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Community and Q&A

Sealing PEX and PVC pipe penetrations

Oak_Orchard | Posted in Building Code Questions on

I am reposting this to the Code section; not getting an answer in General Questions.

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.

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.

I am cautioned that PVC and PEX expand and contract such that they may tear away from foam sealants and some caulks. Also, PEX and PVC squeal and squeak, crackle and pop when heating up and it gets worse when they are 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 (PEX) 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. bsandersga | | #1

    Well, I think it should be more obvious what to use in is this case than can be divined from searching the fine print. People run PEX and people need to install air/fire blocking and if commonly used materials are incompatible with what is being used, then I think it should be spelled out.

    I, myself, used foam backer rod around the PEX and caulked with 3M Fire Barrier Sealant (the blue stuff). If it doesn't work, i guess I will find out in a couple of decades.

    I could, also, have wrapped the PEX with tape THEN either sprayed fire barrier foam or sealant.

  2. heinblod | | #2

    Contact the pipe manufacturer.

    There are special gaskets for fire protection.

  3. Oak_Orchard | | #3

    Its not just for fire blocking. Fire is a low-risk and unexpected eventuality. The main issue is air sealing. It is the PEX and the PVC that create a network of pathways for condensation and wetting and undoing all the good works of external weatherizing, internal air sealing, vapour retarders/airtight walls, etc.

    I see repeated references, videos and photos of spray foams and other chemically volatile and solvent-sensitive compounds as well as flammable materials being recommended/demonstrated for fire blocking and air sealing.

    The fact that I am having a hard time getting an answer to this quesiton on this site is worrysome.

  4. user-1137156 | | #4

    For air sealing nothing beats EDPM boots. PVC is pretty tough stuff & resists most foams & sealants well. PEX is certainly more touchy but rarely needs to cross the "primary pressure boundary" in houses at least.

  5. user-1137156 | | #5

    duplicate deleted

  6. KHWillets | | #6

    Latex foam or caulk is allowed per Pex Supply, and silicone and polyurethane foam: .

    I don't know if the HUD doc considers these "petroleum based" or otherwise prohibited.

  7. Oak_Orchard | | #7

    Gents ... regular latex caulk will definitely NOT work, but the high end fire blocking latex caulks are approved. Regular latex will shrink and separate from the plastics. No VOC's allowed to touch PEX.

    While PVC plumbing pipe is tough stuff, it does expand and contact, as PEX, lengthwise; and so it can shed a sealant that is not adhering well and has insufficient stretch.

    PEX leaving a conditioned boiler room to pass through walls and plates is passing through the primary pressure boundary. I have a small 4 zone situation with 32 rads. That's a minimum of 64 penetrations in the pressure boundary. PEX out of a basement through a plate and into exterior walls and into partitions and retruning is passing the pressure boundary.

    Anyway, even if you don't consider air sealing an issue, the CODE requires fire block sealant at each penetration. That has much higher adhering and non-shrinking standards than air sealing caulks.

    You can't put EPDM collars on PEX and PEX bundles. Every time it heats up, PEX squeals like a banshee if it is forced through EPDM, wood and plastic.

    Here' were PEX Supply got its info:

    DOW says NOT to use its polyurethane foam on PEX. And polyurethane foam will not hold a seal on expanding/contracting tubing.

    What do we use to clean up expanding foam? Petroleum products (solvents). Not advised for PEX.

  8. GBA Editor
    Martin Holladay | | #9

    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.

  9. dinamad | | #10

    I just was researching this for myself and there is a product group from Rectorseal called Metacaulk. I can find assembly fire ratings for PEX pipe for Metacaulk 1000, and they have a number of other useful firestop materials - putty blocks, firestop bricks for larger penetrations, and firestop collars that may be os use). Assembly rating link:

    I haven't totally referenced this against pex manufacturers, but have found references to this as acceptable product in other forums. Realize this is an old post...but might be useful to others.

  10. Gopher_Baroque | | #11

    Appreciating Dina's contribution, note the URL for Metacaulk 950 has been updated to:

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