# Forum Home Renovation Roofing  Adding sarking for an existing tile roof?

## montiee

Looking at beefing up the insulation in my place. With the "free" bulk insulation from the government recently proposed it's a no brainer however I'm also looking at reducing the radiant heat that enters the cavity for the next summer and hence we come to sarking. 
I have an old terracotta tile roof as seen below  
1) How would the sarking be attached to this roof? Can it run along the beams (that the battons and tiles sit on) which would leave it about a 80mm airgap between the tile and sarking or does it need to be right up near the battons the tiles sit on? 
2) Would sarking run vertically or horizontally. 
3) Should the foil be facing the underside of the tiles or facing the cavity. Rumor has it that it should be facing the tiles but it's often put the other way around due to OHS as reflections into the eyes of a roofer make it unsafe. Since this will be a DIY I'd like to do it the proper most efficient way so the insulation works as designed. It's tough finding the answer. 
I've tried finding articles on how to do it for an existing roof but haven't had any luck. If anyone has any links I'd much appreciate it. 
The house is in Sydney.

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## Dave_KB

Check out this thread, a couple of people are doing it:  http://forums.envirotalk.com.au/Roof...772.html&st=97 
The shiny side should face down as the face facing up will eventually get covered in dust etc, thereby reducing its effectiveness. 
Search around on the site above a bit and you'll find heaps of info re the science behind how rfl works.

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## montiee

> Check out this thread, a couple of people are doing it:  http://forums.envirotalk.com.au/Roof...772.html&st=97

  That's a great start. Thanks alot.   

> The shiny side should face down as the face facing up will eventually get covered in dust etc, thereby reducing its effectiveness.

  See that's another thing I heard which kind of doesn't make much sense to me. Nothing personal, just sounding out my thoughts and trying to understand the "theory" better. 
If you reverse it the layer so that the silver is on the bottom then you are essentially, from a heat reflection perspective, covering it even more. First it needs to get through the dirt layer, then through the blue layer understide of the foil. In essence you have now two layers inbetween the tile and the actual foil where as if you had the foil facing the tiles it's only the dirt layer in the way. The other point is that you are now reflecting the heat within the cavity back into the batts which is great if you want to keep your place warmer in a cold climate but that's not what I want. Also it's not about reflecting light so whether the foil is covered with dirt or not it's still going to act as a barrier to heat right?   
Remember I'm doing this to keep the place cool. I can for example see the benefit of puting the foil side facing into the roof cavity (so you can see the shiny side from within the cavity)  if you want to keep the place warm in colder climates (tassy, melbourne etc) but to me logically it doesn't make much sense if you are trying to keep your place cool.  
Am I missing something? I'll read that site a bit more but hoping to start up a discussion here about it for the benefit of others. 
What I want to avoid is just repeating something someone else has done without understanding why. As I've said down south it makes sense to install it foil side facing into the cavity. Then someone from Sydney copies the guy down south but in essence his requirements are the opposite but the mistake keeps getting perpertrated and soon everyone is making the same "mistake" up north. Commercially I could see why it would annoy builders to have the foil facing the tiles so they might take the easy way out. I freely admit I might have it completely wrong but would like to understand why before I put in the hard work. 
Also seems one guy has installed the sarking vertically while the other one horizontally. Does it matter. My preference is to install it vertically. That way if I need to get the the battons for whatever reason I only have one sheet to peal off  easily, especially in the middle of the roof where as if I installed horizontally it'd be alot more work.

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## Bloss

In any case sarking is not all that effective in the application as you are describing. Better value in increasing the R-value of the batts you install eventually. I recall Sydney the minimum is R3.5 - take to R-5 and that will increase your year round comfort. Alternatively spend your money and time getting some more effective summer shading on any north or west facing windows and walls - roller blinds or awnings, trees vines and so on. 
See http://www.yourhome.gov.au/technical/fs47.html and http://www.yourhome.gov.au/technical/fs31.html

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## montiee

Just another question to add. Only hald my roof really gets hit with the sun. Would I get a reasonable benefit from covering only that side to reflect the majority of the heat. I know it wouldn't be as great if the whole place is done but it should still contribute reasonable to cooling the place down.

