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PostPosted: Mon Mar 20, 2017 7:28 am 
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Joined: Sun Jul 05, 2015 8:49 am
Posts: 11
Location: Sydney, Australia
Hi Guys

Hopefully you can offer some advice (and Stuart if you can jump in as you have in the past - it would be much appreciated)

I just need to check before i go any further in my room within a room build.

Building the inner leaf, the inner leaf ceiling joists where they tuck up between the outer leaf joists are lightly touching some of the outer leaf insulation in a couple of places. Just to clarify, there is definitely no wood to wood contact between the inner and outer leaf, just the glasswool insulation of the outer leaf touches the inner leaf ceiling joists.

Here's an image just for illustration / visualisation purposes that I "borrowed" from the internet; here they also appear to have contact between the outer leaf insulation and inner leaf joists.

Attachment:
staggered joists.gif


Is this a problem? Do I need to secure the outer leaf insulation with extra insulation straps so there is a definite air gap, or is a light touch between outer leaf glasswool and inner leaf ceiling joists not a big issue?

Thanks for you advice everyone :-D

David


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PostPosted: Mon Mar 20, 2017 9:05 am 
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Joined: Mon Jan 05, 2015 11:47 am
Posts: 50
Location: Apollo Bay, Australia
Don't think you'll cause any problems with flanking there. A similar question arose in another thread recently in which Stuart replied: viewtopic.php?f=2&t=20761&p=141589#p141532


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PostPosted: Mon Mar 20, 2017 9:32 am 
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Joined: Sun Jul 05, 2015 8:49 am
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Location: Sydney, Australia
Thanks Chris - didn't see that previous comment.

My gut feeling is that it wouldn't be a problem, but wanted to confirm with people smarter than me before it was too late in the process to change.

Cheers
David


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PostPosted: Mon Mar 20, 2017 1:22 pm 
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Joined: Thu Aug 21, 2008 10:17 am
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Location: Santiago, Chile
As long as you are not over-compressing the insulation, then you will be fine. "Over-compressing" is compressing it by more than about 20% of its thickness, give or take, depending on the type of insulation. So for example if the insulation is 4" thick and your joists are compressing it to be just 2" thick, and you are using semi-rigid mineral wool, then yes, you probably do have an issue. But if it is "pink fluffy" insulation, and it is only compressed from 4" down to 3.5", then there is no problem at all.

Can you get an estimate of how much it is compressed?

If it is only "lightly touching" as you say, then it's not an issue.


- Stuart -

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PostPosted: Mon Mar 20, 2017 1:37 pm 
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Joined: Sun Jul 05, 2015 8:49 am
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Location: Sydney, Australia
Appreciate your input, Stuart.

It's only compressing approximately 1 inch into a 4 inch fluffy batt. Potential problem averted!

Thanks for your help as always
David


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PostPosted: Thu Mar 23, 2017 10:12 am 
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Joined: Mon Jan 05, 2015 11:47 am
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Location: Apollo Bay, Australia
A little bit of compression is ok, overcompressing is bad. Now where have I heard that before? :lol:


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PostPosted: Sun Mar 26, 2017 9:07 am 
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Location: Sydney, Australia
:lol:


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