Unpleasant surprise between siding and interior walls.

Discussion in 'Remodel Forum & Blog' started by Rughead, Apr 20, 2010.

  1. Rughead

    Rughead New Member

    Messages:
    48
    Location:
    Scarsdale, NY
    Hi there. In Scarsdale, NY we decided to go with blown-in cellulose insulation but have discovered there is nothing behind our ancient wooden siding and the interior walls. Nothing at all! :confused: No plywood, tar paper or anything to keep the cellulose from coming out from the cracks in the siding when it's blown in. OK the house was built in the 1700's, balloon framed, but one would think in the 2 centuries gone by that previous owners would have done something. Of course every contractor we've had come to look at it tells us we need to remove the siding, then insulate and Tyvek, then new siding. And they're all talking of 10's of thousands of $$ for the job. I don't think so, not when I'm about to retire on a meager pension. Any advice is greatly appreciated. Cheers and best regards, Rughead
    Last edited by a moderator: Apr 21, 2010
  2. Rughead

    Rughead New Member

    Messages:
    48
    Location:
    Scarsdale, NY
    Hi dgold. Yes we looked into expanding foam but from what Dana said about the house needing to breathe, we thought the blown-in cellulose would allow better air circulation and better mold and mildew prevention. Am hoping Dana will chime in here sometime with more of his expert advice. We are now perplexed and back to square one. The project's on hold for now and thank goodness the winter's over... Cheers, Rug.
  3. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,015
    Location:
    New England
    One reason that old wooden siding probably lasted so long is that it can breath on both sides. Not good for your heating/cooling bills, though!

    While it would be tedious, the old stuff could probably be removed, and then reinstalled rather than new stuff installed. Assuming you put in any sheathing, it may be a pain trimming out the windows, etc. If those are original, you might want to consider replacement of those, too.
  4. Lightwave

    Lightwave New Member

    Messages:
    98
    Location:
    Vancouver, BC
    Unfortunately, if you don't have the budget for a complete envelope rennovation then you probably don't have any other option beside leaving things as they are.
  5. Rughead

    Rughead New Member

    Messages:
    48
    Location:
    Scarsdale, NY
    Thanks guys. The previous owner replaced the windows with the cheapest quality double glazed ones he could find. Most have already lost their seal and perspire inside. We'll replace them one at a time. Unless I get 30 years younger and my pension doubles, looks like we're gonna just leave the siding as is and plug any obvious gaps, holes, etc. Cheers and best regards, Rug.
  6. Dana

    Dana In the trades

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    2,841
    Location:
    01609
    Zzzz... ....zzz.... <snork> <koff> Huh? You called?

    Houses don't need to "breathe" from an air movement point of view- in fact air movement is generally BAD. But from a vapor-permability point of view, liquid water that finds it's way into walls (either by water vapor permeating to a component cold enough to condense upon, or leak events) needs to be able to evaporate and escape. Air movement within the insulation can take warmer more humid air to cooler places to condense. This occurs at a much higher rate in fiberglass & rock wool than cellulose- literally a 10/1 difference, but with open-cell foam it's at least a 1,000/1 reduction in air movement, and with closed cell even more. But ALL of these materials pass water vapor, but again at different rates, closed-cell foam being the outlyer, being an order of magnitude less vapor-permeable than open cell foam. At stud-wall thicknesses closed cell foam is essentially vapor impermeable and waterproof- no water gets in, so it doensn't need to be able to dry. Open cell foam is still quite vapor permeable, but air-tight. Cellulose is neither.

    Cellulose has the ability to wick water away from structural elements, and slowly dry without damage as long as it doesn't become saturated. It can handle being over 15% water by weight without damaging the cellulose, but by the time it's 30% water by weight it's soggy, and it'll sag. While it's hygric buffering capacity is high, it's in no way high enough to handle bulk loads of rainwater seepage behind clapboards while in direct contact, and no drain-plane material to reject the bulk of it. In that configuration it'll suck more rainwater in than it'll let leakage & condensation out.

    Foam would also be a problem here- more for the siding than for the studs. Closed cell foam is water proof- the studs would only get wet on the exterior edge, but without even 0.01" of back ventiation the siding would trap water, and you may end up with the more rain-exposed sections rotting in less than a decade. With open-cell it could vapor-dry toward the interior after rain events, but it will end up slowly saturating the foam, with a similar end-result.

    The only options that work here are granular insulations like poured perlite or blown EPS beads ("styrofoam",in bead form not boards.) These are porous enought for back-drying the siding yet stilll offer ~ R2.5/inch of depth. They don't block air movement much (far less than fiberglass or rock wool) but don't vapor-lock things either. It's still very important to air seal (even vapor-seal) the interior walls though, or you could end up with localized condensation issues inside the walls in winter if interior air has a steady leak through toward the cold edge of the stud. Blown EPS beads has even been shown to work the cavity of masonry cavity walls without creating vapor trapping & masonry-spalling issues. It's now common in the UK, but I've yet to hear of companies doing it in the US. The beads are blown with an adhesive to limit settling & sag over time. In a 4" deep full-dimension studwall (or cavity wythe) you get ~R10, which is WAY better than nothing. Even filling 2" masonry cavities gives you R5.