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## montiee

> In any case sarking is not all that effective in the application as you are describing.

  So what good is sarking for?  
PS I do intend to probably put in R4 batts. Perhaps R5 if Rudd decides he wants to pay $1600  :Smilie: . 
Perhaps I should hold off on the sarking and see how it goes with the batts only. Regardless I might as well understand the issues so that if I need to put sarking in I have the answers so if anyone can explain which way sarking should go in a warmer climate to reduce heat I'd appreciate it.

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## sundancewfs

If you turn over a piece of alfoil, you will notice the other side is also......shiny.
Just because the exposed shiny side is facing down, doesn't mean there isn't another shiny side facing up. The heat radiation doesn't care where it encounters it, or if it has a non-glare layer covering it. The sarking is also a barrier for moisture when installed prior to tiling. as a retrofit you will get some, but limited, moisture exclusion. if you do it horizontally. be sure to start at the top and work down as then the overlap will shed any water that may get though in the right direction. Vertically would be a good option and easier to do.Have a look at Aircell's website www.aircell.com.au , they have pics of retrofitted places with their style of product insulation/sarking It's a lot more expensive than standard sarking and the rolls are a lot smaller.  
Before the hot days here in Melbourne I put a piece of sarking over the outside of the bathroom window (northern aspect, single glazed) It was always the hottest room in the house on warm days. The sarking made a big difference. The combimed shading and reflecting works well.  eventually that window will be swapped out for a low-E, double glazed unit. The others already fitted, performed well, with external surface temps in the sun of 65+ deg and internal temps of 32 deg.

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## Dave_KB

You should also spend some time reading some of the threads on the envirotalk site. 
Especially the thread about stacking your roof with bulk insulation...theres some interesting debate about whether in hot climates this just makes your house into a night-time oven as the trapped heat has nowhere to escape...resulting in having to run airconditioning all night. 
Theres also a couple of threads arguing whether whirlybirds do any good. 
Here's an article explaining how radiant barriers work:  http://www.ornl.gov/sci/roofs+walls/radiant/rb_01.html 
I'm not taking sides here, just saying its worth reading.

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## Bloss

> You should also spend some time reading some of the threads on the envirotalk site. 
> Especially the thread about stacking your roof with bulk insulation...theres some interesting debate about whether in hot climates this just makes your house into a night-time oven as the trapped heat has nowhere to escape...resulting in having to run airconditioning all night. 
> Theres also a couple of threads arguing whether whirlybirds do any good. 
> Here's an article explaining how radiant barriers work:  http://www.ornl.gov/sci/roofs+walls/radiant/rb_01.html 
> I'm not taking sides here, just saying its worth reading.

  There's no debate - the laws of thermal dynamics remain unchallenged and unchanged. 
If anyone thinks there is a magic bullet of just one action that will give all year round comfort then they are going to be very disappointed. That's why I continue to provide links to sites that explain passive thermal control. If you create am insulated hot box and leave it closed then it will stay hot. Of you fill it with ice it will stay cold. 
My own house and many other I have done has around double the recommended minimum R-value in the ceiling (and they are minimums - not the 'best'). In hot weather wherever you live need to stop heat getting in as much as you can - and from the outside. Inside heavy curtains and blinds help too, as do things like e-glass and double glazing (although better at stopping heat loss), but it is stopping thermal transfer through the roof, ceiling  walls and windows that matters. 
At a simplistic level heat always travels to cold until equilibrium occurs so the ceiling space heats up during the day and then the heat dissipates at night. Just as those batts stop the heat from above from getting into the house they also stop any heat build-up in the house below the ceiling from   escaping at night too or when there has been a cooler change come through (that's why they work in winter!). 
So this is simply how heat transfer and insulation is _designed_ to work - it is not controversial or subject to debate. 
Given what I describe you need to design the house so that the hot air trapped inside through daytime insolation can escape as the temperature outside becomes cooler than the temperature inside. In my case and in houses I have designed and built that is done by providing good cross ventilation so that overnight the house is opened up (and left open securely) and any breezes are allowed to aid that temperature equalisation process. 
In older places that have not been designed well you can use fans to assist that air exchange - even A/C on fan only can help and can often cool down faster than trying to use the refrigeration cycle wit the house closed up (obviously only when the outside temp is low enough) and certainly at much lower cost to your power bill and the environment. 
The issue about sarking is about bang for buck when retrofitting. It provides about R-.05 to .07 when installed to instructions in a new dwelling, but getting proper installation as a retrofit is often very hard to do. These are not 'insulation wars' to be argued too much - any insulation of any type is better than none. The various types have different costs and different performance and some suit some situations better than others. Do your research and read the links I gave and any others. Look at costs and then choose what you can afford. 
The take home message is use design to reduce heat build-up in the first place (and loss from the heated house in winter), provide paths for heat escape at night and in cool changes. In your case I'd do as you said - try batts first then if you reckon you have the time and money then look at sarkng or the aluminium batts etc if you think you want to spend more. 
I repeat - do the cheap and simple things first as they give best return all year round - without breaking the bank.  :2thumbsup:

