ARC Rockfibre Insulated DPC

Close the reveal, lock out fire, damp and heat loss

ARC Rockfibre Insulated DPC slides between the return block and outer masonry leaf to seal a window or door reveal in one step. The Euroclass A1 rock-fibre core delivers up to 4 hours fire integrity when installed with a 15 mm compression fit, while the embossed polyethylene DPC layer blocks moisture migration and bonds neatly into mortar joints. At 0.037 W/m·K it also knocks out the cold bridge that can otherwise wreck SAP targets and invite mould.

Order before 12:00 and spend £200 ex-VAT for free next-working-day delivery. Need take-offs? Call our building-envelope desk on 0118 922 7941.

What makes Rockfibre IDPC different?

  • Up to 4 h fire integrity / 2 h insulation – independently tested to EN 1366-4, IFC-certificated.

  • Non-combustible A1 mineral wool – no added fire load, Green Guide A+.

  • Embossed DPC sleeve – improves mortar key and meets Approved Document C.

  • Thermal break – cuts Ψ-values at jambs and sills; supports the zero-U party-wall detail.

  • 15 mm compression fit – friction holds the closer; no fixings required.

Size & fire-performance selector

Gap to close (mm)Fire integrity*Product code**Compression fit
10–302 hRFDPC165-15/-305 – 10 mm
35–554 hRFDPC165-35/-5515 mm
604 hRFDPC165-6015 mm

*Integrity + 2 h insulation when stated.
**Select your exact size in the drop-down above; lengths are 1.2 m.

Looking for a full PVC-flanged closer? Browse our Insulated DPC range or ARC Eco-Closer.

Installation – three quick steps

  1. Cut the strip to height so the DPC laps 100 mm past any joints.

  2. Compress & push into the reveal leaving 5–15 mm squeeze for a smoke-tight fit.

  3. Build in the external leaf, bedding the embossed DPC face into the mortar.

Seal junctions with our Sealants & Adhesives if gaps exceed 5 mm. Finish the basket with a roll of standard DPC for the sill.

Compliance & certification snapshot

Regulation / StandardARC Rockfibre IDPC performance
Approved Doc BUp to 4 h fire integrity / 2 h insulation, IFCC 1730
Approved Doc CIntegral polyethylene DPC layer
Approved Doc Lλ 0.037 W/m·K – helps achieve < 0.04 Ψ-value at jambs
Part E Robust DetailImproves flanking dB at window reveals

Frequently asked questions

Do I still need a return block?

Yes—the closer sits between the return block and outer leaf; it is not a structural closer.

Can I achieve the 4 h rating in ALL walls?

Only in traditional brick/block construction with a 15 mm compression fit. Other façades should be assessed by your fire engineer. 

Is a separate cavity closer required?

No—Rockfibre IDPC provides insulation, DPC and fire stop in one component.

What if my cavity is wider than 60 mm?

Step up to ARC Eco-Closer Plus or Kingspan Thermabate for 150-300 mm cavities.

Can I get next-day delivery?

Order before noon, spend £200 ex-VAT and check our delivery information for postcode exceptions.

Complete your reveal detail

Need a spec sheet or U-value calc? Contact us or ring 0118 922 7941 — Spechunter has chased down specialist construction specs for over 35 years.

Spechunter.co.uk – get the detail right, first time. Fact Checked & Updated May 2025

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