Ceiling Insulation Types? Recommendations please?

[ElephantEgo]

Can anyone recommend what they know is a good ceiling insulation variety?

-I would like to have a price around 100-150 THB/Sqm.
-With the good R-factor to keep my house cool.
-Also hopefully some sound-dampening (so I cannot always hear everything in the other rooms).

[CharlieH]

Do a search on this very forum there are topics discussing it at length........see below

 

SCG R37, 150 mm is what I used.

 

 

 

 

 

[eyecatcher]

The SCG staycool is arguably the best 75mm thick insulation around, I thinks it costs about 350bt for 2.4m2 when not on special offer.

 

However during a wander around a Thai watsadu store I noticed that abetter Rvalue could be achieved by using two 50mm layers of a R21 homegrown brand for much less than 350bt.

 

So if I were to do mine again, I would like have an extra inch as I am sure you would!

[Kwasaki]

Thicker the better.

[ElephantEgo]

So I read those two threads and thanks for sharing that!

 

Some say the thicker the better and some said that 2-4 inches is all that is needed. (75 MM is 3 inches). Some are using double that!

 

I guess if I choose the SCG or some homegrown brand, its okay either way perhaps. But I should look at the R value and maybe double up with dual layers.

 

One question that did not get answered is about the sound factor. I would like to block out noise carrying between rooms. Does the SCG stuff help with that? When I was at Homepro they said no, but another brand helps. Any thoughts people?

 

As for the installing: it now costs 200 THB per Sqm at Homepro which is a FORTUNE by Thai labor standards! Last time I checked it was only 150 per Sqm but they increased the price recently.

 

Therefore I have found a few contractors in Phuket who can do for about half that price or even less. But of course I need to be doing some quality control to make sure they do it right and no fires will eventually break out!

 

My understanding is that the insulation gets rolled out and the existing wiring should be re-positioned above that? Ideally of course, the wires will be in yellow pipes already! A problem if they are not, right?

Also holes should be made in the insulation where the light fixtures etc will be. Yes? Even for LED lights that produce less heat?

I have a suspended ceiling so installers will need to cut holes for the suspension wires or place the insulation roles between them.

 

If I understand correctly, the proper installation will require that they also tape up the cut insulation batts to re-seal them or am I misunderstanding something?

 

Thanks for your advice guys!

 

 

[sometimewoodworker]

8 hours ago, JakeR said:

One question that did not get answered is about the sound factor. I would like to block out noise carrying between rooms.

All ceiling insulation will reduce sound transmission through the ceiling to some degree.

 

Most noise transmission between rooms is not through the ceiling.

 

There is a lot of information regarding sound transmission available DAGS and you will find it.

 

Mass is usually your friend, AAC is also good.

[Don Chance]

Heat rises. In a tropical climates you don't insulate ceilings. Actually in any climate. We insulate roofs and walls to keep heat in. Those 'stay cool' products are a scam.

 

You want to keep humid air out by putting a vapor barrier on the exterior.

 

Do you have a condo? You can install drywall on resilient channeling will reduce noise. Same with the walls.

 

Electricity is so cheap in Thailand you don't worry about AC bills. Insulation will likely cause mold problems.

[sometimewoodworker]

2 hours ago, Don Chance said:

Heat rises. In a tropical climates you don't insulate ceilings.

Insulation in ceilings works just as well in a tropical climate. It just has a different purpose.

 

2 hours ago, Don Chance said:

Actually in any climate. We insulate roofs and walls to keep heat in.

No we don't. Insulation is designed to stop heat transfer. It doesn't care which way the transfer happens.

Ovens are insulated. 

Fridges are insulated.

 

Think, tropical house = fridge

house in Greenland = oven

 

Does that make things clear?

2 hours ago, Don Chance said:

Those 'stay cool' products are a scam.

No they are not. They reduce AC bills and reduce sound transmission, neither of these are a scam.

 

2 hours ago, Don Chance said:

Electricity is so cheap in Thailand you don't worry about AC bills.

That is not the attitude of many here. Should you be wasteful just because somthing is cheap?

 

2 hours ago, Don Chance said:

Insulation will likely cause mold problems.

Why? Many, or even most users of insulation also use AC and that keeps humidity down.

[Don Chance]

17 hours ago, sometimewoodworker said:

Insulation in ceilings works just as well in a tropical climate. It just has a different purpose.

 

No we don't. Insulation is designed to stop heat transfer. It doesn't care which way the transfer happens.

