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</o:shapelayout></xml><![endif]--></head><body bgcolor=white lang=EN-CA link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>I will hazard some comments here – dangerous ground for me on this one. RH is as the term implies is a relative humidity. Large open celerestory residential structures can get complicated in terms of air flows and what humidity is contained, where it is stored and where it is released (and how). They get even more complex with levels and clerestory heights and exterior wall exposures. <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Modelling air flows gets even harder but even simple modelling gives some decent information as to what basic provisions can be made. It is not rocket science just providing for some flexible options. if there is a source of dry (dehumidified air) ceiling ducting can be used to air wash windows but you need some source of dried air and movement and hopefully some materials that can hold moisture without degrading. I usually include some ducting or plenum in clerestory structures that allows for some forced or even facilitate passive air movement that can move a conditioned air to a top of building. Doesn’t have to be integrated but if it is it can alter a wall or window condition and air movement within a room. Room to room passive wall air transfer grills are also really effective if sized properly for the room (undercutting doors just doesn’t do it) and there is some draw that provides effective air movement. Properly sized grills can provide for air transfer with even limited draw (low cfm).<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>In moving air across surfaces – those surfaces also need to be able to do what they are capable of in terms of moisture capacity. Large areas of wood (ceilings, floors) are quite amazing in what they can hold and release in terms of moisture safely with limited air flow. Cementious products like stucco are also quite forgiving. Drying air flows across exterior walls that subsequently load interior surfaces with moisture can be quite effective in managing humidity despite high ‘relative’ humidity readings. But it is all about materials and surfaces and their capacity - Gypsum, paper surfacing and layers of latex paint are not so amazing and studies have shown interesting growth between layers of paint...<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Moisture is essentially about materials and their capacity to hold and release moisture without significant deterioration (meaning some deterioration that compromises the health of the material (or occupant). Window manufacturers gave up the battle on that and loaded interior wood with exterior grade fungicides that may or may not outlast the warranty depending on the application – but may look ugly over time. If air movement can be directed to ‘delicate’ conditions (such as wood next to glass) and effect some drying and subsequently moved across ‘less delicate’ surfaces that can deal with a moisture load then you can cope with a relatively higher degree of humidity (which can also be a level of comfort).<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><div><div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0cm 0cm 0cm'><p class=MsoNormal><b><span lang=EN-US style='font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext'>From:</span></b><span lang=EN-US style='font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext'> Greenbuilding [mailto:greenbuilding-bounces@lists.bioenergylists.org] <b>On Behalf Of </b>John Straube<br><b>Sent:</b> October-28-12 7:46 PM<br><b>To:</b> Green Building<br><b>Subject:</b> Re: [Greenbuilding] Airtight windows<o:p></o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><div><p class=MsoNormal style='margin-bottom:12.0pt'><span style='font-family:"Helvetica","sans-serif"'>Hi Sacie<br>I assume you have double-glazed low-e argon Pellas, with wood frames?<br>If you have condensation problems it is very likely too high RH. I am curious about your comment that the RH is within the recommended range.<br>This could be ture, but is that recommended range might be 20%RH or 50%, since I have seen both "recommended" for the Kansas climate. Have seen some significant condensation on low-e Argon filled windows in a large multi-unit building about 1.5 hr drive from Kansas City which was reported to always be bad at this time of year.<br>Condensation like this tends to be worse early in the season as the moisture from building materials is released. In my airtight home this delay is very noticeable (eg RH is stubbornly high until January I find), and I have to ventilate aggressively during this time period to keep my RH within safe levels.<br>As rough guidelines, when it is 30F outside, I would target 30%RH and when it is 10F, I would look for 20%RH. It takes a while to ventilate down to those levels, but once you get there it tends to stay.<br><br>PS I have triple glazed foam filled fiberglass framed windows. Condensation can be made to occur on these rather high performance units merely by letting the RH ride up to, say, 50to 55% during 30F nights. The condensation quantity is small but totally visible.<br>PSS Bob's claim that windows leak outward in cold weather is not true. It is often true for the second storey of homes, but rarely true for the 1st floor of 2 stroey homes and almost never true for windows on the windward side during windy weather.<br><br><br></span><o:p></o:p></p><div><p class=MsoNormal>Dr John Straube, P.Eng. <br><a href="http://www.BuildingScience.com">www.BuildingScience.com</a><o:p></o:p></p></div><p class=MsoNormal>On 12-10-28 1:20 PM, Sacie Lambertson wrote:<o:p></o:p></p></div><blockquote style='margin-top:5.0pt;margin-bottom:5.0pt'><p class=MsoNormal>On Sun, Oct 28, 2012 at 10:36 AM, Bob klahn <<a href="mailto:Home-NRG@dnaco.net" target="_blank">Home-NRG@dnaco.net</a>> wrote:<o:p></o:p></p><div><blockquote style='border:none;border-left:solid #CCCCCC 1.0pt;padding:0cm 0cm 0cm 6.0pt;margin-left:4.8pt;margin-right:0cm'><p class=MsoNormal>Lance,<br><br>One guideline that has been implied but not stated in any reply I've read is that whatever approach you choose, the innermost pane must be the air-tightest to limit condensation. The old "rule of thumb" was five times tighter than subsequent panes, if there is any leakage. This allows any leakage (drying) to be to the outside.<o:p></o:p></p></blockquote><div><p class=MsoNormal>Re Bob's note on tight windows, we're now moving into the winter heating season. Our windows are starting to condensate at the base on the inside. Many of you have suggested this is the penalty of winter. Isn't there anything I can do about it? With the windows I have? Or, are there windows out there that don't condensate in the winter? Are there windows that don't leak cold air to the inside from the outside glass per Bob's dictum? Or is this not a matter of tightness, but rather of the differences in temperature?<br><br>thanks, Sacie<o:p></o:p></p></div></div><p class=MsoNormal><br><br><br><o:p></o:p></p><pre>_______________________________________________<o:p></o:p></pre><pre>Greenbuilding mailing list<o:p></o:p></pre><pre>to Send a Message to the list, use the email address<o:p></o:p></pre><pre><a href="mailto:Greenbuilding@bioenergylists.org">Greenbuilding@bioenergylists.org</a><o:p></o:p></pre><pre><o:p> </o:p></pre><pre>to UNSUBSCRIBE or Change your List Settings use the web page<o:p></o:p></pre><pre><a href="http://lists.bioenergylists.org/mailman/listinfo/greenbuilding_lists.bioenergylists.org">http://lists.bioenergylists.org/mailman/listinfo/greenbuilding_lists.bioenergylists.org</a><o:p></o:p></pre></blockquote><p class=MsoNormal><o:p> </o:p></p></div></body></html>