Controlling Water/Air Leakage and Water Vapour (Part 1) Flashcards
There are 3 sources of water in exterior walls. Name them.
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Name the sources of water in exterior walls.
- Rain
- Groundwater
- Landscaping; i.e improper drainage slopes causing water accumulation in window wells, or sprinkler systems left operating over long periods of time.
Name the sources of water in interior walls.
- Vapour that condenses; i.e thermal bridging of a ‘cold’ beam
- Plumbing leaks
- HVAC equipment malfunctions
- Improper use of water
Name the source of water in construction.
The moisture content of new materials; i.e wood, concrete, firewood, fresh slabs, etc.
There are 3 conditions for rain penetration. Name them.
- Source of water
- Opening in assembly
- Force to drive water through
There are strategies to control rain penetration. Name at least 5.
- Deflect water away from critical areas
- Drain the water that has entered the wall
- Allow moisture that has entered to dry
- Choose materials that are resistant to water
- Seal openings where appropriate with sealants and gaskets ( although you cannot rely on this, they will wear out )
- Neutralize forces
True or False. Removing one of the 3 conditions ( Source, Openings, Forces ) eliminates the threat of rain penetration. All three are required simultaneously to have water leakage.
True.
There are 5 forces that cause rain penetration. Name them.
- Gravity
- Capillary action
- Surface tension
- Momentum
- Air pressure difference
Name the components of a detail pattern.
- Wash
- Overlap
- Overhang and drip
- Drain and weep
- Cold roof
- Foundation drainage
- Capillary break
- Labyrinth
- Upstand/dam
- Rainscreen assembly
What is a wash?
Slope surfaces to drain away from vulnerable areas, such as chimney cap and cricket, pitched gutters, pitched drains ( floor-to-slab )
Where?
- Window sills; away from window
- Parapet; away from roof membrane
- Roof; away from walls
- Grade; away from building
What is the rule of thumb for slopes away from the building?
10% / 10 feet
What is overlap?
To overlap a higher surface over a lower surface. ( ex. shingles overlap to aid in water flow off the building; exception: in cases of ice dams where the water could freeze and travel in the opposite direction )
What does flashing do and what materials is it made out of?
Demonstrates wash and overlap material used to intercept and direct water to desired drainage paths.
Materials include:
- Metals; such as, aluminium, galvanized steel, stainless steel, copper, zinc and lead.
- Membranes; such as, modified bitumen ( rubberized asphalt, i.e BlueSkin ), polyethylene, vinyl, and roll roofing ( NOT tape )
What are the requirements of flashing?
- Water barrier - doesn’t absorb water, only deflects water, has to be able shed water
- Terminations - the ends of the flashings have to be rigid to project water away; flexible to accommodate movement ( because they are installed where there are joints, the two parts might move differently )
- Durability - must resist UV rays, temperature changes, and handling during construction.
- Compatible with surrounding materials - chemical reaction between two materials, galvanic action, corrosion
- Buildability and sequencing - is the detail buildable?
- Maintenance ( vs durability ) - use high durability materials and maintenance becomes less of a problem. On the other hand, the more you are able to maintain a product the less concern you have with durability. ( don’t forget maintenance cost money )
True or False. We design under the assumption that water will always manage to get in.
True.
Explain ‘Overhang and Drip’
A twofold strategy - Trying to keep your building façade as dry as possible, but virtually impossible to keep walls dry all the time.
Assume that water will get in, how do you get it out?
An internal drainage system. ( ex. cavity wall drainage )
True of False. ( Foundation Drainage ) We need moisture barrier under the slab because of capillary action can suck water ‘up’
True.
True or False. A high water table creates pressure and drives water upwards.
True. ( Solution: If in doubt, use transfer pipes through footings and/or double French drain )
What is a ‘Capillary Break’?
A capillary break in construction is the use of a hydrophobic material (non-porous material) that acts as a barrier between two layers of material that is able to stop capillary action. It is typically applied to the outside of the foundation wall.
What is the purpose of a ‘Labyrinth’?
Doesn’t allow any straight line passages on which water can travel.
What are ‘Upstands/Dams’?
Turning up a material; wind pressure can drive water uphill only up to a certain height.
Rainscreen Assembly: Name the components.
- Rainscreen
- Air space
- Air barrier
- Drainage path
- Compartmentalization
Overhang and drip ( Flashing overhangs ) - Moisture barrier
- Weep holes
- Grade
- French drain
- Damp proofing
- Water proof membrane
- Footing and slab
- Footing key
- Sealant membrane
