Rainscreen

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Diagram of Rainscreen construction technique

Contents

Use on Buildings

Rainscreen technology is recommended for buildings in wet climates such as Vancouver. This system is installed as an extra protective barrier to prevent rain from entering a structural cavity.

This mitigates the chance of water entering the area between the building paper and exterior siding. This technology is designed to counteract the forces that drive water into the shell of a building.

Forces at Play

Rain enters a building due in part to a variety of forces at work.

  • kinetic
  • gravity capillary action
  • surface tension
  • Air pressure gradients

Kinetic force refers to rain being driven by the wind. Such forces carry raindrops directly through openings of sufficient size.

Surface tension enables cohesion of water drops to enter a structure against gravity through small openings.

In porous materials such as masonry, capillarity is usually the dominant force in water penetration and will tend to retain this water.

Air pressure can create suction, drawing in water through available leakage paths.

Mind the Gap

Rainscreen1.jpg

What enables rainscreens to be effective is the gap it creates between the elements and the home.

This gap allows water to drain before it enters a structure.

A ¼" gap is common amongst builders, however for homes in wet climates builders prefer gaps that range from ⅜" to ¾".[1] Not only do these gaps aid in drainage, they also provide useful ventilation which assists in the drying process.

Damage

Rain damage on a masonry wall

Rain penetration into a structure can introduce a host of problems. These include

  • corrosion of anchors of exterior cladding
  • efflorescence on masonry
  • damage/staining of interior finishes

According to the Insurance Bureau of Canada (IBC), 40% of personal property claims are related to water damage. Of those those claims, 25% are related to heavy rain or flooding.[2]

Also according to the IBC, precipitation in Canada has increased by an additional 20 days in last 50 years.

Mold and mildew can start to grow on water damaged materials in as little as a few days. If gone undetected, this growth can cause life threatening health problems to residents and their pets.

It is important to have any water damage inspected by a certified professional to insure that the proper precautions are taken to have the damage remediated.

Rain Screens in Building Codes

Rainscreen technology is much more successful and cost effective when integrated into a buildings initial design.

As a result, municipalities such as those found within British Columbia have adopted Building Codes that mandate a minimum 1/4 inch capillary break on structures built after 2006.[3]

This comes in response to numerous lawsuits that had been filed in BC courts on behalf of owners/tenants of leaky condos.

Oregon building codes require a ⅛" capillary break on all residential structures.

Construction Costs

Since rainscreen technology is still relatively new , the costs associated with installation is still considered to be quite high. To achieve the required ¼" capillary gap in accordance to BC buildings codes, developers should expect to pay 60 to 70 cents per square foot. Another more cost effective option is to use a form of house-wrap offered by several brands, these being:

  • DuPont StuccoWrap
  • Pactiv GreenGuard RainDrop
  • Barricade Drainage Wrap
  • Barricade WeatherTrek
  • Valeron Vortec
  • Fortifiber Hydro Tex
  • Benjamin Obdyke HydroGap

Based on the rainscreen system installed and the amount of space provided between the rainscreen and the structure, a developer should expect to incur costs that range from 10% to 30% above the initial budget.

References

  1. Green Building Advisor
  2. Smart Building
  3. Journal of Commerce


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