Russell Moore
Member
Zincalume starts off bright and shiny, and as the years go by it becomes duller and duller and becomes less reflective.
If you do want to paint it, you usually have to wait a year or two for the surface to become 'grippier', so as the paint can get a grip, and not peel off.
Don't know about voiding the warranty though, I can't see how paint would do any harm.
dymonite69
Member
Irradiance calculation is for RFL only as the blanket is not a radiant barrier but a convective one.
Zincalume might be similar to surf mist and classic cream but none of them are the same as white.
The relevant measure is the surface temperature of the underside of the ceiling. Without foil the radiant energy would cause the ceiling surface to heat up significantly.
Foil is a good radiant barrier but a terrible conductive one. Putting your hand on it will quickly draw the heat through it. Use this analogy. Pour boiling water in a stainless steel pitcher. Place your hand near to but not touching it. You won't notice any heat emanating from them. Touch the pitcher and beware!
R-values in the context of radiant barriers is not very meaningful. Their use should be confined to bulk insulators like batts, foam and cellulose.
Think of foil for summer and batts for winter. The foil + air gap should still give you 100mm left to put in R2.4 insulation. From recollection the BCA recommendations use some kind of formula to also include roof, foil, air gap and ceiling plasterboard to provide a final R-value. That should be enough to get you over the line.
Read here:
http://forums.envirotalk.com.au/index.php?s=&showtopic=7876&view=findpost&p=25414
gabs247
Member
Hi all, we're hopefully on teh cusp of signing a contract, and I was interested in getting a quote on sarking for the roof. We are planning to get a Dune or Surfmist for the roofing colour, and something slightly darker for the gutters/fascias, then a darker brick, as a contrast. I think the darker roof would look better, but understand it wouldn't be efficient.
Anyway, the builder has quoted us R1.5 55mm roof blanket, which costs a few k, but is my understanding that sarking or RFL is just the radiant barrier, not a full blown roof blanket? my uncle told me he builds that for warehouses that don't have ceilings, but I'm planning on R4.0 for the ceiling, so do I just ask for the radiant barrier?
So is that correct, I just need the foil + R4 on teh ceiling, not a roof blanket? My uncle said it'd turn into an oven if I had roof blanket + R4 on the ceiling, and he reckons that whirlybirds would be more worthwhile than RFL or roof blanket...
I'd be really interested to hear comments, as the sarking goes in now or never 
ghostgum
Member
Since it is a metal roof, RFL goes in. It helps prevent condensation on the underneath of the roof sheeting due to moisture from below in winter. It improves summer temperatures.
I presume the R1.5 roof blanket is both RFL and bulk insulation bonded together. You could do this instead of the simpler RFL, and it would improve your overall insulation. If I were redoing our roof, I'd either add this, or a layer of reflective insulating board (foilboard, kooltherm etc).
Don't bother with the whirlybirds. I've got a dune coloured colorbond roof, RFL underneath, and the ceiling space temperature never gets more than 5C above ambient. The whirlybird is going to have almost no effect on heat into the house and will just make noise, and make it worse in winter.
Our house colours are dune for the roof and boards above the windows, and woodland grey (slate) for the fascia, gutters, doors and window frames. The woodland grey being relatively dark results in a bit too much heat transfer through the aluminium frames. A lighter colour would have been better. Regarding the roof, our builder said that a darker colour wouldn't affect the heat much (don't entirely agree), but would be noisier and the roof expands and contracts in the sun. The RFL will reflect a lot of the heat, but a lighter roof will always be better in summer.
gabs247
Member
Thanks ghostgum, it's funny as they are similar colours that we're considering so it's good to know your experiences. Also, thanks for the comments about RFL and whirlybirds. I guess the whirlybird can always be done later if required. I think I'll see if I can get a quote for basic foil just under the roof, I think the roof blanket may be a bit of an overkill.
Probably the other two considerations I have are:
- put RFL in the Western Bedroom 3 wall, as it's only got an eave there (other Western wall has a 3m verandah.
- my dad has sarking in a raked section above his loft. after 20 years, the colourbond has really faded, but it's much worse above where the sarking is, anyone experienced that?
ghostgum
Member
If you want to see what the colours look like, I can send you a private link to some photos.
Put RFL or some radiant barrier in all walls. It's easy to do when building.
The roof blanket might be overkill, but it's easy to do now, hard to do later.
If you use light coloured colorbond, then you won't notice the fading
gabs247
Member
Great Morbo, but if I'm summarising correctly, it seems that the tile colours makes a differnence, but 3 of them are almost within half a degree (strangely what seems to be the darkest one included).
Also, teh plain foil, foam or blanket appear to be about the same, keeping the temperature ambient. Whereas plain roofing gets up to almost 7.5 degrees C? difference from what I can see? In fact the plain foil (if that's sisalation) seems to keep a nice middle ground. The builder is telling me that it's pointless with an R value of 0.5 it'll make no difference whatsoever.
Oh, my dad said that it's not just fading, it actually has come off the roof, leaving the bare zincalume beneath showing, after about 20 years.
Morbo
Member
you cannot put an R value to radiative barriers. In my measurments I get 12 deg max for foil.
The other 3 graphs are subfloor insulation of different kinds which I have been trying for over a year now.
The 41 deg is the lawn, and the lawn on any hot summer day was just at ambient, so this would have been a 41 deg day. So if you had a green roof, thats hat you would get, as long there is some green on it. Bare soil would be about same as concrete.
