Philly's Vinyl Jungle, by Katie Masi Burrell & John Manza (CosciaMoos)

Have you looked around Philadelphia and noticed a building being constructed and the exterior finish is… vinyl siding? Well, there are times where this is OK from a code standpoint – but there are also some restrictions on when vinyl can be used. Let's review quickly some red flags you want to know about when you or a client are considering vinyl as an exterior material.

First question you'll need to ask yourself is: What construction type is the building?

The second question is: How tall is my building?

If your building is Type V, no matter what your building height – you are likely able to use vinyl siding.

If your Type V building is less than 40ft high (see 2018 IBC 1404.14 below) you are in the clear – proceed with vinyl, if you'd like!

If your Type V building is over 40ft high, you'll need to submit extra tests and calcs to confirm your compliance with Chapter 16, but you should be good to go with readily available info for most assemblies.

If your building is any other construction type, you have to check out 2018 IBC 1405.1.1, which lists the restrictions for combustible materials in an exterior wall assembly but excludes “plastics complying with Chapter 26.” Vinyl falls under the plastics exception.

Chapter 26 – specifically 2605.3 'Plastic Siding' – gives you a few requirements to meet for vinyl siding. Specifically, they are:

-         1403.9 (testing standard ASTM D3679)

-         1404.14.1 (weather barrier compliance directing you to 1402)

-         1402.5 (requiring NFPA 285 compliance for Types I, II, III and IV above 40ft height)

40ft is the magic number. For all construction types, buildings under 40ft high can usually find a path to use vinyl siding.

WHY? and What does that mean? Per 2018 IBC 1402, our buildings require a weather-resistive barrier. Those barriers are combustible but are allowed based on code section 1402.5. In order to add ANOTHER combustible material (vinyl!) to your exterior assembly, the entire exterior wall assembly would need to meet NFPA 285 if it is over 40ft high for all construction types except Type V. NFPA 285 requires an assembly test or project-specific engineering judgement. We are not yet aware of an NFPA 285 compliant assembly that includes vinyl siding as part of the test. Which means = not allowed.

Here's that 1402.5 code section:

1402.5 Vertical and Lateral Flame Propagation

Exterior walls on buildings of Type I, II, III or IV construction that are greater than 40 feet (12 192 mm) in height above grade plane and contain a combustible water-resistive barrier shall be tested in accordance with and comply with the acceptance criteria of NFPA 285. For the purposes of this section, fenestration products, flashing of fenestration products and water-resistive-barrier flashing and accessories at other locations, including through wall flashings, shall not be considered part of the water-resistive barrier. (See the rest of the code section for Exceptions)

If you needed any further reason to shy away from vinyl for buildings over 40', there are structural limitations of the vinyl siding that need to be accounted for. Per 2018 IBC 1404.14, where the building is taller than 40ft, additional tests are required to show compliance with the site's wind loads.

1404.14 Vinyl Siding

Vinyl siding conforming to the requirements of this section and complying with ASTM D3679 shall be permitted on exterior walls of buildings located in areas *where V_asd as determined in accordance with Section 1609.3.1 does not exceed 100 miles per hour and the building height is less than or equal to 40 feet in Exposure C. Where construction is located in areas where V_asd as determined in accordance with Section 1609.3.1 exceeds 100 miles per hour, or building heights are in excess of 40 feet, tests or calculations indicating compliance with Chapter 16 shall be submitted.* Vinyl siding shall be secured to the building so as to provide weather protection for the exterior walls of the building.

 *This section has been updated in the 2021 IBC but remains largely the same in implications. The other change is related to the fastening requirements in the same 1404.14 section.

Note that, according to the code commentary, you can apply vinyl siding on the lower portion of your exterior walls up to a height of 40ft even if your total building height exceeds 40ft. Weird but possible!

P.S.: Do you remember a time when this was not the case? You would be right. The previous Philly code (IBC 2009) did not have lateral fire propagation (NFPA 285) requirements (currently in IBC 2018 1402.5) for weather-resistive barrier AND only identified the 40ft requirement as applying to architectural trim (1406.2.2). Now it applies to the wall covering.

Stay tuned for code considerations for vinyl soffits and projections. They are different than exterior walls!