Mould on stairs


Mould in New Builds: The 2025 Homeownerโ€™s Guide to a Healthy, Dry Home โ€ฏ๐Ÿ› ๏ธ๐ŸŒฑ

Quick stat: Around 6โ€ฏmillion English homes now suffer damp or mouldโ€”thatโ€™s more households than own largeโ€‘screen TVs! ageing-better.org.uk

Brandโ€‘new houses shouldnโ€™t make that listโ€”but many do. Letโ€™s unpack why, fix existing problems, and futureโ€‘proof your home so you never smell that musty whiff again.


Why Are We Seeing Mould in Brandโ€‘New Homes?

  1. Lockedโ€‘in construction moisture (plaster, concrete, timber arrive wet).

  2. Design shortcutsโ€”minimal eaves, cold bridging, inadequate cavity insulation.

  3. Modern living habitsโ€”high occupancy + energyโ€‘tight envelopes = trapped humidity.

High indoor RH above 70โ€ฏ% is a red flag; mould colonises surfaces in as little as 48โ€ฏhours. HSE


The Damp Triangleโ„ข โ€“ Three Root Causes & How to Break Them

Triangle Point Common Triggers Fast Fix Longโ€‘Term Strategy
Moisture Source Wet screed, cooking steam, unvented dryers Run extractor fans 20โ€ฏmin past use Install humidityโ€‘sensing fans & check plumbing
Surface Temperature Cold bridging at lintels & corners Add insulated plasterboard Specify thermal breaks in future builds
Airflow Blocked trickle vents, furniture tight to walls Open vents, move wardrobes 50โ€ฏmm away Commission a wholeโ€‘house MVHR system

Roomโ€‘byโ€‘Room Danger Zones ๐Ÿ”Ž

  • Bathrooms: ceiling mould above showers; check that fan hits โ‰ฅ15โ€ฏl/s.

  • Kitchens: backs of cabinets; ensure cooker hood is ducted outside.

  • Bedrooms: behind wardrobes on external wallsโ€”keep gaps for airflow.

  • Lofts: cold roof deck where insulation is missing or displaced.

Pro tip: Our inspectors use FLIR thermal cameras to visualise hidden cold spots before mould appears.


Materials That Matter

Highโ€‘Risk Lowโ€‘Risk Why It Matters
Standard gypsum board, paperโ€‘faced insulation, unโ€‘treated softwood Cement board, closedโ€‘cell PIR, kilnโ€‘dried & treated timber Some substrates feed mould; others deny both food and moisture

Ventilation & Drying Roadmap (Firstโ€ฏ90โ€ฏDays After Completion)

  1. Weekโ€ฏ1โ€“4: Run heating at 18โ€‘20โ€ฏยฐC, trickle vents open 24/7.

  2. Weekโ€ฏ2โ€“6: Schedule daily shock ventilation: 5โ€‘10โ€ฏmin wideโ€‘open windows.

  3. Weekโ€ฏ4โ€“12: Dehumidifier on target RH 55โ€ฏ% while plaster cures.

  4. Anytime: Wipe condensation from windowsโ€”donโ€™t let it drip onto sills.

  5. Quarterly: Clean extract fan grilles; dust lowers efficiency by 15โ€ฏ%.

These steps mirror NHBCโ€™s latest โ€œMoisture in New Homesโ€ guide. nhbc.co.uk


Health, Warranty & Legal Essentials

  • Respiratory risk: 60โ€ฏ% of UK occupants report mouldโ€‘related symptoms. Landlord Today

  • โ€œAwaabโ€™s Lawโ€ fastโ€‘tracks repairs of damp and mould hazards within social housing, raising the bar for all developers (full rollout by 2027). The Guardian

  • NHBC treats mould as a latent defect if linked to design or workmanshipโ€”log issues within your 2โ€‘year builder warranty.


DIY vs Professional Inspectionโ€”When to Call Us

  • Condensation on inner surfaces after two heating cycles

  • Visible mould larger than an A4 sheet

  • Persistent RHโ€ฏ>โ€ฏ65โ€ฏ% despite ventilation

Our Droneโ€‘toโ€‘Basementโ„ข survey pinpoints moisture ingress, includes a FLIR heatโ€‘loss scan, and delivers an NHBCโ€‘referenced snag report within 48โ€ฏhrs. Book today and weโ€™ll deduct your ยฃ50 booking deposit from the feeโ€”guaranteed.

๐Ÿ‘‰ See a real client case study


FAQโ€ฏ(2025 Edition)

What causes mould in new builds?
Trapped construction moisture, inadequate ventilation, and cold bridging create a perfect habitat.

Should I โ€œair outโ€ my new home every day?
Yesโ€”5โ€ฏminutes of wideโ€‘open windows twice daily balanced with consistent heating keeps RH below the critical 65โ€ฏ% mark.

Which building materials are most mouldโ€‘resistant?
Cement board, closedโ€‘cell insulation, and treated timber outperform standard gypsum and paperโ€‘lined products.

Can developers refuse mould warranty claims?
They can try, but evidence from an independent RPSA surveyor (thatโ€™s us!) plus NHBC tolerances usually wins the case.

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