# Forum Home Renovation Heating & Cooling  Anyone have ceiling batts and foil insulation under metal roof?

## Geoff2005

I currently have a concrete tile roof and it's needing a spruce up. I was evaluating pros and cons of replacing with Colorbond and am trying to determine if there is a significant difference in aircon requirements in this scenario.  (Already have Goldbatts on ceiling, R3 I think) 
Anyone have any knowledge of performace batts and foil combined? 
Geoff

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## andy the pm

The foil insulation will typically reflect heat coming into the roof space as well as prevent condensation forming on the sheet roofing. 
Coupled with good roof space ventilation there can be a significant reduction in heat. 
If you have a ceiling mounted AC unit (ducted) this will help it run more efficiently as it wont have to work as hard to cool the air. 
Andy

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## SilentButDeadly

Colourbond with foil and ceiling batts works fine in our application.   
Greatest boon over tiles is the substantial reduction in thermal mass compared to tiles so cool down is faster. However, avoid the darker colourbond colours - plain zinc will hit 50 degrees, white 60 degrees but black colourbond will touch 90! 
Pay extra for the heavy duty polymer foils as the lighty duty paper foil is just awful stuff to work with and wrecks easily. 
Other foil options include the flash Air Cell and their ilk but their increased cost could be a barrier....

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## Geoff2005

> If you have a ceiling mounted AC unit (ducted) this will help it run more efficiently as it wont have to work as hard to cool the air. 
> Andy

  
I really noticed that when I started playing around with a temperature gun. The roof space was/is frequently above 40C and sometimes exceeds 50C in summer. The differential temp between inlet and outlet of the AC would be around 10C if the roof space was less then 35C, the differential would drop to around 5C however if the roof space was at 45C. Just the difference in heat flow between roof space and air in the duct starting at 10 - 15C after the heat exchanger.

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## andy the pm

Thats quite amazing really. 
I haven't seen a ducted unit up close, where do they draw the inlet air from? Surely not the roof space?? 
Andy

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## Geoff2005

> Thats quite amazing really. 
> I haven't seen a ducted unit up close, where do they draw the inlet air from? Surely not the roof space?? 
> Andy

  
In my case (as with most ducted reverse cycle units) the air is recycled and the inlet is in the passage way. So the differential I quote is air going in the vs air at duct vent.
If the thermostat is on 23 when the roof space is 35 then the inlet in the passage maybe 23 and the vent discharge maybe 14 (and compressor will cut in and out). If the roof space is 45 then the inlet maybe 24 and the duct exit maybe 19 (and compressor going full time).

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## Geoff2005

> Colourbond with foil and ceiling batts works fine in our application.  
> Greatest boon over tiles is the substantial reduction in thermal mass compared to tiles so cool down is faster. However, avoid the darker colourbond colours - plain zinc will hit 50 degrees, white 60 degrees but black colourbond will touch 90! 
> Pay extra for the heavy duty polymer foils as the lighty duty paper foil is just awful stuff to work with and wrecks easily. 
> Other foil options include the flash Air Cell and their ilk but their increased cost could be a barrier....

  So are those temps the metal skin or roof space? Stll translates to significant differences. 
I havent got as far as a Colourbond quote yet, still getting my ducks in a row

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## SilentButDeadly

> So are those temps the metal skin or roof space?

  They are for the metal.  Not the roof space.  I was up there just after noon on a high 30s day just recently and found the roof space very warm but not uncomfortable...

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## Bloss

Foil as sarking or even retrofitted is a great addition for summer impact, won't hurt, but doesn't make much to winter where batts are the go. Batts slow the transmission of heat, but do heat up and if the airspace above is hot relative to the ceiling the bats are sitting on then the heat in the batts will be transmitted to the room below. 
The aluminium foil has extremely low emissivity so heat hitting the top surface (from the tiles or colourbond) is not radiated to the roof space below. If the roof space temperature can be reduced by even 5 degrees that will improve the performance of the batts in summer and often the temp reduction can be 10-12 degrees or more in the roof and can lower the temp in the house by 3-5 degrees. 
The attached is an old document, but explains the issues quite well - the physics haven't changed!

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## SilentButDeadly

The current issue of ReNew magazine from the ATA has a great article on dark rooves and the choice of roofing material with respect to internal temps and cooling costs.....well worth a look. Alternative Technology Association website » ReNew magazine

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## GraemeCook

> Foil as sarking or even retrofitted is a great addition for summer impact, won't hurt, but doesn't make much to winter where batts are the go. Batts slow the transmission of heat, but do heat up and if the airspace above is hot relative to the ceiling the bats are sitting on then the heat in the batts will be transmitted to the room below.

