Code Q & A

The Questions and Answers (Q & A) contained in this column represent the opinions of Peter Kulczyk and do not necessarily represent the official opinion of the International Code Council (ICC) or anybody else in particular.

As with all code determinations or interpretations, the Building Official (sometimes known as the Code Official) of the jurisdiction has the authority to render interpretations of the code.


Question: Does the code allow the installation of a green roof system (also referred to as vegetated roof and vegetative roof)?

Answer: Most codes do not specifically address green roof systems, although not addressing them does not specifically prohibit their installation.

Many green building programs, including green building codes such as the International Green Construction Code (IgCC) and the National Green Building Standard ICC-700 (NGBS) make reference to and even encourage their installations.

For designers and builders that are considering a green roof system in their project, my recommendation is that they contact the Building Official during the design phase for any particular concerns or issues that need to be addressed.

When proposing a green roof system, it may be best to address it first as a series of individual components that are already address in the code, such as structural integrity of roof, waterproof roof membrane, drainage provisions, and other components for a start.


Question: Does the International Residential Code (IRC) still allow the use of asphalt felt paper to serve as the water-resistive barrier behind siding products?

Answer: Yes, in fact, Section R703 specifically addresses the installation of one layer of No. 15 asphalt felt that complies with ASTM D226 for Type I felt.  This is the ASTM Standard Specification for Asphalt-Saturated Organic Felt Used in Roofing and Waterproofing.  Type I felt is commonly referred to as Type 15 asphalt felt, although the number 15 no longer refers to the weight of the felt as it did in years past.  There are four different grades of Type I asphalt felt, that being A, B, C and D, and there are some provisions that specifically require Grade D.  The user should refer to the entire text in the code for these unique requirements.


Question: Does the International Residential Code (IRC)  allow the use of other materials, such as house sheathing papers, instead of the asphalt felt paper, to serve as the water-resistive barrier behind siding products?

Answer: Yes, when approved by the Building Official of the jurisdiction.  There are provisions in Section R104 of the IRC, and the International Building Code (IBC) that permit the Building Official to approve alternative designs and materials when it is determined by the Building Official that the proposed design is satisfactory and complies with the intent of the provisions of the code.  A proponent of a house sheathing paper would need to submit documentation as required by the Building Official for their consideration, and this may include documents such as manufacturer’s installation instructions, third-party testing, evaluation service reports or other data.  If approved by the Building Official, the house sheathing paper or other approved water-resistive barrier material, would need to be installed exactly as shown in the submittal documents and according to the code adopted by the jurisdiction.  Refer to the Building Official for any additional issues or requirements.  The video link below addresses some of these issues.