Sealed Rigid Insulation + Vapour Barrier?

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andrewmark
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Sealed Rigid Insulation + Vapour Barrier?

Post by andrewmark » Wed Apr 03, 2019 7:02 am

Hi Shannon,
I'm doing a legal accessory suite in a basement and was just given the gears during an insulation inspection for having sealed rigid r5 insulation boards directly on the foundation wall, followed by batt insulation, with a vapour barrier (just like your video).

The inspector says that I've now created 2 barriers which can trap/create moisture in between the barriers and might require me to take the batts out to remove the tape on the seams.

I'm in St. Catharines, ON, Canada.
Thank you in advance

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Shannon
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Re: Sealed Rigid Insulation + Vapour Barrier?

Post by Shannon » Wed Apr 03, 2019 7:48 am

Well that is why I recommend checking your local rules before proceeding with projects because not all areas allow it. Generally using R5 is never a problem it is usually when you use 2" foam that inspector will get worried in some climates. Options may be to remove the interior vapour barrier completely or to remove it and install a newer more advanced type that changes how it works as conditions in the wall and home change. Whatever your local inspector asked you to do really.
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andrewmark
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Re: Sealed Rigid Insulation + Vapour Barrier?

Post by andrewmark » Wed Apr 03, 2019 7:59 am

Thanks for the quick reply Shannon!
I understand checking with the local building code, that's why I hired a BCIN to do the drawings for the city.

But doesn't he inspector actually make sense here?! You are creating 2 vapour barriers on the cold and warm side which WILL trap the moisture in between? I imagine that would be a bad thing no?

Would love to know what you think of this!

magambo
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Re: Sealed Rigid Insulation + Vapour Barrier?

Post by magambo » Wed Apr 03, 2019 9:29 am

doing the same would love to know as I have used 2" foam

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Shannon
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Re: Sealed Rigid Insulation + Vapour Barrier?

Post by Shannon » Wed Apr 03, 2019 9:30 am

So the rating that measures how quickly/easily moisture moves through a product is "Perms" The lower the number the "tighter" it is and the slower moisture can move through it. The idea with a wall assembly is that you know it will get some moisture so you want it to get out faster then it gets in. Warm air usually carries more moisture so generally in Canada and northern US our homes are warmer inside then outside most of the year and the moisture that travels in that warm interior air and gets through the wall surface will condense on cooler surfaces like the rigid foam or concrete wall certain times of the year. Our homes here are generally designed to dry from inside out. Your poly vapour barrier has a perm rating of .06 the 1" XPS insulation has a perm rating of 1.1. So you can see that the foam has 18x more ability to allow the moisture in the wall out. So yes there can be a few weeks each year where the opposite may happen, warmer air from outside is moving from the exterior into the interior where we have the air conditioning on and maybe condensing on the poly or foam but for the most part here it is limited amount of time and it will tryout as the season changes again.
One important thing to note here is this system works at its absolute best when you standard vapour barrier s are sealed as best as possible and as little air transfer into the wall cavity is allowed because this is where the most moisture travels is in warm air.
This subject is debated a lot and there is no perfect answer for every area but this is the general idea . You can also read this info here as well:http://www.foamular.com/assets/0/144/17 ... 5090ec.pdf
Just to keep it more confusing I will add this for the argument to the other side of the fence:https://www.youtube.com/watch?v=kwn0Vjw_ji0

Other alternatives now are the hybrid air/vapor barriers that can change and adapt to the conditions they are facing. Don't ask me how that works but they have figured out how to do that.
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magambo
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Re: Sealed Rigid Insulation + Vapour Barrier?

Post by magambo » Wed Apr 03, 2019 9:57 am

Thanks for the explanation and the video link it looks like it is best to use the foam board and bat so dont understand why the inspector would say otherwise.
I have installed the foam and now going to install the bat and cover with poly.
Wanted to ask a question I have made the heating duct come down. Would I cover the duct with poly as I see the metal gets hot and was just worried that the poly may melt if it touches the duct
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Shannon
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Re: Sealed Rigid Insulation + Vapour Barrier?

Post by Shannon » Wed Apr 03, 2019 4:12 pm

The poly will not melt against the heat run.
If you have not installed you poly you may want to go with the new Hybrid type. Will inspector pass the install?
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magambo
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Re: Sealed Rigid Insulation + Vapour Barrier?

Post by magambo » Thu Apr 04, 2019 9:16 am

Thanks not sure but a friend advised that I should bring the heating vent towards floor instead of leaving it up in the ceiling does that make any difference. if the heating vent is in the ceiling or lowered towards the ground.

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Re: Sealed Rigid Insulation + Vapour Barrier?

Post by Shannon » Thu Apr 04, 2019 8:07 pm

Heat naturally rises so placing them at the floor may help to heat the room from bottom to top better?
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