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I’m to address severe ice dams (8″ thick at eaves)and water back-up on 2 year old home in way north Michigan. After several hours in the attic I learned that: Blown cellulose is R38-48 (12″-16″) no apparent areas of specific heat loss, baffles in place at eaves, ridge vent not covered with snow. All looked fairly decent except for the vinyl soffit which is heavy duty, beaded design, and not the slightest hint of a slit or vent anywhere that would provide air to the attic space. The owner has had ice problems for two winters now. The original contractor told the owner that the water backup into home was due to fact that “shingles have yet to properly seal themselves” – the owner really doesn’t want this guy back again. The contractor also said that the vinyl soffit is “semi-vented”. I’m not at all familiar with the specific phrase and the soffit type is not common in the area (the previous contractors primary experience was in Florida) I wore my best glasses while looking things over and could see nothing remotely resembling venting in or around the soffit. Has technology passed me by? Is vented soffit being made without visible vents? Is the previous contractor perhaps writing a “50 Best Excuses Manual”. Seriously – I’m looking at close to 200′ of soffit with most on second story. I want to have all my ducks in a row and owner seated before I make this announcement. Thoughts? Randy
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Randy,
Why don't you go up there and pop a piece out for closer inspection?
That should be close to enough insulation, though a little more wouldn't hurt. I would think there might be some major bypass for hot air that you aren't seeing. Recessed cans, maybe? Vent stacks with big gaps around them? A partition wall with no top plate? Tray ceiling with an unsealed soffit? Knee walls with side attics?
Steve
*There is a beaded vinyl soffit from Wolverine that doesn't look like it from the ground. Check out a supplier or maybe their site. http://www.siding.com/
*randy.. for two years now we've used Alcoa's Pro-bead..VENTED & Solid.... depending on the application... the vents are slits IN the BEAD.. here's a pic..
*Mike,How well does that stuff work? Questimating that it doesn't meet the code 1/300 - 50%low/50% high rule.(Not that I think that rule bears any relationship to how well an attic vents, but ....)
*bob, without repeating the research.. i thought it complied..especially since we use a fairly wide soffit...12" minimum..but i don't know what the net free vent/sf is...
*The soffit in my post is 16" wide but absolutely no evidence of slits in the bead and I used ladder to 2nd story to look closely. I don't like these situations especially when it appears that a basic venting tenant in this far north country (8000 heating degree days and 200+ inches of snow)has been violated. Photo Mike posted looked very similar to product used on soffit but no slits visible at site. I don't know mfg. of soffit but owner had invoice and it was referred to as "beaded porch panel" which strongly hints that it was inappropriately used as vented soffit. I mentioned Florida connection in my original post as am looking for some rationale as to why soffit would not be vented - thought perhaps it is a geographic difference that was inadvertantly "transferred" to the north country. Yes, I am looking for some reason that original contractor made decision not to vent soffit. This was high end renovation & 2 story addition for Doctor but amount of ice on home is completely out of place when compared to other homes in area. Perhaps this post would have been better under the heading "how to follow-up on contractor who blew it". Randy
*Randy,You could do this discussion board a great favor by trying your solutions to this problem in stages. Some folks here will argue that venting alone would not solve the problem, while others would say it would. Others would argue that insulation and air sealing alone would solve the problem, while others would say it wouldn't.You could start by fixing the venting. If that solves the problem, great. If not, then agressively look for air-sealing flaws and add more cellulose.Conversely, you could do the air sealing and insulation first. That's going to benefit the homeowners whether it solves the ice dams or not, because it would reduce the heating bills and lower the level of moisture getting into the roof assembly. If that solves the ice dams, great. If not, then add the venting.Personally, The issue of whether your problem roof is vented or not--which it seems not to be--is secondary, to my way of thinking. I believe there is some heat loss problem that has yet to make itself plain that is causing the ice dams in your case.I think that if the thermal envelope at the roof is properly air-sealed, and there is enough insulation, you should be able to avoid ice dams, vents or no. Witness the case of a spray-foam insulated roof, or a properly done SIP roof, neither of which are "cold", yet both of which are superior in their resistance to ice dams.What do you think? You up for a little experimenting (or should I say is your client up for it?)Steve
*Randy, there isn't a big heat source in the attic, is there? Such as a furnace? Air handler? Ductwork? Andy
*Gentlemen. See Chapter 23 Attic Ventilation in my book, Complete Building Construction, 4th Edition. Go to page 610 and read section on Soffit Vents which discusses, in detail, the cons of Vinyl soffit vents. Also discussed is the need for a balance between ridge abd soffit vents and where in the soffit to locate the soffit vents. GeneL.
*gene.. the pro-bead has about 1.7 sq.in. NFVA / sfand.. on pg. 613.. is my personal favorite for ridge vent.. Shingle VentII (by Air-Vent..now a Certainteed company )
*Sure appreciate the input. Was able to track down vinyl soffit - is "Invisibly Vented" from Certainteed with 1.1 sq. in. free air /sq. ft. Some basic calculations revealed it doesn't even meet minimum flow requirements for this attic under typical 1/300 rule. Factor in a steeply pitched roof meaning more cfof space, and a few seemingly minor problems, and end up with inadequate venting as highest on list of potential causes of only ice dams in neighborhood, in this relatively mild winter in Severe Cold country.I searched long and hard for significant point heat loss in attic but found none. Ice dams were universally common along eaves, so more evidence of generally warm space.Some espouse that a properly sealed attic with adequate insulation does not require venting. I'm having tough time buying into that offering and would sure like to see some data oriented to Severe Cold climate zone. No question in my mind that proper sealing and barrier would negate moisture entry and much heat loss (splice boxes, light fixtures)but what to do about heat which will eventually make its way through insulation? I recall reading somewhere that R value in 90+ range pretty well does away with heat loss but that very difficult (if not impossible) to attain in typical attic. I consider myself very open to new thoughts and ideas but am unwilling to be first on the block to institute. Venting may be way to make up for imperfect construction and materials or it may be answer to basic physics law - will take someone smarter than me to find answer. Geez I'm rambling this morning. Randy
*Mike. When I read your post I gasped. The first thing on page 613 is Drip-Edge Vents. I said Mike must be kidding. And then I read on and saw you meant the shingle over vents. If I have to vent the Air Vent Shingle over is also my choice. GeneLRandy. Check out Joe Lstiburek's web page http://www.buildingscience.com. He done thousands of non-vented attics. No failures so far. PS. I strongly urge you to read the Chapter on attic ventilation in my book, Complete Buidling Construction, 4th edition, published by Macmillan. GeneL.
*Thanks Gene. I have Joe L's book "Cold Climates" and am also interested in reading yours. He spends much time on vented roofs and some on well sealed "hot roofs".I know venting is often (always ???)used to counter inadequate sealing and poor insulation as have seen many homes with 6" attic insulation with mucho venting and no ice dams (these are often somewhat comic situations where 'Energy Advisor' from natural gas company evaluates insulation, calls it good, then owner springs for more venting to rid attic of heat. Something to do with circular logic I guess - but that's another subject). Randy
*Steve: You may some good points and I note that the gauntlet has been thrown down (so to speak). Typically though I do the experimenting on my own home. Some successes, alas, also some failures.Randy