Rain Screen Use - The "wet" Coast and Beyond!

Leaky condo… two words that strike terror in the hearts of condo owners in BC. Unfortunately, the “leaky” part was not restricted to just condos. The prolonged wet winters on the West Coast take their toll on single residences as well.

In 2006 the B.C. Building Code, Part 9 was amended to include “rain screen” requirements. Changes to the Building Code mean that in some parts of Canada, in particular coastal areas with high precipitation, rain screen (RS) detailing is now mandatory. Whether the code requires a rain screen or not, it is being lauded as a better way to clad the exterior walls of buildings. In fact, some building areas outside of the rainforest parts of BC have implemented rain screen requirements as well.

Rain screen, otherwise known as a capillary break, is essentially a built-in gap or cavity between the cladding of a building and the building paper or wrap layer. This gap allows water that may get beyond the cladding an ‘planned’ escape so that it does not seep through to the sheathing or framing where long term damage could occur.

Typical details for rain screen call for pressure treated strapping over the building paper or wrap to separate the cladding from the building paper. This cavity or capillary break allows for drying and drainage of incidental moisture and helps to ensure moisture will not penetrate the paper and come in contact with the sheathing. Most cladding will require rain screen including stucco, metal cladding, cedar siding, cultured stone veneers and fibre cement siding products. Some claddings such as real brick already have a cavity as part of the normal application. There are also systems specifically developed which use non-moisture susceptible, open mesh materials. When amendments to the Building Code are introduced, they are seen as improvements to building practices and as a means of incorporating new techniques and new products. The rain screen amendment for single-family houses was adapted from a multi-family building technique in an effort to improve the performance of single-family homes. This amendment will make good homes that much better.

Does this mean homes without rain screen will leak? All houses leak, even ones with rain screen. All cladding has  the potential for water penetration due to driving wind and rain and other moisture creep along any of the many seams and joints. The key difference is how this moisture is managed. Without rain screen, the exterior cladding is tight against the building wrap, and moisture has nowhere to go. This results in mold and rot. The addition of rain screen provides a capillary break, allowing air into the space and directing moisture to weep out the bottom.

Will houses look different with rain screen? Rain screen is a technique that adds a cavity or separation between layers in a wall. Nothing about a rain screen wall will look different before or after the code change comes into effect.

Will houses with rain screen cost more? There will be modest increases for labour and material as there is greater attention paid to the water-stopping details around windows and other through-wall breaks such as vents and hose connections. In the overall cost of a house, these very modest cost increases are far outweighed by the better wall design and the confidence that the wall assembly will perform at a higher level with rain screen.

Do I need to include rain screen detailing when applying for a building permit? This will vary from area to area. It is important to note that building techniques must be in accordance with the applicable building code as a minimum standard. To accommodate the potential requirement of written detailing, the new home warranty companies operating in BC banded together and developed a package of standardized details for typical conditions found in house construction to provide builders some guidance. The resulting Reference Guide of Typical Rainscreen Wall and Window Details PDF is normally sufficient for these agencies.

The details can be downloaded here and should be attached to the front of your plans, if required. Special thanks to the National Home Warranty program for providing the Details and some of the content within this blog entry.

More rain screen information: Building & Safety Policy Branch, Office of Housing and Construction Standards (British Columbia) bulletin ; Information about the Building Envelope Guide for Houses: Part 9 Residential Construction – Home Owner Protection Office;
Homeslicker & Mortairvent ;
Sure cavity ;
Sill Saver;