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## woodbe

> Given what I describe you need to design the house so that the hot air trapped inside through daytime insolation can escape as the temperature outside becomes cooler than the temperature inside. In my case and in houses I have designed and built that is done by providing good cross ventilation so that overnight the house is opened up (and left open securely) and any breezes are allowed to aid that temperature equalisation process.

  Bloss. 
Daytime insolation and nightime insulation. As you point out, these can work against each other. Get it wrong, and you will pay. In fact, we almost need different insulation setups for day and night, winter and summer. 
Be that as it may, sisalation AKA 'radiant barrier' helps deal with daytime insolation. It's 'R' value is nil or negligible because it doesn't deal with the kind of heat transfer that bulk insualtion is good at preventing. As an added bonus, it costs a pittance, especially if you are able to install it yourself. 
So montiee, install it, yes. Under the beams, shiny side down to prevent dust buildup. Horizontal is probably best, starting at the top so you may pick up some moisture penetration protection as a bonus. Of course, also install as much bulk insulation to the ceiling as you can reasonably install. Also consider walls, windows and weatherseals. 
woodbe.

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## montiee

> So montiee, install it, yes. Under the beams, shiny side down to prevent dust buildup. 
> woodbe.

  Shiny side down you mean shiny side is visible from within the roof cavity right? 
If so we get back to my original question, Why?  
You've stated to prevent dust build up but my initial question remains. Why care about dust. The aim is not to reflect visible light? If you do install it so the shiny side is visible from within the cavity then the heat needs to travel through the dirt and a certain level of material before it hits the shiny side. In essence as I've stated the heat has to go through two layers before hitting the layer that is supposed to reflect the radiant heat.  
This is the thing I don't understand about putting the shiny side so it's visible from within the roof cavity if your goal is to keep things cool by minimising radiant heat from the tiles. If anyone can explain it scientifically why heat passing through dirt, then material to finally hit the foil that reflects it is better than just heat passing through dirt and then being reflected I'd be really interested.  
To me once you've flipped the sarking over so the non reflective side is facing the tiles you have already obscured the reflective material like dirt would and then added dirt on top of it. This is of course ignoring any sarking that has foil on both sides which doesn't seem that readily available these days. 
I've tried reading the forum but I keep hearing the "dirt" excuse which to me seems like a little bit weird and illogical since by flipping it as I've stated you've essentially obscured the reflective surface from the heat source (tiles) anyway. It's like a double wammy. 
From sundancewfs pic it's obvious that the silver side of the batts are facing towards the tile to reflect the radiant heat from them entering the cieling. This makes perfect sense to me. If we were to adopt the argument that's used for sarking these batts would be upside down since they will eventually get dirt on them anyway but obviously that is not the way they are meant to be installed. This is what doesn't make sense when it comes to the "dirt" argument..

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## sundancewfs

> This is of course ignoring any sarking that has foil on both sides which doesn't seem that readily available these days.

