Always contact me if you need help: 📤 [email protected] 📞 07802 300099 🌐 www.londonflatroofing.co.uk
❄️ WHY YOUR ROOF IS SWEATING (2026 COLD SNAP) My phone hasn't stopped ringing since the cold snap started. Every roofer in London is dealing with the same problem: sweating roofs and condensation damage. If you are seeing water dripping, it might not be a leak.
HERE IS THE SCIENCE (WHY IT IS HAPPENING):
Warm internal air (20°C at 55% RH) holds 9.5ml of water per cubic metre Cold external air (3°C at 70% RH) holds just 3.5ml per cubic metre
That 70% RH outside? It's actually DRIER than 55% inside The counterintuitive truth: higher RH percentage doesn't mean more water when temperatures are different. ☕ THE COFFEE CUP EXAMPLE I've created a visualisation to explain this. Using standard conditions (Outside: 3°C/70% RH; Inside: 20°C/55% RH):
To fill a standard 300ml coffee mug with water gathered from the air: Internal air: You only need to empty 32 cubic metres External air: You would need to empty 86 cubic metres! In a 90m³ room, that's 855ml of internal moisture vs 315ml external. That is a difference of nearly
TWO COFFEE MUGS of water looking for somewhere to condense.
🏗️ WHY YOUR ROOF IS SWEATING Modern homes are well-insulated but poorly ventilated. That moisture-laden warm air migrates upward, hits cold roof decks, and condenses. Add inadequate vapor control layers and insufficient roof ventilation, and you've got the perfect recipe for:
💨 THE SOLUTION ROOM LEVEL: Cross-ventilation through windows 2-3 times daily ROOF LEVEL: Maximum soffit-to-ridge airflow (BS 5250) VAPOR CONTROL: Proper VCL installation below insulation Cold external air is DRIER - it pulls moisture out of both your rooms and your roof construction.
⏱️ CHAPTERS 0:00 - Why Your Roof Is Sweating (2026 Cold Snap) 0:23 - Relative Humidity Explained Simply 0:48 - Warm Air vs Cold Air: The Real Difference 1:43 - How Much Condensation Is In Your Roof 2:10 - Why Ventilation Stops Condensation 2:40 - Roof Ventilation: Tile Vents & Soffit Vents
🔧 SERVICES: LONDON ROOF SURVEYS We offer independent roofing expertise including:
Comprehensive Roof Condition Surveys (all roof types) Pre-Purchase Property Inspections & Insurance Renewal Assessments Condensation & Moisture Investigation Building Defect Analysis Drone Roof Surveys & Expert Witness Reports Remote Video Consultations Need a survey or repair? Get in touch: 📤 [email protected] 📞 07802 300099
