Asked & Answered: Do ICFs Need a Weather Barrier?

One of the questions we are frequently asked is the need for an additional weather barrier or house wrap in ICF construction.

The short answer to the question is no.

ICFs are a more effective and higher class vapor and water barrier than any house wrap product. ICFs must only be protected from sunlight and impacts through coverings such as brick, stone, stucco, EIFS, siding, etc.

Building wraps such as DuPont™ Tyvek® and other house wrap products are designed to shed bulk water such as heavy, wind-blown rain. They also allow the moisture that occurs in cavity walls to escape. Cavity (stud) walls are prone to moisture cycles and condensation because of the lack of thermal mass and the transmission of air through the walls. As the temperature and humidity outside changes so does the temperature and humidity inside the walls.

If these systems didn’t allow moisture to escape then you have the high probability of creating mold, rot, and other dangerous conditions in the structure as well as greatly reducing the insulation efficiency of the wall.

ICFs do not suffer from this loss of insulation value, even if the ICF foam were to be saturated with water.

The Long Answer is still no.

Examining the 2012 IRC beginning in section R611.4.3:

R611.4.3 Exterior wall covering. 
Stay-in-place forms constructed of rigid foam plastics shall be protected from sunlight and physical damage by the application of an approved exterior wall covering complying with this code. Exterior surfaces of other stay-in-place forming systems shall be protected in accordance with this code. 

Requirements for installation of masonry veneer, stucco and other finishes on the exterior of concrete walls and other construction details not covered in this section shall comply with the requirements of this code.

Further examination of the 2012 IRC section R703.1.1:

R703.1.1 Water resistance. 
The exterior wall envelope shall be designed and constructed in a manner that prevents the accumulation of water within the wall assembly by providing a water-resistant barrier behind the exterior veneer as required by Section R703.2 and a means of draining to the exterior water that enters the assembly. Protection against condensation in the exterior wall assembly shall be provided in accordance with Section R702.7 of this code. 

Exceptions:

1. A weather-resistant exterior wall envelope shall not be required over concrete or masonry walls designed in accordance with Chapter 6 and flashed according to Section R703.7 or R703.8.

These sections refer to flashing from the ICF outward around the exterior finish. Proper flashing at windows, doors, and the roofline are essential to any home, and ICF is no exception. Once flashed to the exterior face of the ICF, it has a full drainage plane to the footing or slab.

From DuPont’s website: http://www.dupont.com/products-and-services/construction-materials/building-envelope-systems/faqs/wb-faq.html

Is DuPont™ Tyvek® a vapor barrier?

No, DuPont™ Tyvek® is not a vapor barrier. It is made with unique material science to keep air and bulk water out while allowing moisture vapor inside walls to escape. 

BuildBlock ICFs are a Class II Vapor Barrier and have higher performance than Tyvek . This eliminates the need to use Tyvek or similar products, which are designed to help shed bulk water but allow vapor to pass through freely. BuildBlock will resist both bulk water and water vapor in above grade applications.  Even below grade, the addition of an air gap membrane is sufficient waterproofing for many applications.