  
As usual, Bloss is spot on about the effect of sisalation on summer cooling, but I think understates its effect on winter heating.   By minimising air leaks or drafts in the ceiling the sarking will add significantly to your insulation envelope, but not in a way that is measured by the usual parameters.  (The parameters measure where insulation is;  drafts are the result of where insulation is not ! ) 
Most rooms lose 20% or more of the heat through leakage - under doors, skirtings, windows, etc.   Never seen figures that I trust on the roof cavity leakage, but get up in the roof on a windy night, with a candle, and you will be amazed as to how much wind whistles inside the roof. 
Cheers 
Graeme

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## Geoff2005

Thats good info. 
Polished aluminium is streets ahead in terms of high reflectance/ low emittance accoring to the chart. Off topic but is there a product incorporating the aluminium layer suitable for seasonal installation under a colourbond patio? I currently throw some shade cloth over the top. 
With respect ot airflow through the roof there is currently a fair bit with leakage around the tiles. I have two whirlybirds in the higher part of the roof but still get quite a convective flow of hot air if I get on the roof and slide a tile back.

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## SilentButDeadly

You could put heavy duty wall wrap on a roller blind underneath your tin....there's also the new Thermatech coating available in some Colourbond colors too Thermatech

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## Bloss

> As usual, Bloss is spot on about the effect of sisalation on summer cooling, but I think understates its effect on winter heating.   By minimising air leaks or drafts in the ceiling the sarking will add significantly to your insulation envelope, but not in a way that is measured by the usual parameters.  (The parameters measure where insulation is;  drafts are the result of where insulation is not ! ) 
> Most rooms lose 20% or more of the heat through leakage - under doors, skirtings, windows, etc.   Never seen figures that I trust on the roof cavity leakage, but get up in the roof on a windy night, with a candle, and you will be amazed as to how much wind whistles inside the roof. 
> Cheers 
> Graeme

  But the problems you refer to should be fixed at source. Sisalation or foil under the roofing material will not assist heat loss in winter if the batts are not fully across the ceiling and over the edges of the wall plates. As you no doubt know batts are often not installed with sufficient care - ideally there should be no gaps at all across the whole of the insulated area. It is important to close off the top of the wall cavity gap too in cool climates - the airflow from the under the house up the walls and out through the roof is a big source of heat loss. Sarking under roofing will help a little with that. 
That is also why exhaust fan covers should be installed for bathrooms/ toilets vented into roof spaces and why downlights are so useless when the regulation safety space is allowed in the batts (as it must be to stop heat problems or fire) - the fittings leak like mad and the area around is uninsulated. I have seen houses with 18 and 20 in a room - maybe 3-5% or more of the batt area. Their design works like a chimney too and much heat is lost - no sarking can helps that. The answer is no downlights or CFC or LEDs. 
But that's sarking - directly under the roofing material. Were you to install foil over the batts then that might assist with closing off gaps, but the installation would have to be done so that an air gap of at least 20mm remained between the foil and batts - otherwise heat can be transferred both ways. I have done this by laying foil across top of the bottom chord of trusses, but it is fiddly and also means that there is another impediment to access in the roof space. Rating for cabling needs to be considered here too - mostly all that is needed is uprated circuit breakers (or breakers to replace wire fuses). 
But the critical part is the sealing of the batts - that applies to foil batts too - as Graeme says gaps are a no no!

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## GraemeCook

We are talking at cross purposes here, Bloss, the result of sloppy drafting by me.  I'll try again. 
With tile roofs there are lots of gaps between tiles.  With corrugated metal roofs there are lots of gaps at the ridgeline and eaves - basically a half circle at the end of each corrugation.   These air gaps allow the free circulation of air in the roof cavity - moving air moves or removes more heat than still air.   In heating mode this air movement makes the ceiling insulation work a lot harder.   Stop or minimise that air movement and you significantly improve your overall insulation envelope. 
It is the same argument used for "super sealing" super insulated buildings in Europe and the americas where they actually pressurise the buildings to search for air leaks. 
Cheers 
Graeme

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## Bloss

Ah - now I geddit!  :Redface:  One thing that is often neglected by builders with sarking that can be fixed by home owners is to do what you ay and tape up all joins and seal the gaps too.  :2thumbsup:

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## Geoff2005

While looking at the foil type insulation info another alternative to replacing tiles with Colorbond occured, which I will follow up.  
There are two components, firstly remove the ridge capping and several rows of tiles from a section of the roof, remove battens in that area, lay out insulation over rafters and re batten. Move tiles from next strip down and lay them on the newly battened area. Repeat process in sections till retiling complete and redo mortor on ridge capping.  
Then paint roof with this  http://www.nutechpaints.com.au/nutechtechinfo.pdf 
nutech heat reflective paint. 
Anyone have any comments?