Ovens are insulated. 

Fridges are insulated.

 

Think, tropical house = fridge

house in Greenland = oven

 

Does that make things clear?

No they are not. They reduce AC bills and reduce sound transmission, neither of these are a scam.

 

That is not the attitude of many here. Should you be wasteful just because somthing is cheap?

 

Why? Many, or even most users of insulation also use AC and that keeps humidity down.

Yes think of a refrigerator. What happens when you turn off the frig? It needs to be vented or it will quickly turns to mold. Are you going to run your AC 365 days a year 24/7? What if you leave?  Even AC's are not that efficient. Also a frig is a continual insulated wall.

 

The concrete walls need to dry out, concrete absorbs moisture. You have to ask yourself why so many Thai building have mold.

 

It is not the heat what is the problem it is the humidity. AC works by removing humidity not heat.  Heat and humidity will always rise even if you have AC and fans running. If you have insulation up there you are asking for mold problems, it needs to rise up and dispersal through the roof. The roof blocks the sun which shades you house and keeps it cool. Many Thai building hardly have a roof or even exterior water proofing.

 

In cold climate the heating drys out the building for 8 months a year. You keep the heat in with insulation and vapour barriers. The summer is not so hot or humid like Thailand.

 

The best thing you can do is keep you house light and dry with lots of air gaps so things can dry out. Have drywall in the interior with a gap.

Keep the moisture out from the ground and walls with exterior vapor barriers. Most building in Thailand have a wet slab from the ground which pushes a lot of moisture into the building, AC is not enough to remove, worse in the monsoon. So that is most important way to reduce energy and humidity in a building, is have a raised bungalow or rubber/foam barrier under the slab in the ground.

 

 

[alan grice]

Thicker the better.

Where can You buy Irish Insulation in Thailand.?.


Sent from my iPhone using Thailand Forum - Thaivisa mobile app

[sometimewoodworker]

2 hours ago, Don Chance said:

It is not the heat what is the problem it is the humidity. AC works by removing humidity not heat. 

Do get yourself an education, or even if you have one, stop inventing rubbish.

 

AC transfers HEAT from inside to outside, removing heat. As cool air holds less moisture than hot air it also removes that by either pumping it outside or by gravity.

 

It can also function in dehumidifying mode, though that usually also removes heat.

2 hours ago, Don Chance said:

If you have insulation up there you are asking for mold problems, it (moisture) needs to rise up and dispersal through the roof.

More BS. How dose moisture disperse through metal roofs?

 

2 hours ago, Don Chance said:

Most building in Thailand have a wet slab from the ground which pushes a lot of moisture into the building, AC is not enough to remove, worse in the monsoon.

More BS my AC (small) in my old house was perfectly adequate to keep the humidity down to between 60% & 70% during both the hot and wet seasons, it did not run 24/7 probably 8 or so hours a day.

 

2 hours ago, Don Chance said:

The concrete walls need to dry out

That is true after building.

 

2 hours ago, Don Chance said:

concrete absorbs moisture.

BS it only absorbs water if it is wet and has no coating to prevent that. 

 

You have heard that even Thai people paint their walls haven't you? This lets water run off the walls easily, or didn't you notice that?

 

2 hours ago, Don Chance said:

Yes think of a refrigerator. What happens when you turn off the frig?

My fridges turn off quite often ???? (when they get down to the set point)

2 hours ago, Don Chance said:

Are you going to run your AC 365 days a year 24/7?

No I'm not, no I don't, there is no need as just like my fridge it only needs to run some of the time to either reduce the temperature or humidity in the house

 

FYI the humidity during the last rainy season (there is no monsoon in northeast Thailand) inside the house was around 60%~70% whilst outside it was 80%~100% our AC ran at night in one room and occasionally during the day in our main room.

 

2 hours ago, Don Chance said:

Also a frig is a continual insulated wall.

The short form is fridge, 

 

you do realise that the talk of fridges and ovens was so you would understand how insulation works, as from your posting you seem to have little grasp of the principles.

[Kwasaki]

10 hours ago, alan grice said:

Where can You buy Irish Insulation in Thailand.?.
 

If your in Bkk you can get insulation from a place on the left 22 turning before KFC. 

[Don Chance]

8 hours ago, sometimewoodworker said:

More BS. How dose moisture disperse through metal roofs?

