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I’m getting ready to insulate the attic space over my woodworking shop and I’m wondering what type of insulation ( blown in) to use. Any adavantages of using one over the other? TIA.
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You can search this forum for your answer and a lot of good discussion, but to sum it up cellulose is allmost allways better.
*Virgil,I just finished reading the insulation chapter in Gene's book Complete Building Construction. In it, he presents the results of testing various types of insulation in various indoor/outdoor climatic conditions. They noticed that blown in fiberglass loses up to 50% of it's R value at cold temps. This is caused by convection currents within the fiberglass. The temperature at which convection occured was around 50 degrees F. At 10 degrees F the University of Illinois recorded a 50% loss of R value in 14 inches of Certainteed's INSUL-SPRAY III. "But loss of R value was not brand specific" the report states.The drop in R value occurs at around 30 degrees F and gets big at 10 degrees F. If you live in Florida this probably won't be a problem for you. (and if it ever is, then it'll be the least of your problems. Cellulose was subjected to the exact same test and no loss in R value was observed. Cellulose insulation settles over time though, so it too loses R value. But it loses a smaller percentage, and if you blow in extra initially, you can count on your expected R value after settling. Cellulose will settle 25%, so blow in 125% of what the R value says to blow in. For example, if 11" = R-40, blow in 14 inches. The only down side is that you'll have incredible insulation at first then only excellent insulation.Cellulose's bum rap comes from fire hazzards. Cellulose manufacturers treat their products with fire retardants such as borax and boric acid in an attempt to elimenate this danger.Well here's a little story for y'all.Happened not a month and a half ago.I had built this addition. Onto the back corner of a house. There was an exterior spotlight out there on that corner. The electricians came out before I had the footings dug out to disconnect some underground wires leading to a former pool and sprinkler system. They never did shut off that spotlight. We demo-ed the roof eave and left the light tacked to the knee wall by a piece of soffit. Anyway, that light stayed tacked to that knee wall while we framed the walls and roof and hung rock and installed trim till we finally blew in the insulation. Since the electricians had a bunch of wires stubbed out, we figured they's remove the light when they came back to hook up the attic lights. Somehow it got dislodged from thwe kneewall and someone inside turned the (supposedly dead) switch "on" and never turned it off. The spotlight was on in the attic. We had installed some OSB panels in the attic after insulating. The spotlight was laying on one of them.And it was on.It burned it's way through the OSB and into the cellulose insulation. where it continued to stay on till I sent the rookie up there to tidy up the place. He was pretty white faced when he told me what I was going to find when I climbed up that ladder.I just about puked when I saw it.Thank God that the cellulose is really fire proof. There was a nice family with a grandmother and two children living there.I still feel like puking when I think about it...Go with Cellulose, blow it thick. Compared to Fiberglass, it's more safe for the installer too. By a long shot.Dan
*I used Cellulose in my cabin. Place where I bought it also provided a free blower. Did it myself. Big mistake. The stuff settled quite a bit. It also drifted away from the eaves a bit. I am using Cellulose in my new house. This time I am having the job done by professionals. They use a product that is blown in damp and sets up. Not hard but resistant to drifting and settling. First chance I get I am going to have the cabin done again - the right way.
*Well I've used both and have to say it depends on where you live and the building site. The biggest heat loss is through air infiltration so be VERY sure you have that taken care of by sealing EVERY opening. Then find out what works best in your climate. Use that.
*OK, This ought to put some fuel on the fire!A few days ago I talked to an insulation mechanic who had just blown a attic with cels. I asked him "Why not cellulose"?He said - "I've been doing insulation for 20 years. We used to use cellulose, but we found that it would rot if exposed to any repetitive moisture."OK, perhaps... Now here comes the good part:He says: "We also found that the fire retardant chemicals that were sprayed on the cells lost their effectiveness over a period of years. Had several severe house fires where cells was ignited by an electrical spark. We don't use cells any more".Anyone got some 10 or 20 yr old cells they want to try burning?Well there it is - unsubstantiated, but from what appears to be a good source??
*Matt G. First forgive the nit picking. If the insulation contractor had just "blown a attic with cels," why did you ask him "Why not with cellulose?" Are not cels and cellulose the same thing? The cellulose contractor's comments about the negative qualities of cellulose are interesting. But he gives no information that allows us to evaluate his reasons. I did note your unsubstantiated. How does anyone know if the cellulose was fire retardant treated, or what kind of retardant was used? And so on. Fiberglass is not immume to fire; it may not burn but is does melt, GeneL.
