Developing Durable CLT Building Enclosure Assemblies

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Vernon Watkins
6 years ago
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1 Developing Durable CLT Building Enclosure Assemblies Dr John Straube, P.Eng. University of Waterloo Faculty of Engineering / Architecture Co Investigators: Dr Hua Ge Ruth McClung / Robert Lepage

2 Durable Wall Assemblies Durability: The ability of a building, or any of its components, assemblies, or materials to perform its required function(s) in its service environment over a period of time without unforeseen cost for maintenance or repair Functions required of all enclosure walls Support Control Heat, air, moisture, etc. Finish Many walls also must provide service distribution

3 The Perfect Wall Concept Source: Straube. J.F., High Performance Enclosures, Building Science Press, 2012.

4 The Perfect Wall Not a new idea Division of Building research, NRC Hutcheon, 1964 perfect because Structure is protected Condensation is avoided Rain penetration can be drained and dried quickly Becoming common in commericial buildings Hutcheon, 1964

5 Best Practise: North America Risky: Some European Projects Source: LIMNOLOGEN, Sweden

6 Problem CLT hygrothermal performance and properties not yet fully understood Limited field experience Susceptible to the same moisture problems as wood (rot, mould, swelling, shrinkage, etc) Thick sections reduces drying rate Construction moisture may cause problems

7 Research Approach Measure material properties Not small clear wood samples, but CLT samples Measure full scale, natural exposure performance Calibrate / validate hygrothermal computer models Extend models to different climates and different assemblies

8 CLT Sample Material Properties Gravimetric rate of drying test Rate of moisture uptake test

9 Water Uptake Results m w

10 Wet Dry Test Results

11 Field Experimental Facility Natural Exposure & Test Facilty Realistic hygrothermal loads: intensity, duration, co incidence

12 16 different wallettes Variables includes Different air water barriers (vapor barrier or permeable) Different vapor permeance insulations (low, medium, high) Different wood species (western, European) Interior insulation w/poly Over 200 sensors, read every 5 minutes

13 A1 A4 are vapor barriers WAB Exterior, w/ Water Air barriers

14 Exterior Insulation / Cladding CLT test wall with insulation, strapping and cladding. After installation of water resistive barriers

15 Field Drying Results All exterior insulated wetted panels dried very quickly in summer conditions of test Interior insulation + poly dried slowly Exterior Insulation + permeable membrane Interior Insulation + poly

16 Hygrothermal Simulations Used WUFI (Wärme und Feuchtentransport instationär) Fraunhofer Institut fuer Bauphysik, Germany Transient heat and moisture simulation software Simulation accuracy verified by numerous fullscale field studies Empirically calibrated

17 WUFI Data Input Wood is more complex than many materials

18 Hygrothermal Model Calibration Good Fit possible, but measurement & calibration required

19 Vancouver Edmonton Winnipeg Ottawa Québec St. John Simulated Climates

20 Modeling Results If starting moisture content is dry and no construction imperfections, all walls examined work well If wood start wet or gets wet Exterior insulation + vapor permeable membrane work well Interior insulation results in high risk of failure Exterior insulation + vapor barrier membrane works in dry climates, risky in wet climates

21 We know how to build durable CLT walls will industry listen? Conclusions 1 CLT assemblies wetted during construction can dry inward (if no vapor barrier) and outward (if no vapor barrier) Exterior Insulation over vapor permeable water and air barrier is fastest drying Control construction moisture via measurement on site to ensure MC <20% before close in Insulating inside of CLT is a marginal design: high risk of wetting, slow drying

22 Future Industry should develop protocols to avoid excess construction wetting of CLT Appropriate material properties for hygrothermal modeling needs further research Simulation provides useful results, but not very accurate in some cases More study of material property moisture dynamics is needed

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