Results 1 to 6 of 6
  1. #1
    Join Date
    Sep 2002
    Posts
    23,763
    Post Likes

    Vapor barrier at exterior wall surface ?

    As I recall; a vapor barrier is best placed on the interior of the structure's outside walls. I assume this is to avoid the condensing of moisture inside the walls. Paint and the various sidings are somewhat porous and so allow moisture to escape outwards and the interior vapor barrier restricts the movement of moisture into the wall.

    Please correct me if I am wrong about that.

    I routinely experiment with envelope-improvements - most recently centered around the 'first; keep the heat out' concept. This in Florida.

    I have found that a white solar reflective roof is astonishingly effective in that regard. I have also done white selective-coating metal and also latex costing on other substrates.

    Recently I painted an entire house, to below grade, with white latex roof coating. With the idea that if sun reflects away from the roof - the walls will also benefit from the same effect. But . . . what afterwards occurred to me is that I have essentially created a 'vapor barrier' at the exterior wall surface of the entire house.

    I guess my basic question for you all now is: How bad of an idea was this? <g>
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  2. #2
    Join Date
    Jul 2010
    Location
    US of A
    Posts
    4,870
    Post Likes
    I think you may be fine doing that in Florida but probably isn't advisable in most other areas.
    Signature removed Violated rule #15

  3. #3
    Join Date
    Mar 2013
    Location
    Treasure coast, FL
    Posts
    7,478
    Post Likes
    The vapor barrier just needs to be on the warm/humid side of the wall.

    In Florida, it's outside the wall.

    If you were doing this in Joisey I might be a little concerned for "trapping" moisture between your existing and "incidental" vapor barrier.

    Let's see... If I think of air handlers in attics, there is typically foil-faced insulation inside of the cabinet, and then the metal of the cabinet would act as another vapor barrier. On properly functioning systems this doesn't seem to cause problems. Nor does externally-insulated sheet metal ductwork, for that matter.

    So I think you've got nothing to worry about.

    Sent from my Moto Z (2) using Tapatalk

  4. #4
    Join Date
    Sep 2002
    Posts
    23,763
    Post Likes
    Thread Starter
    My thought was that using a good interior paint almost certainly 'water proofs' the inside of the wall and now I have actually water-proofed the outside of the wall. <g>

    Freezing weather is extremely rare here - although every winter there are some nights in the 30-40Ί range.

    This house is slab-on-grade' and was pretty 'damp' inside when I bought it. I started running a dehumidifier set to 45% inside the house some months ago and that made a notable difference. But the property was sort of bowl-shaped with the house at the bottom of the bowl. All rainwater ran towards the house. The Gulf is very close and the house is 3' above sea level - so actual drainage was a problem.

    It appeared to me that the walls were actually 'wicking' water up into them. Under the peeling paint they felt 'damp' to me and joint compound repairs could sometimes take days to dry. And the lower on the wall they were - the slower they dried.

    After recently painting the exterior with white latex roof coating to well below grade I re-contoured the entire property with a backhoe/loader - creating a swale at the property line and using the removed soil to raise the grade along all the walls of the house.

    Oh; and installed rain gutters and ran the downspouts out to the swale.

    There is a city maintained drainage ditch along the front street and I tunneled 8" PVC under the front sidewalk to connect my new swale to that ditch. I was too lazy to get down in the mud and pack the dirt back into the 'tunnel' around the pipe so I drilled 1/4" holes in the sidewalk and 'back-filled' around the 8" PVC pipe with cans of spray foam. <g>

    I don't actually have the drainage ditch across my property - mine is a buried culvert - but my east neighbor has the exposed ditch I could connect to. I thought he might object to me installing the PVC over to his ditch but he never said anything and it's done now. <g>

    PHM
    ------------


    Quote Originally Posted by pageyjim View Post
    I think you may be fine doing that in Florida but probably isn't advisable in most other areas.
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  5. #5
    Join Date
    Sep 2002
    Posts
    23,763
    Post Likes
    Thread Starter
    I was going back and forth about it. On one hand the sun and exterior ambient heat would tend to drive moisture out the tops of the walls.

    BTW: the walls are concrete block. They are stucco'ed outside. Inside there are 3/4" furring strips, rock lath, and wet-wall plaster finished.

    The bottom of the concrete blocks are on the edge of the floor slab, unsealed I am sure, and the top of the block walls just have a 2 by 6 plate that the ceiling joists and rafter attach to.

    But on the other hand; sealing both sides of the walls vapor tight seemed contrary to everything my northern-trained-mind was used to doing. <g>

    PHM
    --------------


    Quote Originally Posted by shellkamp View Post
    The vapor barrier just needs to be on the warm/humid side of the wall.

    In Florida, it's outside the wall.

    If you were doing this in Joisey I might be a little concerned for "trapping" moisture between your existing and "incidental" vapor barrier.

    Let's see... If I think of air handlers in attics, there is typically foil-faced insulation inside of the cabinet, and then the metal of the cabinet would act as another vapor barrier. On properly functioning systems this doesn't seem to cause problems. Nor does externally-insulated sheet metal ductwork, for that matter.

    So I think you've got nothing to worry about.

    Sent from my Moto Z (2) using Tapatalk
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  6. #6
    Join Date
    Jul 2010
    Location
    US of A
    Posts
    4,870
    Post Likes
    To be safe I would invest in a moisture meter to see if it becomes an issue. Might want to log the readings along with the interior space and outdoor weather conditions. I say this based on limited knowledge. I hope this works out well for you.
    Signature removed Violated rule #15

  7. #7
    Join Date
    Feb 2016
    Location
    Louisburg Kansas
    Posts
    2,241
    Post Likes
    Poodle there has been a long standing argument on where to place the vapor barrier. I have read several articles (none recently) on this subject and both sides have good points. I don't remember all the arguments but one is if you place the barrier on the inside wall you trap the moisture between the barrier and the wood structure. I put mine on the inside walls and haven't noticed any problems. Most articles I have read on below grade vapor barriers strongly promote the barrier be on the outside. One thing I do know is unless you have a lot of re-bar in a concrete wall the barrier will be stretched beyond it's elastic limit and become useless. In short I don't know the answer to your question and I don't know if you will find a definitive answer.
    No man can be both ignorant and free.
    Thomas Jefferson

  8. #8
    Join Date
    Apr 2003
    Location
    St. Louis
    Posts
    882
    Post Likes
    I agree with pageyjim getting a moisture meter. Putting roof coating on shouldn't be any different than flat roof that has insulation and drywall but if there's a vapor barrier already in the wall that could be a problem trapping moister between the two. Why not call the coating company and ask them what they think.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  

Related Forums

Plumbing Talks | Contractor MagazineThe place where Electrical professionals meet.