Need Help Cooling My House/Attic in Bangkok

[IMHO]

I disagree, PU foam applied to the back of roof tiles has been proven by many posters to be a viable solution that reduces roof void tempreture by up to 10 degrees.

a Thai bullshit fairy tale does not change the laws of thermo-physics. many posters who claim the above have actually no idea what they are talking about. the application of foam insulation is only propagated by many contractors because the preparation to apply foam on ceilings is quite difficult (ceiling lamps, electrical distribution boxes, etc. must be still accessible and have to be protected). spraying foam on the roof tiles is a breeze. any honest contractor with a minimum of technical knowledge will admit that my claim is correct.

So, you are saying that the PU foam - such as what this guy offers - http://www.lohr-trade.com/foam - sprayed to the underside of the roof tiles is a GOOD or a BAD thing? Thanks.

From the POV that you want to reflect, not insulate at the tiles, yes, a waste of time.

The order of effectiveness is always: shade, reflect, insulate.

If you have a new construction, always use foil under the tiles to reflect as much heat as possible, then use insulation on the ceiling to stop whatever heat did get through from making it into the living space.

Spraying anything on the ceiling as an afterthought is always going to be tricky. Using fiber/wool batts is less tricky, but can result in unwanted visitors taking up residence in your roof. Best is just to just use Gyproc Thermaline gypsum for the ceilings in the first place (or re-do your ceilings as a retrofit).

[Naam]

I disagree, PU foam applied to the back of roof tiles has been proven by many posters to be a viable solution that reduces roof void tempreture by up to 10 degrees.

a Thai bullshit fairy tale does not change the laws of thermo-physics. many posters who claim the above have actually no idea what they are talking about. the application of foam insulation is only propagated by many contractors because the preparation to apply foam on ceilings is quite difficult (ceiling lamps, electrical distribution boxes, etc. must be still accessible and have to be protected). spraying foam on the roof tiles is a breeze. any honest contractor with a minimum of technical knowledge will admit that my claim is correct.

So, you are saying that the PU foam - such as what this guy offers - http://www.lohr-trade.com/foam - sprayed to the underside of the roof tiles is a GOOD or a BAD thing? Thanks.

PU foam is an excellent (perhaps the best) material used for insulation apart from a vacuum (which is not a material) but it depends on its application (how and where) to get the most bang for the buck. this thread concentrates on insulation of an attic and ceilings bordering the attic.

in this case, i repeat, that PU foam applied to roof tiles causes only a temporary insulation effect if the attic is not properly ventilated and this effect might even be undesireable when the ambient temperature changes, e.g. after rain or cool nights. in other words... the attic will still heat up, albeit slower, and will affect the rooms below in a negative way if the ceilings are not insulated.

[jsgatse]

I just went up to my attic - it's not so hot today because of the rain.

Here's what I found...

It's a single peaked roof (like a pyramid shape).

Two sides of the house have soffits decent incoming air access.

The roof is a standard tile roof, with metal frame support.

Under the tiles (so on the INSIDE side of my attic) there is some foil like paper - in other words, I can't see the tiles unless I pull back this foil like paper. This substance looks like cheap tin foil sandwiched around a piece of VERY thin cardboard like paper. It's about as thick as a magazine cover, I would say - and can be ripped.

Is this foil insulation that is noted as a good source of REFLECTION?

THe ceiling of my 2nd floor is basically the floor of my attic - basically sheet rock suspended by some wire cables tied to the metal frame of the house.

I have no whirlybird or anything else up there.

Based on this, what would you suggest?

Thanks!

[Naam]

Is this foil insulation that is noted as a good source of REFLECTION?

it is reflective but the efficiency is quite low. no matter what you do do with additional insulation, your first mandatory step is ventilating your attic.

Two sides of the house have soffits decent incoming air access.

how/where's the air going out and what is "decent"?

[IMHO]

I just went up to my attic - it's not so hot today because of the rain.

Here's what I found...

It's a single peaked roof (like a pyramid shape).

Two sides of the house have soffits decent incoming air access.

The roof is a standard tile roof, with metal frame support.

Under the tiles (so on the INSIDE side of my attic) there is some foil like paper - in other words, I can't see the tiles unless I pull back this foil like paper. This substance looks like cheap tin foil sandwiched around a piece of VERY thin cardboard like paper. It's about as thick as a magazine cover, I would say - and can be ripped.

