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Old 06-03-2006, 07:27 PM   #1
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Fibreglass Okay On Side?


Would fibreglass insulation be less effective if installed between roof trusses with its edge facing the room and the cold side vs. the normal way of the flat face facing inside and outside? I'd like to do this because I have trusses on 1 foot centers and 2 pieces of R20 would fit nicely between them. I would cut a 23 inch batt down the middle giving me 2 pieces 11.5 inches wide. Installed "edgewise" that would give me about R42...with very little waste (the motiviation for doing this edgewise thing). Any thoughts?

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Old 06-03-2006, 07:39 PM   #2
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Fibreglass Okay On Side?


Why not take the cut pieces and install them conventionally, kraft side down? The R value you are seeking won't really happen, especially since the truss bottom chords will still be exposed. The best solution is to blow cellulose insulation as deep as you can handle...thoery behind this is you only pay for insulation once.

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Old 06-03-2006, 07:45 PM   #3
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Fibreglass Okay On Side?


Actually, I have high heel open web style trusses and the fibreglass has no kraft paper. I am putting white styrofoam inside the webs...so for ease (2 thinknesses fit perfectly) and less waste, I want to put the fibreglass in sideways. Sorry, I forgot to mention this is a 45 degree cathedral ceiling...so "blown in" would "roll out". Thanks for the reply.
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Old 06-03-2006, 10:02 PM   #4
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Fibreglass Okay On Side?


Works for me..I would still lay it down, there has to be a barrier of some sort, and laying R20 down, 2 thick, gives you the same as on edge, with some vapor stop.
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Old 06-03-2006, 10:07 PM   #5
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Fibreglass Okay On Side?


Vapor barrier is going on after the fibreglass is in. I was just wondering if fibreglass was less effective if installed edgewise, due to the way it is made. I want to use it on edge because in my situation it will be easier and make less waste, but I don't want to do it and then find out I've reduced my R-value. There is no barrier on the batts that I have here in Canada, so poly goes on the walls and ceiling after the insulation is in.
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Old 06-04-2006, 11:05 PM   #6
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Fibreglass Okay On Side?


A vapor barrier is not required if the 'attic' is ventilated. (At least under International Resdiential Code. Canadian code may be different.)

You could simply 'fold' 24" wide fiberglass in half and install it between the joists without cutting and achieve the effect you desire.

Otherwise the 'orientation' of the fiberglass does not matter. Density is what determines R value.

The thicker and denser the better the R value and insulating capacity.

Last edited by manhattan42; 06-04-2006 at 11:08 PM.
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Old 06-05-2006, 05:53 AM   #7
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Fibreglass Okay On Side?


Thanks manhattan42...yes, code does require vapour barrier here in Canada. I don't think I will fold the batts because this will partially compress them...but cutting them in half is no problem.
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Old 06-05-2006, 07:58 AM   #8
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Fibreglass Okay On Side?


There should be an 800 phone number on the label/package for the insulation. I would contact the manufacturer and ask. I would say that it should be acceptable to lay the insulation on it's side but insulation seems to have layers from top to bottom. It may have better insulating value (R) if it is layed down the normal way. But the R value is determined by the thickness.:confused:
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Old 06-06-2006, 12:16 AM   #9
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Fibreglass Okay On Side?


Interesting question, I have wondered this myself on occasion when installing ins. but never got around to asking the question. May I ask you to tell us what you find out if you talk to the manufacturer? Thanks.
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Old 06-06-2006, 06:59 AM   #10
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Fibreglass Okay On Side?


Talked to manufacurer's rep, who checked with others in the company to make sure. Like manhattan42 said, it's the thickness, not the fibre alignment, that determines the R-value...so no problem using it this way as long as the fit in the cavity is not loose. I have half the room done and the only problem I have encountered is with batts that aren't "puffing up" well (end pieces). I'm putting those aside for conventional use. Thanks everyone!!

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