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"I have learned so much thanks to the searchable articles on the FHB website. I can confidently say that I expect to be a life-long subscriber." - M.K.
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Ron, I'm guessing that we confused you. What's your question?
Andy
*Vaulted Ceiling Insulation/Ventilation Quandry.I'm in way north Michigan and have been asked to address the formation of ice dams and water back-up on a vaulted roof of a two year old home (built by someone else). Rafters are 2x10, packed with fiberglass, no venting channels, ceiling is painted drywall, no plastic vapor barrier, condensation is occurring in cavity at plywood sheathing. Though I have been following the various threads on vaulted ceilings I keep coming back to tried and true method for addressing moisture and ice dams - remove drywall and insulation, provide full length vent channels along with ridge and soffit venting, re-install insulation along with poly vapor barrier and drywall. I'd like to give owner a couple proven options. It is obvious from the many comments that there may be other methods available. Your comments will be greatly appreciated.
*randy.. you piggybacked on another thread...but we always used your fix.. and it worked..today.. i'd still vent, but we'd use cellulose instead of the fiberglass/ poly vapor barrier...if you vent , it has to be continuous from soffit to ridge...and ron.. that's a good question...but could you elaborate?
*Mike: Thanks for response. My intention was to start a new thread - I'm blaming it on this new and faster computer which allows me to get in trouble at breakneck speed. Randy
*Randy and Mike. Why not get rid of the warm moist air leaking into the space? GeneL
*gene, not to beat a dead horse... but i don't have any air leaking into the space...
*Randy,I'm in mid north Mich (between 44 and 45th parallel) and have to face the cathedral ceiling issue. I have 18" deep TGI 12" oc holding up a nearly flat roof (1/4" fall per foot) covered with Duralast roofing. Parapets and roof drains. I'm putting on EIFS siding in the spring and do not want to have vents at the roof line if I can avoid it. My architect passed on something called "The Cellulose Insulation Journal" by Applegate Industries. It has a very interesting article on cathedral ceilings, with lots of studies cited."Our recommendation for the installation of (cellulose insulation) is not to have an air space above the material in a cathedral ceiling application." Claims to have 40 years experience in mid-Mich. Continues:"New research in building science has confirmed that the tight blown, unventilated cathedral ceiling method is best."Also has two web addresses (which I haven't checked) http://www.ApplegateInsulation.com and http://www.ThermoCon.com 1-800-627-7536. Maybe you already have this information.
*I've tried to ask a question before--but they don't appear. What am I doing wrong?I want to know how one can establish that a company blowing in cellulose has the blower capacity to "dense-pack?" I ask them if they do, and they all say "sure, lady." But when I examined a rafter space in a house I was renovating, the insulation wasn't packed at all.
*harriet, most machines can achieve the required density... it mostly depends on the installer..also.. you can get dens-pak in a wall.. but it is harder to get it in a rafter bay.. unless the bay is sealed so the material has something to pack against..if the rafter bay was open at one end, it's almost impossible to get packing.....ask you installer how he defines dens-pak and what he does differently from normal installs to get it... if he doesn't have an answer, then he isn't doing dens-pak
*I have used the non-vented dense pack cells construction method in all of the cathedral ceilings of the custom homes I have built for the last 16 years. I have experienced no problems. Stop all air leakage, control and condition air flow, and ventilate.
*Bob,What is the climate you are building in? How many homes have you done this way?Steve
*Steve, I build in the Chicago area. It gets a little cold around here this time of year. I would estimate over 16 years I probably have built 100 to 125 homes having cathedral ceilings insulated with this method.
*Bob, could you tell me how you got past your building inspector? Mine in Salem, VA, is saying he'd rather we had an R7 attic roof with ventilation than R40 with none. (As we have no soffits, it's a moot question.) Fred Lugano is wonderful help with theory and procedure--but that don't get us past the ogre at the bridge.
*Hi Harriet -- Been reading your indexes for years. If your building inspector doesn't want to sign off on this code variance, get a PE to stamp your plans. Andy
*In my opinion, a cathedral ceiling is nothing more than a leaning wall. I treat it the same way I do a wall. I seal it completely and dense pack it. I have never had a problem with this method. I have been doing this since 1982.