   

> From sundancewfs pic it's obvious that the silver side of the batts are facing towards the tile to reflect the radiant heat from them entering the cieling.

  This pic is from Aircells website.   

> AIR-CELL Retroshield<SUP>®</SUP> (IP Australia Patent Pending No. 38983/01) features two opposing faces of high polish aluminium foil surfaces

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## montiee

> This pic is from Aircells website.

  Hmm ok so it's double sided. To keep the discussion simple lets proceed as if the sarking only has foil one side.

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## kammerhofer

Builders install the sarking facing downward only to make it safer and easier to install. The line about dust is a myth. If you are retro fitting you can install it either way - it will do the same job. The advantage of installing it shiny side down is that it will illuminate your entire roof space if you have a light up there.

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## sundancewfs

Or you could install 2 layers..... one foil up, one foil down.  
Now that would foil them!  :Biggrin:

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## woodbe

> Shiny side down you mean shiny side is visible from within the roof cavity right? 
> If so we get back to my original question, Why?

  It comes down to the dust, and the emissivity characteristics of shiny metal surfaces. 
If you mount it shiny side up, facing the roof, it will work by reflecting the radiant heat back from whence it came. (I think we agree on this) Over time, dust build-up on the shiny face will reduce that reflection, and create a warmer surface on the sisalation that will heat up the sisalation by conduction. Once that happens, the non-shiny surface will radiate into the ceiling space. 
Ok? 
Now, the shiny side facing down into the ceiling area. Dust will still accumulate on the topside of the foil, but that surface is not reflecting heat anyway and so it will be absorbing heat (maybe a bit more with the dust, as it's probably a darker colour) So the sisalation gets hot. It doesn't radiate this heat into the ceiling space because the shiny metal surface has very low emissivity, so the hot sisalation radiates back towards the roof. 
If you think this all sounds like BS (I wouldn't blame you)  :Smilie:  here's a link to some data on emissivity values for common materials. Smaller numbers are better. Thanks to Morbo on the envirotalk forum for posting that link. 
So, how am I doing? Is there a light at the end of the tunnel yet? 
woodbe.

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## Bloss

> Or you could install 2 layers..... one foil up, one foil down.  
> Now that would foil them!

  lol  :Smilie:  
And woodbe is correct - shiny side faces down. This is advised by manufacturers on their sites and on every roll - and from the site I gave before: http://www.yourhome.gov.au/technical/fs48.html
Roof
'A second layer of RFL (either sarking or foil batts) beneath the roof will increase resistance to radiant heat. This may be useful in hot climates. Ensure that there is at least a 25mm gap between reflective surfaces. Place RFL sarking directly under the roofing material between the battens and the rafters with the shiny side facing down.' 
Biggest issue is that to have laminated foils to work best as reflective insulation they also recommend a minimum of 25mm air gap - that is almost never allowed for. But any even badly installed is always better than none at all. I now I am a broken record, but IMO you'll get better bang for buck doing other stuff first.

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## montiee

> Over time, dust build-up on the shiny face will reduce that reflection, and create a warmer surface on the sisalation that will heat up the sisalation by conduction. Once that happens, the non-shiny surface will radiate into the ceiling space. 
> Ok? 
> Now, the shiny side facing down into the ceiling area. Dust will still accumulate on the topside of the foil, but that surface is not reflecting heat anyway and so it will be absorbing heat (maybe a bit more with the dust, as it's probably a darker colour) So the sisalation gets hot. It doesn't radiate this heat into the ceiling space because the shiny metal surface has very low emissivity, so the hot sisalation radiates back towards the roof.

