Hello Tim: The situation does look as if you are asking to supersaturate the cellulose insulation. I would suggest you provide a contiguous ceiling, wall and floor waterproof barrier under the tile.... or a fiberglas shower unit.... combined with a pretty good exhaust fan. I've always been nostalgic about the switched half-window 30x30 half- window bathroom exhaust fan my wife and I had in our first apartment in an Art Deco building. It really worked to suck out the vapor in a short time. Jonathan Miller, FCSI, AIA JMMa Specs On Dec 18, 2008, at 7:27 PM, Tim Yandow wrote: >> I am interested to know if anyone has an opinion about or >> experience with > the following situation: > I am currently constructing a 2000 sq ft double wall, dense pack > cellulose > house. Due to a number of factors, an upstairs shower stall, 4' X > 4' ended > up in an outside corner of the house (north west corner). I know > this is > not a great spot for it, but there it is. The tiler would like me > to place > a vapor barrier over the framing before the hardy backer and tile > go on. > There is 12 inches of cellulose in the walls with a thermal break > (2- 2x4 > walls) behind the shower. This I presume is to keep moisture from the > shower away from the insulation. I am wondering if this is a good idea > given the porous nature of tile and hardy backer. Any input? Thanks. > Tim Yandow > > > > I am not sure what makes the most sense here >> >> --- On Tue, 12/16/08, William C Badger AIA >> <[log in to unmask]> wrote: >> >> >> Stain may be fine for certain applications, but white stain does >> not cut >> it on a 19th Century Greek Revival building. There are many >> applications >> where paint is the only suitable coating and our wall sandwich has to >> accept that. >> >> Acrylic water-based primers and paints are relatively vapor >> permeable, as >> long as they don't have lead or zinc oxide pigments. >> >> I have been on the scaffolding and seen soggy paper mache that was >> once >> cellulose insulation pulled out of walls. >> >> Without the forensic analysis that would determine the source of the >> moisture, that anecdote indicates nothing. >> >> Try telling the owners of a late 18th Century library that all the >> books >> and shelves need to be removed and the wood paneled walls painted >> with >> vapor barrier paint. For that matter, any old house with an >> historic or >> just well finished interior is not a candidate for an interior vapor >> barrier. >> >> Many of the early cellulose retrofits had insufficient density to >> prevent >> the air movement that is the primary vector of moisture in walls. If >> properly dense-packed, and interior humidity levels are appropriately >> controlled (and there are no sources of bulk moisture, such as wet >> basements or crawl spaces or ice dam leakage), cellulose retrofits >> do not >> require a vapor retarder. In fact, one cellulose manufacturer - >> Applegate >> - will void their warrantee if a vapor retarder IS used. >> >> More attention is being paid to the "flow-through" concept of >> moisture >> control, allowing drying in both directions. >> >> >> In 1979 a field study in Portland, Oregon (4,792 degree days) >> concluded >> there is no risk of moisture damage in mild climates without a vapor >> barrier >> >> A second major field study was done in Spokane, Washington (6,835 >> degree >> days) by George Tsongas, Ph.D. P.E. Professor of Mechanical >> Engineering at >> Portland State University. The exterior walls of 103 homes were >> opened, 79 >> with retrofitted insulation and 24 uninsulated as a control group. >> “This >> study strongly concludes that the addition of wall insulation >> without a >> vapor barrier does not cause moisture problems in existing homes in >> climates similar to that of Spokane.” Bonneville Power Administration >> provided funding for this study. >> >> A 2004 study released by building scientist Erkki Kokko of Finland, >> ”Hygroscopic Cellulose Fiber Insulated Structures” found the use of >> permeable building materials resulted in improved indoor air >> quality. The >> absence of a vapor barrier, such as polyethylene film, allowed the >> wall to >> absorb and desorb relative humidity. This enables the interior >> relative >> humidity to remain more constant and comfortable to the occupants. >> They also found a 30% reduction in the carbon dioxide levels. >> >> The EEBA’s Builder’s Guide for Cold Climates states in Appendix III, >> “Polyethylene on the inside of building assemblies in cold, mixed- >> humid, >> mixed-dry, hot-humid, and hot-dry climates is not generally a good >> idea.” “A classic flow-through wall assembly should have a permeable >> interior surface and finish and permeable exterior sheathing and >> permeable >> building paper drainage plane.” This permits drying to both the >> interior >> and exterior. >> >> In a December 2001 presentation in Proceedings of Thermal >> Performance of >> Building Envelopes VIII, Asst. Prof. John Straube stated “In many >> practical situations, a low permeance vapour barrier will not improve >> hygrothermal performance, and may in fact increase the likelihood of >> damaging condensation or trap moisture in the system. In some >> cases, a >> low-permeance vapour barrier may be called for, but in many practical >> high performance enclosures, none is needed, and eliminating them >> will >> actually improve performance by encouraging drying and avoiding >> solar-driven diffusion wetting. >> >> I would pose a typical problem building for group comments. A late >> 19th >> Century structure with some timber frame and some stick built >> walls. The >> bulk of the walls are uninsulated with clapboards nailed directly >> to the >> studs (no sheathing). The interior walls are lath and plaster with >> 1/2" >> Celetex over it and 1/4" plywood paneling over that. It has a stone >> foundation and slate roof. The attic is vented and the attic floor is >> insulated with a nominal 12" of fiberglass, but electricians over the >> years have done their best to rearrange it. The paint tends to >> hold fairly >> well, but is a mix of relatively new coatings and what ancient >> bits have >> still hung on. Will dense pack cellulose exert enough pressure to pop >> clapboards off (small cut nails are what was used)? Will moisture >> transfer >> peal the paint? >> >> As long as moisture sources are mitigated (stone basement?) and >> interior >> humidity levels are controlled with appropriate ventilation, this >> might be >> a good candidate for dense-pack cellulose. It's unlikely that the >> installation would pop the cladding nails, as aged wood has amazing >> holding power, unless previous rusting has deteriorated the bond. >> >> Ironically the potential problem in this case might be the >> presence of an >> interior vapor barrier - the Celotex, with its double foil >> facings. Since >> the exterior cladding has no weather-resistant barrier (not even >> sheathing), there is a potential for wind-driven moisture >> penetration, >> particularly if there is a high exposure level (no trees or other >> adjacent >> buildings as protection). >> >> This wall structure would have to do all its drying to the >> outside; but >> since there should be little moisture drive from the inside, the >> outward >> drying force may not be sufficient to lift the paint. >> >> But, if I were interested in preserving this building, I would >> consider >> removing (and either saving or replacing) the exterior cladding and >> installing a weather-resistant barrier (probably 15# felt or grade D >> building paper). Without such a secondary drainage plane, it's >> likely that >> you would be up on that scaffolding again removing soggy cellulose >> and >> rotted wood. >> >> Removing the cladding would also allow the cellulose to be blown >> in behind >> InsulWeb netting for a more complete installation (around knee >> braces, >> etc), then covered with WRB and siding.