 

 

[sometimewoodworker]

2 hours ago, Don Chance said:

 

[MikeN]

On 9/29/2019 at 10:45 AM, Don Chance said:

Heat rises. In a tropical climates you don't insulate ceilings. Actually in any climate. We insulate roofs and walls to keep heat in. Those 'stay cool' products are a scam.

Tell me why people in Australia insulate their ceilings then, when it gets hotter there than in Thailand ? The ceiling insulation is not a one way thing .. in cold climates it does keep warm air inside the room, but in hot climates it also stops hot air coming down through the ceiling.

[willi2006]

On 10/1/2019 at 3:05 PM, MikeN said:

Tell me why people in Australia insulate their ceilings then, when it gets hotter there than in Thailand ? The ceiling insulation is not a one way thing .. in cold climates it does keep warm air inside the room, but in hot climates it also stops hot air coming down through the ceiling.

Australia's government distinguishes several major and more than 60 minor climate zones. The recommendations, e.g. for ceiling insulation, are different according to the climate zone. See YourHome http://www.yourhome.gov.au.

Thailand is tropical, i.e. hot and humid, similar to the Northern Territories.

Interesting is the case study "Darwin River, Northern Territory" http://www.yourhome.gov.au/case-studies/darwin-river-northern-territory

[willi2006]

On 9/30/2019 at 10:14 PM, sometimewoodworker said:

 

There are no simple answers to such questions. The simple answers take into account only one or a few parameters. But to keep a house cool or to calculate the energy needed to cool a house has to take into account tens, may be hundreds of parameters. There are parameters depending on location, site, building, usage. They also vary with date and time.
In regard to location there are e.g. temperature, humidity, sun radiation, wind, rain, clouds. These parameters vary with date and time.
In regard to site there are e.g. shading, ground temperature. Some of  them vary with date and time.
In regard to building there are e.g. shadings, construction of walls, windows, ceiling, roof. Some of  them vary with date and time, e.q. windows opened, ventilating fans running.
In regard to usage there are e.q. people, electrical equipment, other heat producing stuff. Is air conditioning used? To which temperature, humidity is it set? Some of  them vary with date and time.
The best I know is using BEST https://www.buildingenergysoftwaretools.com/.
E.g. EnergyPlus https://energyplus.net/.
You not only can see how the required cooling energy changes with construction but also how much it changes. In addition you can look how output variables like room or roof temperature change with date and time.
Calculating one case showed that a "fly roof" construction
http://www.yourhome.gov.au/sites/prod.yourhome.gov.au/files/pdf/YOURHOME-PassiveDesign-DesignForClimate_0.pdf
without insulation requires less cooling energy per year. A 4 m high hip roof requires 100% more. The hip roof with 90 mm fiber ceiling insulation and 50 mm roof insulation as shown in the quoted image requires 75% more. With additional roof ventilation at 10 m³/s 63% more is required.
Of course these results will differ from case to case as the parameters are different.

Remind: No simple answers to complex situations.

[sometimewoodworker]

@willi2006 the difficulty with using Australian examples is that very little of Australia is relevant in that mostly it has lower humidity than Almost everywhere in Thailand.

 

So the recommendation to ventilate works there but here you will probably have  uncomfortably high humidity by doing that.

[willi2006]

Using any Australian recommendations is no good idea because climate is very different there. The recommendations for the Northern Territories are useful as the climate there is similar to Thailand: tropical, i.e. hot and humid. See my first post.

https://en.wikipedia.org/wiki/Darwin,_Northern_Territory#Climate

 

Calculations were done with climate data from Khon Kaen, Thailand.
High humidity can cause discomfort in rooms but hardly when it's in the roof.

[Don Chance]

5 hours ago, willi2006 said:

 

Calculations were done with climate data from Khon Kaen, Thailand.
High humidity can cause discomfort in rooms but hardly when it's in the roof.

Yes humidity is the problem. It is like a shower or kitchen with high humidity it needs to be vented. If you put insulation up there how will it vent? The insulation will act like a vapour barrier and cause mold.

You want to have a ceiling which is just drywall so the humidity can transfer to the roof structure and then be vented out.

 

To keep heat out you can use a radiate heat barrier.

 

[sometimewoodworker]

5 hours ago, Don Chance said:

Yes humidity is the problem. It is like a shower or kitchen with high humidity it needs to be vented. If you put insulation up there how will it vent?

Easily as any competent design will extract the humid air using an extractor fan or cooker hood it will exhaust the humid air through the walls no architect worth their pay will design like that, they will certainly not allow venting into a roof space.