  hmm not convinced. Here is why. 
Once installed as per instructions it will look like this Sun->Tiles->Heat->dirt->backing->foil. Since the backing is so thin it will easily be overcome with heat on a warm summer day. It'll almost be useless at stopping anything with the amount it's being bombarded with. Infact it's going to be hit with radiant heat coming form the tiles and radiant heat being reflected by the foil. 
 Now if installed as per instructions the foil is obscured by the backing. It's like the foil would be obscured by dirt. No difference. There is no direct heat to foil barrier in either case so who cares if it's dirt obscuring the foil or the actual backing + a layer of dirt in essence obscuring the foil? The foil is still as shiny under the dirt as it is under the backing. This is where the argument about dirt falls down in my eyes.  
 If installed as per instruction the reflected heat will flow as follow: foil->heat->backing->dirt->tile to keep the house cooler. Logically it follows that if it's efficiently reflecting heat through two layers then the foil should have no problem directly radiating it  just through dirt since it's already doing that and more if installed as per instructions. 
To me the backing seems like it's there to   stop the foil ripping as well as to stop the small amount of heat that may radiate as the foil heats up while it's reflecting heat . This should only be a small amount which is why the backing is so thin. It doesn't seem like it's meant to help radiate the heat back out in any way nor does it keep the surface any more shiny since it's obscuring it anyway just like dirt would. Infact one could almost think of the backing as just another man made layer of dirt when it comes to the foils reflectivity of heat. 
It really sounds like things are @rse backwards to the way it should be on every single line of reasoning. The more I think about it the more I'm thinking that whomever designed sarking had the intention of making the foil face the tile but perhaps due to industrial action or tradies not wanting to install it because of it being hard on the eyes while installing a roof they took a compromise and flipped it. It still works but less efficiently but no complaints from OH&S or tradies the way it is. I can fully understand roofers being pissed off working in the middle of the day being cooked day in day out by reflected heat not to mention the reflected UV and hence higher chance of cancer from the foil not to mention light getting in the eyes etc. 
Personally until I'm convinced by a sound argument or someone can point out the flaw in my thinking if I ever install sarking it will be foil towrads the tiles. Sounds like I made up my mind but I'm all for someone convincing me otherwise but as yet the arguments I've presented seem to be right and counter the well established reasons. With the pitfalls and dangers (eye problems due to bright light reflections, cancer from reflected UV, heat exhaustion do to increased working temps) for tradies to install it the "optimum way" I can see why manufacturers would recommend the "less optimum" way if their product was to be adopted and to avoid lawsuits. 
Can anyone point out the flaw in my thinking above specifically?

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## Bloss

Probably all those manufacturers and installers are wrong? . . .  :Wink:  
Stop doing all that thinking - you'll go blind.  :Biggrin:  Go get some foil and put sarking in - if ya like shiny both sides buy it both sides  - no glare when the roof's already on. Go on - ya know ya wanna do it . . .    :2thumbsup:

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## montiee

> Probably all those manufacturers and installers are wrong? . . .

   Sometimes convenience outshines perfection. I'm not trying to pick any fights. I understand that the industry recommends it a certain way. However you will have to admit plenty of standards in the past which the industry has followed have been wrong and detrimental because it wasn't *thought* through. 
 If you genuinely can find a flaw in my arguments I'd really like to hear which parts. It's easy to say "the industry does it so it must be correct" until one takes note of the number of standards and ways things are changed because they are found to be false or detrimental a decade or more after they have been set. I don't see it as too far fetched that the sarking would be reversed from the way it was designed due to the number of negatives regular installers face of placing the sarking on the roof first and then spending a whole day with the heat/UV roasting them as they are working putting tiles over it. Especially if they do it for a living and facing it everyday. Reversing it would reduce efficiency a bit but the positives for installers would be large from an OH&S perspective. 
Retrofitting sarking once a roof is on is an atypical application of the product so the guidelines must be chosen for the more common case of sarking first followed by tiles/colorbond.

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## intertd6

you could do some simple tests yourself of shining a powerful light & or a radiant heater onto some sarking on the top of a simple box with a thermometer inside & record the heat gain over time, bye the way the most sarking is double sided & the coating on it is for ease of installation to reduce glare 
regards inter

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## woodbe

> hmm not convinced. Here is why. 
>  Now if installed as per instructions the foil is obscured by the backing. It's like the foil would be obscured by dirt. No difference. There is no direct heat to foil barrier in either case so who cares if it's dirt obscuring the foil or the actual backing + a layer of dirt in essence obscuring the foil? The foil is still as shiny under the dirt as it is under the backing. This is where the argument about dirt falls down in my eyes. 
> [..] 
> Can anyone point out the flaw in my thinking above specifically?

