OT: open cell vs closed cell foam home insulation

Engineer or Architect's

Jim in Burlington On

>I'd get a engineer's opinion for a few hundred it's worth it. I'm not sure what the snow load is in your area but that's a pretty shallow pitched roof and adding closed cell might be to much weight. Closed cell is alot quieter that may add to your decision.The chances of closed ever leaking are very small. You could buy sheet insulation and seal it around the edges with 2 part foam you can buy in large canisters instead of small can's.

Re: OT: open cell vs closed cell foam home insulat

Barry Irby

>I am not an Engineer, but I do have a degree in Building Construction from VA Tech and years of experience as a Builder and Home Inspector.

I have seen a number of cathedral ceilings similar to yours fail here in VA. I am assuming the Madison you speak of is in Wisconsin.

I would suggest one of three things. 1. Leave it the way it is. It has apparently functioned for over forty years and has not rotted itself to pieces.

2. Increase the thickness of the cavities and add more batt insulation like fiberglass. The cavities should be about twelve inches deep and have about ten or more inches of FG. Try for and R-38 or more, and do not compress the batts. Do anything you can to eliminate or reduce air and vapor flow into the cavities from the "living" side but leave the outdoor side vented or open or "looser" to let the moisture out. This might include upgrading any recessed or can lights to sealed units that do not exhaust moisture laden air and heat into the cavities. You could also paint the ceiling with enamel or "vapor barrier" paints.

3. Fill the cavities with Icynene foam. (Google "icynene foam insulation" to find out more and get an installer) Eliminate any ventilation. This is a sprayed in foam that completely fills the cavities. This approach eliminates the moisture/ventilation/air flow issues. Be careful about any can lights and replace them with ones rated to be buried in foam.

There is a possible alternative which is to spray the ceiling (assuming you are working from the top side) with about a half inch of urethane foam to completely seal the cavities and then fill them with fiberglass batts and install the roof, eliminating the ventilation.

I am slightly skeptical of installing "Planks" of foam either open cell or closed. If they are fitted poorly there may be enough airflow into and through the cavities to start condensation issues. The framing and sheathing could rot or delaminate. If I went this way I would want to seal the ceiling and light fixtures very carefully as mentioned above.

There are other issues. (this is a case of "if you change one thing, you change everything). Just changing the color or thickness of the shingles might make enough difference to start condensation problems you did not have before. If the cavities start to sweat, you won't know until it is too late and then your only alternative will be to tear it all out and start over.

Most asphalt roofing shingles are "rated" of installation at 4 in 12 or greater slope. 3 in 12 is marginal and you should look into a "low slope application". Go to your shingle manufacture's web site or to an industry site get the guide lines. It should call for double felt (18" exposure) and reducing the exposure of the shingle down to abut three inches to give you triple coverage. You also want to demand "Ice and Water Shield" along the eaves (3') and maybe a foot wide strip up the rakes.

And one more thing, Be extremely careful about removing the existing insulation. There were version of insulation that contained a rare form of asbestos. One of the asbestos tainted products that can be deadly with a minimal exposure. It was sold by the WR Grace Company. Not at all sure you have it, but if you do, treat it like poison.

Re: OT: open cell vs closed cell foam home insulat

Bob Fawcett

>I second the Icynene.

I have it sprayed on the under side of my roof. I would say it is about 5" thick. We don't get that cold here, but we do have summer heat. The inside of my attic is almost as comfortable as the inside of my house all summer.

Re: OT: open cell vs closed cell foam home insulat

Tony - Memphis

>Not much real cold weather here either. I did some research before we built and found a reasonable solution for our area was to spray foam as a sealant, then add the regular fiberglass bats as usual. I can't say for sure that it has made a big difference, but it wasn't that expensive and at least I know things are sealed. Now, if only we had spent more on windows! Next time....

Good luck with your project. One issue with open cell foam that concerns me in my business is moisture. Sometimes you want it to flow through, but sometimes you don't! And you normally don't want it to hold moisture.

Tony

Re: OT: open cell vs closed cell foam home insulat

Bill White

>Don't forget to consider the tax allowances that are available for retrofitting for energy savings. It'll help some.

Bill

Eliminate roof ventilation???????

Tim Greif - West of Chicago

>Barry, I'm probably wrong here, but I was always under the impression that you have to have inside roof ventilation to help cool the shingles, or their life is substantially reduced. I understand that sealing it up eliminated moisture and condensation issues with the wood roof sheathing, but aren't we still concerned with heat issues on the shingles? This same issue is often used as a recommendation to NOT put a second layer of shingles on a house since the double layer can't cool as well as a single layer, and the life of the second layer of shingles is substantially less than if it were applied by itself. Not trying to start an argument. I just want to understand this.

Re: Eliminate roof ventilation???????

