In inspecting a home under construction, I recently ran into an issue dealing with a weather-resistant barrier. This barrier is one that protects exterior wall materials from weather exposure, particularly water. So, the best place to begin this discussion is by defining what a weather-resistant barrier is. The American Vinyl Siding Institute states the following on their website:
What Is a Weather Resistant Barrier System? It is a system that includes water shedding materials and water diversion materials. Weather resistant barrier systems commonly consist of a combination of exterior cladding, flashed wall openings and penetrations, weather resistant barrier material, and sheathing. Effective weather resistant barrier systems will shed the water initially, control moisture flow by capillary and diffusion action, and minimize absorption into the wall structure. The level of weather resistance required is determined by the applicable building code and structure.
The 2007 Ohio Building Code, which basically is taken from the 2006 International Building Code, defines a water barrier, which is basically one of the major purposes of a weather resistant barrier, as:
WATER-RESISTIVE BARRIER. A material behind an exterior wall covering that is intended to resist liquid water that has penetrated behind the exterior covering from further intruding into the exterior wall assembly.
This code further details a weather-resistant barrier as:
1403.1 General. The provisions of this section shall apply to exterior walls, wall coverings and components thereof.
1403.2 Weather protection. Exterior walls shall provide the building with a weather-resistant exterior wall envelope. The exterior wall envelope shall include flashing, as described in Section 1405.3. The exterior wall envelope shall be designed and constructed in such a manner as to prevent the accumulation of water within the wall assembly by providing a water-resistive barrier behind the exterior veneer, as described in Section 1404.2, and a means for draining water that enters the assembly to the exterior. Protection against condensation in the exterior wall assembly shall be provided in accordance with the International Energy Conservation Code.
1404.2 Water-resistive barrier. A minimum of one layer of No.15 asphalt felt, complying with ASTM D 226 for Type 1 felt or other approved materials, shall be attached to the studs or sheathing, with flashing as described in Section 1405.3, in such a manner as to provide a continuous water-resistive barrier behind the exterior wall veneer.
1404.1 General. Materials used for the construction of exterior walls shall comply with the provisions of this section. Materials not prescribed herein shall be permitted, provided that any such alternative has been approved.
1404.2 Water-resistive barrier. A minimum of one layer of No.15 asphalt felt, complying with ASTM D 226 for Type 1 felt or other approved materials, shall be attached to the studs or sheathing, with flashing as described in Section 1405.3, in such a manner as to provide a continuous water-resistive barrier behind the exterior wall veneer.
Section 1405.2 Weather protection. Exterior walls shall provide weather protection for the building. The materials of the minimum nominal thickness specified in Table 1405.2 shall be acceptable as approved weather coverings.
In looking at the home under construction for the first time, I noted that a weather-resistant barrier was not installed on the home. Most people will recognize a weather-resistant barrier as the usually white paper-like wrap, most commonly with the name Tyvek printed on it in large letters. Other similar wrap or other materials are also used. That is where the problems began.
In inquiring about the lack of weather-resistant barrier, I asked for the drawings. In reviewing the drawings, I noted that no weather-resistant barrier was specified. When I inquired about why none had been installed, the builder informed me that the Hamilton County, Ohio Building Department did not require it. Apparently, the building department believes that vinyl siding, which was being installed on this home, was an adequate weather-resistive barrier.
I decided to investigate further on the ultimate authority. On the internet, I found that the Vinyl Siding Institute states in its Vinyl Siding Installation Manual (http://www.abtco.com/kp_abtco/docs/ABTCO_Vinyl_General_Installation_Instructions_.pdf):
Weather Resistant Barrier
Vinyl siding has always been designed as an exterior cladding, not a weather resistant barrier. Vinyl siding is designed to allow the material underneath it to breathe; therefore, it is not a watertight covering. Because of its design and application, it provides a supplemental rain screen that enhances the weather resistant barrier system by reducing the amount of water that reaches the underlying weather resistant barrier.
What Is a Weather Resistant Barrier System? It is a system that includes water shedding materials and water diversion materials. Weather resistant barrier systems commonly consist of a combination of exterior cladding, flashed wall openings and penetrations, weather resistant barrier material, and sheathing. Effective weather resistant barrier systems will shed the water initially, control moisture flow by capillary and diffusion action, and minimize absorption into the wall structure. The level of weather resistance required is determined by the applicable building code and structure.
Best Practice: To achieve designed performance, vinyl siding must be installed over a weather resistant barrier system that includes 1) a continuous weather resistant material and 2) properly integrated flashing around all penetrations and where vinyl siding interfaces with other building products such as brick, stone, or stucco. Refer to the manufacturer’s installation manual for specific product applications and recommendations. Whichever product(s) you decide to use as part of a weather resistant barrier system, be certain the materials meet the applicable code by contacting the manufacturer of the weather resistant barrier material(s). Always consult the applicable building code for minimum weather barrier requirements in your area. Keep in mind that additional measures may provide better protection against water intrusion than the minimum requirements of the building code.
The Vinyl Siding Institute clearly states that vinyl siding is not an acceptable weather or water resistant barrier. Since vinyl siding is not considered to be a weather or water resistant barrier, installing vinyl siding without a proper weather-resistant barrier cannot meet the requirements of the building codes for Hamilton County, as taken from the Ohio Building Code and the International Building Code and cannot be considered as proper building practices. Furthermore, The Vinyl Siding Institute states that vinyl siding needs to be installed over a weather-resistant barrier, and basically describes the properties of a material such as Tyvek, although it is not the only weather-resistant barrier available. This Institute further states that proper flashing is required for the siding.
So, am I making much ado about nothing. I hope not. Water, especially from wind driven rain can get behind any siding material, but more so vinyl siding. This water then can reach the underlying wood materials. The problem areas might not be behind where the water reaches the underlying materials, they usually are where that water flows after landing on the materials. Water that gets behind the siding will flow down the face of the sheathing to points where it can pool, such as above windows and doors and at the base of walls. At these points, it can enter into the wall cavity itself if those areas are not properly flashed. It can also enter through gaps between the sheathing.
Once inside a wall, the water can be absorbed by the insulation. Insulation holds water really well--nearly as well as a sponge. If enough water is present, mold will grow because mold spores and their food sources are endemic. Mold can further cause wood rot. Other moisture-related damage can also occur, particularly to materials made from oriented strand board (OSB), a very common building material and one that has a bad habit of delaminating when exposed to enough moisture. Do you think that repairing these materials can be expensive? You betcha it can, particularly if structural members are involved.
What is the bottom line here? If you have the abilities to review the construction drawings, do so very carefully and inspect closely for a proper weather-resistant barrier. If you don't have this expertise or ability, then hire someone who does, such as a capable architect or engineer. And remember this point, drawings are best reviewed BEFORE construction begins. My clients learned that lesson at a cost of $1800, and even then, the weather-resistant barrier was not ideal because the windows and doors were not properly flashed according to the manufacturer's recommendations.
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