  I can see what you are saying, but you are wrong  :Smilie:  
Think of the shiny foil installed up as you suggest. 
Think of a layer of dust sitting on it. 
Think of the dust absorbing radiant heat from the tiles. 
Ok? Now, that dust is in *contact* with the foil. The transfer of heat to the foil will not be by radiation, it will be by conduction/convection. The dust acts as a short circuit to the radiant heat protection, heats up the foil and the backing which then radiates the heat into the attic space. 
If you're still not convinced, take Bloss' advice or you will go blind  :Biggrin:  
woodbe.

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## montiee

> you could do some simple tests yourself of shining a powerful light & or a radiant heater onto some sarking on the top of a simple box with a thermometer inside & record the heat gain over time

  I think I'll have to do that. :lol   

> Think of the dust absorbing radiant heat from the tiles. 
> Ok? Now, that dust is in *contact* with the foil. The transfer of heat to the foil will not be by radiation, it will be by conduction/convection. The dust acts as a short circuit to the radiant heat protection, heats up the foil and the backing which then radiates the heat into the attic space.

  Hmm but the backing is in contact with the dirt. The heat from the dirt is conducted to the backing the backing because it is attached to the foil conducts the heat to the foil. For heat to be exchanged by radiation only the backing would not have to be in contact with the foil. 
I guess if the backing itself if it's a sort of honeycomb miniature air cell could achieve heat being radiated rather than conducted. I can kind of buy that that if it's the case. The backing could act as a air cell that just radiates heat and the foil reflects it back out. 
That's the first explaination I've heard that sounds like it may have merit why the silver is facing the cavity assuming the backing is a sort of honeycomb structure. I'll also concede that the dirt would act as a conductor directly onto the foil. I didn't consider the backing to perhaps be honeycomb like to send radiant heat rather than heat via conduction.

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## woodbe

> Hmm but the backing is in contact with the dirt. The heat from the dirt is conducted to the backing the backing because it is attached to the foil conducts the heat to the foil. For heat to be exchanged by radiation only the backing would not have to be in contact with the foil.

  Yes, in the recommended application, the dirt will be on the backing. The backing will be heated by both radiation and conduction from the dirt. The foil side will be heated from the backing by conduction, absolutely no question. It would be somewhat less with the aircell product, but it will definitely happen regardless. 
This is where emissivity comes in. The hot foil has very low emissivity, so it will not re-radiate that heat into the roof space. So while the shiny surface is well known to reflect radiant heat, it also strongly resists radiating heat from it's surface. (I think it's about the same effectiveness for either) 
If you go back to the emissivity of common materials link I posted before, it might help now. 
woodbe

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## Bloss

> However you will have to admit plenty of standards in the past which the industry has followed have been wrong and detrimental because it wasn't *thought* through.
> .

  Standards change as does science as knowledge improves - why would anyone think they wouldn't? We can only ever know something is 'right' until it is proved 'wrong' - that doesn't mean we simply ignore the evidence we have right now. 
Your roof awaits - get the sarking (double sided so all arguments win . . . ) and whack it in. Then report back to us on your findings.  :Smilie:  
Meanwhile I'm on me bike on this thread - see if I can help members who want to get their job done too not just the discussion . . .  :Rolleyes:

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## montiee

> Standards change as does science as knowledge improves - why would anyone think they wouldn't? We can only ever know something is 'right' until it is proved 'wrong' - that doesn't mean we simply ignore the evidence we have right now.

  That's not true. We admit we don't know. We don't assume it's right. That's the proper way science addresses things. It's put through a hypothesis and then we go about proving it to be right or wrong.    

> Meanwhile I'm on me bike on this thread - see if I can help members who want to get their job done too not just the discussion . . .

