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Community and Q&A

Pex plumbing retrofit + crawlspace insulation

Barbara Keating | Posted in Green Building Techniques on

Hi, I live in an older (1920’s?) single story 1200 sf wood frame house on a post & pier foundation; small rural town in far northern coastal CA. The water table is high in the winter & indeed can have standing water of several inches around and under the house for short periods of time in non-drought years (and, yes, I’ve considered a sump pump, but nowhere to pump the water to that wouldn’t flow back or, if not, compromise my neighbors property/dwellings). This is why I’ve not considered any kind of ground level vapor barrier etc., as there is no way presently to close off the crawl space & only has a perimiter wood skirting to keep (most) critters out.

I am considering some home improvements (and figuring out how to pay for them on a retiree’s budget!). In additon to a needed new roof & air sealing, etc., a recent energy assesment suggested crawlspace insulation. If I win the Lotto (yeah, I know you have buy tickets first) it will also inclue grid-tied solar and air-source heat pump, as my home only has an ancient natural gas wall heater in the hall by the back door (why o why was it put there?!) & wood heat in the front, so no existing ductwork. Replacing my very old galvanized plumbing pipe is high on the list as well. Here are my questions related to the plumbing and crawlspace:

1) Before doing either, is it recommended to do a pest inspection BEFORE proceeding and take care of any negatives found? The house was treated some 25 years ago for powder post beetles just after I purchased it. My concern is not to cover up any potential problem (hopefully I don’t/won’t have one).
2) If I am able to replace the plumbing, I am considering pex both for cost and ease of retrofit, tho’ have not yet parsed the method of run. My go-to plumber prefers thick gauge copper, but he also admits he’s old-school (not that that’s a bad thing!). If I decide on pex, I’ll preview & review potential installers & get bids.
3) If I am able to do all this, is it recommended to run the pex first THEN insulate (anticipate closed cell foam) or the other way round? I’ve tried Googling this question in different iterations w/o success, hence my questions here (I trust your input!). My concern is pipes buried under spray foam in case it needs to accessed, and that any curing heat put off by the foam would compromise the pex. On that note, if the spray foam is done BEFORE the plumbing, would the installation of the pex mess up the foam job, or would I have to have someone come and remediate any damage to the insulation?
4) Are there other considerations on this crawlspace/pex plumbing issue that I’ve not considered & that I should know and learn more about?
Sorry I’m so wordy, but appreciate any help & insights you can offer.
Blue Lake, CA

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  1. User avatar GBA Editor
    Martin Holladay | | #1

    If you have an open crawl space, you shouldn't have any standing water in there. You should be able to grade your property so that water flows away from your house, not toward your house. Unless access is very tight, one solution is simply to add a few inches of soil or gravel (with fines) under your house, so that the grade of your crawl space is higher than the surrounding grade.

    Yes to a pest inspection first.

    Yes to doing plumbing work before insulation work. Either PEX or copper tubing will work.

    The best way to insulate an open crawl space in a mild climate like yours, in my opinion, is to install a layer of foil-faced polyiso under your floor joists, followed by a protective layer of OSB or plywood. Of course, you need a plan to ensure that your plumbing pipes don't freeze.

  2. Richard McGrath | | #2


    Concerning piping choice and method . Pex will last quite some time and you or the people for the next 100 years probably won't need to be concerned about it . Copper will deteriorate at some time due to friction , copper has not yet reached the 100 year mark for widely accepted use in potable water systems (30s - 40s) as can be seen in your home where galvanized was used . If choosing Pex , go with a PexA product from Uponor , Rehau , Mr Pex , these are Pex A products and have a superior manufacturing and crosslinking process . Uponor has in my opinion the best fitting method using cold expansion which also creates no flow restrictions as do the crimp ring products having fittings with a small diameter . As far as method , your plumber of choice should probably use the Uponor Logic method . This will lessen the installed cost and use less fittings while offering the lowest pressure drop .

    Spray foam and Pex . Make sure if you install the pex first (advisable) that your insulation contractor performs spray passes in no more than 1" lifts and allows time to set before making another pass . Any more than that and the Pex and your home could be in danger . Plenty of articles about over spraying online .

    Good luck with your project .

  3. Malcolm Taylor | | #3

    Aren't there still jurisdictions in California that won't allow Pex to be used for residential plumbing?

  4. Richard McGrath | | #4

    Not positive about jurisdictions but statewide it has been approved

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