 

Now you can be a cheap Charlie and not do a proper job, but done right there is minimal humid air venting into the roof space.

 

5 hours ago, Don Chance said:

To keep heat out you can use a radiate heat barrier.

 

If you are thinking that that video has its science correct you are sadly mistaken. That website is selling their product and have a poor understanding of the science if the videos they publish are a guide. Certainly installing radiant barrier like that is better than not installing it but is is less effective that a radiant barrier installed directly onto or under a roof material, because it permits the area between the roof and barrier to heat the air in in that region.

 

From the Oak Ridge National Laboratory 

Quote

A radiant barrier reduces the amount of heat radiated across an air space that is adjacent to the radiant barrier.

From the US department of energy 

Quote

A radiant barrier is typically a layer of aluminum foil-reflecting material placed in the attic next to an air space to block radiant heat transfer between a heat-radiating surface (such as a hot roof) and a heat-absorbing surface (such as conventional attic insulation).

Note it may reflect heat back but it mainly functions by NOT radiating heat.

 

From roof surface 

 

From foil surface. Note it is single sided so no reflective function.

 

[sirineou]

On 9/28/2019 at 11:45 PM, Don Chance said:

Heat rises. In a tropical climates you don't insulate ceilings. Actually in any climate. We insulate roofs and walls to keep heat in. Those 'stay cool' products are a scam.

 Heat does not rise, what rises ia hot air. Heat radiates . heat radiation is impeded by insulation,  

When not in Thailand , I live in Florida. where the climate is similar to Thailand.

  All houses in Florida have  ceiling insulation of at least R30 for all living areas.

"Residential requirements for insulation are divided by the location in the home. Framed wall insulation must meet or exceed R-13. For block walls, interior insulation must meet or exceed R-7.8, and exterior insulation must be R-6. Ceiling insulation must be much higher at R-30, and a raised floor must be at least R-13 "

https://www.myenergymonster.com/fl/brief-overview-insulation-requirements-florida/

These  codes were developed by experts on the subject. 

 

[willi2006]

2 hours ago, sometimewoodworker said:

a radiant barrier installed directly onto or under a roof material, because it permits the area between the roof and barrier to heat the air in in that region.

 

From the Oak Ridge National Laboratory 

Quote

A radiant barrier reduces the amount of heat radiated across an air space that is adjacent to the radiant barrier.

From the US department of energy 

Quote

A radiant barrier is typically a layer of aluminum foil-reflecting material placed in the attic next to an air space to block radiant heat transfer between a heat-radiating surface (such as a hot roof) and a heat-absorbing surface (such as conventional attic insulation).

That's quite different:

"a radiant barrier installed directly onto or under a roof material"

and

"an air space that is adjacent to the radiant barrier"

and

"placed in the attic next to an air space".

An air space is required. Attaching the foil directly to the roof material, e.g. roof tiles or metal sheets, without air gap just increases the thickness of the roof material which has almost no effect. Only an air gap between roof material and foil reduces heat conduction and heat radiation.

See also "Heat Transfer" https://en.wikipedia.org/wiki/Heat_transfer.

EnergyPlus simulations achieve the same result.

[sfokevin]

My modern Thai house has simple concrete board ceiling suspended on a steel frame the entire house tile hip roof has a 1+ meter overhang and about a dozen steel frame sliding glass doors... There is absolutely no way putting a layer of insulation above the ceiling concrete board would cause any vapor barrier within the house or in the attic - There are just too many ways for air to flow... The tile roof has million of cracks around each tile (I can see light in my attic everywhere)... the overhangs all have vents where they meet the tile roof... Every sliding door is of basic design and in no way creates a vapor block so humidity is in no way going to accumulate in my attic or house by placing insulation above the ceiling boards... Before I had insulation installed the ceiling was hot to the touch inside now it is the same as room temp... The insulation stops the hot attic air from moving into the house and there as plenty of ventilation... I also have fans to circulate fresh cooler air into the attic... I also replaced all the old pot lights (There were over 30 of them - Basically each a 4” hole in the ceiling!) with LED lights and sealed the lights so air from attic can not flow into the house... The insulation has worked very well for me...

[willi2006]

3 hours ago, sirineou said:

...

When not in Thailand , I live in Florida. where the climate is similar to Thailand. ...

These  codes were developed by experts on the subject.  ...

Imho they aren't similar, especially in regard that the experts of the U.S. DOE define 24 °C as comfortable.

