Breathability, An Introduction - Natural Building Technologies

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Breathability, An Introduction - Natural Building Technologies

  1. 1. Breathability: an introduction
  2. 2. Changing demands on the building shell over past 50 years1. From outdoor to indoor living - up to 90% of our time insides buildings2. Changing demands – Such as energy or water, warmer during winter, more light, MVHR, …3. Better buildings – better airtightness, better thermal performanceThese changes affect the biology of buildings, with a consequentimpact on both human health and fabric health
  3. 3. Challenges for building shell• Airtightness: • big impact regarding heat loss • moisture risks through convection • Indoor air quality (IAQ)  often ventilation system does not perform as planned• Thermal performance • Internal insulation  risk for interstitial condensation • External insulation • Thermal bridging  can lead to problems• New building materials • Breathable and non-breathable materials
  4. 4. What is the effect of breathable materials?What is breathability?• Vapour Permeability• Capillarity• Hygroscopicity
  5. 5. Vapour permeability• How much moisture in form of vapour can pass through a material• Different terms • Vapour resistance [MNs/g] • Vapour resistivity [MNs/gm] • Sd-Value [m] • µ-Value [no unit]
  6. 6. Vapour Permeability Table with some typicalbuilding materialsMaterial µ-Value Typical thicknexx Sd-Value (=typical) in construction In typical [mm] construction [m]Air 1 (reference) 100 0.1Dense Concrete 60– 250 (200) 100 20Bricks 5-30 (10) 100 1Expanded polystyrene, PU 30-50 (40) 100 4Mineral wool, flax, hemp, sheepswool 2-5 (5) 100 0.5insulations, Woodfibre insulationSpruce, pine, 45-400 (150) 100 15OSB, plywood 100-700 (200) 10 0.2Metals and metal cladding, some 250,000 - ∞ 1 1000plastics and asphalts
  7. 7. Golden rule for Vapour permeability• Construction should get more vapour open to the outside• Vapour check internally and construction is fine?
  8. 8. Capillarity• Physical process caused by cohesion force of the water and adhesion force of the capillary (tube)• Depending on capillary diameter• Plays an important role in transporting moisture in materials
  9. 9. Hygroscopicity• Ability to adapt to different relative humidity• Important to buffer moisture• Speed of hygroscopicity is varies hugely between different materials
  10. 10. HygroscopicityMaterial Density Hygroscopic Hygroscopic Speed of [kg/m3] potential (increase capacity (density hygroscopic in EMC: 50% to x potential – in take up 85% RH) kg/m3)Fired Clay Brick 1700 0.1% 1.7 MediumUnfired Clay Brick 1700 3% 52 Very FastMineral wool 30 1% 0.3 MediuminsulationEPS, PU, PIR 20-30 0% 0 N/AinsulationWoodfibre insulation 200 9% 18 Fast
  11. 11. Importance of breathable constructions?• NOT to ventilate buildings!• To protect fabric (particularly external envelope) when building failures occur• To enhance IAQ (through moisture buffering and healthy fabric) and provide back up to ventilation for moisture control
  12. 12. Comparing breathable and non-breathableconstructions Standard 140 Standard 89 + 60 Pavaclad 89 + 60 • 12.5mm plasterboard • 12.5mm plasterboard • 12.5mm plasterboard • VCL • VCL • 25mm service void • 140 studs full filled with • 89 studs full filled with PU • 9mm OSB acting as air mineral wool insulation (without foil) tightness layer • 9mm OSB • 9mm OSB • 89mm studs full filled with Pavaflex woodfibre • Breathable membrane • 60mm PU insulation • 60mm Pavatherm Plus • 40mm vented cavity • 40mm vented cavity • 40mm vented cavity • 20mm timber cladding • 20mm timber cladding • 20mm timber cladding
  13. 13. Different build-ups compared in London Comparison Standard Construction - Pavaclad, London 1% 22.0 21.0 20.0 moisture level stud [M-%] 19.0 Standard 89 + 60 18.0 17.0 Standard 140 16.0 Pavaclad 15.0 89+60 14.0 13.0 12.0 11.0 01/10/09 01/04/10 30/09/10 31/03/11 29/09/11 29/03/12 27/09/12 time
  14. 14. Different build-ups compared in Swansea Comparison Standard Construction - Pavaclad, Swansea 1% 28.0 27.0 26.0 25.0moisture level stud [M-%] 24.0 23.0 Standard 22.0 89+60 21.0 Standard 140 20.0 Pavaclad 19.0 89+60 18.0 17.0 16.0 15.0 14.0 01/10/09 01/04/10 30/09/10 31/03/11 29/09/11 29/03/12 27/09/12 time
  15. 15. Conclusion• Breathability is not only vapour permeability, but also hygroscopicity and capillarity• Breathable products help to protect the building fabric as well as the people by regulating moisture content and relative humidity, enhance IAQ• Breathability is not a cure for everything  better understanding of the building necessary
  16. 16. Thank you for listening Questions?

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