  Well you could of always bowed out of the discussion at any time. I wouldn't of taken it personally. I appreciate your advice so far however I'm not one to just take things on face value. I like to know why I'm doing something *if it flies in my initial understanding of how it should work*. Hence this discussion. Plenty of people do things without understanding, I'm just not one of them given my background. 
I'm sure plenty of people will be using this thread as reference for which way the sarking goes AND why. This isn't just about discussion for discussion sake. When the time comes to put sarking in I now know which way to place it in and more importantly I have a have an explanation why it is done that way rather than just "because".   

> If you go back to the emissivity of common materials link I posted before, it might help now.
> woodbe

  Appreciate all your patience and effort in the discussion. I think now I have a handle on it and what you've been getting at given our last exchange and how emmisitivity positions itself into the picture between the backing material and the foil.

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## GraemeCook

> *Probably all those manufacturers and installers are wrong? . . . *  
> Stop doing all that thinking - you'll go blind.  Go get some foil and put sarking in - if ya like shiny both sides buy it both sides  - no glare when the roof's already on. Go on - ya know ya wanna do it . . .

  
And the CSIRO is also wrong!   I think not. 
Cheers 
Graeme

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## GraemeCook

> Probably all those manufacturers and installers are wrong? . . .  
> Stop doing all that thinking - you'll go blind.  Go get some foil and put sarking in - if ya like shiny both sides buy it both sides  - no glare when the roof's already on. Go on - ya know ya wanna do it . . .

  
Bloss, my understanding is that the manufacturers coloured one side of sarking for occupational health and safety reasons and ordained that the coloured side face heaven - so that that vicious sun did not reflect off the shiny silver side into the eyes of the workers installing it. 
Do you know if there any truth in this? 
Cheers 
Graeme

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## woodbe

Graeme, 
I'm sure Bloss will have an answer to that (I don't have anything specific) but if you had ever stood on a roof applying sarking, in sunlight, in the 'bad old' days, you would know why it is done. It could be that it took OHS regulation to get it done, or maybe market competition drove it, but the glare off the sarking without protection is unbelievable. 
Sunburn in about 5 minutes...

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## Bloss

> Bloss, my understanding is that the manufacturers coloured one side of sarking for occupational health and safety reasons and ordained that the coloured side face heaven - so that that vicious sun did not reflect off the shiny silver side into the eyes of the workers installing it. 
> Do you know if there any truth in this? 
> Cheers 
> Graeme

  My recollection is that yep - so far as I am aware that's right. Others might be able to offer more, but I know that when foil sarking first came into popular use (in the late 60s early 70's I think) it was shiny both sides and as Woodbe says - anyone who has ever installed it on roof or walls on a sunny day will tell you it is diabolical - glary and hot. Sunnies were the go for some time. My understanding is though that after some studies and use in building there became more performance-based reasons and the structure changed too as more research was done on what worked in what situation. 
Remember that sarking was originally the timber used under slate shingles and tiles or the wooden shingles or shakes used on roofs in 'scrim & sarking' construction. Later felt and 'malthoid', tar between sheets of kraft paper, was used too. The purposed was to add another sealing layer mainly to stop wind and then to stop dust getting in and cold getting out with a little moisture protection added (so long as it was installed from the bottom of the rafters to the top and overlaps on top!). 
Laminated foil sarking was brought in for the same purposes - the improved insulation from the reflective properties (if a suitable air gap is left and if an interior paces was fully sealed and tape up) was a bit later. It became competitive as Australia developed its own aluminium industry - with heavily subsidised power - hydro in Bell Bay in Tassie, and later, still subsidised, on the mainland. It was better than malthoid too as the old tar-based sarking used to soften and deform in the Oz heat - even melt in some parts of the country. 
So although the initial foils were all double sided now they are of different reflectivity, thickness and composition based on the intended use. That's why it is important to fight the habit of a lifetime (for blokes) for each type and read the instructions the manufacturer provides.  :2thumbsup:

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## barney118

> daytime insolation and nightime insulation. As you point out, these can work against each other. Get it wrong, and you will pay. In fact, we almost need different insulation setups for day and night, winter and summer.