Is this foil insulation that is noted as a good source of REFLECTION?

THe ceiling of my 2nd floor is basically the floor of my attic - basically sheet rock suspended by some wire cables tied to the metal frame of the house.

I have no whirlybird or anything else up there.

Based on this, what would you suggest?

Thanks!

The foil under the tiles is indeed the type of reflective barrier the correct posters here have been taking about.

Based on this info, here's what you should be doing:

1. See if there's any way to shade the roof and walls. Trees? Solar panels?

2. Either insulate the ceiling with batts, or rip it out and install thermaline (best), or foil backed gypsum (not as good, but still much better than plain gypsum).

3. Bear in mind that heat also comes in via windows and walls too - look for problems here - especially the West and South sides of the house.

4. Is there any airflow up there whilst you have a prevailing breeze? if no, consider replacing more of the soffits with ventilated boards, and/or consider a whirlybird/gable vents (if you have gables). Ventilated soffits being the single most effective solution if you only choose one.

Edited April 23, 2015 by IMHO

[chiang mai]

I disagree, PU foam applied to the back of roof tiles has been proven by many posters to be a viable solution that reduces roof void tempreture by up to 10 degrees.

a Thai bullshit fairy tale does not change the laws of thermo-physics. many posters who claim the above have actually no idea what they are talking about. the application of foam insulation is only propagated by many contractors because the preparation to apply foam on ceilings is quite difficult (ceiling lamps, electrical distribution boxes, etc. must be still accessible and have to be protected). spraying foam on the roof tiles is a breeze. any honest contractor with a minimum of technical knowledge will admit that my claim is correct.

I don't see what the difficult in applying the foam has to do with its effectiveness as an insulator, or did I miss something in what you wrote?

Indeed most contractors who apply foam to roofs say that there is an up front task of making or protecting some areas but again, I don't see what that has to do with the effectivness of the foam or otherwise.

And actually, the last time you and I debated aspects of PU foam in this forum, you claimed that PU foam was ineffectve because its application was almost wafer thin, which is something that is not entirely true in most cases. I accept that if it were applied in such a wafer thin layer then its usefullness as an insulator would be reduced by posters claim otherwise, perhaps some of them will comment here.

[chiang mai]

I just went up to my attic - it's not so hot today because of the rain.

Here's what I found...

It's a single peaked roof (like a pyramid shape).

Two sides of the house have soffits decent incoming air access.

The roof is a standard tile roof, with metal frame support.

Under the tiles (so on the INSIDE side of my attic) there is some foil like paper - in other words, I can't see the tiles unless I pull back this foil like paper. This substance looks like cheap tin foil sandwiched around a piece of VERY thin cardboard like paper. It's about as thick as a magazine cover, I would say - and can be ripped.

Is this foil insulation that is noted as a good source of REFLECTION?

THe ceiling of my 2nd floor is basically the floor of my attic - basically sheet rock suspended by some wire cables tied to the metal frame of the house.

I have no whirlybird or anything else up there.

Based on this, what would you suggest?

Thanks!

If my suspicion is correct you will find that the layer of foil acts as a barrier that channels the hot air, the air between the foil and the roof tiles, upwards to a vent at the ridge tile? It's usefullness as an insulator is therefore minimal since it's purpose is to channel the hot air upwards.

[jsgatse]

Is this foil insulation that is noted as a good source of REFLECTION?

it is reflective but the efficiency is quite low. no matter what you do do with additional insulation, your first mandatory step is ventilating your attic.

Two sides of the house have soffits decent incoming air access.

how/where's the air going out and what is "decent"?

Yes, that's the main issue...there are the two sets of soffits on 2 parallel sides of the roof...but there is nothing else...no whirlybird or anything to suck in the cooler air/remove the hotter air.

I don't know how to quantify decent - but. each of the two sides of the roof overhang has 3 intake strips for the air - about 1.5 cm wide each - and this runs for about 7m.,..this is just an eyeball guestimate, however.

So, my first step would seem to install a whirlybird/some sort of exit for this hot air, yes?

[Crossy]

Yup ^^^ let the hot air out.

Do you have gables? Gable vents would look nicer than whirlybirds and be equally effective, and you could add fans later if they weren't enough.

[IMHO]

I just went up to my attic - it's not so hot today because of the rain.

Here's what I found...

It's a single peaked roof (like a pyramid shape).