    If you bite the bullet & re-side the place, the best bang/buck would usually be wet-sprayed cellulose, in the cavites, foam around the windows, with EPS or XPS foam sheathing (with no foil or poly facers in your climate zone- it has to be at least semi- vapor-permeable) over the structural sheathing (tape & caulk the seams of the structural sheating, then lap the seams of the foam to form an air-barrier, then tape or mastic-seal the seams on the foam.) It still needs a drain-plane (either housewrap or 15# felt, both of which are VERY vapor-permeable), then use furring (or ripped down 3/8-1/2" plywood) though-screwed to the studs to mount the siding to. With a back-ventilated rainscreen gap behind the siding very little rain moisure finds it's way into the wall, the siding dries as evenly as it ever did, and the house lasts forever.

    If you use XPS for sheathing insulation you're limited to ~2" before it's impermeable enough to be an issue, but as long as it's more than ~35% of the total R value, impermeable is fine in your climate. 1" (R5) is more common. By putting insulating over the exterior, the studs stay warmer (=drier, less mold hazard), and the whole wall R-value goes way up, since the framing is a thermal short-circuit through the cavity insulation. (Wood is only ~R1/inch, compared to ~R2.5/inch for perlite, ~R3.7/inch for cellulose or open-cell foam or medium density fiberglass.)

    Whether you insulate now or not, air-sealing from the interior can be a huge improvement. With a window fan you can alternately pressurize/depressurize the house running around with smoke pencil (or incense stick, if you can stand the stink) and a can of foam, caulk, tape, and labels to mark larger leaks. Most houses have huge air leakage at the foundation sill, and sealing/insulating the flundation sill & band joist with at least an inch of closed cell, or 2" of open cell foam is worthwhile. (The larger DIY foam kits are good for this, but in NY there are probably rebates for letting the pros do it, an it'll end up being cheaper in the end.) If you seal the foundation, and seal the attic, the "stack effect" drops significantly, lowering forces that drive air infiltration. Am empty-cavity studwall no-sheathing house like yours probably has 6-10 air changes/hour (ACH), and it would take a HUGE effort to seal it to the point where active ventilation was required (~0.35 ACH). But getting it under 2 is probably doable and cost effective, and will improve the heating & AC bills significantly, while improving overall comfort.

    In general, when retrofitting a house the most cost-effective measures, in order of cost-effectiveness are:

    1: air sealing

    2: insulating

    3: higher-efficiency HVAC.

    Better windows tend to be way down the list, unless they're very leaky and can't be repaired. Storm window retrofits over single-pane windows that are in otherwise decent repair are usually cost-effective. They're less money, and more efficient than bottom-of-the-line insulated glass replacement windows with only 1/4" between the panes of the sealed glass. But if you're doing the whole residing with insulating sheathing, that's the time to bite the bullet on better windows too.

    [edited to add...]

    When painting the interior of the exterior walls (and the upper floor ceiling) applying vapor-retardent latex before going to the color coating is worthwhile. It's special stuff- most standard paints are fairly permeable, but vapor-retardent latex has permeability comparable to kraft facers used as vapor retarders on fiberglass batting. This will be more important after you insulate than before, and isn't nearly as important as air-sealing in terms of keeping interior moisture from condensing inside the walls during the winter. (A square inch of air leak holes is worth more than 50 square feet of vapor permeability through plaster or wallboard in terms of the volume of water transported.)
    Last edited: Apr 23, 2010
  7. Rughead

    Rughead New Member

    Messages:
    48
    Location:
    Scarsdale, NY
    Thanks Dana for this detailed explanation (and to whoever for the cool avatar). I'll need to re-read and study this a few more times to properly understand so much information. Almost like rocket science to me. But it seems there a quite are few things we can do to improve our insulation values and reduce our energy costs, which BTW were horrendous this past winter, our first in this expensive old house. Am sure I'll be back with more questions as this project progresses and again thank you for your time and expertise. Stay tuned. Cheers and best regards, Rug.
  8. Dana

    Dana In the trades

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    2,841
    Location:
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    There's a ton of well-written stuff along these lines on the Building Sciences Corporation website. The stuff concering water vapor & moisture control would probably be of interest. They also have detailed recomendations for particular sorts of situaitions like basement insulation etc. Their internal search function can be useful when trying to figure out some of the particulars.

    A lot of the wall condensation/vapor control stuff boils down to the ability to read a psychrometric chart and looking up the weather data for your location though. Once you understand the physics of the proceses it's pretty easy to estimate the moisture hazards of a particular wall or ceiling material stackup in a particular climate zone.
  9. Rughead

    Rughead New Member

    Messages:
    48
    Location:
    Scarsdale, NY
    Thanks Dana. Will research the site and educate myself. I only have an MBA, not a PhD in physics. My cousin Pat who's got PhD's in physics and engineering will be quite helpful in this case. Give him an excuse to come for a visit. He over-engineers everything he does, from injecting cement into the foundation of our old family cottage by the Susquehanna river, to rebuilding his mom's attic where he lives, into a prime batchelor pad. Many thanks for your sage advice. Promise to come back when things are moving, hopefully in the right direction. Cheers and best regards from Budapest, Rug.

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