                     Miami    Bangkok     Khon Kaen
Record high    37.0 °C     40.2 °C     42.6 °C
Average high   27.4 °C     33.3 °C     32.8 °C
Daily mean     24.6 °C     28.6 °C     26.9 °C
Average low    21.7 °C     24.9 °C     22.3 °C
Record low      0.0 °C     10.0 °C       6.4 °C

 

Miami, tropical monsoon climate: https://en.wikipedia.org/wiki/Climate_of_Miami
Bangkok,  tropical savanna https://en.wikipedia.org/wiki/Bangkok#Climate
Khon Kaen, tropical savanna: https://en.wikipedia.org/wiki/Khon_Kaen#Climate

 

These are just characteristic figures for temperature. Much more exact is using the waveforms for temperature, humidity, sun radiation, wind, rain, cloud coverage over a full design year which are derived from the climate data of many years, as used in building energy simulation https://www.buildingenergysoftwaretools.com/.

[willi2006]

1 hour ago, sfokevin said:

... Before I had insulation installed the ceiling was hot to the touch inside now it is the same as room temp... The insulation stops the hot attic air from moving into the house and there as plenty of ventilation... I also have fans to circulate fresh cooler air into the attic...

Which temperature is in the roof space? I bet in summer and during day hotter then outside. I measured up to 65 °C. Ventilation of about 1 m³/s had no measurable effect.

Insulation doesn't stop heat conduction. It gets only reduced. Without cooling it still gets hotter in the house but slower when the attic is hotter then the room. In the night when it's hotter in the room then in the attic the heat which is already in the room and the heat which is produced by people and electric appliances in the room also gets out slower through the insulation. This has been reported and pointed out already several times in this forum, e.g.

When parking a car in an open space it gets very hot inside even when it's cloudy and there's no sun to see up to and more then 60 °C. Applying window screens or using a blanket can slow down the heating. Also opening the windows a little bit won't help much. All doors must be open to see an effect.

 

Parking the car in a carport makes a big difference. Only the outside air temperature and radiation which is reflected into the carport heats the car.

 

It's about the same with all these closed roofs. In a tropical climate as in Thailand it's hotter, much hotter inside the roof space then outside, during the day except on some cold winter days and cold nights. Better then insulating the roof is a fly roof which shades the building as a carport shades the car. Between the fly roof and the ceiling it should not be or only a little bit hotter then the outside air.

 

For more information see "Australian Government - YourHome Design for climate"

http://www.yourhome.gov.au/sites/prod.yourhome.gov.au/files/pdf/YOURHOME-PassiveDesign-DesignForClimate_0.pdf

or "What is a fly roof?" https://inexpensivehomebuilding.blogspot.com/2007/04/what-is-flying-roof-how-to-make-flying.html

or search the internet for "fly roof".

 

[sirineou]

1 hour ago, willi2006 said:

Imho they aren't similar, especially in regard that the experts of the U.S. DOE define 24 °C as comfortable.

                     Miami    Bangkok     Khon Kaen
Record high    37.0 °C     40.2 °C     42.6 °C
Average high   27.4 °C     33.3 °C     32.8 °C
Daily mean     24.6 °C     28.6 °C     26.9 °C
Average low    21.7 °C     24.9 °C     22.3 °C
Record low      0.0 °C     10.0 °C       6.4 °C

 

Miami, tropical monsoon climate: https://en.wikipedia.org/wiki/Climate_of_Miami
Bangkok,  tropical savanna https://en.wikipedia.org/wiki/Bangkok#Climate
Khon Kaen, tropical savanna: https://en.wikipedia.org/wiki/Khon_Kaen#Climate

 

These are just characteristic figures for temperature. Much more exact is using the waveforms for temperature, humidity, sun radiation, wind, rain, cloud coverage over a full design year which are derived from the climate data of many years, as used in building energy simulation https://www.buildingenergysoftwaretools.com/.

 For then purposes of this discussion they are similar

[GarryP]

16 minutes ago, willi2006 said:

Which temperature is in the roof space? I bet in summer and during day hotter then outside. I measured up to 65 °C. Ventilation of about 1 m³/s had no measurable effect.

Insulation doesn't stop heat conduction. It gets only reduced. Without cooling it still gets hotter in the house but slower when the attic is hotter then the room. In the night when it's hotter in the room then in the attic the heat which is already in the room and the heat which is produced by people and electric appliances in the room also gets out slower through the insulation. This has been reported and pointed out already several times in this forum, e.g.

