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
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
The Perfect Wall Concept Source: Straube. J.F., High Performance Enclosures, Building Science Press, 2012.
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
Best Practise: North America Risky: Some European Projects Source: LIMNOLOGEN, Sweden
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
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
CLT Sample Material Properties Gravimetric rate of drying test Rate of moisture uptake test
Water Uptake Results m w
Wet Dry Test Results
Field Experimental Facility Natural Exposure & Test Facilty Realistic hygrothermal loads: intensity, duration, co incidence
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
A1 A4 are vapor barriers WAB Exterior, w/ Water Air barriers
Exterior Insulation / Cladding CLT test wall with insulation, strapping and cladding. After installation of water resistive barriers
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
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
WUFI Data Input Wood is more complex than many materials
Hygrothermal Model Calibration Good Fit possible, but measurement & calibration required
Vancouver Edmonton Winnipeg Ottawa Québec St. John Simulated Climates
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
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
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