4 ms·

Do you see that in modern construction? As long as there is adequate insulation and the vapor retarding layer is in the right place (per code) the OSB shouldn't

Do you see that in modern construction? As long as there is adequate insulation and the vapor retarding layer is in the right place (per code) the OSB shouldn't ever be more than damp for any extended amount of time.

forgetfreeman 4y ago
I've seen catastrophic moisture damage in every form of home construction utilized in North America from the 1850s to present day. Anecdotally the most common failure modes break down roughly thus: 1850s-1960s: Termite damage followed by rot. This time frame is notable for ready availability of dense, tightly grained building materials. Lumber from this time period shrugs off all but the most egregious wetting cycles. So what happens is high humidity attracts termites which break down the structure. This in turn gives rot a plate to establish a foothold and spread (slowly). 1970s-1990s: This period is notable for a steady decline in quality of building materials and introduction of first and second generation engineered products. First-to-market siding products, condensation issues due to the aluminum craze in the 80s, and material adhesives edging out toward the end of their life expectancy all contribute to problems with mold/rot. Looser grained building materials also mean that when a problem is present it will quickly spread to larger areas of the structure than older materials would permit under similar conditions. 2000-2010: Easily the absolute nadir of home building in the US. The industry saw a massive influx of "budget" engineered materials, with no substantive changes to code to address the deficiencies of these materials. My personal favorite from this era include OSB siding that turned into a kitchen sponge whenever the paint layer was breached. 2010-present: same as it ever was. The market is still flooded with engineered materials that have a fraction of the life expectancy of more traditional materials. Building codes have largely caught up with the obvious limitations of these materials, however now the biggest issue is as a nation we are short two full generations of trained craftspeople in the construction industry and as such installation errors are rampant. This leads to more and bigger issues, bigger abatement projects, and in significantly newer homes. Case in point: a pinhole leak in a caulk seam on a window surround that resulted in all of the structural members surrounding that window, the wall cladding, the sill beam, a section of the floor, and several joists rotting out in short order. Root cause: didn't use plywood. Engineered sheathing acted like an enormous sponge both retaining and broadcasting moisture to all of the surrounding materials. So yeah, you're not wrong inasmuch as according to theory and per code it is within the realm of possibility to use these construction methods and materials successfully. In practice, however, the least competent subcontractor on any given jobsite presents a hard ceiling to what one can get away with. You design a fault-intolerant system that has any flavor of complexity to it's installation and odds are good someone's going to screw something up. The Achilles Heel of modern vapor tight building systems is the fact that houses leak. Either through incompetence during the initial build or breakdown of materials over time all houses leak. Whereas older construction methods would tolerate this to varying degrees, newer systems do not.
- wpietri 4y ago
  This is fascinating stuff. So what would you do if you were building a house today?
  - forgetfreeman 4y ago
    Assuming I was building in the Southeast where I live, that someone handed me a blank check, and without drilling down to specific products? - Hardwood timber framing - Stone or masonry curtain wall from the foundation to the bottom of the window sills. - Fully sealed crawlspace with inline registers broadcasting conditioned air into the space - Insulate the curtain wall instead of the interstitial space between floor joists - Standard soffit-to-peak venting in the attic space - Two layers of plywood subfloor separated by a layer of tar paper - Double layered sheetrock on all interior walls - Wall-to-wall sheet vinyl floor treatments in all of the rooms where water is a thing. - 3/4" hardwood flooring everywhere water isn't a thing. - Passive/active solar combo meal on the roof to offset any efficiency losses incurred by "loose" construction methods - Temperature & humidity sensors in the crawl space & plenum - Wood window frames and sills. Modern plastic window frames and sills are excellent at hiding a problem until it's turned into a $50k project (see also: aluminum siding). By comparsion wood trim acts as a bellwether. I'd much rather have to scrape, recaulk, and paint a window than be looking at deconstructing an exterior wall that's rotted to the foundation.
    - hedgehog 4y ago
      Fascinating, I understand most of it but why vented attic vs conditioned?
      - forgetfreeman 4y ago
        Simplicity. Sealed crawlspace prevents the plenum from ingesting ground moisture, so as long the roof is maintained that space shouldn't see any significant issues at any point in the next century.
    - saeranv 4y ago