  I originally had no sisilation until I installed new C/Bond, so the place was heating up during the day but cool in the morning. I installed a whirly bird and it solved half the problem. Also I have vents in the eaves which assists in cool air entering and hot air escaping thermal dynamics. 
I installed the sisilation (with 2 whirlys) and found an improvement in both, more toward the cooling than the heating. (it prevents transfer of radiant heat under the wooly stuff) dont think of it as reflection its like a barrier. 
I then put the batts in the roof and that helped heaps in the heating side of things (keeping it in) but I have found if the heat gets in on a hot day then its hard to cool down cause of the batts (I have only noticed when hot air is around on those stinky days). 
I would go with Bloss and try the simple things that dont cost too much, It depends on which is the greater evil heat or cool. I find it harder to cool than heat, I avoid A/C and use fans, I dont want to live inside on hot days as Im in the pool  :Cool:  and as long as inside is cool enough to sleep, cause its easy to chuck on more blankies :Biggrin: .

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## Bloss

> but I have found if the heat gets in on a hot day then its hard to cool down cause of the batts (I have only noticed when hot air is around on those stinky days).

  Looks like your doing the right stuff barney. Very important to note - when you create a thermally protected box (to keep heat out and heat in), and you plan on living in it, you need to make sure you can move air in and out when you need to (in summer at night when you want to move hot air out and cool air in) or stop it from moving in and out (in winter when you want to stop cold air getting in and heat getting out - especially if you are using energy to increase the heat). 
So the suggestion I have seen around that you shouldn't use batts 'because they keep the heat in at night' is rubbish - the whole house has to be deigned to allow heat movement when you want it and to stop it when you don't. 
And like all management of thermal transfer for human comfort (ie: in the range 17-27 degrees) the best way is not to let it get far outside that range in the first place. That means shading on the outside in the summer and getting sun to the inside in winter. And as with most things a number of things need to be done (with planning to work together) - there is not single magic bullet. Not rocket science, but it is science and that's what should be used to decide what's best.  :2thumbsup:

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## barney118

Bloss, 
It seems like you need to be able to stop the whirly birds on the cold days by something and even put a motor on them for the hot days. (I have even thought of attaching some electrical device to generate electricity ! how many $$$ could that make!). 
To be able to control the movement of air is the key. need to design a clutch to the whirly's ... maybe you will see me on the new inventors down the track.....

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## Bloss

I am not a great fan of whirlybirds - the evidence I have seen indicates they move too little air too slowly to be effective in summer - although I guess if enough were installed they would work. Some designs have auto closing vents that close them over in winter. 
The main thing is to get any hot air moved out of the living area of the house itself as soon as the outside is cooler than the inside. That's why solar passive designs incorporate one or more 'solar chimney's' - they allow hot air to escape as cooler night air is drawn in. Again they need to be controllable so they do not create a source of heat loss in winter in temperate or cold climates. Knowing the predominant summer evening wind direction is useful when working out how to best cool - and cross ventilation is critical.   :Ranton:  Funnily enough we focus on heat as though that is the biggest problem in Australia - for about 3/4 of our population that just isn't so for most of the time. Most live in temperate climates - with a need for winter cooling and the major part of the year manageable by simply selecting the right clothing and doing things like being in shade or in the sun! 
It's a recent phenomenon too - this expectation that rather than dressing and living to fit within a reasonable range of comfort for humans (that is 17-27 degrees - humidity can make it feel worse) we expect to be able to control so many of our environment (cars, homes, offices, theatres etc) to within 21-23 degrees. That is just silly, unreasonable and unsustainable too. It's because of that and our use of low quality A/C to do it that in NSW for example fully 15% of the generating capacity is needed to meet a peak demand that lasts just 24 hours over a year - the rest of the time it is not used! Just crazy!  :Rantoff:   :Biggrin:

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## GraemeCook

A belated thankyou Woodbe and Bloss for confirming my frail remembrances. 
Cheers 
Graeme

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## KT000000

Hi, 
Im new to this forum and found this site while looking for info on retrofitting sarking. 
Have you completed your project? I am going to do the same to our place. 
Just wondering what sarking you used and tools (staple gun etc..) 
Cheers,
KT

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