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</o:shapelayout></xml><![endif]--></head><body 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'>The best study I have seen on attic ventilation was a canadian cmhc study that set up trial houses in bc wet zones (similar to Washington) and in our Midwest climate. The study sealed attics and ventilated attics looking at moisture control. The end result was basically that exterior ventilation was outweighed by interior moisture migration to the attic area. There was virtually no difference between vented or unvented assemblies in both climates. The best answer I have ever gotten about attic ventilation is that ‘it is not science – it is history’.<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'>So yes I think the general consensus is that the major concern in terms of building science is air sealing between the conditioned space and the attic as well as adequate ventilation of the conditioned space. It still leaves the question as to attic ventilation.<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 the PNW ventilation airflow in an attic space consists of drawing pretty moist winter air through the cavity between insulation and the roof sheathing. It defeats common sense but that is still the state of the art. In an older house the soffit venting would be entering the roof space at the wall junction through a 4” cavity (2x4 truss or roof framing). To allow for the ventilation that means the insulation is tapered to 2.5-3” which is not adequate so typically there is a lot of condensation and molding of sheathing at the eaves. That is what I have seen in numerous buildings. The other concern for me with airflow is reducing the effectiveness of the insulation – but supposedly with cellulose that is less of a consideration than it would be with fibreglass<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'>Codes still require ventilation here but as mentioned I think that is primarily in consideration of how difficult if not impossible it is to achieve an airtight ceiling in a living space. I am surprised to hear that Listiburek is adamant about airflow for the PNW. I would still argue that drawing moisture laden air into a potentially leaky attic space is an invitation for trouble. . I think Listiburek is considering new construction and the fact that builders can’t create good air seals.<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'>I have had to comply with soffit ventilation in an older renovation at ceiling level so as a result I compromised and I specified a foam board that was ˝” shy of the roof sheathing along the perimeter (3x6 over the top plate so it ran a few inches in) cellulose was blown in and roughly tapered to the foam edge. Inspectors argued that they wanted 1 ˝” clearance but I argued that the ˝” met the roof soffit/ridge ventilation ratio and they accepted that (at the time). Normally I would look at insulating at the roofline if allowed or create a vent gap at the roofline and insulate. This allows for conditioning the attic space as it is good storage and I like the building roofline to be part of the envelope.<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'>Roofs are complicated in our older buildings and can turn into a mess. In some ways ignorance is a blessing. Just blow in 12” of cellulose or more and mostly it creates a decent air seal and blocks the soffit ventilation and the building will be fine.<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 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"'>From:</span></b><span lang=EN-US style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'> greenbuilding-bounces@lists.bioenergylists.org [mailto:greenbuilding-bounces@lists.bioenergylists.org] <b>On Behalf Of </b>Sacie Lambertson<br><b>Sent:</b> November-10-11 6:14 PM<br><b>To:</b> Greenbuilding<br><b>Cc:</b> Dan<br><b>Subject:</b> [Greenbuilding] attic insulation in Seattle house<o:p></o:p></span></p></div><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><span style='font-size:13.5pt;font-family:"Tahoma","sans-serif"'>All, I would appreciate advice. I am going to Seattle to help our son install insulation in an unconditioned attic in a 1906 house that has been completely upgraded with insulation everywhere except the attic. (As an aside, I was amazed to find in Seattle NO pre-50s houses on the market had attic insulation and most had none in the walls either--pretty amazing).<br><br>We plan to carefully seal any openings between the conditioned space below and the attic, then blow in however much cellulose we need.<br><br>J. Listiburek is quite adamant about the need for a wash of air via continuous soffit ventilation when insulating this way. But no one in the Seattle marine climate has continuous soffits vents. What is our alternative? What else should we be concerned about? Ice dams btw are not a problem in Seattle.<br><br>L. doesn't like one to store anything in the attic either, but if one has walk-in space up there, why not? What are the considerations here?<br><br>Thanks, Sacie</span><o:p></o:p></p></div></body></html>