Barry Irby

>Tom, unfortunately the answer to any roof ventilation question is yes, no, well it depends, maybe, uhhh wait and see. The truth is that we really don't know as much as we should. And there has not been very much long term legitimate research as you would think. Much of what we think we know is based on the idea that we have always done it that way so it must be right.

There are two arguments about attic ventilation. Let the heat out to avoid cooking the shingles, and let the moisture out to avoid condensation/delaminating/rot.

This is very complex and would take several semesters in college to catch everyone up, so let me see if I can give the Readers Digest version.

There is very little indication that ventilating the attic will cool the shingles. The sun radiates the outer surface and they heat up, in turn heat the sheeting through conduction. Some of the heat in the sheeting radiates to any cooler surface it can "see" and some is conducted to the air. If the vents are high and low the air may rise along the bottom of the sheeting and pass out the top, taking some hat with it, but not a lot. If the vents are in the ends the air in the rafter spaces pools up against the sheeting and tends to cling there actually insulating the sheeting. So the only ventilation that stands a chance is the ridge and soffit vents. The others cause the air to flow longwise of the building and leave the air in the rafter spaces pretty much undisturbed.

I can go on for hours about attic fans, but will shorten it to say that studies indicate they would have to move 2 cfm per square foot of ceiling area and have about a 2HP motor. Such fans would be noisy and expensive to operate, negating any savings and driving the occupants nuts. Thus, they are small and underpowered to make them invisible on the electric bill and just audible enough to trick the owner into a sense of satisfaction, but completely ineffective. I know this to be true from observation. I'm a home inspector (over 20 years) and I see no evidence roofs with fans last any longer that those without.

The concept of ventilation assumes it is beneficial. Moving moisture and heat out. Fans can be controlled on thermostats and we can set them to run when it is hotter in the attic that outside (good) and we can design attics to self vent because it is hotter inside that out (good), but humidity gives us fits. How do we control ventilation relative to humidity? If we sue a humidity sensor, what would it do? When its humid inside the attic, isn't it likely to humid outside as well? Think of a rainy day. Not a good time to be venting. Would not want warm afternoon air passing through an attic that had snow cover.

SIPs or Structural Insulated Panels have brought this to a head. These are panels that have 2 x 4's or 2 x 6's for ribs and OSB on both sides and are "blown" full of insulation. These are sometimes used for a roof deck and created the roof and ceiling in a single piece. The roofing industry at first refused to offer any warranty on shingle installed over an insulated deck. Pressure form the industry demanded better treatment of this up and coming product. I have heard they are offering a half warranty (15 years rather than 30) The truth is they had no idea how the products would act over an insulated deck. I gather most of them are doing well and may last as long as their brothers on vented decks, but only time will tell.

So, If you could construct a roof with insulation that was so perfectly filled with non-hygroscopic insulation (does not absorb water) that was vapor proof (water vapor is very different than liquid water)and there were no air passages to allow moisture laden air to pass through, it is very unlikely you would have a moisture/condensation/rot problem.

Or you could build one you let "breath" to the outside. Looser on the outer side than the inner side and let the vapor escape. This is the traditional method. If your house has and air change an hour your only problem is likely to be your heat bill. If you get it below one every three hours you may start to have problems.

We also don't see a lot of evidence second layer roofing lasts much less than the first layer. This may have been true or "truer" when the shingles had felt or paper backing, but now that most of them have fiberglass in them, it is less true. Perhaps ten percent. It would be worth ten percent to cut the energy bills as much as a well done roof deck would cut it.

As An aside, we recently looked into a roof that had 50 year or lifetime shingles. They appeared to be identical in construction to the thirty year ones. The manufacturer was unwilling to explain how to visually tell the difference or to send a field rep. We are now suspicious they are identical, you just pay twice as much and they take the chance YOU won't live another thirty years.

Re: OT: open cell vs closed cell foam home insulat

Geoff in Madison

>Thanks Barry and everyone else.

I was leaning to the spray-in open cell foam and you are helping to keep pushing we that direction (Icynene is open cell). Locally Icynene is $0.50/ bdf. Another option is made by Bio-based insulation which derives their base material out of soy rather than petroleum.

Also, Tim, there are Department of Energy studies throwing the need for roof ventilation into question. Barry is right, you could fill several books on the roof ventilation question.

Re: OT: open cell vs closed cell foam home insulat

Barry Irby

>If we laid all the "experts" on ventilation end to end, they still woudl not reach a conclusion.

In fact, the researchers refufe to admit they understand any of it. If they understook it, the research would be over.

That's Why

Mark Mandell - Gone Round In Jersey

>We call it "practicing" law. If I had it all down, I'd be a judge, right?

What worries me, though, is people who "practice" medicine. I mean, like, "practice" on somebody else, then let me know when you can do it right and I'll be back.

|;-}}}}

Obbliusly, Aye neid a spell sheckur.

Barry Irby

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