When parking a car in an open space it gets very hot inside even when it's cloudy and there's no sun to see up to and more then 60 °C. Applying window screens or using a blanket can slow down the heating. Also opening the windows a little bit won't help much. All doors must be open to see an effect.

 

Parking the car in a carport makes a big difference. Only the outside air temperature and radiation which is reflected into the carport heats the car.

 

It's about the same with all these closed roofs. In a tropical climate as in Thailand it's hotter, much hotter inside the roof space then outside, during the day except on some cold winter days and cold nights. Better then insulating the roof is a fly roof which shades the building as a carport shades the car. Between the fly roof and the ceiling it should not be or only a little bit hotter then the outside air.

 

For more information see "Australian Government - YourHome Design for climate"

http://www.yourhome.gov.au/sites/prod.yourhome.gov.au/files/pdf/YOURHOME-PassiveDesign-DesignForClimate_0.pdf

or "What is a fly roof?" https://inexpensivehomebuilding.blogspot.com/2007/04/what-is-flying-roof-how-to-make-flying.html

or search the internet for "fly roof".

 

Okay. So Thailand is similar to zone 1 in the first link. It says that you should only insulate in the ceilings of rooms that are to be air-conditioned. Therefore, if I build a bungalow, I would then only be insulating the ceilings above the two bedrooms and my workout room. We would not use air-con in the living room, kitchen or bathrooms so no insulation above those. Sounds weird. Surely, if I make sure the roof is well insulated with reflective insulation, there is a good airflow and the roof eaves are wide, then insulating the ceilings of all rooms would be best. 

 

I want a comfortable house in which I can sit in the living room and watch TV without the need for aircon, but my fear is that this would be so much more difficult in a bungalow than a two storey house.    

[willi2006]

1 hour ago, GarryP said:

...

I want a comfortable house in which I can sit in the living room and watch TV without the need for aircon, but my fear is that this would be so much more difficult in a bungalow than a two storey house.    

Well, I would like to do the same.

Currently I think about a bungalow with fly roof with overhang of 3 m. Calculations with EnergyPlus resulted in 50% more cooling energy over the design year for 1 m overhang and 10% less for 6 m overhang. Thus 3 m seems to be quite okay. 3 m overhang results also in a veranda around the house with a lot of space to sit outside when possible. The major design points are as close as possible to a typical current house in Thailand to avoid problems with workers lacking any required special skills:

• Foundation 200 mm concrete.
• Slab 150 mm concrete, tiled.
• Walls 3 m high, plastered 75 mm AAC.
• Windows and doors single glass 6 mm.
• Ceiling 50mm concrete board  with 75 mm AAC on top.
• Fly roof metal sheet with 50 mm PU to reduce heat transfer and noise from rain.
• Internal heat sources: 2 people and 350 W electrical equipment around the clock.
• Simple air conditioning set at 28 °C around the clock for living and sleeping rooms.
• Other space free running.
• Climate data of Khon Kaen.
• Terrain suburbs.
• Ground temperature 25 °C all year.
• Simulation period full calendar year.

As I don't (yet) have the thermal parameters of the materials available here standard values are used. The geometry of the model used for the EnergyPlus simulations looks like:

Remind there's no simple answer to a complex case. As there are a lot of parameters which interact with each other it is not possible to simple transfer results to a similar case. Better use BEST https://www.buildingenergysoftwaretools.com/

[sometimewoodworker]

6 hours ago, willi2006 said:

An air space is required. Attaching the foil directly to the roof material, e.g. roof tiles or metal sheets, without air gap just increases the thickness of the roof material which has almost no effect. Only an air gap between roof material and foil reduces heat conduction and heat radiation.

You are misunderstanding the physics. There is no air gap needed on the hot side of a radiant barrier in Thailand where keeping heat out is required. Radiant barriers aren't concerned about conduction.

 

You are talking about the reflective properties of double sided material, this is incidental to the poor radiant property's and will degrade over time as you get dust building up on the top side of the material.

 

The important fact is that the silver (aluminium) foil is a very poor emitter of radiation in the infrared (heat) it only radiates 5% compared to a black body.

 

There are 3 recommend ways (US department of energy) of fitting a radiant barrier in a new build. They are equally effective. The choice of fitting method is dependent on the construction process.

 

note that only method 2 and 3 work in Thailand (unless you like termites) please also note that both types 1 and 2 can use single sided material and that if you use that, it MUST be installed shiny side down.