metal roofing and reflective foil

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metal roofing and reflective foil

Postby Traveler » Thu Mar 05, 2009 2:52 am

I hope I don't open a can of worms with this post, but the previous discussions about these materials were often only an exchange of opinions and beliefs, rather than actual facts based on physics.

Those who oppose metal roofing and try to argue with "clay tiles have been used for a thousand years and therefore must be better" seem to forget about a couple of important factors.

In which climate zones were those clay tiles used ?
Mostly in the mediterranean or continental climates, which don't have a high humidity around year and also have cold winters. Therefore those roofs had to deal with a different environment and can't be compared to roofs in the tropics.

What were the alternatives for roofing material a thousand years ago ?
Actually NONE, except maybe for some organic materials which aren't durable but cheap and therefore were used by the average Joe. All other available materials had a lot of disadvantages.

Additionally it's hardly an argument to say" it was always done that way".
Acting by this rule would prevent any progress and I wonder if they still light their houses at night with torches instead of using electric lights. Torches were also used thousands of years ago, electricity only about one hundred, but which is better ?

Aesthetics may be an argument but solely a subject one which everybody has to decide for himself. It doesn't affect the suitability of any material, it's just a personal opinion, (good or bad) taste. :D

On the other hand the expectations or views of others shouldn't guide your decisions. So if you believe you must use clay tiles instead of Colorbond ONLY because you believe your neighbours may expect it or will otherwise look down and you, then grow up, get some self respect and confidence.

You don't need to know much more about thermodynamics than what you may have learned in elementary school, it's no rocket science. Energy levels always equal out by traveling from high level to low level - or here from hot to cold. All you got to know is which ways it can take and how to block them as good as possible.
This is all very simple to understand just by common sense.

I totally agree with Itchy, who stated that any measure taken must fit into the overall concept.
But I disagree that it is desirable to raise convection and therefore foil should not be used.

I guess it's obvious that such behaviour is counterproductive. The logical consequence would be that any kind of insulation will reduce convection and should therefore be avoided.

Why should I allow higher temperatures in the roof to drive up convection just to bring in hot air from the outside ?
Isn't it better to keep the cool air inside rather than exchanging it with hot air ?

A rise of temperatures should be prevented at all stages and as "early" as possible. That's why shading the perimeter of your house with plants helps quite a lot as it reduces all three ways of heat transportation into your building. If the temperature under your roof will rise over the day, so will the convection. It should only do its job when necessary but not before.


metal roofing (Colorbond)
=========================

When we decide for a certain material we have to look in which environment the material is used and how good it fits into it, the costs involved, the availibility of the material and the knowledge of your workers. The best material may be reduced to rubbish if improperly installed or used.

In the tropics - where the temperatures and humidity are high, but the differences between day and night are low - it is best if not mandatory to use materials with low thermal mass. Clay tiles and concrete for example have a high thermal mass compared to metal. Due to this fact alone, metal roofing is already superior to them.
Additionally metal roofing is very light weight, resulting in lower costs for the supporting structure. It's also faster to install, again reduced costs. It's very durable too, hardly gives any room for leakages and may stop "cockroaches" of all sorts to enter via the roof (which is quite common in LOS).

Due to it's low thermal mass metal roofing won't stay hot very long and cools down quite fast at night, which results in lower temperatures in the below building. Isn't that what we want ?
Metal roofing - just like any other roofing material - will heat up in bright sunshine and radiate a fair part of the heat into the below building.

This is the point where we turn to ...


reflective foil
===============

There has been a huge misunderstanding why reflective foil should be used.

Let's have a short look at the involved physics.
Heat can be transported by three ways : convection, conduction and radiation.
Reflective foil adresses all three aspects.

Reflective foil creates a barrier for the hot air directly below your roof thus preventing it to mix up with the cooler air in your attic, so it can't neither conduct the heat to the air nor to your ceiling and into the rooms.

So what's left is radiation
The intensity of radiation largely depends on the surface. A shiny surface radiates less than a dark one.
This is the reason why the reflective side of the foil can face down, away from the heat source. It's not intended to reflect any heat radiation back to your roof but rather to not radiate itself. The low thermal mass of the foil adds up to this effect. The hot air above the foil can not conduct much of it's energy (=heat) to the foil, due to the low heat capacity of the foil.

Now you should also understand why it is mandotory to have a "gap" between the foil and any other material below it. It's not only because air is a good isolator but also because you would bring conduction back into the equation.

In short : reflective foil is a radiation barrier, widely available, light weight, easy to apply, very cost effective and cheap, without any disadvantages. What else can anybody wish for ?


