Tempo:
Drainage: surfaces (such as the back side of cladding, or the sheathing membrane) within assemblies that redirect any water that enters the envelope downwards and out to the exterior. Drying: features that encourage vapour diffusion and air movement to transport water vapour, and evaporate moisture from surfaces. These features include vapour permeable materials (which allow water to diffuse to the surface of materials), and in some cases, vented or ventilated air cavities located on the interior side of the cladding. The following sections describe the water penetration control aspects of some common building envelope assemblies: basement floors, below- or above-grade walls and roofs.
Basement Floors Basement floors are usually constructed on dry sites or have sufficient drainage such that water penetration control is not a primary concern. Polyethylene sheet dampproofing is normally placed over granular material before the concrete slab is poured to reduce the amount of moisture entering the basement from below the slab. When bulk water penetration is a concern, a waterproof membrane is applied over a slab at least 75 m m (3 in.) thick, and a second slab at least 75 mm (3 in.) thick is poured over the membrane. The waterproof membrane must be connected to the wall membrane to form a complete seal.
the site is wet with some probability of hydrostatic pressure occurring, additional measures must be taken to provide adequate water penetration control (such as using a waterproof membrane, and crack and control joint waterproofing details). See Chapter 7 for more information.
Walls Above Grade Cladding such as wood siding, stucco or brick veneer provides a first plane of protection against precipitation ingress in above-grade wall assemblies. In geographic locations where the probability of wetting due to precipitation is high and the drying potential of the walls is low, a capillary break (an air space) must be provided between the first and second plane of protection in exterior walls. This configuration is commonly called a rainscreen. The need for a rainscreen is determined by the Moisture Index (MI) for a particular geographic location. MI values are provided for many locations in Canada as part of the climatic data tabulated in building codes. The capillary break, or air space, allows precipitation that penetrates past the cladding to readily drain on the backside of the cladding, or alternately on the sheathing membrane, which provides a second plane of protection against precipitation ingress. The air space also allows materials to dry by means of evaporation and exchange of air. Capillary breaks can be provided by:
Walls Below Grade Dampproofing (usually a bituminous coating) acts as the primary barrier (the first plane of protection) against water penetration from the exterior side of the foundation wall. The concrete foundation wall can be considered a second plane of protection. The use of a drainage composite product can also provide improved drainage at the exterior surface of the wall. Neither of these planes of protection will address water penetration control at joints or cracks in the concrete. So if
a 10 mm (7⁄16 in.) gap between the sheathing membrane and the cladding (usually furring strips are used) so that water droplets do not infiltrate between the cladding and the sheathing and can drain back to the exterior; a mesh material not less than 10 mm (7⁄16 in.) thick and at least 80 per cent open; common horizontal metal and vinyl siding, without contoured insulated backing, that is loosely fastened to the sheathing and is designed with a 10 mm (7⁄16 in.) space at the bottom of each horizontal strip; or
Basement Floors Basement floors are usually constructed on dry sites or have sufficient drainage such that water penetration control is not a primary concern. Polyethylene sheet dampproofing is normally placed over granular material before the concrete slab is poured to reduce the amount of moisture entering the basement from below the slab. When bulk water penetration is a concern, a waterproof membrane is applied over a slab at least 75 m m (3 in.) thick, and a second slab at least 75 mm (3 in.) thick is poured over the membrane. The waterproof membrane must be connected to the wall membrane to form a complete seal.
the site is wet with some probability of hydrostatic pressure occurring, additional measures must be taken to provide adequate water penetration control (such as using a waterproof membrane, and crack and control joint waterproofing details). See Chapter 7 for more information.
Walls Above Grade Cladding such as wood siding, stucco or brick veneer provides a first plane of protection against precipitation ingress in above-grade wall assemblies. In geographic locations where the probability of wetting due to precipitation is high and the drying potential of the walls is low, a capillary break (an air space) must be provided between the first and second plane of protection in exterior walls. This configuration is commonly called a rainscreen. The need for a rainscreen is determined by the Moisture Index (MI) for a particular geographic location. MI values are provided for many locations in Canada as part of the climatic data tabulated in building codes. The capillary break, or air space, allows precipitation that penetrates past the cladding to readily drain on the backside of the cladding, or alternately on the sheathing membrane, which provides a second plane of protection against precipitation ingress. The air space also allows materials to dry by means of evaporation and exchange of air. Capillary breaks can be provided by:
Walls Below Grade Dampproofing (usually a bituminous coating) acts as the primary barrier (the first plane of protection) against water penetration from the exterior side of the foundation wall. The concrete foundation wall can be considered a second plane of protection. The use of a drainage composite product can also provide improved drainage at the exterior surface of the wall. Neither of these planes of protection will address water penetration control at joints or cracks in the concrete. So if
a 10 mm (7⁄16 in.) gap between the sheathing membrane and the cladding (usually furring strips are used) so that water droplets do not infiltrate between the cladding and the sheathing and can drain back to the exterior; a mesh material not less than 10 mm (7⁄16 in.) thick and at least 80 per cent open; common horizontal metal and vinyl siding, without contoured insulated backing, that is loosely fastened to the sheathing and is designed with a 10 mm (7⁄16 in.) space at the bottom of each horizontal strip; or
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