In some parts of Canada, in particular coastal areas with high precipitation, rainscreen detailing is mandatory. However, whether or not the code requires a rainscreen, it is a better way to detail exterior cladding of buildings. After all, moisture problems attributed to poor cladding installation details have even been discovered in the dry climates of the prairies. Renovator, writer and TV personality Jon Eakes provides an in-depth look at this issue in his article, “Rainscreen Detailing and the Canadian Building Code”.
The main purpose of rain screen siding is to prevent the risks of entrapped moisture. Once moisture has penetrated deep into a wall system through the weather resistant barrier and into the exterior sheathing, the wall is deep wet. The air flow that exists in most wall systems is a slight draft that will not dry this condition out in a timely manner. The result is a compromised wall system with rot, rust, and mold potential. The structural integrity of the wall is at stake, as is the health of the occupants. The longer the wall remains wet, the greater the risk. 50% percent of homes suffer from mold problems. Billions of dollars are spent annually on litigation involving mold and rot problems stemming from entrapped moisture; this has created an entire industry centered around construction litigation. Such litigation has caused insurance premiums for contractors to increase significantly and has made it difficult for contractors involved in moisture related lawsuits to obtain insurance at all. An effective rainscreen drainage plane systems mitigates this risk. You can learn more about rainscreen, it's history, and technical data here.
One of the largest claim items that has driven up home insurance costs today is mold which is caused by moisture trapped behind the siding and inside the home. If not addressed properly, mold can cause sickness and ultimately destroy a home. Rain screen siding is considered one of the best deterrents from wind- blown rain – the leading cause of moisture getting trapped behind siding. This trapped moisture grows mold in the walls which permeates throughout the home.
A report release by HUD in March 2006 titled, “Moisture-Resistant Homes”, details and compares the different types of wall envelopes and their comparable performance. The report concludes that rain screen siding scores the highest effectivity level in all types of wind-blown rain environments.