Cheers
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Re: metal roofing and reflective foil

Postby geordie » Thu Mar 05, 2009 5:51 am

one small point would be the noise a metal roof transmits surely the density of a concrete tile is more desirable than metal mabe even the corugated cement sheets should be considered
my comments may be wrong but never deliberately
If it aint broke, dont fix it
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Re: metal roofing and reflective foil

Postby thaifly » Thu Mar 05, 2009 11:32 am

GIDDAY TO TRAVELER AND ALL...its the thai fly from mae rim...same old chest nut..over and over again..there are numerous soloutions to this topic discussed on the board over the years and many of them are great posts on the topic giving handy info on what route to take...or what takes your fancy...all in all..its purely your decision on which way to go...just like doing the form in a horse race... choose what you think is a winner for your build..and go for it...its a SMOKY C/MAI GIDDAY TO ALL..its the thaifly from mae rim
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Re: metal roofing and reflective foil

Postby thaifly » Thu Mar 05, 2009 11:52 am

gidday to traveller... sorry i overlooked to say that your post was a very informative as well..THE SMOKES GETTING TO THAIFLY GIDDAY TO ALL its the thaifly from mae rim
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Re: metal roofing and reflective foil

Postby thaifly » Thu Mar 05, 2009 12:07 pm

Traveler wrote:
In short : reflective foil is a radiation barrier, widely available, light weight, easy to apply, very cost effective and cheap, without any disadvantages. What else can anybody wish for
its a third gidday to all its the thaifly from mae rim...to allan the builder who i am sure is LURKING IN THE SHADOWS.. take note of the above... ITS A FOIL OF A GIDDAY TO ALL ..ITS THE THAIFLY FROM MAE RIM
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Re: metal roofing and reflective foil

Postby Traveler » Thu Mar 05, 2009 4:55 pm

geordie wrote:one small point would be the noise a metal roof transmits surely the density of a concrete tile is more desirable than metal mabe even the corugated cement sheets should be considered

geordie,

I personally like the noise of rain on a roof.
I will also put some fiberglass insulation in the roof. In combination with the ceiling it will reduce the noise.

Regards
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Re: metal roofing and reflective foil

Postby brent roberts » Sun Mar 07, 2010 3:04 am

Hello from downunder. I agree with you Traveler I also like the sound of the rain on the roof.The insulation in your ceiling will help to reduce this.When I build our house I will be using colourbond.I will be using the thicker one though it cost a bit more but I think this is worth it as it will not dent easily if you need to get on the roof. I have found company just south of C M that can make upto 17m long the only colour in the thicker one is gray but I think this will be ok.all the best brent
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Re: metal roofing and reflective foil

Postby Ians » Sun Mar 07, 2010 10:03 am

brent roberts wrote:Hello from downunder. I agree with you Traveler I also like the sound of the rain on the roof.The insulation in your ceiling will help to reduce this.When I build our house I will be using colourbond.I will be using the thicker one though it cost a bit more but I think this is worth it as it will not dent easily if you need to get on the roof. I have found company just south of C M that can make upto 17m long the only colour in the thicker one is gray but I think this will be ok.all the best brent


Would be interested in a contact name / number etc for the company south of CM who can supply the roofing material.

Thanks
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Re: metal roofing and reflective foil

Postby fredlk » Sun Mar 07, 2010 10:16 am

This is from the brochure I have:
Screen shot 2010-03-07 at Sunday - 07 Mar 2010 - 10.14.21 .png

Let me know if you can't read it - I'm looking at it on an extra large screen.
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Re: metal roofing and reflective foil

Postby Ians » Sun Mar 07, 2010 11:57 am

Thanks for thr prompt reply.
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Re: metal roofing and reflective foil

Postby cruzing » Wed Mar 10, 2010 3:32 pm

Attachments
Fine Homebuilding, Passive cooled house_resize.jpg
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Re: metal roofing and reflective foil

Postby ningnong » Wed Mar 10, 2010 5:14 pm

Thanks Cruzin, I was just researching that particular topic as when I recieved your post. That that looks etremely interesting and I have downloaded the PDF to read in detail later, however the pic you included in the message is not in the article you linked too :o Is there another one :?:
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Re: metal roofing and reflective foil

Postby cruzing » Wed Mar 10, 2010 5:38 pm

actually it's from Fine Homebuilding but a very old issue. I think I still have everything on my pc I'll have to check...usually use the laptop. It might be a couple days before I get back to you...

cruzing
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Re: metal roofing and reflective foil

Postby Puffo » Sat Mar 13, 2010 1:38 am

I read someone do by this kind insulation against water, heat, cold and sound with Polyrethane foam by spraying . Here is a site who show how work.: http://www.phuketinsulation.com/index.html
It can help to reduce noise from metal roofing and increase insulation.
Anybody has used it? What do you think? How about cost? shoul be a good idea to use for a outside wall insulation too?
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Re: metal roofing and reflective foil

Postby brent roberts » Sun Mar 14, 2010 2:43 am

Here is the name of the roofing company I went to see in Lamphun. el .cheng industrial co. ltd .ph 053 552078-9.I asked if their price was from factory to site which it was. My roof will be just over 14.0 m long our section is in the country so the roads are not very wide.They will have people to carry the sheets the last 5 or 6 hundred meters to the house.They also can do curved roofs and will bend any flashings you want :D
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