Two sides of the house have soffits decent incoming air access.

The roof is a standard tile roof, with metal frame support.

Under the tiles (so on the INSIDE side of my attic) there is some foil like paper - in other words, I can't see the tiles unless I pull back this foil like paper. This substance looks like cheap tin foil sandwiched around a piece of VERY thin cardboard like paper. It's about as thick as a magazine cover, I would say - and can be ripped.

Is this foil insulation that is noted as a good source of REFLECTION?

THe ceiling of my 2nd floor is basically the floor of my attic - basically sheet rock suspended by some wire cables tied to the metal frame of the house.

I have no whirlybird or anything else up there.

Based on this, what would you suggest?

Thanks!

If my suspicion is correct you will find that the layer of foil acts as a barrier that channels the hot air, the air between the foil and the roof tiles, upwards to a vent at the ridge tile? It's usefullness as an insulator is therefore minimal since it's purpose is to channel the hot air upwards.

The foil reflects heat directly back out through the tiles.

[IMHO]

I disagree, PU foam applied to the back of roof tiles has been proven by many posters to be a viable solution that reduces roof void tempreture by up to 10 degrees.

a Thai bullshit fairy tale does not change the laws of thermo-physics. many posters who claim the above have actually no idea what they are talking about. the application of foam insulation is only propagated by many contractors because the preparation to apply foam on ceilings is quite difficult (ceiling lamps, electrical distribution boxes, etc. must be still accessible and have to be protected). spraying foam on the roof tiles is a breeze. any honest contractor with a minimum of technical knowledge will admit that my claim is correct.

I don't see what the difficult in applying the foam has to do with its effectiveness as an insulator, or did I miss something in what you wrote?

Indeed most contractors who apply foam to roofs say that there is an up front task of making or protecting some areas but again, I don't see what that has to do with the effectivness of the foam or otherwise.

And actually, the last time you and I debated aspects of PU foam in this forum, you claimed that PU foam was ineffectve because its application was almost wafer thin, which is something that is not entirely true in most cases. I accept that if it were applied in such a wafer thin layer then its usefullness as an insulator would be reduced by posters claim otherwise, perhaps some of them will comment here.

PU foam directly under the tiles is also going to insulate from heat *getting out* through the tiles once the sun goes down. Naam is correct - he's saying all it will do is shift the heat to another time of day. Reflect heat at the tiles, insulate at the ceiling.

[Naam]

I just went up to my attic - it's not so hot today because of the rain.

Here's what I found...

It's a single peaked roof (like a pyramid shape).

Two sides of the house have soffits decent incoming air access.

The roof is a standard tile roof, with metal frame support.

Under the tiles (so on the INSIDE side of my attic) there is some foil like paper - in other words, I can't see the tiles unless I pull back this foil like paper. This substance looks like cheap tin foil sandwiched around a piece of VERY thin cardboard like paper. It's about as thick as a magazine cover, I would say - and can be ripped.

Is this foil insulation that is noted as a good source of REFLECTION?

THe ceiling of my 2nd floor is basically the floor of my attic - basically sheet rock suspended by some wire cables tied to the metal frame of the house.

I have no whirlybird or anything else up there.

Based on this, what would you suggest?

Thanks!

If my suspicion is correct you will find that the layer of foil acts as a barrier that channels the hot air, the air between the foil and the roof tiles, upwards to a vent at the ridge tile? It's usefullness as an insulator is therefore minimal since it's purpose is to channel the hot air upwards.

The foil reflects heat directly back out through the tiles.

i [not so] humbly beg to differ but a detailed discussion would be a waste of time because the reflection measured in comparison to the actual heat transfer not reflected is miniscule.

[Naam]

I disagree, PU foam applied to the back of roof tiles has been proven by many posters to be a viable solution that reduces roof void tempreture by up to 10 degrees.

a Thai bullshit fairy tale does not change the laws of thermo-physics. many posters who claim the above have actually no idea what they are talking about. the application of foam insulation is only propagated by many contractors because the preparation to apply foam on ceilings is quite difficult (ceiling lamps, electrical distribution boxes, etc. must be still accessible and have to be protected). spraying foam on the roof tiles is a breeze. any honest contractor with a minimum of technical knowledge will admit that my claim is correct.

I don't see what the difficult in applying the foam has to do with its effectiveness as an insulator, or did I miss something in what you wrote?

