Insulation

[jumbo]

I am planning to build a house. In Europe we build 'double walls' wiht some airspace between them and we have roofinsulation

I wondered if something like that would help to keep the heat out as well?

Any suggestions?

J

[ilyushin]

You can use mineral wool, fiber glass, Expanded polystyrene (EPS) or insulation foil. There are also a number of injection methods and bio mass.

[jumbo]

You can use mineral wool, fiber glass, Expanded polystyrene (EPS) or insulation foil. There are also a number of injection methods and bio mass.

Thanks for the reply, I some of the methods but I was more wondering if it would be effective

What do you think

J

[ilyushin]

You can use mineral wool, fiber glass, Expanded polystyrene (EPS) or insulation foil. There are also a number of injection methods and bio mass.

Thanks for the reply, I some of the methods but I was more wondering if it would be effective

What do you think

J

You must consider heat retention and heat expansion. Check google search. This will depend on interior and exterior wall materials. Insulation like Wool and fiber glass don't allow heat to pentrate the exterior walls and also don't allow interior air cool or hot to escape acting as a trap if the windows and doors and windows proper shut. The EPS will retain heat olny for a short period and also traps the cool or hot air like the above mentioned. Foil is mor refective and doesn't retain heat and only acts as a trap depending on the thickness. Bio mass can retain and trap. It depends on the mass, but some do create a nest for bugs and the like if not properly sealed.

[ilyushin]

FYI

Insulation is rated in terms of thermal resistance, called R-value, which indicates the resistance to heat flow. The higher the R-value, the greater the insulating effectiveness. The R-value of thermal insulation depends on the type of material, its thickness, and density. In calculating the R-value of a multi-layered installation, the R-values of the individual layers are added. Installing more insulation in your home increases R-value and the resistance to heat flow.

The effectiveness of an insulated wall or ceiling also depends on how and where the insulation is installed. For example, insulation which is compressed will not give you its full rated R-value. Also, the overall R-value of a wall or ceiling will be somewhat different from the R-value of the insulation itself because some heat flows around the insulation through the studs and joists. That is, the overall R-value of a wall with insulation between wood studs is less than the R-value of the insulation itself because the wood provides a thermal short-circuit around the insulation. The short-circuiting through metal framing is much greater than that through wood-framed walls; sometimes the metal wall's overall R-value can be as low as half the insulation's R-value.

[ilyushin]

Form Method of Installation Where Applicable Advantages

Blankets: Batts or Rolls

Fiber glass

Rock wool

Fitted between studs, joists and beams All unfinished walls, floors and ceilings Do-it-yourself.

Suited for standard stud and joist spacing, which is relatively free from obstructions.

Loose-Fill

(blown-in)

or Spray-applied

Rock wool

Fiber glass

Polyurethane foam

Blown into place or spray applied by special equipment Enclosed existing wall cavities or open new wall cavities;

Unfinished attic floors and hard to reach places

Commonly used insulation for retrofits (adding insulation to existing finished areas).

Good for irregularly shaped areas and around obstructions.

Rigid Insulation

Extruded polystyrene foam (XPS)

Expanded polystyrene foam (EPS or beadboard)

Polyurethane foam

Polyisocyanurate foam

Interior applications: Must be covered with 1/2-inch gypsum board or other building-code approved material for fire safety.

Exterior applications: Must be covered with weather-proof facing

Basement walls

Exterior walls under finishing (Some foam boards include a foil facing which will act as a vapor retarder. Please read the discussion about where to place, or not to place, a vapor retarder.)

Unvented low slope roofs.

High insulating value for relatively little thickness.

Can block thermal short circuits when installed continuously over frames or joists.

Reflective Systems

Foil-faced paper

Foil-faced polyethylene bubbles

Foil-faced plastic film

Foil-faced cardboard

Foils, films, or papers: Fitted between wood-frame studs joists, and beams Unfinished ceilings, walls, and floors Do-it-yourself.

All suitable for framing at standard spacing. Bubble-form suitable if framing is irregular or if obstructions are present.

Effectiveness depends on spacing and heat flow direction.

Loose-Fill

(poured in)

Vermiculite or Perlite Not currently used for home insulation, but may be found in older homes

[GuestHouse]

You can, but be careful as I have seen many applications where the application of insulation and building methods is patched together wrongly – If you are designing a house you should consider how the insulation works as a ‘system’ rather than individual elements.

Example: Double wall insulation.

In a cold climate, this works by providing a barrier to the heat loss from within the building (heat is traveling outwards). Air is trapped in the inner space, to help prevent heat flow from inside to outside.

However, this basic idea can be improved on. The main problem with the basic design is air will still move in the gap, stripping heat from the inner core as it does so.

