MARGIN Builders By Kaylen Handly
Drainable housewraps vs. rainscreens B
increasingly recognizing the importance of building science-driven design in creating homes that are resistant to moisture intrusion and air leakage. As such, it’s critical that dealers understand the elements of high-performance wall systems and how the products they sell work together. One of the most essential parts of a well-designed wall system is a drainage plane that allows bulk water that breaches the cladding to drain away and also provides airflow to dry out the cavity. That drainage plane is typically created in one of two ways: via a rainscreen or a drainable housewrap. nderstanding the differences between the two, and which is most suited for each project, can help your customers make the right product selections.
The Wall System High-performing walls perform best as a system, so simply swapping out one product type for another could cause the envelope to fail or not live up to its potential. If a project specifies a rainscreen, for example, switching it out for a drainable housewrap under the assumption that it will do the same thing isn’t advised without examining the potential impact on the other products in the system. Think of the drainage plane in a good-better-best scenario: A flat housewrap is good, a drainable housewrap is better, and a rainscreen is best. he primary difference is the volume of bulk water than can drain away and the amount of air that can move through the system to effectively rid it of moisture. A rainscreen is the more robust of the options and can be created by at-
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BENJAMIN OBDYKE’S HydroGap SA is a self-adhered drainable housewrap with 1mm spacers to create 96% drain efficiency.
taching furring strips to the housewrap and sheathing or with a roll-on 3-D matrix material. Some claddings have rainscreens built into the backside of the material. The rainscreen creates a capillary break that causes it to drain downward, and also creates a larger airspace for drying. A drainable housewrap incorporates spacers onto the face of a traditional wrap, either via an embossing texture or with physical bumps. A drainable wrap releases the pressure that builds up to drain but doesn’t increase the wall system’s drying potential. There are important considerations within the drainable housewrap category, as well. For example, an embossed or textured wrap doesn’t create a true drainage space, causing friction that holds a lot of water. A drainable housewrap with a 1mm space, however, provides greater drainage efficiency of up to 96%. For these reasons, some siding
Building Products Digest August 2021
manufacturers recommend or require certain types or brands of drainable housewraps, so ensure your customers specify what the project’s siding requires.
Product Considerations What system your customers should choose depends on several factors. First is climate: A rainscreen should be one of the first considerations in wetter regions like the acific orthwest and the Northeast, but may not be necessary in drier areas. Builders will also need to weigh budget and cladding. With a tighter budget, a drainable housewrap could be good enough for cladding materials like fiber cement and composites. ut a rainscreen is a crucial investment under wood siding and masonry. Rainscreens prolong the life of wood claddings by (Continued on page 13) Building-Products.com
