Design for Durability Cross Laminated Timber CLT

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CLT Building Envelope Design Guide,Objectives,Provide designers with guidance on CLT. building envelope design,Remind designers of durability considerations. Photo courtesy Vaxjo University,Document Development Team. Graham Finch RDH Building Engineering Ltd,Dave Ricketts RDH Building Engineering Ltd. Jieying Wang FPInnovations,Constance Thivierge FPInnovations.
Paul Morris FPInnovations,Peer reviewers,Annette Neylon Mark Porter George de Ridder. Associated Engineering,Douglas L Watts Read Jones Christoffersen Ltd. Mark Lawton Morrison Hershfield Ltd,Mario D Gon alves Patenaude Trempe Inc. General Principles of Design for Durability,CLT does not change basic wood characteristics. CLT does not change basic durability principles,Keep wood dry wherever possible.
Minimize wetting during shipment construction,Prevent wetting in service. Allow drying in case wetting occurs,CLT may dry slowly due to the mass of wood. Anticipate persistent wet conditions or other hazards. Preservative treatment,Use naturally durable wood,General Principles of Design for Durability. CLT does not change basic building physics, Assess climatic load and control water heat air and vapour. Use 4 D s to protect assembly from water penetration. Deflection Divert water off building,Drainage Remove bulk water.
Drying Facilitate drying of wood, Durable material Treated or naturally durable wood. General Principles of Durability by Design,General guidelines on design for durability. Best Practice Guide for Wood Frame Envelopes,in the Coastal Climate of BC CMHC 1999. Building Enclosure Design Guide Wood Frame,Multi Unit Residential Buildings HPO 2011. Consult with building science professionals,Required in some jurisdictions.
Interface detailing critical,CLT Building Envelope Design Guide. Focuses on unique aspects of CLT,Tries to answer, Why important to prevent wetting during construction. How to prevent rain penetration into envelopes,How to meet envelope energy requirements. How to place choose insulation,How to deal with vapour retarder barrier. How to build air tight,How to make CLT more durable.
Construction Moisture Management,CLT construction may reduce wetting potential. Prefabrication reduces construction time,CLT may get wet and trap moisture when exposed to. Potential to absorb or trap moisture influenced by. Wood species,Amounts of permeable sapwood versus heartwood. Gaps within and between laminae,Use of edge gluing. Any water repellant coating membrane applied,Construction Moisture Management.
On site protection needed in most climates,Much attention paid in Europe temporary roofs etc. Simple protection measures can make a difference,Temporary shelters etc. Consider season for construction, Try to avoid CLT installation in rain without protection. Design assembly to,Allow drying in case wetting occurs. Photo courtesy Vaxjo University,Enclosure Rainwater Management.
Rain is usually the largest water source,Building design important to reduce wetting. Overhangs and sloped roofs,Rainscreen walls proved to be effective. Two drainage planes,Cladding and sheathing membrane. Capillary break,Pressure moderation,Ventilation,Provide redundancy for dry areas. Enclosure Thermal Insulation Design,CLT provides considerable insulation.
Inherent R value about R 1 2 per inch,R 4 2 for 3 thick panel. Solid panel reduces convection in the assembly,Exterior insulation helps keep wood warm and dry. Cladding attachment must meet structural requirements. Insulation permeance has impact on wall performance. Enclosure Thermal Insulation Design,Required CLT CLT insulation Additional. nominal thickness insulation,insulation thickness,R value RSI inch mm R value RSI inch mm R 4 inch. 2 0 50 2 4 0 42 4 5 114,3 5 89 4 2 0 74 4 102,5 5 140 6 6 1 16 3 5 89.
Table 1 Building Enclosure Design CLT Handbook,Enclosure Vapour Flow Control. Overall principle,Prevent vapour condensation and facilitate drying. Control layer on warm high vapour pressure side,CLT is a vapour retarder barrier. 3 solid wood 3 30 ng Pa s m2 0 05 0 5 US Perms, No need for interior vapour retarder barrier in cold climates. Enclosure Vapour Flow Control,Assemblies should be breathable.
Based on simulation study by Paolo Baldracchi U,Trento and RDH. Dry out from initial wetting, Present lower risk if building envelope leaks occur. Enclosure Vapour Flow Control,Risk increases when impermeable materials used. May not dry out when initially wetted wetted in service. Moisture level may exceed the margin of safety,Don t place potential vapour barriers retarders. www fpinnovations ca Design for Durability Cross Laminated Timber CLT Construction

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