Water/Vapor Barrier
Moisture enters through a building by...
- Bulk moisture: water enters through holes/cracks/gap (have rainscreen & cavity) - Capillary action: moves liquid through porous material (must use sealant) - Air leakage: carries water vapor through holes & cracks - Vapor diffusion: moisture moves from high to low
Vapor barrier vs vapor retarder
- Class I or II of vapor retarder is considered a vapor barrier *Use barrier in cold climates * Use retarder in all other climates
Types of waterproofing materials
- Sheet membrane (built-up layers that may be loosely applied) - Fluid-applied systems (Cont./seamless membrane) - Cementitious systems (portland cement, sand & waterproof agent) - Bentonite systems (expands in presence of moisture)
Blindside waterproofing
- When an adjacent building buts up against a new building - Put in place against existing building before concrete wall is formed
vapor retarder
- material of low permeance installed in construction to prevent moisture from entering a point where it can condense into a liquid. METAL FOIL, PLASTIC, TREATED PAPER, FLUID-APPLIED MEMBRANES Warm side
Methods of dampproofing
-admixture in concrete -bituminous coatings -cementitious coatings -membranes -plastics
Perm rating for aluminum foil
0
Class I Vapor Retarder & examples
0.1 or less perm (backside of interior gyp board in cold climates) - Polyethylene rubber sheet - Glass - Sheet metal
Class II vapor retarder rating & examples
0.1-1.0 perm rating (backside of interior gyp board) - Asphalt coated paper (30lb) - Polystyrene - Plywood
Class III vapor retarder rating & examples
10 or more (only on interior side of frame wall) - Gyp board - Fiberglass insulation - Cellulose insulation - Concrete block - Brick - House wrap - Board lumber
Vapor-impermeable barriers
Acts as both an air barrier and a vapor barrier *Air leakage carries water vapor through holes & cracks
Vapor retarder classes
Class 1: Impermeable (0.1-1.0 perm) least moisture to pass through) Class 2: Semi-impermeable (0.1-1.0 perm) Class 3: Permeable (1.0-10 perm) most moisture to pass
Polyethylene sheet is what level of class vapor retarder
Class I (0.1 perm or less) MOST EFFECTIVE VAPOR RETARDER
Residential building codes require what level of class vapor barrier
Class I or II
Damp proofing
Typically refers to coatings used on slabs and foundations below grade - NOT BELOW WATER TABLE (hydrostatic)
Perm ratings and terminology
Vapor impermeable: Less than 0.1 Semi-impermeable: 0.1 - 1.0 Semi-permeable: 1.0 - 10 Permeable: 10 or over ANYTHING LESS THAN 1 = VAPOR BARRIER
______ air holds more water than _____ air
WARM air holds more water than COLD air
Permeance and moisture protection
Want lower permeance = better for moisture protection
In cold climate what side of wall is vapor barrier placed?
Warm side of insulation
What side to place vapor barrier
Warm side of insulation
5 materials commonly used for moisture protection (in buildings)
Methods of damp proofing - Admixture: add to concrete to repel water (may reduce strength) - Bituminous coatings: asphalt/coal-tar (material applied to exterior side of foundation wall) - Cementitious coatings: Portland cement mortar troweled over foundation wall - Membranes: built-up layers of hot/cold applied asphalt felts - Plastics: used above grade dampproofing
capillary action
Moves liquid through porous material (surface tension)
Water proofing positions
Positive: most common, placed on side with moisture Negative: Place on side NOT with moisture Blindside: Applied before element in place
Permeance
Property of a material that prevents water from diffusing through it. A lower permeance is better for moisture protection
Sheet-applied membrane
Seamed system that could lead to weaker protection Not good for water moisture area
Dew point
temperature at which air is saturated and condensation forms
Purpose of air barrier
Control air leakage in the building enclosure - NOT MOISTURE
water proofing
Control of moisture and water that is subject to hydrostatic pressure BELOW WATER TABLE
Damp proof vs water proof
Damp: control moisture NO hydrostatic pressure Water: Hydrostatic pressure
Temperature at which water vapor is not condensing into water any faster than water would be vaporizing into air....known as
Dew point
Bulk Moisture
Flow of water through holes, cracks, and other discontinuities into walls
liquid-applied membrane
Fluid system Good for odd shapes