*hey , g.lalonde.. did i tell you how much fun we had with your "regal" wall ?great technique..thanks
*Mike, Glad to hear things worked out for you....but was it REALLY fun?? I bet you learned a few things along the way too! By the way, I'm on my third new Hitachi gun since listening to your sales pitch. They really are Grrrreat!
*g. it was really FUN..my building inspector loves cellulose and he was really impressed with the regalwall... we got about 3.5 lb/cf in the walls...tried pl200, pl400 & pl urethane... decided that pl 200 was the best for gluing the mesh.. been using a borrowed machine.. think i'll buy a Krendl 250A with a 309 blower...any advice ?
*Yup, PL 200 is the best stuff...Sorry I can't give you any advice on the other blowers. All we use are the Predators..without a doubt, the best machine I have ever used. Apparently Regal doesn't supply products in your beautiful part of the country. We are insulating a 9000 sq.ft home right now. (Around a 1000 bags) This is an unusually large job for us. These machines chew up a bag in about a minute or less so they keep you running. As I said before, I use a 2" hose right out of the machine to throttle it down a little when blowing walls with the open mesh and get almost exactly 4# fill. This is just the characteristic of that particular machine set up the way I have it. I find this to be the fastest, easiest and most consistent way to do it. I would buy the most powerful machine you can find. You can always adapt if for jobs that require less output (blowing existing walls for instance) and then turn it loose to fill the attics.
*g. who makes the Predator.. and are there different models ?... is it a thru-the-blower or an air gate by-pass?
*You can contact Regal for the latest info on that machine. I'm not aware of any different models. The ones we use are thru the blower types. These are the ones that don't work well with any other cellulose except Regal's. I think you have their number and web site don't you? If not, I'll find it for you.
*;-)brian
*Dense Pack cellulose sounds like excellent method for cathedral ceilings and should be considerably less expensive than a cold roof but I don't know what geographic area most comments are coming from. Anyone using method in severe cold region with significant snow fall - a line that includes Upper Peninsula of Michigan, north half of Wisconsin and north (8000 heating degree days or greater). My concern is ice dams and water back-up caused by heat loss. Vaulted roofs are notorious for this up hereso would like to hear experience from that area and also rafter depth/R- value being attained. None of my references, including Joseph Lstiburek's Builder's Guide To Cold Climates, mention the method though I know it has been used for years in some regions. Method will be very hard to sell to inspectors without something in writing, preferably by PE. Thanks, Randy
*don't know..6000 degree days here... but Canada has a LOT of cold climate research.. keep digging
*I use a Krendl 250 with a 309 blower, but have never been able to get over 3 lbs, usually just above 2.5. I think next time I'll use the same machine but rent another blower motor and do an in-line set up to increase pressure. Krendl has a nice schematic of this set-up on their web site: http://www.krendlmachine.com/309%20blower%20back.htmlGio RobsonprairieHOUSE Restoration and Development
*I have some questions/concerns about the use of dense-packed cellulose (DPC) in our climatic region (mountainous southwestern Virginia). It seems that many of the successful uses of DPC in unvented cathedral ceilings have occurred in northern areas. I wonder about the applicability of this insulation method in our area. I know that humidity can be a problem here and that there have been some rather severe problems with mold forming in "wet" buildings. Our temperatures and dew points swing wildly here. I also wonder how you prevent the DPC from absorbing moisture. I can see how one could use vapor barriers to prevent most infiltration but what about sealing the soffit areas. Do those that advocate this method dense pack the soffit area also or seal the space between the rafters at the bottom?Also, what happens if the roof itself leaks but not so much that it makes it to the ceiling? It seems that the DPC's water absorbing qualities could allow large amounts of water to collect between the vapor barrier (behind the ceiling) and roof decking. Another issue: what about he added weight of the DPC. What I've read seems to indicated that it must be much heavier than fiberglass batting as installed. Is this significant enough that the roof must be designed stronger?And the last issue: doesn't the nature of this type of insulation make proper DPC installation (no voids) extremely critical. How can anyone be sure without x-ray vision that voids aren't inadvertently produced despite the best efforts of a competent installer? I can visualize nails protruding through roof decking and large "splinters" hanging from OSB decking preventing complete intimate contact between insulation and roof.Thanks, Andy
*first andy, you have to control the moisture.. if it is normal ambient humidity.. it will be absorbed & released.. if it is excessive .. you are going to have problems no matter what the strategy..if the roof leaks.. you're screwed.. but you are with fiberglass too.. it's just a factor of two or three instead of one.. ie: the more insulation you have in the system.. if it gets wet, the more problem you have to clean up..don't let the roof leak!the added weight? 3 lb/cf is not excessive and well within the design limits of ceiling structuresand last... blow some cells for yourself , or observe a lot of it being blown.. it's a pretty forgiving medium.. and flows quite well.. some installations lend themselves to a higher success rate than others.. try to design it into your building systemb but hey, whadda i no ?
