Roof Pipe Flashings Done Right

You probably don’t want to think about pipe flashings, and if they are installed properly can be worry free. Wherever you have a pipe penetrating the roof deck there is potential for water entry because the opening in the deck forms a direct path to the interior of the building. If you have any dynamic deck deflection from wind loading, foot traffic or equipment installations, additional stresses are placed on the flashing and seal.

Each different roofing material has different requirements for pipe flashings and there are some alternates within material groups. Cost is often a design consideration and better devices are available at additional cost. For example Chem Curb makes a versatile, excellent urethane based fluid applied sealant poured within a fixed enclosure “the curb” that works well with a variety of systems and is especially useful when pipes are clustered with limited spacing.

The illustration on the left above shows a lead pipe flashing. These are also very durable installations, albeit at somewhat higher cost. These flashings last because the lead is bent over the upper pipe opening, and the field flashing portion of the lead deforms less that the typical light gauge sheet metal during temperature change.

Various other configuration are determined by the material manufacturer. With single ply membranes, pre formed boots are common. They are often cut to size on site, and terminated with compatible sealant and a band clamp.

It is helpful to understand the chemistry of the sealants used. Higher polymer content with less filler is always helpful and varies between manufacturers.

When using asphalt based built up roofing we always recommend polymer modified sealants rather than the standard cut back asphalt mastics.

Feel free to call us with your design, specification, quality control or bid and budget questions.

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