Turning Fire Regulation Hurdles into a Seamless Build

Loft conversions in London demand more than carpentry and insulation—they require a precise choreography of fire safety measures that protect both inhabitants and neighbouring properties.

On our recent project in South East London, we worked hand-in-glove with architects, fire engineers, structural consultants, and specialist installers to meet every regulatory requirement. Here’s how we tackled each major challenge:

1. Achieving Class A Sheathing on New Dormers

The Issue

Standard fire-rated OSB sheathing provided only Class B performance—short of Building Control’s Class A requirement.

Our Solution

• Composite Build-Up: We fixed 9 mm OSB onto a 75 mm timber stud frame, then overlaid it with 12 mm fibre cement board—achieving a Class A fire resistance.

• Engineering Sign-Off: Our structural engineer confirmed the studs carried all racking loads, eliminating the need for additional steelwork.

• Single-Pass Installation: Carpenters set the framing, installed both boards in one visit, and sealed joints with intumescent mastic—creating a continuous Class A envelope.

  
  

2. Integrating Automist with a Fire-Rated Pocket Door

The Issue

Building Control approved a two-nozzle Automist system (per BS 8458) only if paired with a certified fire door.

Our Layout

• FD30S Pocket Door: A 900 mm wide fire-rated door installed at the top of the stairwell—forming a 30-minute egress barrier.

• Two-Nozzle Automist:

  • Living Room: Central nozzle to protect the open-plan escape route.

  • Kitchen: Positioned above the cooktop, covering the high-risk zone.

Installation Steps

1. Framing: Recessed the stud wall to spec and installed the door frame square and plumb.

2. Services: Routed control wiring for the door’s self-release mechanism.

3. Commissioning: Pocket door and Automist system were installed and calibrated per Ashton Fire’s layout.

   
   

3. Fire-Stopping Every Penetration

The Issue

All service penetrations must resist fire and smoke for 30 minutes.

Our Solution

• Reactive Collars: Used on large-diameter SVPs.

• Fire-Rated Caulk: Filled smaller pipe and cable gaps.

• Mineral Wool Slabs: Packed tightly into medium-sized voids.

• Photo Documentation: Captured before-and-after images for every seal—allowing instant Building Control sign-off.

  
  

4. Harmonising Thermal, Acoustic & Fire Layers

The Issue

Balancing fire compliance with thermal and acoustic targets required a coordinated approach.

Our Solution

• Comprehensive Layering:

  • 100 mm Rockwool on the loft floor

  • 150 mm PIR on the dormer roof

  • Fully detailed in coordinated section drawings

• Acoustic UnderScreed:

  • Laid Hush membrane after lightweight screed to achieve ≥ 62 dB sound reduction

• Waterproofing Interfaces:

  • Applied Mapei Mapeguard WP200 and 6 mm backer boards in wet zones—validated via onsite meetings with tilers and the Mapei tech rep.

    
    

5. Pre-Inspection Walkthroughs to Eliminate Last-Minute Snags

The Issue

Even minor issues during formal inspections can delay handover.

Our Solution

• Custom 12-Point Checklist: Covered fire stops, door seals, Automist pressures, insulation depths, etc.

• Live Video Walkthrough: Pre-board inspection streamed to Building Control—only two minor issues flagged.

• Fast Sign-Off: The final in-person inspection took just 30 minutes.

  
  

Why This Matters

By weaving fire regulation compliance into every phase—design, trade sequencing, documentation, and communication—we:

• streamline construction

• prevent expensive reworks

• deliver safer, regulation-compliant homes

  
  

At Alt Construction, we don’t just build homes—we build peace of mind.