Over the course of the last 30+ years, the building science community has studied the importance of drainage and drying within our building assemblies and continues to take strides towards perfection when it comes to perfecting the structural integrity of buildings.
Studies that were initiated as a result of building assemblies that failed found that failures were a result of bulk water leaking into the susceptible areas of the building. Wet wood over a period of time degrades and becomes food for mold, fungus, and resultant rot.
We all are aware of this physical phenomenon. Wet wood, if it stays wet for long, fails. It rots, gives off odors, and makes for poor living conditions. From a builder or contractor perspective, this leads to complaints and, worst yet, lawsuits.
Hundreds of thousands of forensic investigations into these failures have been performed over the past few decades. The failure of the assembly to control bulk water intrusions as well as to allow for drying constitutes the vast majority of the failures. Bulk water intrusion into wood assemblies is a recipe for disaster. Our physical environment is harsh and cruel. It will damage and degrade if we let it.
Evolve Stone understands these challenging conditions and has developed an installation system that maintains excellent drainage and drying best practices, has been extensively tested in both lab and real world installation settings as the product itself as well as the full wall assembly, and has been proven over time to be an excellent solution for reducing liability when it comes to water issues.
First, we build into our assembly a robust water control layer. These are typically called a ‘ventilation resistive barrier’, ‘weather resistive barrier’ or WRB. These barriers come in multiple forms; fabric type (Typar, Tyvek, etc), self-adhered commonly called Peal ‘n Stick (WR Grace Blueskin and others) as well as a liquid applied (Tremco ExoAir). In general, the most robust costs the most.
Most WRBs come in the form of a wrap designed to be cap nailed over the sheathing. These wraps must be installed per the manufacturers’ instructions. Careful attention must be paid to the required taping and sealing. Reading and following the manufacturers’ instructions is the first step towards an acceptable bulk water control layer.
Second, we require a drainage gap between the WRB and the cladding. In our case, we recommend a 1/8” dark rain screen. This gap can be built into the assembly in a multitude of ways. The purpose of this gap is to allow unfettered drainage. The gap is critical it must not be restricted or damned in any locations. An unrestricted gap of 1/8” to 3/8” will not allow hydrostatic pressure against the WRB. Leaks do not form without hydrostatic pressure. A continuous drainage gap ensures against this pressure.
There are countless studies, experiments and real-world investigations that show drainage gaps are good – They are required for the assembly to be robust, sustainable, and durable. Gaps, in all the right places, keep us out of trouble. Conversely, restricted gaps and no gaps at all leads to bad situations.
Third, the unrestricted drain gap performs triple duty. It drains the bulk water, encourages drying, and allows for the assembly to be vapor open, if desired. The gap drains water, which quickly precludes water build up and eliminates hydrostatic pressure. It allows air into the assembly so that drying can take place. Back drying of the cladding takes place here as well as drying of the residual water drops that cling to the WRB.
Drying is excellent. Things that are dry last a long time. Think of dried fruits or meats. Think of dry OSB and wood studs.
There are many ways to create a drainage and drying gap. We can space the cladding off the WRB by the use of 1 x 4 vertical strapping or other similar means. Multiple manufacturers have developed various plastic entangled mask products. These products allow for unrestricted drainage and drying even with the cladding pressed firmly against it. These products are stout enough to withstand cladding pressures such as wood or cement siding being pressed against them and seamed firmly. They ensure the gap is unrestricted and open for drainage and drying.
Studies have shown that a 1/16” gap will suffice for most claddings, and 1/8” works very well. One thing is for certain, an unrestrictive gap is necessary. It allows us a buffer when things just are not installed perfectly. Most cladding systems are not perfectly installed all the time. We know water will intrude most assemblies. What is important in ensuring drainage and drying are possible. Eliminating hydrostatic pressure is a huge deal.
The introduction of these drainage and drying materials into our assemblies will ensure a long lasting and robust assembly. In short, it will keep us out of trouble.
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