Woodworm in cellar -> Remediation advice

[bicyclefluttering]

Hello,

I’d like to get some advice on the best course of action to remediate active woodworm in the suspended timber floor above my cellar.

Situation:

• End of terrace 1900s house in North London
• Partially below ground cellar (35m2)
  • Solid brick walls
    • Original slate damp proof course visible
  • Uninsulated timber suspended floor above
    • Hallway has original tiling
    • Living rooms have parquet floor
  • 1.5m access height under hallway (10m2)
  • 1m access height under living rooms (25m2)
  • A previous owner has had the interior cellar walls tanked
• Ventilation
  • Vent under the front door
  • 2 x small vents under the bay window
  • 1 x vent in the side elevation
  • No ventilation possible in the rear elevation -> modern extension
• External
  • Cement based render plinth
  • Block pavers
• Elevations
  • At front elevation approx 0.4m of cellar height is above ground
  • At side elevation, above ground cellar height increases from 0.4m to 0.75m over 7m
• Environmental
  • RH 68% at 15.5degC (livable sections of the house 50% RH 19degC)

Issues:

• Woodworm exit holes present at the front of the cellar in joists and original floorboards
  • Timbers were sprayed with insecticides in January
  • Frass visible in April so we know it is an active infestation
  • New floorboards that were installed at least >10yrs ago so no signs of exit holes
• One end of joist is rotten where it contacts the exterior wall
• Earth floor in the crawlspace under the living rooms is visibly damp
  • Except by the vent in the side elevation
• A down pipe from the roof was discharging directly onto the block pavers in the front corner of the house (area of greatest concern)

Remediation plan:

1. Connect downpipe direct to gully (done)
2. Increase ventilation
   1. add additional air bricks to side elevation (min 1 per alcove)
   2. Increase size of air bricks under bay window
3. Increase breathability
   1. Remove external cement render plinth and replace with lime mortar

Questions:

1. Does the extent of woodworm look significant - should I be considering removing all the affected timbers (and all the disruption/cost that will entail)?
   1. I plan on living in the house for at least 10 years so would also take the opportunity to add insulation (likely following best practice solution here)
2. Can the tanking on the internal cellar wall be removed to improve breathability?
3. What is the best course of action for the rotten timber joist?
4. Any other considerations or course of action I should be taking?

Thank you!


Floor plan with annotations




Cellar General condition


Woodworm




Rotten beam


Floor Condition -> Damp


Floor Condition -> dry