Thermo-loc FRstop Cavity Stop Sock for Timber Frame

Fire-rated thermal and acoustic cavity stop sock designed to restrict the spread of smoke and flames within external masonry.

1-hour fire integrity and Class O surface spread of flame classification.

FRSTOP will also further minimise the effect of flanking noise pollution at wall junctions.


  • To restrict the spread of smoke and flames within external masonry
  • To further minimise the effect of flanking noise pollution at wall junctions

Product Information

FRstop Cavity Stop Sock for Timber Frame

Product CodeCavity WidthDimensionsFire Integrity
TFACSS5050mm65 x 65 x 1200mm1 hour
TFACSS7575mm90 x 75 x 1200mm1 hour
TFACSS100100mm115 x 120 x 1200mm1 hour
TFACSS125125mm140 x 120 x 1200mm1 hour
TFACSS150150mm165 x 120 x 1200mm1 hour

  • FRstop cavity stop socks are lengths of low resin, non-combustible, rockfibre mineral wool, sleeved in 50-micron polythene for on-site weather protection
  • 1-hour fire integrity
  • Polythene encapsulated cavity stop sock
  • Available in standard widths of 50, 75, 100, 125 and 150mm
  • Special cavity widths are available on request
  • Meets the requirements of the Robust Detail, Part B and NHBC Standards
  • Flanged stopsock for timber frame applications
  • Satisfies all NHBC requirements
  • Complies with all relevant Building Regulations
  • Meets all relevant British Standards
  • Non-combustible to BS476 : Part 4 1970 (1984) Class 1
  • Surface spread of flame to BS476 part 7 1987
  • Class O to the Building Regulations
  • Manufactured using rockwool mineral wool.
  • Rockfibre uses no CFCs, HCFCs in the manufacturing process.
  • Thermal conductivity of Rockfibre insulation 0.037w/mK.
  • FRstop must be compressed and friction fit with timber frame and fixed through flange. For vertical applications both flanges are fixed to timber frame. For horizontal applications only the top flange should be fixed. Fix flanges using clout nails at 150mm centres.
  • The plastic coating only offers weather resistance and offers no application performance. Any joints should be tightly butted together with no gaps. The stop sock must fill the whole cavity width and cavity insulation worked around.
  • To calculate quantities, divide the overall length of the required cavity wall run by 1.2m, allow an additional unit for each corner for cutting.
  • Always round up to the next whole number.
  • Determine and stipulate the cavity width that the FRstop needs to suit.

F30 Accessories/sundry items for brick/block/stone walling


  • Manufacturer: Timloc Building Products, Timloc House, Ozone Park, Howden, East Yorks. DN14 7SD. T: 01405 765 567 W:
  • Types(s) and location(s): FRstop – thermal and acoustic fire stops to be installed vertically and horizontally as work proceeds. Position where a party wall meets the cavity wall or at floor levels, supplied in 1.2m lengths and butt jointed.
  • Reference: TFACSS Range
  • Options:
    • TFACSS50 – 50mm cavity
    • TFACSS75 – 75mm cavity
    • TFACSS100 – 100mm cavity
    • TFACSS125 – 125mm cavity
    • TFACSS150 – 150mm cavity

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