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Air sealing and fire blocking PEX and PVC penetrations

Oak_Orchard | Posted in General Questions on

What do I use to meet code-required fire blocking and good weatherizing/air sealing for the circumferential individual tube/pipe and ganged tubes (a cluster of tubes), penetration gaps for PEX-to-wood (and plywood) and PEX-to-PVC pipe, and for PVC-to-wood, and PVC- & PEX-to-drywall?

With manifold distribution and multiple zoning of (1) HW heating supply and return (wall hung rads), and (2) potable water supply, there are a lot of penetration points in my walls, partitions, floors and ceilings. As well, rigid PVC drain and vent pipe penetrates plates and the roof deck, passes from exterior wall cavities into conditioned spaces, all-season spigots penetrate the siding; etc. These materials are oxygen barrier PEX, and Red and Blue PEX, and PVC; passing through drywall, plywood, dimensional lumber.

PVC and PEX expand and contract, tearing away from sealants and foams. They squeal and squeak, crackle and pop when heating up and when/if tighly anchored, rounding bends, rubbing against each other, against wood framing; etc

What the problem looks like:

Viega Manablock Parallel Water Distribution Manifold:

Pex leaving and returning to mechanical space passes through walls, floors, plates:

According to

Do not allow tubing to come in extended contact with commonly encountered construction materials – This list is not complete:
Pipe thread sealing compounds
Fire wall penetration sealing compounds. Exception: water soluble, gypsum-based caulking or other sealants approved by the PEX tube manufacturer
Petroleum-based materials or sealants such as: Kerosene, Benzene, Gasoline, Solvents, Fuel Oils, Cutting Oils, Asphaltic Paint, and Asphaltic Road Materials, Acetone, Toluene, and/or Xylene
Do not place any PEX tubing in heavily contaminated soils or other heavily contaminated environments.
Petroleum-based caulks or sealants should not come in direct contact with PEX.

Look at this list … these materials and solvents are everywhere and in most tool boxes and used without much thought as to what might be compromised by them. We use PVC caulking and Great Stuff foam for weatherizing the plywood and framing joints; but they are strictly not to be used with PEX and; then there are the clean up solvents (mineral spirits, et al) and asphalt based window and panel sealing will also harm PEX.

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  1. GBA Editor
    Martin Holladay | | #1

    For years, many builders have sealed plumbing vent pipes that penetrate top plates with an ordinary roof boot (roof flashing for pipes). It's designed to be watertight, but it also happens to be airtight. The rubber flashing seals the penetration.

    For walls, you can use flashing from Quickflash designed for just that purpose, or you can use Kaflex flashing from Four Seven Five.

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