Indeed most contractors who apply foam to roofs say that there is an up front task of making or protecting some areas but again, I don't see what that has to do with the effectivness of the foam or otherwise.

And actually, the last time you and I debated aspects of PU foam in this forum, you claimed that PU foam was ineffectve because its application was almost wafer thin, which is something that is not entirely true in most cases. I accept that if it were applied in such a wafer thin layer then its usefullness as an insulator would be reduced by posters claim otherwise, perhaps some of them will comment here.

i have read perhaps a dozen nonsensical claims from posters and their perceived temperature drops. they are the equivalent of the hundreds nonsensical comments and "advices" in the various aircon threads. i usually only participate in this threads if there is a forum-member who asks for advice/assistance.

[jsgatse]

Yup ^^^ let the hot air out.

Do you have gables? Gable vents would look nicer than whirlybirds and be equally effective, and you could add fans later if they weren't enough.

Nope, no gables, as my roof is like a pyramid...the only solution is to let this air out would thru a whirlybird, as I see it.

Edited April 23, 2015 by jsgatse

[chiang mai]

I just went up to my attic - it's not so hot today because of the rain.

Here's what I found...

It's a single peaked roof (like a pyramid shape).

Two sides of the house have soffits decent incoming air access.

The roof is a standard tile roof, with metal frame support.

Under the tiles (so on the INSIDE side of my attic) there is some foil like paper - in other words, I can't see the tiles unless I pull back this foil like paper. This substance looks like cheap tin foil sandwiched around a piece of VERY thin cardboard like paper. It's about as thick as a magazine cover, I would say - and can be ripped.

Is this foil insulation that is noted as a good source of REFLECTION?

THe ceiling of my 2nd floor is basically the floor of my attic - basically sheet rock suspended by some wire cables tied to the metal frame of the house.

I have no whirlybird or anything else up there.

Based on this, what would you suggest?

Thanks!

If my suspicion is correct you will find that the layer of foil acts as a barrier that channels the hot air, the air between the foil and the roof tiles, upwards to a vent at the ridge tile? It's usefullness as an insulator is therefore minimal since it's purpose is to channel the hot air upwards.

The foil reflects heat directly back out through the tiles.

I don't believe that a layer of foil reverses the direction of heat penetration to a degree that's worth mentioning.

Poster jsgate: It's often the cases with houses in Thailand that they will have soffit/eves vents but no exit point higher up to vent the hot air. The belief amongst many locals, builders and occupiers is that the soffit vents provide a means for the hot air in the roof void to escape and I can't begin to imagine how many times I've had that discussion whilst house hunting.

But the exsitence of foil on the underside of your roof, despite the fact that you tell us you have a pyramid roof, leads me to suspect you may indeed have some form of vent on one (or more) of the ridges or at the peak, often such ridge vents are quite low profile and not always easy to see hence they are not always that efficient. Perhaps the next time you visit a Home Mart store you might want to look at the ridge tile products which can be retrofitted to newer roofs, mostly they are simply ridge tiles thaqt sit on four legs to provide an air gap along the tile to allow hot air to escape.

[chiang mai]

PU foam directly under the tiles is also going to insulate from heat *getting out* through the tiles once the sun goes down. Naam is correct - he's saying all it will do is shift the heat to another time of day. Reflect heat at the tiles, insulate at the ceiling.

I'm afraid I don't buy that either, heat rises and doesn't disperse from the roof tile in a downwards direction (which is where the foam is located). That fact notwithstanding, I may be able to agree of naams point about delay, as mentioned previously, subject to a better understanding of the thickness of foam applied. My suspicion is that thinly applied foam on a very hot day will be defeated quickly, a thicker layer of foam under more normal conditions will likely work well.

[Naam]

Yup ^^^ let the hot air out.

Do you have gables? Gable vents would look nicer than whirlybirds and be equally effective, and you could add fans later if they weren't enough.

Nope, no gables, as my roof is like a pyramid...the only solution is to let this air out would thru a whirlybird, as I see it.

roof fans are available but bloody expensive. my stupid contractor did not consult me and purchased/installed one for 17,000 Baht (three-phase and overkill wattage). had to spend another 15,000 Baht on a frequency controlling device to reduce RPMs stepless.

lesson learned! a couple of years later i built a small house for our staff, had a whirly bird installed and attached an electric fan to the whirly. total cost if i recall correctly was approximately 5,000 Baht which also included a cheap timer.

