ARC Cavity Stop Socks

Instant compliance at every floor & party-wall junction

ARC Cavity Stop Socks are pre-compressed rock-fibre barriers that slide straight into the external-wall cavity, sealing off unseen fire routes in minutes. Each 1.2 m length expands on site to fill the void, providing up to 4 hours fire integrity and a minimum 15 minutes insulation to EN 1366-4, with IFC certification (IFCC 1727/1728). 

• Euroclass A1 non-combustible mineral wool – no added fire risk. 
• Widths 65–165 mm suit cavities 50 – 150 mm; deeper sizes available on request. 
• Polythene encapsulation keeps product dry until the brickwork is closed.
• Compatible with Robust Detail party-wall specs to cut flanking sound paths. 

Need the party-wall version? See our dedicated ARC Party-Wall Cavity Socks.

Why specify ARC Cavity Stop Socks?

• Fire strategy ✓ – meets Approved Document B requirement for cavity barriers at every compartment line and floor level.

• Thermal break ✓ – λ 0.037 W/m·K limits cold bridging behind lintels and floors. 

• Acoustic boost ✓ – mineral wool core helps hit Part E targets by damping flanking noise.

• No fixings needed ✓ – friction-fit installation shaves minutes off every lift of brickwork.

Selecting the correct size

Tip: Leave a 5 mm compression allowance—socks perform best when tightly squeezed.

How to install in three simple steps

1. Cut to length so joints land snugly against studs or masonry returns.

2. Compress & slide the sock into the cavity flush with the outer face of the inner leaf.

3. Tape or fire-seal joints where runs exceed 1.2 m or meet corners.

Pair with our fire socks & barriers range for soffits, spandrels and service penetrations.

Frequently asked questions

What fire rating can I expect?

ARC Cavity Stop Socks achieve up to 4 hours fire integrity in masonry walls when installed to the test configuration. 

Are they suitable for timber-frame walls?

Yes—ARC supplies a timber-to-timber variant; contact us for lead times.

How many do I need per elevation?

Install at every separating floor, party-wall line, and cavity break—typically one length per metre run. Our team can mark-up your drawings; just contact us.

Can I get next-day delivery?

Order before 12 : 00 and spend £200 ex-VAT for free next-working-day delivery. Check our delivery information for postcode exceptions.

Spechunter.co.uk – Chasing down specialist construction specifications since 1988. Fact checked and updated May 2025.