the party-wall edge?
Where moisture ingress is a risk, use our ARC Party-Wall DPC Cavity Socks which add an integral DPC layer.
Can I use these in timber frame?
For timber-to-timber party walls switch to ARC TCB Timber Cavity Barriers—sized and tested for timber studs.
How high should I install the socks?
Fit a continuous line the full storey height at every compartment floor and roof junction; Building Control may also ask for intermediate breaks on walls taller than 10 m.
Are brackets needed?
No—friction alone secures the sock. Just keep the cavity width within the stated 5 mm tolerance.
Can I get proof for my fire strategy?
Absolutely—download the IFCC certification or request the full EN 1366-4 test report via Contact Us.
Complete your party-wall package
Horizontal breaks? Add ARC Spandrel Barriers.
Edge seals to external cavity? Use ARC T-Barrier Masonry.
Need damp protection too? Check ARC Party-Wall DPC Horizontal.
Order now for next-day UK delivery—or call 0118 922 7941 and let our 35-year building-envelope team chase down the spec for you.
Spechunter.co.uk – Chasing down specialist construction specifications since 1988. Fact Checked and updated May 2025.
