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Missing Moisture Membrane

Discussion in 'Residential Energy Codes' started by stevet6, Oct 23, 2017.

  1. stevet6

    stevet6 New Member

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    I'd like to get some clarification regarding an issue I am having with my house and the missing moisture membrane between the sill plate and the foundation. My house has a vented crawl space and our builder had an engineer write a letter stating, "In Chapter 11, there is Table N1102.4.1.1 that list criteria for which air barriers are to be sealed. In this table underneath the component “Walls” it states, “The junction of the foundation and sill plate shall be sealed.” However, this would only apply to slab or sealed Crawlspace foundation conditions. This is explained earlier in the chapter when discussing the building thermal envelope." They also stated, "Given that the Crawlspace is vented on all sides, applying a sealant to the interface between the foundation wall and the sill plate would do nothing to improve the energy efficiency of this foundation system."

    I live in South Carolina where the city goes off of the 2015 IRC not the SC version.

    From what I have read, there is no mention of this in this chapter. Also, are there any other possible issues besides energy efficiency with not having the membrane there?

    Any help would be great on this. Thank you.
     
  2. cda

    cda Sawhorse

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    Welcome

    Give it a day or two for replies
     
  3. cda

    cda Sawhorse

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    N1102.4 (R402.4) Air leakage (Mandatory).
    The building thermal envelope shall be constructed to limit air leakage in accordance with the requirements of Sections N1102.4.1 through N1102.4.5.

    N1102.4.1 (R402.4.1) Building thermal envelope.
    The building thermal envelope shall comply with Sections N1102.4.1.1 and N1102.4.1.2. The sealing methods between dissimilar materials shall allow for differential expansion and contraction.

    N1102.4.1.1 (R402.4.1.1) Installation.
    The components of the building thermal envelope as listed in Table N1102.4.1.1 shall be installed in accordance with the manufacturer’s instructions and the criteria listed in Table N1102.4.1.1, as applicable to the method of construction. Where required by the building official, an approved third party shall inspect all components and verify compliance.





    https://codes.iccsafe.org/public/document/code/553/9849024
     
  4. conarb

    conarb Sawhorse

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    Why in the world would you want an air barrier sealing a crawl space? You want as much air as possible circulating through your crawl space, as a builder I've never put one there. As to CDA's cites the crawl space is outside the thermal envelope.
     
  5. cda

    cda Sawhorse

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    BUILDING THERMAL ENVELOPE. The basement walls, exterior walls, floor, roof and any other building elements that enclose conditioned space or provide a boundary between conditioned space and exempt or unconditioned space.
     
  6. steveray

    steveray Sawhorse

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    If it is an unconditioned crawlspace, then there would be no energy code basis for air sealing between the sill and concrete...Is the sill pressure treated?
     
  7. stevet6

    stevet6 New Member

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    Steve, The sill is pressure treated.
     
  8. steveray

    steveray Sawhorse

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    Kindof like Conarb said then...If it is a vented crawlspace, the more air the better as long as they install the proper air barrier at the bottom of the floor...
     
  9. mark handler

    mark handler Sawhorse

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    First of all I see no reason for the foundation and sill plate shall be sealed in this case.

    Some have questioned the Crawl space vapor barrier there are reasons to provide vapor barriers over the dirt
    A vapor barrier over the dirt slows or prevents the evaporation of ground moisture into the crawl space air. Excess moisture supports the growth of mold, dust mites, insects, and other pests.
    Excess moisture also may cause structural damage to the wood framing and degrades some forms of insulation, fiberglass in particular.
    A vapor/air barrier in the crawl space can also slow or block most of the movement of harmful gases, such as radon, from the soil.
    I am not saying do not ventilate a Crawl space, I strictly enforce the requirement
    [​IMG]
     
    #9 mark handler, Oct 24, 2017
    Last edited: Oct 24, 2017
  10. Mark K

    Mark K Platinum Member

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    Enclosing the sill plate under the membrane prevents the sill plate from drying out and thus ensures an early failure due to rot. Treated lumber will delay not prevent rot.
     
  11. conarb

    conarb Sawhorse

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    This is bad advice, put poly down in a crawl space and all kinds of mold starts growing, in fact mushroom farmers put poly over their mushroom beds to trap the moisture under the poly and start the propagation of the mold spores. For some reason Home Inspectors are the biggest advocates of this practice, many make it a condition of their home inspection that poly be placed in the crawl space, if there aren't holes put in it while placing it somebody like a plumber will soon crawl under there putting all kinds of holes in it allowing the propagated "mushroom" beds to release all kinds of mold spores into the air. I've seen it so bad the the whole house wreaks of the smell of mold, I tell them to get the poly out of there and the smell goes away, it's a messy job getting it out since there is a moldy mud bed under it.

    You want the surface of the dirt exposed and plenty of air circulation through the crawl space so mold doesn't start propagating in the first place. This can be a horrible problem with the new "sealed crawlspaces", many use the home HVAC system to circulate the air from the moldy crawlspace throughout the home, if one wants a sealed crawlspace it should have an entirely separate ventilation system. BTW, I have no problem with 2+" of concrete ratproofing even with poly under it. I've seen sealed crawlspaces like Mark H shows above where they attempt to tape the poly onto the foundation walls, Mark K is correct, if this is done the poly should never cover sill plates, all the sealed-in moisture will soon destroy the covered plates (or anything else sealed under there).

    Just to see for yourself, if you get some poly in packaging, take it out and lay a piece on your lawn overnight, lift it up in the morning and see all the moisture both in the lawn and on the bottom of the poly.
     
  12. Pcinspector1

    Pcinspector1 Platinum Member

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    Getting off a bit but...Your vented crawl space could eventually be spider infested when the little buggers find a void between the foundation and the sill plate. Another reason to caulk or use sill sealer IMO.
     
  13. Builder Bob

    Builder Bob Sawhorse

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    Be aware of SC energy code, by state law we are mandated to use the 2009 IECC, not the 2015 IECC.....
     

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