1. Breathability: an introduction

2. Changing demands on the building shell over
past 50 years
1. From outdoor to indoor living - up to 90% of our time insides
buildings
2. Changing demands – Such as energy or water, warmer
during winter, more light, MVHR, …
3. Better buildings – better airtightness, better thermal
performance
These changes affect the biology of buildings, with a consequent
impact on both human health and fabric health

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. What is the effect of breathable materials?
What is breathability?
• Vapour Permeability
• Capillarity
• Hygroscopicity

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. Vapour Permeability Table with some typical
building materials
Material µ-Value Typical thicknexx Sd-Value
(=typical) in construction In typical
[mm] construction [m]
Air 1 (reference) 100 0.1
Dense Concrete 60– 250 (200) 100 20
Bricks 5-30 (10) 100 1
Expanded polystyrene, PU 30-50 (40) 100 4
Mineral wool, flax, hemp, sheepswool 2-5 (5) 100 0.5
insulations, Woodfibre insulation
Spruce, pine, 45-400 (150) 100 15
OSB, plywood 100-700 (200) 10 0.2
Metals and metal cladding, some 250,000 - ∞ 1 1000
plastics and asphalts

7. Golden rule for Vapour permeability
• Construction should get more vapour open to the
outside
• Vapour check internally and construction is fine?

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. Hygroscopicity
• Ability to adapt to different relative humidity
• Important to buffer moisture
• Speed of hygroscopicity is varies hugely between different
materials

10. Hygroscopicity
Material 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 Medium
Unfired Clay Brick 1700 3% 52 Very Fast
Mineral wool 30 1% 0.3 Medium
insulation
EPS, PU, PIR 20-30 0% 0 N/A
insulation
Woodfibre insulation 200 9% 18 Fast

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. Comparing breathable and non-breathable
constructions
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. 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
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time

14. Different build-ups compared in Swansea
Comparison Standard Construction - Pavaclad,
Swansea 1%
28.0
27.0
26.0
25.0
moisture 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
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time

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. Thank you for listening
Questions?