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Thread: Roof Headaches

  1. #1
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    Roof Headaches

    Can anyone help with suggestions on roofing materials that would be appropriate to finish our roof?

    Originally the architect suggested metal sheeting, which I thought was a horrible idea. He told me that Long Khu roofing sheets could also be used and that was what we planned to use but have since been told that given the lack of slope in the roof that we will have problems. The front and back of the roof are almost flat (very slight backward slope), and it has a gradual slope in the middle (perhaps about 10 degrees). I have a picture of the roof framing which I can provide, but don't seem to have rights to post images yet? We have consulted with lots of engineers and roofers, but are getting mixed opinions on what will and will not work. I hate the idea of using metal sheeting, but if we have to resort to that, will it make the house horribly hot? I have 5mm insulation with double sided foil to put in the roof, would that be enough to keep the house cool?

    Any help would be greatly appreciated.

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    If you use metal sheets (corrugated?) on a shallow slope, make sure you have a decent overlap downwards otherwise water can be driven up and over

    the same would go for the big concrete corrugated tiles, which I would prefer

    as for heat, if you insulate well, there should be no problem.

    You could always lay a poured concrete roof as they do in Europe for shallow slopes, it works well there
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    ^ Concur. In a rented house a few years ago the corrugated shallow roof became covered in leaves which then became rain sodden forming a barrier to rain running down and off. The water backed-up under the overlaps, which were substantial, but nonetheless flooded the roof space and ruined the ceiling.
    Before tiling I'd consider raising the slope.

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    yeah, what andy said.

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    Metal roofing is used a lot in Australia because it is good in a tropical climate (apparently), but as Andy said, make sure it is well insulated, as every other roof material needs to be here.

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    Bluescope Colourbond can be installed to a min. roof slope of 2 degrees and can be made to any length.
    And as the Doc said ďif you insulate well, there should be no problem.Ē
    The Thai web site is www.bluescopeltysagth.co.th just use Google translate or go the the BlueScope Steel Australia: BlueScope Steel Products in Australia for English.

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    Quote Originally Posted by BKKBILL
    roof slope of 2 degrees and can be made to any length
    that would solve any leakage problems

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    The other consideration with slope is that a shallower slope decreases reflectivity. The roof material is a minor consideration in the ability to reflect solar radiation, the roof colour is a major factor with white being the best reflector.
    White vinyl roofs, which are inherently reflective, achieve some of the highest reflectance and emittance measurements of which roofing materials are capable. A roof made of thermoplastic white vinyl, for example, can reflect 80 percent or more of the sun’s rays and emit at least 70% of the solar radiation that the building absorbs.
    There is a company in Bangkok making the best roofing of all, a Long run sandwiched laminate, very reflective, and good thermal insulating properties.
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    Thanks to Humbert I went to the Architect10 at Bitec Monday. Got loads of information on roofing and building. Talking the the rep. from Colorbond about the most reflective roof and he told me the best is unpainted zincalume (their registered name for galvanizing I think).

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    Quote Originally Posted by BKKBILL
    the best is unpainted zincalume (their registered name for galvanizing I think).
    Strange, I always understood that cream coloured was best.

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    anything shiny is best, more reflection of the heat

    the colour determines the amount of heat absorption

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    Iím afraid thats untrue Dr A,
    In tropical climates Zinc Galv sheeting, usually corrugated does not reflect heat as well as White / Cream does.
    Primarily this is because metallic surfaces or unpainted metal roofing and in fact all non ferrous metal sheeting have a very low Emmittance (below 1%) That is why buildings with these roof structures become hot boxes at night, and because the materials have low thermal inertia they heat up very quickly the next day

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    Seems the rep was wrong. Loosing my faith in sale personnel.

    Cool roof - Wikipedia, the free encyclopedia
    "In tropical Australia, zinc-galvanized (silvery) sheeting (usually corrugated) do not reflect heat as well as the truly "cool" color of white, especially as metallic surfaces fail to emit infrared back to the sky "

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    Quote Originally Posted by peterpan View Post
    Iím afraid thats untrue Dr A,
    In tropical climates Zinc Galv sheeting, usually corrugated does not reflect heat as well as White / Cream does.
    Primarily this is because metallic surfaces or unpainted metal roofing and in fact all non ferrous metal sheeting have a very low Emmittance (below 1%) That is why buildings with these roof structures become hot boxes at night, and because the materials have low thermal inertia they heat up very quickly the next day

    I was referring to shiny, not the standard matt zinc, PP

    anyway, with good insulation the heat will not transmit into the house much

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    Most of the houses I have seen in Australia with metal roofs have an industrial design theme. If your house is traditional I would stick to concrete tile. Siam Cement Group has a great roofing section and knowledgable consultants at the Crystal Design Center in Bangkok.

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    I’m sure your right Humbert. Was planning to use metal but my wife took one look and winced. Guess we are off to the Crystal Design Center.

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    Steel sheeting does allow heat transfer in and out of the roof space faster than tiles.Heat will build up below quicker but it also allows a faster cool down of the roof space at the end of the day.Tiles will hold their heat longer due to their greater mass.
    As noted decent insulation is important with foil immediately below the foofing along with a properly insulated ceiling . It's a good idea to vent the roof space too.
    Steel should be easier to fix allowing far less joints for leaks and is better for security reasons.It is a hell of a lot lighter also so you should be able to cut down on the roofing structure materials and costs.
    One important criticism for steel is that it tends to "talk a lot " with temperature changes, especially at night and this can be an issue for some people. Good installers are aware of this and will back off a tad with their fixings which will allow the materials to slip with temp changes rather than jumping and causing those "what the hell was that ?'' comments .

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    Thanks very much for all of the help.

    The metal sheeting I mentioned actually is not the small standard size sheets available, but can be special ordered in long sections to cover the entire roof. It has a small squarish corrugation pattern. The problem was that they can put convex bends in it but not concave. That, and as I said I don't like the idea of using it.

    We have since brought in a more sophisticated builder from Bangkok. He is going to adjust the roof a little to take out some of the angles and make it somewhat straighter. It will now have a gentle slope on the back half (close to 10 degrees), but the front will still be close to flat. The transition between will be minimized. With this and some special techniques (that as I understand it involves cutting corners off the sheets) he is confident we can use Long Khu roof sheets without any problems. I am still a little concerned considering how flat the top is, but he assured me that it will be ok as long as the adjustments I described are made to eliminate the difficult joins between roof sections.

    Any concerns with that?

    I couldn't get the Thai Bluescope Colourbond website, but had a look at the Australian. The product looks fairly similar to the metal sheet roof I mentioned, but without the colour.

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