*I worked for RI Energy in the 80's and "60 Minutes" had just cranked up that old urban mythology about cellulose insulation being a fire hazard. So my boss used to go to the home shows and put a handful of cellulose in his hand and a penny and then he would heat the penny with a plumbers torch until it was cherry. The cellulose wouldn't burn.Still no one bot it. so he had me build (3) 4' x 4' "houses" and we set them up in a field and insulated one with fiberglass, and one with cellulose, and one with nothing.And the cellulose won that one hands down. So I built (3) 8x8 houses and we invited all the building officials and the fire chiefs and the State Fire marshall to "the big burn".plywood walls, sheetrock finish, sheetrock ceilings (flat) Asphalt shingle roofs, and a gallon pail of paint thinner poured on the floor as an acelerant.The uninsulated was a pile of coals in an hour, the fiberglass melted, and the plate burned thru and vented the roof and it was down in two hours, and after 3 hours they put the fire out in the cellulose one , peeled the charred sheetrock off and the cellulose was just like they had installed it. A little charring on the face of the studs where they were in contact with the sheetrock.Cellulose with borax: pure fire protection.A month later we had a big fire in town, a big Victorian burned to the ground , except the kitchen that had been remodeled and the walls blown with cellulose, the studs wern't even charred.I have 18" of cellulose in my attic, I only use 'Glass when it seems appropriate, like high density in the walls, or high density in cathedral ceilings, but retro blow-in walls or attics, its cellulose for me.
*Thanks Mike, I've been trying to decide for the job I'm doing right now and you just about convinced me.
*Sorry Gene & all:I mis-typed - What I ment to say was that the insulation contractor had just blown the attic with fiberglass.
*Mike. It was good hearing from you. I well remember that demonstration, and the large timers timing the burning.It is unfortunate that cellulose still has so many myths attached to it.GeneL.
*Myths, or disinformation?Mike, why do you prefer high-density fg for cathedrals? I'm thinking of blowing in cels for a partial cathedral, using netting or Tyvek as a restraint.
*Andrew: I don't know wether its urban myth or disinformation, but the latter would assume that Owens Corning et al were buying TV ads and the cellulose mfr's weren't........nah...never happen in AMERIKAb re: Cathedral Ceilings:As to the high density batts, If I had a system of working with the same Insul sub. I might develop a method of getting cellulose in there. But , you know , you go with what works. The system we have uses Propa -vent for each bay, high density batts as much as we can get in the rafter system with the propa-vent, Then 1" foil faced foam, 6 mil vapor barrier, and then we furr the ceiling.The electrician doesn't penetrate our ceiling unless we've got some cans or recess, and I try to avoid those, he runs his wires behind the furring, and if I have a heavy fixture, or some track , we can always put a special 3/4" ply. pad where the fixture goes and pull the wire thru.I would prefer cellulose in my cathedrals, but I can't handle the extra logistics. I can supervise the batts, and if its a small job, or we're trying to meet a schedule, we'll install all of the insul. ourselves.I keep looking at the wet packs,etc, but it really screws up the schedule if you're in remodeling. And I don't like the cost of ICF's.What did I miss ?
*Mike. Why the double vapor diffusion retarders--vapor barriers? GeneL.
*I figured it was logistics, and wasn't doubting you. I have the same problem in mind...Foil foam (if taped) plus plastic does seem overkill.
*Gene: this post moved so far down I missed it,I guess the double vapor barrier answer would be:no good reason.....but:I don't trust tape & I think that gaps develop during the installation of foam, and it gets punched by hammers and nail guns, and various penetrations, I mean its a cathedral ceiling and people are either on ladders or staging and ....well , you've been there.So, I use the poly vapor barrier on the warm side of the ISO foil-faced foam, then we furr the ceiling, then the elect. can run his wires by pushing them between the back of the furring and the vapor barrier. The poly is a vapor barrier I can see and its easier to maintain the integrity,so ......I think cathedral ceilings have a larger delta-T and are more susceptible to moisture problems. I've done some extreme installations like indoor swimming pools , freshly poured slabs, high humidity in the summer near the seashore. I've gone in before the vapor barriers were installed and it was RAINING, for crying outloud. The same thing that happens in the upper atmosphere was happening in those conditions........and at a smaller rate , but more insidious, I know it happens where people can't see it occuring, when you rip open some of these roof systems you see the damage done.I think some of the Canadien sealed systems have a lot of merit, but I think I already know how to build a good vapor barrier, and how to vent a roof system, and how to vent an attic area, and I want a verifiable installation.I start to sound like some of the O.F.'s I worked with in the 70's. You, know, "don't insulate your walls, the house can't breathe", or "we don't use felt under our asphalt shingles because the shingles can't breathe". but I hope that most of what we do has some basis in home building science (oxymoron ????).b Like my Daddy used to say, if you insulate a house right, you can heat it with the energy of ten people dancing....
