What is Vapour Barrier?
vapour barrier
Vapour barrier or moisture insulations are materials or systems that sufficiently reduce the transfer and penetration of water vapour or moisture from one environment to another and if Properly covered, they will withstand plenty of adverse conditions. Vapour and moisture in the air can accumulate under the roofs and interior walls and places that have lower temperatures, and due to condensation, turn into water droplets. Water is one of the main elements of wear and tear in all buildings and equipment and can cause significant damage in the long run. The vapour barrier can prevent water vapour from condensing inside the building.
When do you need moisture insulation?
In general, there is no specific method for determining the need for waterproofing, and the designer and architect of the building must determine where to use steam insulation based on the information that the building owner gives him about the use of building spaces. However, in the following cases, the use of moisture insulation is strongly recommended:
- Buildings in which the average ambient temperature in autumn and winter falls below 40 degrees Celsius.
- Buildings and structures in which activities are carried out that produce high humidity (above 65% relative humidity), such as laundry, paper preparation and printing, bakeries, kitchens, etc.
- Buildings that are completely covered and a lot of evaporation takes place in them.
- In the design, suitable moisture insulation should be considered for extremely wet places such as swimming pools, bathrooms, etc.
Where should the vapour barrier be installed?
In places that are cold in winter, the vapour barrier should be installed on the inside of the building to the side that is warmer in winter. In humid places or places where a lot of ventilation is used, the vapour barrier should be installed on the outside of the wall.
Harmful effects of moisture on structures and equipment:
*Moisture penetration into the floor and ceiling of the building can have destructive effects such as erosion and decay of carpets, discoloration of wood or parquet floors, unpleasant odours and fungal contamination and bacterial growth.
*Reducing the time of repair and replacement of structural materials, especially metal materials
*Moisture penetration in one part of the roof and wetting that part and the dryness of another part of the roof, cause temperature changes in building materials and structures. The cooling and heating of these two parts continue during the day and night until the structure cracks.
Mechanisms of moisture transfer inside building components:
Air leakage: Air leakage is the primary mechanism of condensation in buildings. Due to the fact that cold air always flows to the floor of the building and hot air to the roof, air leakage causes the outside air to penetrate the building and bring the temperature of the interior space of the building below its condensing temperature.
- Buildings in which the average ambient temperature in autumn and winter falls below 40 degrees Celsius.
- Buildings and structures in which activities are carried out that produce high humidity (above 65% relative humidity), such as laundry, paper preparation and printing, bakeries, kitchens, etc.
- Buildings that are completely covered and a lot of evaporation takes place in them.
- In the design, suitable moisture insulation should be considered for extremely wet places such as swimming pools, bathrooms, etc.
A brief list of common vapor barrier coatings:
Cover Infiltration coefficient
Kraft cover (kraft paper) 1.0
Polyvinyl chloride (PVC) 0.8<
1.4 Inch plywood 0.7
Kraft foil coating (laminate) 0.5
0.004 inch thick polyethylene cover 0.08
EPDM elastomeric insulation with a thickness of 1.5 0.03
0.001 inch thick aluminum foil 0.01
Polyethylene foam cross-link XLPE 0.001>
Composition of fiberglass and bitumen (isogum) 0.001
In designing moisture insulation for the roof, the final temperature of the two insulation levels must be considered so that the insulation surface temperature is always warmer than the condensation point. The surface temperature of moisture-proof insulation is a function of the temperature of the air inside and outside the building and the thermal resistance of the thermal insulation system. Using the following approximate relation, the surface temperature of the anti-moisture insulation can be estimated, where:
TX: Temperature insulation surface temperature
TI: Indoor air temperature (controllable by designer)
T0: Outdoor temperature (colder than Ti)
RX: The sum of the coefficients of thermal resistance of the material from the inside to the level of thermal insulation
RT: The sum of the coefficients of thermal resistance of all elements of the roof structure.
The surface temperature of the waterproofing must always be lower than the density temperature. Its condensing temperature can be extracted from the ASHRAE handbook with its relative humidity. If the insulation temperature reaches the condensing temperature, more thermal insulation should be applied to the moisture insulation, which in turn increases the value of Rt. The table below shows the density temperature relative to the relative humidity and temperature inside the building.
vapour barrier advantages:
There are many benefits to installing a vapour barrier on your wall or ceiling:
*it can help prevent moisture damage
* Easy and hassle-free installation
* increases energy efficiency
* Cheap and practical
*lower the risk of mould and bacteria-related health issues.
*Keep Moisture Out.
* Can be used in any cold or tropical region
*Prevent Mold and Structural Damage.
*Prevent Rust and Corrosion.
*Improve Energy Efficiency.
The relative humidity in different places in winter is almost as follows:
Type of location relative humidity (in winter)
office 30-50%
Hospital 30-55%
Computer room 40-50%
Warehouse 40-50%
Pool 50-60%
Textile workshop 50-85%
The following equation can also be used to approximate the minimum R (heat transfer coefficient) required to prevent condensation, in which the parameters are as follows:
RX: The thermal resistance coefficient is the minimum that must be present on top of the thermal insulation to prevent condensation.
RRV: Thermal resistance of all waterproofing elements below
TI: Internal temperature
T0: Outdoor temperature
TVR: The required temperature of the waterproofing surface so that no compaction occurs. For example, a temperature 2-3 degrees above its density point
RE: Thermal resistance of all high insulation elements (roof elements) that do not include RX.
Tips on vapour barrier and moisture coatings and insulations:
* Because vapour barrier and moisture coatings are exposed to moisture, chemical and fungal contaminants and organisms in the soil, they must maintain their stability and properties in the long run. It is better not to use recycled resins in making this type of insulation because they decompose in the soil against chemicals. Paper laminates are also not resistant to moisture.
* Most of the problems that occur after the installation of moisture or vapour barrier insulation, are related to defects such as tears, cracks and holes in the insulation surface. Care must be taken during installation to minimize damage to the insulation. Good mechanical properties, such as high tensile strength and puncture resistance, along with low moisture penetration, are characteristics that must be considered when choosing a vapour barrier.
Sources: www.m3.com
