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FHB Crawl Space Ventilation Article

jimmiem | Posted in General Discussion on January 24, 2015 08:47am

Anybody remember what issue had an article about crawl space ventilation?  The point I remember is that in the 1980’s it was recommended that crawl spaces be vented but venting is no longer recommended.

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Replies

  1. calvin | Jan 24, 2015 02:34pm | #1

    Jim

    you looking for an issue from the 80's?

    Venting crawl spaces.  Bob Syvanen    issue 30     December/January 1985/1986

    go to FHB.com and see if you can find the magazine index.  Not sure if you need a membership to view.

    1. jimmiem | Jan 24, 2015 03:46pm | #2

      Calvin

      I am looking for a more recent issue....within the last year.  It talks about how the current crawl space ventilation practices have  changed from those used in the 80's based on what has been learned since way back then in the last century.

      1. calvin | Jan 24, 2015 05:42pm | #3

        Doesn't ring a bell, but....

        If I can come across it in one of the half dozen places the mag resides here, I'll let you know.

        the search on crawl spaces shows no recent articles.

        have you used the search box above ^ ?

        or perhaps gone to green bldg advisor and looked?  I'm sure there's opinions and info there.

        1. jimmiem | Jan 24, 2015 06:31pm | #5

          Calvin

          Thank You.

          Don't  spend a lot of time looking for it.  I keep all my mags so I should be able to find it.  It's also possible that the info was included in some on-line info related to crawl space moisture barriers.    

  2. DanH | Jan 24, 2015 06:17pm | #4

    I might have had that issue in a box of magazines down in the crawl space.  But when I closed off the ventilation everything got all moldy, so I threw them out.

    1. jimmiem | Jan 24, 2015 06:34pm | #6

      DANH

      So maybe crawl space ventilation should not be closed off?  The proof is in the pudding, or in this case the mold?

      1. DanH | Jan 24, 2015 10:33pm | #7

        (That was a joke, by the way.  Would be quite foolish to build over a crawl in this part of the country.)

        1. jimmiem | Jan 25, 2015 06:26am | #8

          DANH

          I read your response and then checked your profile.  Computer guy humor so he must be joking. 

  3. IdahoDon | Jan 25, 2015 09:41am | #9

    going without venting requires a bit of work to seal off sources of moisture - more than just a simple vapor barrier and either installing a dehumidifier or making the crawl open to the rest of the house (it would have to be very well sealed for that to be a good option), or some other method of monitoring and correcting overly high humidity. 

  4. AndyEngel | Jan 30, 2015 09:25am | #10

    A perennial conversation

    There are a lot of advantages to sealing up a crawlspace, including reduced energy use because you aren't inviting outside air to below your floor. In humid climates, odds are you can dry the space out, too, because moisture from humid outside air entering cool crawlspaces tends to condense. The detailing is critcal, though. VB on the floor, no active water leaks, and perhaps active dehumidification. Take a look at greenbuildingadvisor.com for details. 

  5. renosteinke | Jan 30, 2015 01:05pm | #11

    Let's Open the Discussion

    I am, like the salmon, going toswim upstream, aganst the flow of current opinion about crawl spaces.

    I. for one, like well vented crawlspaces.

    I suppose some of the debate stems from the sple fact that nobody 'designs' crawl spaces. Nope. They're just the space left over as the result of choosing piers as the foundation method. How the space turns out is left to pure chance, and whatever the builder sees as the cheapest, quickest, easiest way to do things.

    Let's back off a moment, and as what else a crawl space CAN be.

    First, it can provide a break between the house and the ground beneath. Advantages? Maybe isolating the house from freeze / thaw ground movement, and preventing ground-source radon from entering the structure. This will also help prevent vermin (especially termites) from attacking the house.

    Next, it can provide a ready means to access plumbing, run ducts, and route electrical circuits.This is especially handy when there is a need for maintenance or changes are made. A crawl space can make inspecting the house much more effective.

    Those things can happen only if there is enough space to move around, the space is not blocked by the ducts and pipes after you run them, and only if there  is good access. IMO, code requirements are completely inadequate for a truly accessible space. The openings are too small, the clearances too tight. The situation is often worse when the space is below grade.

     Reality #1 is that moisture WILL enter a crawl space - whether from the air or the ground. I've seen ductwork dripping with condensed humidity, and I've seen ground-water flow turn crawl spaces into active rivers during rains.nIMO, the key is to provide for the water to leave.

    To that end, I really like a layer of fine, smooth gravel in a crawl space. I'd even approve of this gravel being then covered by a fabric, mesh tarp, or even old  carpet- just so long as the covering lets moisture drain, and does not absorb it.

    Next is the matter of ventilation. Moist air needs to be vented. Code requirements for vent opening are completely inadequate. They need to be supplimented by an actual exhaust fan, one activated by humidity levels. This means flow must be designed ... fresh air in one place, moist air out another.

    (I speculate on whether it's a good idea to vent this moist air out via the attic - cooling the attic in the process. I just don't know)

    One thing to realize is that the crawl space of a house is often the source of the 'make up air' needed by house appliances. We just never notice it, but we need this fresh air. We need it for the  furnace, the water heater, the kitchen range, and for every exhaust fan. This air usually comes in through plumbing openings ... ever look under your tub drain? Your kitchen sink? Behind the range?

    Don't forget to allow for this fresh air intake in your plans.

    Cold floors are uncomfortable. Thus, we need to insulate our floors. With floors insulated, and fresh air in the crawl space, we now need to ensure that our pipes and drains don't freeze.  Having vents closed in freezing weather, and even running heat tracing on the pipes,is quite reasonable.

    Can we avoid this by 'sealing' the crawl space, and making it part of the 'conditioned' space?  Not often. The real kicker is ground water. Especially when a house is at the foot of a hill, a lot of water will try to flow under that house. You won't keep this out for long - far better, IMO, that you make sure it can leave once it enters.

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