Definition: What is Rainscreen Siding?

A Rainscreen siding system refers to the way of installing and fastening the siding material to your structure. Rainscreen siding systems provide an air gap between the siding material and the structure itself. This air gap is typically 3/4" and offers a number of benefits which include thermal insulation and moisture stability for your siding boards - which is very important when using high density hardwoods such as Ipe, Tigerwood, Garapa, Batu and Cumaru.

In modern day Rainscreen siding systems that are attached with clips, there is an additional air gap between the actual siding boards themselves. The gap is very small (typically around 1/16") and it is completely invisible when looking at the finished Rainscreen system after installation.

Historical Rainscreen Siding Systems- Rainscreen wood siding systems have been around for centuries. Amazingly, some of these all wood structures were designed and built in the 12th century in Norway and are still standing today. The key design principal is mostly the same then as it is with modern Rainscreen Siding Systems today. There is an air gap between the structure and wood siding boards, which is important. This protects both the structure underneath and it keeps the outer cladding boards perfectly stable because there is airflow or ventilation not only on the outside but behind the wood siding boards as well.

How does the Rainscreen Siding Airflow and Ventilation Typically Work? As shown in the photo below, air is allowed to circulate around the perimeter of every individual piece of wood siding. Regardless of whether the air is moist or dry it is still able to circulate and flow evenly around your boards. Keeping the humidity levels consistent on both sides of your individual wood siding boards helps to keep them stable and prevents cupping/warping of your boards. It should also be noted that both hardwoods and softwoods will still expand/swell when the material is exposed to higher average humidity levels and that the boards will shrink when exposed to drier, lower humidity levels. The movement can be addressed in the clip design and is the reason that we designed this patented Rainscreen Clip System.

The Dynamics of Hardwood & Softwood to Changes in Humidity.

The reality of designing anything with wood is that you must account for the potential swelling or shrinkage in your wood design, especially when you know that humidity levels will not be consistent throughout the year. This is also the case with exterior siding, your wood will swell when exposed to high humidity levels such as on a rainy or foggy day; so conversely, your wood will shrink during dry Spring, Summer and or Fall weather conditions.

Why wood is Clearly the Best Choice for Rainscreen Siding: It is pretty obvious that using composites or PVC could create numerous problems in a Rainscreen Siding application. Expansion gaps of 1/4" would need to be designed for a minimum of every 12'. Long runs of PCV or composite siding boards just cannot be used. If PVC or composite were used the end result would be buckling of your siding on hot days.

Wood, by contrast, doesn't move significantly with changes in temperature, only with changes in its moisture content. Which is always a result of exposure to varying levels of humidity or direct exposure to moisture.

Wood is a unique material in that it does not move evenly in all three directions. Wood is an orthotropic material having different material properties in each direction. Think about a piece of wood in terms of how it is cut from the tree itself - the length of the piece is in the same vertical direction as the tree would grow out of the ground, which is referred to as the longitudinal direction (in terms of the orthotropic definition of sawn lumber or wood).

In each of the three directions, longitudinal, radial and tangential, sawn lumber behaves differently with respect to changes in its humidity and/or moisture content. In the longitudinal direction, wood is extremely stable exhibiting practically no movement whatsoever with changes in moisture content. In the radial direction (from the center of the tree to the bark) wood moves about half as much as it does in the tangential direction (along the growth rings of the tree). Wood is the most stable when the growth rings are oriented in the same direction as the thickness of the piece, this is commonly referred to as vertical grain or quarter sawn lumber. The largest amount of movement by percentage is therefore isolated to the smallest dimension, which is the thickness.