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## SilentButDeadly

> Anyone have any comments?

  Yep.  You must be a glutton for punishment. 
In this circumstance, it'd be "easier" to fit the insulation to the underside of the battens (or even rafters) rather than pfaffing about with the tiles.  Murphy's Law also says "it'll rain when the job is 3/4 done".

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## Bloss

:What he said:  I have done a number of retrofits of foil- sometimes onto underside of battens and sometimes under the top chords of the trusses. Always a hot and fiddly and uncomfortable job (must be done in winter!), but relatively fast and trouble free compared to lofting tiles re-pointing etc - and the result will be the same. I did a cathedral ceiling with exposed beams by lifting tiles and inserting batts, but did not use foil on that one as it could not be done to leave an airgap. Added styrofoam between the beams and re-sheeted with plasterboard. 
Just as an aside my roofer's estimate is that a new colourbond (and i'll have him include foil & blanket under neath) will be cheaper than a re-point and paint for my 35 year old concrete tiled roof. And reckons he can even sell the old tiles!

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## Geoff2005

> Just as an aside my roofer's estimate is that a new colourbond (and i'll have him include foil & blanket under neath) will be cheaper than a re-point and paint for my 35 year old concrete tiled roof. And reckons he can even sell the old tiles!

  Thats good to know!  
I have a list of a couple of businesses in Perth that do tile roof makeovers or tile to Colorbond conversions that I was going to start getting estimates on differerent options. I was sort of feeling that repoint and paint tiles would be 5 - 10k and reroof with Colorbond would be 15 - 30k but it looks like I'm way off. 
In considering the installation of foil from within the roof I was looking at the diffuclty of getting the areas around the roof boundaries 
I've appended pic of roof, don't know how much the number of ridges and valleys will complicate things

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## Bloss

Be worth getting a quote for both anyway. The other thing is that regardless of claims and 'warranties' a repainted tile roof will be lucky to last 10 years looking good. Re-painting makes no difference to the watertightness (the re-pointing does though) - it is just aesthetics. 
Also worth getting a quote for a re-tile with new tiles - depending on the state of the old roof battens etc this too can be more competitive than you might imagine - I have seen a friend's one done recently and it was less than the cheapest re-point and re-paint quote (that she would have accepted - there were a couple that were way too cheap and likely poor work).

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## Geoff2005

I guess another factor in the equation is how long would you expect a Colorbond roof to last, 20yrs, vs repoint/repaint 10yrs? 
I see a big advange in painting (other then asthetics) if the heat reflective paint works as claimed.

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## Bloss

> I guess another factor in the equation is how long would you expect a Colorbond roof to last, 20yrs, vs repoint/repaint 10yrs? 
> I see a big advange in painting (other then asthetics) if the heat reflective paint works as claimed.

  Colorbond in most areas will last 40 years or more, and warranties for the steel itself go to 30 years (but usually only 12-15 for the paint finish). Note that thermally reflective finishes are now available for Colorbond and other roof materials too - in any case as always lighter colours are better than darker - in Oz we should all have white roofs! 
Prep and re-coat for a color bond roof (with reflective paint or not) is easier and faster than for tiles too). 
If cost is a consideration the the thermal reflective paints are expensive - if the heat was area concern then simply a lighter colour would be a better choice. There are also a lot of 'dodgy bros' out there claiming all sorts of stuff for paints (and I'd be wanting to know that the paint i was promised was actually used too). Like all painting, in fact more so due to the extremes of exposure preparation is critical for longevity - and that's the main area that separates the professionals for others in rood restoration. 
But technology is moving fast with better and more thermally efficient finishes and as more become used the cost will go down. But I am for doing what gives the best bang for buck - and am sceptical of magic bullets (eg: claims about superior thermal performance of a dark roof coating that might be better than an equivalent dark standard coating, but remains worse or little better than a standard light coating). 
The US Energy Secretary understand this: http://www.independent.co.uk/environ...e-1691209.html

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