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  1. #1
    Newbie Austin 7's Avatar
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    Footings and sub floor design

    Hi All,
    Building regs differ in various parts of the world which means certain things have to be adhered to when starting a new build, simple things such as a damp proof course (DPC) in the footings and as we get abundant rainfall in the south of Thailand I was wondering if anyone has seen this in a new build here? I suppose this would not apply to any build on stilts or one that has a crawl space, but what about a building with footings and floor in contact with the earth?

    Also a concern in the west is the build up of Radon gas in buildings. Radon is a natural occuring gas that seeps up from the earths surface, through thick concrete floors and accumilates in buildings over many years. This gas is highly carsenegenic and studies in the US have shown that it is the second highest cause of lung cancer after smoking. That is why in the west building regs require new builds to have a radon barrier put in the sub floor and vents in the walls for this gas to escape into the atmosphere where it will disapate naturally. below is data from a preliminary study of indoor radon in Thailand

    Office of Atomic Energy for Peace, Bangkok.
    A preliminary study of indoor radon was carried out at 176 sites in different buildings in Bangkok (n = 83), Nonthaburi (n = 79), Pathumthani (n = 7), Samutsakorn (n = 3), Samutprakarn (n = 2), and Nakornpathom (n = 2). Elevated radon concentrations were encountered in 19.28 per cent of the buildings in Bangkok and in 29.11 per cent of the buildings in Nonthaburi. Levels were not beyond the threshold in the four other provinces. The prevalence of buildings with elevated radon concentrations between Bangkok and Nonthaburi showed no statistically significant difference (P > 0.05). The arithmetic means and the standard deviations of the elevated concentrations were 226.31 +/- 81.95 Bq.m-3 for Bangkok and 417.96 +/- 455.27 Bq.m-3 for Nonthaburi. With regard to the age of the buildings, those less than five years old had a higher rate of elevated radon concentration when compared with buildings five or more years old (P = 0.60 = no statistical difference). There was evidence suggesting that poor ventilation might be a factor in the elevated concentrations of indoor radon.


    Most of us may be blinded by the stats etc, but has anyone any thoughts?

  2. #2
    Thailand Expat

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    From what I have seen the standard Thai building technique is to use suspended concrete floors. Which is why they work on the maximum 4 meters between foundation piers.

    Why they insist the land has to be filled and left settle for a year before building is beyond me when the supporting piers are always dug down into the natural ground below the fill anyway.

    And why they throw all the loose rubble under the slab is also a bit of a mystery to me as it is of no structural value at all. Perhaps its just somewhere to dump the construction rubbish and save carting it away.

    Since the concrete floors are of the suspended type anyway, a vented under floor airspace would eliminate the need for an under floor damp proof barrier.
    The only thing I can think of, why they put loose fill under the floor, is that it might aid in making the floor into a "heat sink" to keep the floor cool since Thais spend so much time sitting on the floor. A ventilated underfloor space with airflow would no doubt raise the temperature of the floor slab a few degrees.

  3. #3
    Member deepee's Avatar
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    Want to get rid of radon gas ? try opening your windows!You should open them up on a regular bases anyway as radon is only one of a multitude of build up gases in the home .
    Many tests have show "off gasing "of common household items like paints and furniture create a soup of gases most of which are not too pleasant for our health.
    Radon accumulation in buildings is usually associated with poorly vented areas such as cellars w/o windows where, obviously being closer to the ground ,receive the seeping gas.
    As cellars and basements are less typical in Thailand so it should not be such a major issue.
    An underfloor moisture barrier( poly film) will help both gas and, more importantly moisture intrusion(mould) into the home.
    Radon gas can also be present in water drawn up from underground and it commonly off-gases when the water is heated - as in taking a warm show- in fact this is seen as the major source of radon when it comes to bad health issues in the home .
    OPEN YOUR WINDOWS!! REGULARLY- unless u live in BKK wher u are probably doomed for ill health anyway.

  4. #4
    Newbie Austin 7's Avatar
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    deepee,
    I hear ya about BKK. Take your life in your hands walking down the street breathing in all that lovely air.... Stay indoors and take your chances with the Radon and "Nam Pla" LOL!

  5. #5
    Thailand Expat
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    if your slab is sitting on the earth, just lay sand then a plastic sheet to isolate the possible damp

  6. #6
    Thailand Expat

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    ^ Do they even use that building method in Thailand?

    Here in Australia concrete slab floors are almost always laid on the natural ground with a layer of bedding sand and covered with a plastic damp proof layer.
    In Thailand, from what I have seen, they almost always go for suspended slabs between piers dug into the natural ground (which could be a meter or more below the built up ground level of fill).

  7. #7
    Newbie Austin 7's Avatar
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    Yes the suspended floor is the norm and as you say the earth is mostly pushed underneath and the sides sealed by walls, concrete paths etc, therefore creating a somewhat void underneath the floor. This would allow for the potential build up of radioactive Radon gas which will eventually seep up through the concrete floor and enter the building. A normal DPC is ineffective as it takes a special Radon barrier to be laid in the sub floor, also a Radon vent as used in Europe. Has anyone ever heard of this or Radon barriers in LOS ?

  8. #8
    Thailand Expat

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    One way to avoid the build up of Radon gas in the home might be to open a window?

  9. #9
    Dan
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    ^ Quite. It seems a bit odd to be concerned about this in Thailand. We could have mustard gas coming up through our floor and I don't think I'd notice.

  10. #10
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    Quote Originally Posted by Dan View Post
    ^ Quite. It seems a bit odd to be concerned about this in Thailand. We could have mustard gas coming up through our floor and I don't think I'd notice.
    Probably you would not notice anything because you would be dead

  11. #11
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    I've never heard of Radon gas buildup. Do not ever mention that to the crazies in NorCal...just another way for building inspecs to be jerks and cost you money. As it gets to 90>100 in the daytime and 60 at night, I always open my windows.
    Subfloors here are OSB > I call them old sona you know what. They warp when exposed to water and when you try to put tile on Hardibacker, the 4x8's will sag.
    I just did my bathroom floor in ceramic tile and now tomorrow...the shower

  12. #12
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    Quote Originally Posted by Panda View Post
    ^ Do they even use that building method in Thailand?

    Here in Australia concrete slab floors are almost always laid on the natural ground with a layer of bedding sand and covered with a plastic damp proof layer.
    In Thailand, from what I have seen, they almost always go for suspended slabs between piers dug into the natural ground (which could be a meter or more below the built up ground level of fill).

    of course, but only if you ask, and the ground is not 1 metere below

  13. #13
    Newbie Austin 7's Avatar
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    Anyone have a basement floor in their house in Thailand? does the temp differ vastly from the rest of the house.

  14. #14
    Newbie Austin 7's Avatar
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    Example of a Radon gas sump fan as used in Europe.

  15. #15
    Thailand Expat
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    Quote Originally Posted by Austin 7 View Post
    Anyone have a basement floor in their house in Thailand? does the temp differ vastly from the rest of the house.

    did you know Bangkok was known as "The Venice of the East"?

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