I'm intrigued that you think that R5 batts are 150mm deep! What material are you using? 
I understood that fibreglass R5 batts are 210mm deep.
cathedral ceilings & insulation.
(103 posts) (32 voices)-
Rosskestle
MemberThermilate is an insulation paint additive which could be used to paint the underside of your ceiling. Google Thermilate for some help.
We also have a polystyrene cube which we pump-in to cavities (usually minimum cavity width of 50mm. The product INSULBLOC has a rating of R4 for 100mm. Also good for wall cavity brick veneer, double brick and clad homes. Hydrophobic so it will not track moisture.Posted Monday 7 Mar 2011 @ 11:41:38 pm from IP # -
Ben1
Memberghostgum,
I am a bit confused about the orientation of RFL. If one side (the shiny side) is reflective and the other side (anti-glare) has low emissivity, then why would you place RFL shiny side down in a roof when you want to reflect incoming radiation in summer? Isn't that the wrong way around? I understand the motivation to keep the shiny side free of accumulated dust, but it just seems that it is facing the wrong way.
Thanks.
Posted Thursday 10 Mar 2011 @ 11:20:26 pm from IP # -
ghostgum
MemberBen1,
From an infrared (heat) perspective, both sides are shiny, reflect heat, and have low emissivity. The anti-glare side is usually outwards to avoid blinding the person installing it or the roof. The anti-glare side is usually blue or green in the visible spectrum, but transparent in the infrared spectrum.
Actually this is not entirely true, the anti-glare side has slightly worse performance than the shiny side, but the difference isn't enough to worry about.
Posted Friday 11 Mar 2011 @ 1:52:14 am from IP # -
Ben1
MemberThanks, ghostgum, that helps me a great deal. The only thing I am wondering about now is which side the air gap must be on. Am I correct in understanding that the air gap must be on the opposite side of the foil to the radiant heat source?
If double sided RFL is used and an air gap is placed on both sides of the foil, will the insulation work in both directions? (With approximately similar performance, as you've indicated.)
Posted Friday 11 Mar 2011 @ 9:42:20 am from IP # -
ghostgum
MemberYou want an air gap on each side.
Given a heat source, the near side of the RFL will reflect most of the heat back. Some of the heat will be emitted from the far side of the RFL. If you touch the far side against something (e.g. wall insulation batts) then it will conduct even more heat than if it has an air gap on that side.
If there is an air gap on one side only, then it I expect it should be on the side with the heat source.
Posted Friday 11 Mar 2011 @ 8:38:48 pm from IP # -
matas
MemberBen1, I am also thinking of enclosing my exposed rafters, for insulation.
But am a bit worried this will leave cavities (between the rafters where the insulatin is), that can never be accessed or inspected.
Does anyone think this could be a problem ?Posted Friday 11 Mar 2011 @ 11:20:43 pm from IP # -
Ben1
MemberIt is a possible problem, I suppose, but no one has mentioned it until you did.
The two problems I can imagine are termites and moisture ingress. The first is not a problem where I live and the second will surely become apparent when it reaches the second lower ceiling?
Posted Saturday 12 Mar 2011 @ 2:08:45 am from IP # -
matas
Member"The first (termites) is not a problem where I live"
Lucky you.
Yes, I suppose I was mainly worried about termites not being seen, and possibly other insect nests and vermin.
It is sort of reassuring now, to be able to see all the timber exposed (or at least one side of it)Posted Saturday 12 Mar 2011 @ 5:54:09 am from IP # -
cloudjinx
MemberIn a typical brick veneer wall the outer surface will increase the cavity R-value from around R0.16 to R0.6, obviously depending on the emissivity of the anti-glare coating used.
I'm trying to figure out what kind of value the inner surface would be providing if it has no air gap and is in contact with the bulk insulation.
I've seen the single sided RFLs being used and I've always wondered whether that inner surface alone is actually having any insulative effect at all.
Posted Sunday 13 Mar 2011 @ 2:31:41 am from IP # -
Ben1
MemberWhen sealing up an exposed rafter ceiling, I would like to know what others think about the idea of sandwiching an insulating material (perhaps XPS) between the new ceiling lining and the undersides of the rafters. The rafters (on 800mm spacings), running the full length of the ceiling, are in contact with the roof and I imagine will be a significant thermal bridge.
Is it worth insulating this bridge and, if so, what is the best material to use?
Posted Friday 17 Jun 2011 @ 2:44:29 am from IP #