Vapour Barriers In Home Construction

Front 1

Vapour Barriers

Back 1

special class of materials which offer a high resistance to the flow of water vapour. In general are specifically designed: building papers, membranes or coatings aka "sheet material"

Front 2

True or False:

There are other building materials that are used as that may act as vapour barriers.

Back 2

True,

Coating, membrane or board.

BUT They can be avantagoues or can also create problems

Front 3

What do water vapour permeance coefficients indicate?

Back 3

the rate at which water vapour will diffuse through the material under a given set of conditions. Expressed in units called 'perms'

Front 4

What do Perms measure and what does the rating indicate?

Back 4

One perm is a transfer rate of one grain per square foot per hour under a vapour pressure difference of one inch of mercury. The lower the rating the greater the resistance of the material to vapour movement.

Front 5

What is the general rating for vapour barriers in house constructions?

Back 5

0.75 or less

Front 6

What are some general classes and types of vapour barriers?

Back 6

Asphalt coated felts and papers, Asphalt laminated papers, Heavy roofing papers, Metal foils of copper or aluminum, Polyethylene film, aluminum paint, asphalt paints and coatings, varnish vehicle paints, some latex emulsion paints, exterior grade plywood, celular glass insulation, cellular plastic insulation.

Front 7

What are some properties of a material that should be considered in the selection of a vapour barrier?

Back 7

Permeability of water vapour, tensile strength, pliability, tear resistance, durability under bacterial action, freeze and thaw or wetting and drying.

Also design and care during construciton

Front 8

What is the most common use of vapour barriers?

Back 8

providing vapour protection for insulated frame walls in winter.

Front 9

How can condensation within exterior walls be reduced?

Back 9

by increasing the resistance of interior cladding assemblies to water vapour transfer. Simplest and most common is to apply sheet-type VB over the insulation immediately beneath the interior cladding

Front 10

True or False:

If a completely impermeable interior cladding is achieved it is important to allow for moisture from condensation in exterior walls to escape.

Back 10

True

Front 11

What should be done (to control vapour flow) when using impermeable materials such as metal or glass in cladding applications ?

Back 11

provisions must be made for venting the interior of the wall to the outside. They are most effective when located at different levels and connected by air spaces, promoted by chimney action. Also, precautions must be taken to control for excessive ventilation and air movement.

Front 12

What are the common contributors to openings through a VB?

Back 12

electrical fixtures, plumbing, ductowrk, vents,

Front 13

What is a factor of greater significance that creates issues for openings through VB's in ceilings and roofs?

Back 13

The tendency for moist interior air to flow upward through the openings due to the chimney action of the building it self.

Front 14

Chimney action aka Stack Effect

Back 14

is the movement of air into and out of buildings, chimneys, flue gas stacks, or other containers, resulting from air buoyancy. Buoyancy occurs due to a difference in indoor-to-outdoor air density resulting from temperature and moisture differences. The result is either a positive or negative buoyancy force. The greater the thermal difference and the height of the structure, the greater the buoyancy force, and thus the stack effect. The stack effect helps drive natural ventilation, infiltration, and fires

Front 15

How does the shape of the roof effect the control of moisture for Flat vs Pitched roofs?

Back 15

Pitched roofs: offer means for the removal of the moisture by natural ventilation - either by hot (greater moisture-carrying capacity) air in the attic or chimney effect inducing ventilation (requires properly placed vents)

Flat/low pitched roofs: more difficult, do not provide height for chimney action, a common alt solution is to use rigid insulation on flat roofs applied over a VP (BUT insulation value must be sufficient to ensure the decking/structure temp does not fall below the dew point...this means finished ceilings and air spaces above should have minimal thermal resistance)

Front 16

What is the general rule for the size of vents in an pitched roof attic?

Back 16

one square inch for each square foot of ceiling area, and located so that the total vent area is distributed equally between caves and ridge

Front 17

In flat roof designs with rigid insulation moisture can accumulate in the insulation from rain, leaks etc. What can be done to prevent early roof failure of flat roofs designs which use rigid insulation?

Back 17

Either a suitable venting arrangement is used to relieve the pressure developed within the insulation or the sue of insulations with low water and water absorption properties.

Front 18

What type of special VB can be used to prevent moisture transfer from the ground into concrete slab floors or crawl spaces?

Back 18

Roll roofing (45-lb weight or greater), or polyethylene film 4mls or greater.

When poly film is used under concrete slabs placed on gravel or crushed rock fill, a layer of ordinary building paper should be placed between the polyethylene and gravel to prevent excessive puncturing of the film

Front 19

What is the most important principle to be followed in the design and installation of a VB?

Back 19

Reduce the number of openings to a minimum and when they are necessary ensure care is taken to seal the barrier for continuity.