[Naam]

PU foam directly under the tiles is also going to insulate from heat *getting out* through the tiles once the sun goes down. Naam is correct - he's saying all it will do is shift the heat to another time of day. Reflect heat at the tiles, insulate at the ceiling.

I'm afraid I don't buy that either, heat rises and doesn't disperse from the roof tile in a downwards direction (which is where the foam is located). That fact notwithstanding, I may be able to agree of naams point about delay, as mentioned previously, subject to a better understanding of the thickness of foam applied. My suspicion is that thinly applied foam on a very hot day will be defeated quickly, a thicker layer of foam under more normal conditions will likely work well.

...but only delays the heat built-up without attic ventilation.

note: not all heat rises / disperses "UP". any heated up medium radiates in all directions be it roof tiles, roof steel structure, hot air and even pussies. (thermo-physics 100.01²)

[Preacher]

One more question preacher, is this a new build that you can adjust?

The building will start this week, so there is time to adjust the plans. The current plan is what appears a closed roof with no vents, only vents at the bottum side where it will hangover the wall.

Many houses built here in Uttaradit and we are the hottest province in Thailand with tempertures reaching 44 degrees once in a while. Good insulation wil definatly be worth it.

[chiang mai]

In that case you have lots of choices, a smaller top hat type roof at the peak to let the hot air out, a gable or two to achieve the same, vented ridge tiles perhaps not the best solution given that you don't appear to have a horizontal ridge. Alternatively, if you can get them shipped in from OS, the following are great and inexpensive:

http://www.universaltileventilators.com.au/index.php/products/tile-ventilator

Click on Products, roof ventilation and watch the video, I found it really useful.

[chiang mai]

Actually I now have a related question that pertains to attic insulation:

It's been agreed that foil backed insulation needs to be installed with the foil side facing the heat source, in Thailand that means installing it with the foil facing the roof, this to prevent condensation and to reflect the heat back towards the roof.

But most attic insulation in Thailand seems to be encased entirely in foil. Whilst that allows for heat to be reflected back towards the tiles it must surely mean that there is a potential for condensation build up on the underside, or have I missed something?

[NeverSure]

Some very good stuff here.

It is important to get sufficient ventilation in both roof/ridge/gable and also in the soffits. HERE is a calculator. Sorry it isn't metric. Scroll down to do soffit sizes too.

I've never heard of attic floor insulation having foil as mentioned earlier and I can see where that would cause moisture problems. The two ways I've seen it is in fiberglass batts or battens and as loose blown in fiberglass. It needs to breath a little.

Attic floor insulation is much better than under the roof. As Naam said that just slows the heat down. It's important to isolate/insulate the rooms below, from the attic.

To recap, heat rises and it's vital to have airflow being pulled in at the soffits by hot air that is rising and exiting up high. That is the power to evacuate the attic continuously, replacing it with outside air the moment it begins to heat until it is back down to outside temperature at some point. Insulate the hotter attic from the living space and that's the best you can do.

Cheers

[jsgatse]

Hi All,

I'm the guy who originally started this thread - thanks to all who have replied.

But, I'm now having "analysis paralysis" based on all the info (a lot of it conflicting!).

I'd like to take this a step at a time....

So, based on what you all know, and have read...as my first step, should I:

1) Put a whirlybird at the highest possible point in my attic roof (fyi, i do have some soffits in the roof overhang/lowest part of my attic which would allow for cooler air to be drawn in)?

or

2) Insulate the interior attic ceiling (aka, the bottom of my roof tiles) with foil reflective insulation?

or

3) Put down insulation on the interior attic floor (aka on the ceiling of my 2nd/top floor)?

If you guys were going to take one step this year - which one of these would you do?

Thanks!

-Scott

[Forkinhades]

Whirlybird

[NeverSure]

Please do the calculation to be sure you have enough ventilation area both at soffits and up high. Without that, and it's the cheap part, everything else will suffer.

With the turbine you introduce additional possible problems. They do wear out, bearings get noisy, and they can attract critters of many sorts. I've seen them damaged by high winds. There is already a lot of power generated by the heated air rising. It won't stay in the attic at all if there's enough ventilation. Up to you.