forgetfreeman 4y ago

I've seen catastrophic moisture damage in every form of home construction utilized in North America from the 1850s to present day. Anecdotally the most common failure modes break down roughly thus: 1850s-1960s: Termite damage followed by rot. This time frame is notable for ready availability of dense, tightly grained building materials. Lumber from this time period shrugs off all but the most egregious wetting cycles. So what happens is high humidity attracts termites which break down the structure. This in turn gives rot a plate to establish a foothold and spread (slowly). 1970s-1990s: This period is notable for a steady decline in quality of building materials and introduction of first and second generation engineered products. First-to-market siding products, condensation issues due to the aluminum craze in the 80s, and material adhesives edging out toward the end of their life expectancy all contribute to problems with mold/rot. Looser grained building materials also mean that when a problem is present it will quickly spread to larger areas of the structure than older materials would permit under similar conditions. 2000-2010: Easily the absolute nadir of home building in the US. The industry saw a massive influx of "budget" engineered materials, with no substantive changes to code to address the deficiencies of these materials. My personal favorite from this era include OSB siding that turned into a kitchen sponge whenever the paint layer was breached. 2010-present: same as it ever was. The market is still flooded with engineered materials that have a fraction of the life expectancy of more traditional materials. Building codes have largely caught up with the obvious limitations of these materials, however now the biggest issue is as a nation we are short two full generations of trained craftspeople in the construction industry and as such installation errors are rampant. This leads to more and bigger issues, bigger abatement projects, and in significantly newer homes. Case in point: a pinhole leak in a caulk seam on a window surround that resulted in all of the structural members surrounding that window, the wall cladding, the sill beam, a section of the floor, and several joists rotting out in short order. Root cause: didn't use plywood. Engineered sheathing acted like an enormous sponge both retaining and broadcasting moisture to all of the surrounding materials. So yeah, you're not wrong inasmuch as according to theory and per code it is within the realm of possibility to use these construction methods and materials successfully. In practice, however, the least competent subcontractor on any given jobsite presents a hard ceiling to what one can get away with. You design a fault-intolerant system that has any flavor of complexity to it's installation and odds are good someone's going to screw something up. The Achilles Heel of modern vapor tight building systems is the fact that houses leak. Either through incompetence during the initial build or breakdown of materials over time all houses leak. Whereas older construction methods would tolerate this to varying degrees, newer systems do not.

wpietri 4y ago
This is fascinating stuff. So what would you do if you were building a house today?
- forgetfreeman 4y ago
  Assuming I was building in the Southeast where I live, that someone handed me a blank check, and without drilling down to specific products? - Hardwood timber framing - Stone or masonry curtain wall from the foundation to the bottom of the window sills. - Fully sealed crawlspace with inline registers broadcasting conditioned air into the space - Insulate the curtain wall instead of the interstitial space between floor joists - Standard soffit-to-peak venting in the attic space - Two layers of plywood subfloor separated by a layer of tar paper - Double layered sheetrock on all interior walls - Wall-to-wall sheet vinyl floor treatments in all of the rooms where water is a thing. - 3/4" hardwood flooring everywhere water isn't a thing. - Passive/active solar combo meal on the roof to offset any efficiency losses incurred by "loose" construction methods - Temperature & humidity sensors in the crawl space & plenum - Wood window frames and sills. Modern plastic window frames and sills are excellent at hiding a problem until it's turned into a $50k project (see also: aluminum siding). By comparsion wood trim acts as a bellwether. I'd much rather have to scrape, recaulk, and paint a window than be looking at deconstructing an exterior wall that's rotted to the foundation.
  - hedgehog 4y ago
    Fascinating, I understand most of it but why vented attic vs conditioned?
    - forgetfreeman 4y ago
      Simplicity. Sealed crawlspace prevents the plenum from ingesting ground moisture, so as long the roof is maintained that space shouldn't see any significant issues at any point in the next century.
  - saeranv 4y ago