Can closed cell spray foam help control moisture in continuous insulation applications?
Practical evidence and research has shown that exterior cladding materials on an exterior wall can prevent most, but not all, moisture, particularly rain water, from entering into a wall. Cladding systems, as well as their joints and seams can have moisture prevention limitations specially during severe wetting events and can degrade over many years of weather exposure if not properly maintained. So, building designers should expect that most cladding systems are at best not entirely waterproof or airtight. In addition, moisture can enter around wall penetrations, like windows, doors, piping and vents. Given this reality, a secondary moisture control system would be prudent to have to supplement the cladding system and keep a wall dry and performing well over the long term.
The Water Resistive Barrier
Having a backup moisture control system behind the cladding to control moisture by shedding it harmlessly to the exterior is important for the long term durability of an exterior wall. A significant component of the backup moisture control system is often called by building envelope designers a drainage plane or a water resistive barrier (WRB) and their prime purpose is to protect the majority of the wall area from moisture intrusion. The best WRBs follow the shape of the wall, so that no noticeable coverage gaps exist and where water can easily enter. Image 1 shows spray foam multi-tasking as exterior continuous insulation, a water resistive barrier, and an air barrier along a curved wall.
IMAGE 1. The continuous, seam less and shape conforming aspects of the water resistive barrier created by medium density spray foam are on display in this wall. Note that a tight water barrier is created around the cladding attachments and at the window penetrations. Installation of the exterior cladding would be the next construction step.
All of Icynene’s medium density, closed cell, spray foam products are considered as water resistive barriers since they are capable of shedding water and limiting moisture intrusion. Icynene ProSeal and Icynene ProSeal Eco have been evaluated according to ICC-ES AC71, the Acceptance Criteria for Foam Plastic Sheathing Panels Used as Water-Resistive Barriers, and are officially designated as water resistive barriers. Since there are no joints to tape or overlapping practices to maintain, water barrier performance is more easily assured on the construction site with spray foam insulation since it forms a continuous layer.
In an exterior continuous insulation system, water that may have gotten past the cladding system, and forced by pressure towards the interior, would meet the spray foam’s exterior surface and drain down and not continue progressing into the wall assembly where it could cause damage. A key component of the system is to ensure that this water can be diverted back to the outdoors by following a flashing system and exit path (like weep holes) incorporated at strategic points in the wall assembly. Such a moisture control system is particularly important to have in coastal or high precipitation areas where driving rain is common. Figure 1 shows a typical path driving rain would take in a wall with exterior continuous spray foam insulation.
Integration of medium density spray foam products with flashing membranes is a key component of the water resistive barrier system, as shown in Figure 2. Fortunately, the two components are compatible with each other and many spray foam insulation contractors are experts at applying both successfully in the field. In addition, Icynene has tested the compatibility of self-adhering and liquid-applied membrane products with their medium density, closed cell, spray foam products.
Want to read more about how spray foam insulation controls moisture in exterior wall applications? Download the complete white paper by clicking the link below.