Once you have that proper ventilation the next step would be to insulate the ceiling of the top floor, putting the insulation on the floor of the attic. After that everything you do is marginal, incremental, and questionable as to being worthwhile. When you insulate the floor of the attic be sure it's restrained from blocking the soffit vents.

Cheers

Edited May 1, 2015 by NeverSure

[chiang mai]

Hi All,

I'm the guy who originally started this thread - thanks to all who have replied.

But, I'm now having "analysis paralysis" based on all the info (a lot of it conflicting!).

I'd like to take this a step at a time....

So, based on what you all know, and have read...as my first step, should I:

1) Put a whirlybird at the highest possible point in my attic roof (fyi, i do have some soffits in the roof overhang/lowest part of my attic which would allow for cooler air to be drawn in)?

or

2) Insulate the interior attic ceiling (aka, the bottom of my roof tiles) with foil reflective insulation?

or

3) Put down insulation on the interior attic floor (aka on the ceiling of my 2nd/top floor)?

If you guys were going to take one step this year - which one of these would you do?

Thanks!

-Scott

Easy, attic floor insulation, hands down.

I have a friend who just installed a whirlybird, he's very disappointed with the performance.

Although, whilst you say you have soffit vents I presume you don't have an exhaust or exit vent in the roof, hence the whrlybird? That being the case, maybe there's a fourth option which is to instal an exhaust vent in either the gable, ridge or peak.

[chiang mai]

Some very good stuff here.

It is important to get sufficient ventilation in both roof/ridge/gable and also in the soffits. HERE is a calculator. Sorry it isn't metric. Scroll down to do soffit sizes too.

I've never heard of attic floor insulation having foil as mentioned earlier and I can see where that would cause moisture problems. The two ways I've seen it is in fiberglass batts or battens and as loose blown in fiberglass. It needs to breath a little.

Attic floor insulation is much better than under the roof. As Naam said that just slows the heat down. It's important to isolate/insulate the rooms below, from the attic.

To recap, heat rises and it's vital to have airflow being pulled in at the soffits by hot air that is rising and exiting up high. That is the power to evacuate the attic continuously, replacing it with outside air the moment it begins to heat until it is back down to outside temperature at some point. Insulate the hotter attic from the living space and that's the best you can do.

Cheers

In the US they sometimes instal a plastic sheet which acts as a vapor barrier, in the UK and Europe it's mostly aluminum foil coating on fiberglass.

[NeverSure]

I have never seen a vapor barrier in an attic. They are standard directly on the ground under the house if there's a crawl space. That crawl space is also vented.

Without ventilation moisture can cause all kinds of problems. Moisture in room air will migrate through the ceiling and into the attic where it can move out with attic ventilation.

I have seen insulation encased in Kraft paper which isn't moisture proof and this helps protect current and future people including the worker from the fiberglass fibers which are a bit nasty. Kraft paper slows moisture down a bit but doesn't stop it.

It is important to never have a place that can't dry out.

[NeverSure]

Venting the attic isn't just to control heat, it removes moisture. Look at THESE pictures of attic mold.

[chiang mai]

I have never seen a vapor barrier in an attic. They are standard directly on the ground under the house if there's a crawl space. That crawl space is also vented.

Without ventilation moisture can cause all kinds of problems. Moisture in room air will migrate through the ceiling and into the attic where it can move out with attic ventilation.

I have seen insulation encased in Kraft paper which isn't moisture proof and this helps protect current and future people including the worker from the fiberglass fibers which are a bit nasty. Kraft paper slows moisture down a bit but doesn't stop it.

It is important to never have a place that can't dry out.

"I have never seen a vapor barrier in an attic".

"In order to prevent condensation from forming, a vapour barrier should be placed on the warm side of your insulation to stop warm, moist air from condensing on a cold surface inside your wall.

In cold climates like Canada, for most of the year the vapour barrier should be on the inside of the insulation. In hot climates like the southern U.S. for example, it should be installed on the outside of the insulation.

In both cases, the vapour barrier is tasked with preventing warm, humid air from shedding its moisture as it meets a cool surface, no matter which direction it is travelling.

The most important thing to realize is that there is no fixed rule regarding vapour barriers. Building practices should always be determined by the climate in which you are building".

http://www.ecohome.net/guide/difference-between-air-barriers-vapour-barriers

And this, this with emphasis on the words aluminum foil, ceiling, roof, condensation.

http://en.wikipedia.org/wiki/Vapor_barrier