*Andy,I'm guessing that your climate is mixed. That is to say that you must heat in the winter and cool in the summer. If that's the case then you are best off with no vapor barrier at all, since it'll be on the wrong side half of the time. DP cells is particularly suited to the absence of a vapor barrier because its high resistance to airflow keeps moisture migration via air movement to a minimum, yet it allows the wall to dry to whatever side is lower in humidity.Weight is not an issue. Leaks are an issue, but as mike says they will be regardless of your inulation choice.Steve
*No interior vapor barriers. The DP is the air barrier. No air moving is key.near the stream,aj
*Andy,PS: I wouldn't pack the soffits. Make a little dam at the end of the rafter bays out of rigid foam. Makes future repairs less messy, plus that's a high probability area for moisture intrusion. Steve
*All:Somehow I'm having trouble with the idea of what basically amounts to an organic sponge (DPC) being used as a vapor barrier. Would using a vapor barrier on either side of the DPC (back of the ceiling material and underneath the roof decking) be of benefit or cause any problems? Steve:Great solution on the sealing at the rafter bays using the foam blocks. Do you know if this is commonly done? Thanks, Andy
*Andy, the theory is that 99% of moisture moving into a framing cavity such as a wall or ceiling is carried there by air movement. The remaining bit gets there by vapor diffusion, and is in most cases easily handled by building structures that can dry. DP cellulose blocks air movement, and consequently also blocks the vast majority of moisture. Adding a vapor barrier to the equation won't stop much water vapor, and can prevent liquid water which has condensed in the cavity from escaping. So goes the theory. I think, however, that the further north you go, the greater the winter vapor drive. By the time you get to the colder bits of Canada, vapor barriers may begin to make sense.I've heard some building scientists say that interior vapor barriers should never be installed in houses that will be air conditioned for even a week or two a year.
*Andy A,The cells are not an effective vapor barrier, as Andy E explains. They are an air barrier. The main question in my mind is how much of an air barrier are they? Joe Lstiburek says they are not a complete air barrier and that therefore, in climates that are strictly heating or strictly cooling--where you have a constant vapor drive in only one direction--you have the option of putting in a seperate vapor barrier, such as Poly sheating on the warm side of the wall. But as soon as you are dealing with a mixed climate--one that has both heating and cooling needs, you need to ditch the vapor barrier altogether, since it will be on the wrong side of the wall part of the time. In those instances I would think Cellulose would really shine, since it will stop air movement better than fiberglass, thereby reducing the moisture loading of the wall, yet it will not create a condensing surface like a vapor barrier on the wrong side of the wall will. Plus it will allow what moisture loading does occur to dry to either side of the wall at any given time.I still lean towards thinking that you are better off, even in full-time heating or full-time cooling climates to forego the poly to allow the wall to dry to either side. I think in the long run the gains you get by allowing the wall to "breath" to either side via vapor diffusion (not via air movement however) outweigh the moisture loading that you may get due to vapor diffusion. But that's just a gut-level reaction, not based on any hard science. I know I'm in a tiny minority on that issue. Maybe not in very cold, very damp climates, though-- like Juneau.How's that for equivocating?Steve