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Old 02-26-12, 12:48 PM   #11
herlichka
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It is actually the vapour that you want to stop: if water vapour is allowed to travel from the warm interior of your home into the insulation it will eventually reach a point where it is cool enough to condense. This condensation will eventually cause mould, mildew and will cause structural decay. This is why we install a vapour barrier on the "warm" side of the wall, and a house wrap such as Typar or Tyvec on the outside. The house wrap is an "air barrier", it prevents wind and wind driven rain from penetrating into the wall from the outside, but does allow the insulation's accumulated moisture to dissipate to the outside. Moisture can accumulate simply from the change of seasons, and the moisture content of the outside air. To deal with the moisture inside the house we must install some form of mechanical venilation, and/or a Heat Recovery Ventilator.

I have seen horrendous water damage inside the cavity of exterior walls adjacent to kitchen, bath or even laundry rooms, caused not by actual water penetration, but condensation from moisture seeping out to the cold side of the insulation. I have even seen ice in the insulation above ceiling light fixtures in the attic, from moist air traveling upward from the interior of the house through the electrical devices. Our winter temperatures in Ontario can drop to -30c or more for extended periods, so these ice deposits can become substantial in size, and when the temps rise and the ice melts the wall surfaces can be damaged, people often think that they have a leaky roof.

All for the price of a roll of plastic and a roll of tape.


Last edited by herlichka; 02-26-12 at 05:54 PM.. Reason: Afterthought
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Old 02-26-12, 10:09 PM   #12
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If you air seal and use cellulose and use a LOT of it this doesn't happen. In an R 40 wall of cellulose there is so much hygroscopic mass that it matters not at all. You obviously need to properly deal with moisture created inside by exhaust fans or HRV's or whatever.
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Old 02-27-12, 04:06 PM   #13
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I agree with herlichka about stopping moisture transmission past the interior envelope. I too have experienced moisture condensation on the inside of the exterior side of a wall, mold forming between the insulation and the OSB. Warm air readily absorbs moisture and when it finally trickled past the insulation the moisture condensed on the exterior side of the wall cavity and the colder air trickled down and out the bottom. Stopping the air flow stopped the moisture flow and consequently the condensation.

Foaming in the can should stop the moisture transmission as well as the heat shouldn't it? I don't understand how the foam can stop one without the other.

I like the idea of using the fire foam instead of regular foam, if the price the same why not? What is the difference of melting point of the two? Not that it's a big deal but it would be nice to know how much extra (if any) thermal integrity it has.

Thanks for the discussion. This is really great stuff.

I know, bad joke =)
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Old 02-29-12, 05:46 AM   #14
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Unless you are making contact with a hot pipe there is no effective difference between the resistance to heat of the two products. I'm not sure about great stuff but I assume it's about the same as regular gun foam.

About vapor barriers. It's been beaten to death for decades now. There is an overwhelming body of empirical evidence showing that when cellulose is used a vapor barrier can actually be hazardous. There's no way to make it air tight so if you do have an overly moist house all of that water will seek out the seams and you will have a moisture problem in those spots. There are many reasons to avoid vapor barriers. I didn't think anyone actually used them any more. Maybe the people who install fiber glass in new construction use it.
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Old 02-29-12, 06:46 AM   #15
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The Ontario Building Code, which is virtually identical to every Provincial and Territorial code in Canada, requires a Vapour Barrier over every moisture permeable insulation product in exterior walls. A vapour Barrier has to be there in one form or another.

Most simpler installations consist of 6mil poly over fibreglass, mineral fibre, cellulose, and so on. These products are marketed under numerous names.

Where people are getting creative, and staying legal, is with the use of Closed Cell spray insulation. Closed cell insulation is considered an acceptable vapour barrier, in that no additional barrier needs to be installed. The Code allows the Vapour Barrier to be located up to 1/3 of the way into the insulation, as measured by R-value, from the warm side. This means that you can spray the stud cavities part way, install your wiring and plumbing, and finish with a thin layer of vapour permeable insulation and drywall. This approach can be varied by several diferent ideas, the wall can be strapped, or a second stud wall can be built.

Another product that can be used as a Vapour Barrier is closed cell rigid styrofoam board. Again, there are numerous names attached to these products. Insulation board can be installed on the inside, under your drywall. This requires extreme attention to the details, and every joint must be properly sealed, as per the manufacturers instructions.

Open cell spray insulations must be treated as vapour permeable, these products can actually become waterlogged if installed incorrectly.

And finally, beware of the possibility of accidentally installing a second vapour barrier. For instance, the example of the 1/3 rule where there is a layer of moisture permeable insulation overclosed cell spray. Avoid the temptation (if you are so inclined) to install a layer of 6mil poly, or foil backed drywall. You can trap moisture in between.

I am a firm believer in a properly installed vapour barrier. I do renovation and home repairs, so I often get to dig into walls and see what's happening in there. I price my work slightly higher when I suspect there is no, or a poorly installed vapour barrier. I know I will likely find mould, and people hate mould. In new construction, in my opinion, the proper installation of the vapour barrier is one of the steps that produces the highest returns on investment

Last edited by herlichka; 02-29-12 at 06:50 AM..
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Old 05-03-12, 06:40 PM   #16
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What you can do if you have access to attic space above lights is to make a box out of 1/2" drywall to fit OVER the high hat lighting fixture. Use the fireproof spray foam to seal the box airtight to the underside of the ceiling. This will allow you to insulate over/around the box
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Old 05-07-12, 07:57 AM   #17
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I'd LED the can lights, and foam the bejesus on top of it with fire resistant greatstuff. If they last around 15 years, I'd figure incandescents will be pretty dead by then anyways. The LED lumens/watt do tend to be dissapointing most of the time, but imo .they compensate by being an inherently directional lightsource.
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Old 05-07-12, 09:53 AM   #18
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Originally Posted by menaus2 View Post
I'd LED the can lights, and foam the bejesus on top of it with fire resistant greatstuff.

I totally agree with putting in LED's. The problem is if someone else comes along in the future and changes out to incandescents & the light can gets insulated over, you will have the potential for trouble because of heat build up. Heat build up will also reduce the life span of your lamp.

The tried & tested way(and only approved methodology in Pennsylvania) is the 1/2" drywall box method explained previously. It allows enough space to not have heat build up problems.
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Old 05-15-12, 08:58 PM   #19
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Yes LEDs have very low operating temperatures, It'd hardly heat up even if you leave it overnight as compared to incandescents

In my case. since I'm too heavy for my ceiling to support (gypsum ceiling boards) My only option was to work from below to seal it. I used transparent neutral silicone sealant (leftovers from working on car windshields). A very fine point, a steady hand and lots of patience is needed. oh and a sturdy ladder would help too

Hope this helps
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Old 05-15-22, 05:14 AM   #20
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Can you show us a photo fo how it turned out?

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