*Mike Smith. I appreciate your concerns. I fault you not for erring on the conservative side.I too would certinly womder about the tape longevity, but am more comfortable with it on the interior than on the exterior. I make those trades that penetrate the vapor diffusion retarders (VDR) repair them.However, I'd like to run this by you. If, IF your air retarder--usually the gypsum wall board (GWB) is free of penetrations then the holes in the ISO do not matter. If on the other hand the air retarder is full of holes than it does matter. In my houses this is no problem because the ceiling below the attic is sheet rocked before the interior partitions are installed. Thus the VDR is eliminated. GeneL.
*Gene, as I follow the concept, if you use fiberglass, you need a vapor barrier, if you use cellulose, you only need a Vapor Diffusion Retarder and I assume this is because the cellulose absorbs the moisture under heavy vapor pressure and loses it when the atmospheric conditions change ?The phrase that rises out of the mist of my memory is "hygroscopic" (sic.?) cellulose absorbs and releases moisture vapor. and Fiberglass does not, it only acts as a facilitator , as a surface for moisture vapor to condense against.So, am I following you, .....?if I switch to cellulose I can lose the vapor barrier, and if I have my usual Hybridmix (some fiberglass ) then I still need my vapor barrier.Or do I have to go back to "Air sealed houses 101"Getting ready to do a cathedral ceiling design and I want to have some fun with this one.
*Mike - forgive me for interupting - but keep in mind that most moisture that can be driven through a wall is moved by air - convection. I think I've read like 80 or 90%. The rest moves by difussion. And even poly allows some to diffuse.Couple this with the idea that a hole in the air retarder (drywall, plaster, poly, whatever) is like a hole in a container of water - all the air with all its moisture leaks out quickly - especially up high in a container like a house where the temperature differences makes it bouyant an dpush it out.Second - related but separate - the cellulose if dense packed retards air movement quite well. Fibreglass was invented as a filter and air moves through and around it quite eaisly. Thus fibreglass makes movement of moisture in the air easier - from inside to exterior (colder and therefore likely condensing) surfaces. But it also makes the movement of warm air - transferred from the back of the drywall or plaster, etc. or out through holes - to the exterior easier.This all became much clearer to me from reading in Home Energy about the air movement within walls and how even a 1/4" gap between a fibreglass blanket and the drywall can significantly lessen its effectivess. The whole point of that article was to keep the thermal insulation tight to the air barrier and to keep both continous.
*Mike. Bill Conner has pretty much answered you. The main culprit in moisture in walls and ceilings is moisture laden moving air. Stopping--very difficult- the air movement stops the moisture movement. Therefore, what is needed is an air retarder.I say retarder rather than barrier because it is extremely difficult, if not impossibler,to stop air movement. The best one can do it to slow it down , retard it. Even if I were using fiberglass (ugh) as long as my air retarder was as perfectly sealed as possible the vapor diffusion retarder is unnecessary. Cellulose is not a vapor diffusion retarder. In my MESH houses(Micro Energy System House) there is no wiring, plumbing, ductwork in exterior walls or in the ceiling below the attic--attic floor. The gypsum wall board (GWB) is thus free of penetrations except for the doors and windows (fenestration). The only penetration of the ceiling below the attic GWB is the stack vent. As noted previously, the ceiling below the attic GWB is installed first then the partitions are erected. This of course requires a trussed roof. Hope this helps. GeneL.
*We're doing the finishing touches on a new home, and still have the attic insulation to do. A couple of questions:1. We installed R13-fiberglass in the walls before the sheetrock went up. Is it possible to have the sheetrock go up first, then come back and blow insulation down into the wall cavity from the attic? Is this effective? Just a thought.2. Insulating the attic...we've got 9' ceilings everywhere except the "great room" which is vaulted.It's a 6/12 pitch that is 16' tall and spans 28'.If I go up into the attic over the 9' ceilings, it's flat, so I can see blowing cellulose in until I reach my 12" or 14" depth. I guess you just cover up the rafters? How would I walk around up there if they're covered up?Which leads me to ask about the vault. Do I just blow it in and cover everything up? Don't worry, I'll make sure to leave enough space for the soffit vent so they can breath. But I guess I'm confused about blowing in 12" when I don't have a 12" cavity to blow it into. Follow?
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I'm getting ready to insulate the attic space over my woodworking shop and I'm wondering what type of insulation ( blown in) to use. Any adavantages of using one over the other? TIA.