Will MVHR solve my mould problem?

If mould caused by inadequate ventilation: largely yes. MVHR maintains RH below 55% throughout the dwelling, eliminates condensation on cold surfaces. Combined with insulation upgrade (eliminating cold spots) and airtightness: complete solution. MVHR alone won't fix interstitial condensation in cold cavity — need fabric upgrade too. Verify MVHR commissioning and balance — under-commissioned MVHR underperforms.

Are mould treatments worth using?

Anti-mould paint (Sandtex Anti-Mould, Dulux Mould Inhibitor) treats surface and slows regrowth but doesn't address moisture root cause. Mould wash (Astonish, Dettol Mould Cleaner) removes visible mould. Apply only after fixing ventilation + insulation; otherwise mould returns within 3–6 months. Don't paint over mould — spores grow through paint within weeks.

Is mould a health risk?

Yes. Respiratory: triggers asthma, bronchitis, sinusitis. Allergic: rhinitis, eye irritation, skin reactions. Immunocompromised severely affected — Aspergillus infections in transplant patients, cancer patients on chemotherapy, AIDS patients. Children: developing lungs more vulnerable. Awaab Ishak (2-year-old who died of fungal exposure in social housing, 2020) catalysed Awaab's Law — landlord obligations to act on mould complaints urgently. Health professionals advise: never sleep in mould-affected rooms.

Condensation Mould London Renovation 2026 | Builderr

How Are Condensation and Mould Managed in a London Renovation?

Condensation and mould in London homes occur when warm humid air contacts cold surfaces — windows, thermal bridges, behind furniture. Managed by: (1) ventilation (MVHR or dMEV continuous; humidistat bathroom/kitchen extract), (2) insulation continuity to eliminate cold spots, (3) airtightness preventing warm moist air migrating into cold cavity, (4) heating to maintain surface temperatures above dew point. Mould is a health risk: respiratory, allergic, immunocompromised severity. Awaab's Law (2025) increases landlord liability.

Why it happens

Air holds water vapour; warm air holds more than cold. When warm air contacts a cold surface, the air cools and water vapour exceeds saturation — condenses into liquid water on the surface. Sustained moisture + organic matter (dust, paint, paper) = mould growth within 24–72 hours. Mould species: Aspergillus, Penicillium, Cladosporium common in UK domestic; Stachybotrys (toxic black mould) in chronic damp. Source of moisture in London homes: occupant breathing (300ml/person/night), cooking (1L/day for family of 4), showering (0.5L/shower), drying clothes indoors (2–4L per load), gas heating combustion (now rare in new boilers). Total moisture generation 8–18L/day in family household. Without adequate ventilation, this moisture deposits on coldest surfaces.

Diagnosing problems

Visible signs: black spots on cold corners (typical at floor-wall junction North-facing exterior wall, behind wardrobes, in window reveals), condensation on windows in cold months (cold glass meets warm room air), peeling paint, musty smell. Surface vs interstitial condensation: surface (visible mould on internal face) addressed by ventilation + insulation; interstitial (moisture in wall cavity, hidden, eventually rots structure) addressed by vapour control layer + airtightness + insulation continuity. Diagnose with: humidity logger (data logging hygrometer £25–£85 left in problem room for 2 weeks shows pattern); thermal imaging (£350–£950 reveals cold spots); humidistat measurement at suspected cold surface (relative humidity at the surface, not in room air — dew point at surface).

Solutions

(1) Improve ventilation: dMEV continuous extract in wet rooms (£185–£385/fan); MVHR whole-house if major refurb (£4,800–£12,500). Reduce indoor RH from typical 65–75% to 45–55%. (2) Improve insulation: eliminate cold spots — insulate cold external wall (EWI preferred, IWI if EWI impossible), insulate reveals around windows (25–40mm PIR in reveal), insulate party wall against unheated neighbour space. (3) Improve airtightness: prevent warm moist air migrating from heated rooms into cold cavities where it condenses on cold cavity face. (4) Heating: maintain rooms at 18–21°C consistently rather than allowing cold spells; cold surfaces below dew point develop condensation. (5) Reduce moisture sources: extract during cooking + showering; dry laundry outside or in vented utility (not on radiators in living spaces); fix any plumbing leaks fast. Awaab's Law (Social Housing Regulation Act 2025): landlords must investigate damp/mould complaints within 14 days and fix within reasonable timeframe; criminal liability for repeat failure.