Keep in mind the temperature difference can be extremely high. Perhaps 23Deg C inside the building, with air in the core near freezing (air entering from air vents can be well below freezing), so this ‘heat stripping can be considerable’.

The improvement is to add foam or insulating rock wool to trap the air, reduce it’s movement and prevent that stripping motion.

So in a cold climate, zero air movement is a good thing.

Now consider a hot climate.

The outer surface is getting heated by direct sunlight, there is also an ambient air temperature, in Thailand the ambient air temperature is usually between 26DegC and 32DegC, just a little above what most of us find comfortable.

The outer wall temperature can easily reach 70DecC in direct sunlight (depending on wall color) – Witness burned feet on pure white (normally reflective) sand.

Now here’s a problem. The outer wall has a thermal mass, once hot it will stay hot until it radiates it’s heat to its surrounding. If you trap air in an insulating layer between the outer layer and the inner layer, you will allow that to heat up and pass the heat into the inner core. (Even if the inner core is insulated, the heat is going inwards, perhaps slowed by the insulation, ie Q-Block, but it is nevertheless going inwards).

Note here the inner insulation Qblock is only reducing the rate of heat flow, it is not stopping it.

To reduce this inward flow of heat you can do one of three things, you can reduce the amount of heat stored in the outer wall, or you can reduce the amount of heat passing across the air gap.

Reducing the heat stored in the outer wall can be done in several different ways.

Use lower thermal mass materials (wood cladding being an example) This has the effect that as soon as the sun goes off the wall it rapidly cools to the ambient air temperature. I’m sure we’ve all walked past a wall that is still radiating heat well into the late evening (that is a high thermal mass wall and not what you want on a house in a hot climate).

Color is important, painting your outer walls white will reflect heat rather than allowing heat to be absorbed.

Growing plants, creepers and trees to throw a shade on walls exposed to the sun reduces heat up take. Adding a screen near a wall does the same thing.

And then, making best use of the wall’s air gap, you can encourage airflow between the walls. Remember, the wall might reach 70DegC but the ambient air temperature is very likely to be lower than 32DegC.

To increase airflow, simply add vents at the bottom of the wall and allow the gap of the wall to continue right into the loft space. Then add a vent (or two) to the loft space and close up as many gaps into the loft as possible (especially under the eves).

Now as the roof heats up, hot air rises in the loft space and moves out through the vents, as it does so it draws cold air in through the vents at the bottom of the walls.

This air movement will strip heat from the outer walls and allow it to flow up through the roof vents.

Ideally you would use all these components together to create a system of insulation and cooling. But don’t forget to add bug screens to all the vents!!!

Why Insulation Systems and not Components?

You now have to give some thought as to how to insulate your loft. If, as is popular with Farang builds in Thailand, you add reflective insulation under your roof tiles, you are reducing the heat into the loft space and removing the driving force that is sucking air through the wall space.

So if you are using this wall space draught method, don’t insulate under your tiles, but do add loft insulation mats above your ceiling (I suggest at least 4inches of rock wool with a reflective surface underneath.

Of course if you are not using the cavity walls and air movement to cool the building then the reflective insulation under the tiles is not going to cause a problem with the insulation design of the house. And is a cheap effective way of keeping the roof space cooler. Though I would still add vents and loft matting.

Edited August 24, 2006 by GuestHouse

[ilyushin]

You can, but be careful as I have seen many applications where the application of insulation and building methods is patched together wrongly – If you are designing a house you should consider how the insulation works as a ‘system’ rather than individual elements.

Example: Double wall insulation.

In a cold climate, this works by providing a barrier to the heat loss from within the building (heat is traveling outwards). Air is trapped in the inner space, to help prevent heat flow from inside to outside.

However, this basic idea can be improved on. The main problem with the basic design is air will still move in the gap, stripping heat from the inner core as it does so.

Keep in mind the temperature difference can be extremely high. Perhaps 23Deg C inside the building, with air in the core near freezing (air entering from air vents can be well below freezing), so this ‘heat stripping can be considerable’.

The improvement is to add foam or insulating rock wool to trap the air, reduce it’s movement and prevent that stripping motion.

So in a cold climate, zero air movement is a good thing.

Now consider a hot climate.

The outer surface is getting heated by direct sunlight, there is also an ambient air temperature, in Thailand the ambient air temperature is usually between 26DegC and 32DegC, just a little above what most of us find comfortable.

The outer wall temperature can easily reach 70DecC in direct sunlight (depending on wall color) – Witness burned feet on pure white (normally reflective) sand.

Now here’s a problem. The outer wall has a thermal mass, once hot it will stay hot until it radiates it’s heat to its surrounding. If you trap air in an insulating layer between the outer layer and the inner layer, you will allow that to heat up and pass the heat into the inner core. (Even if the inner core is insulated, the heat is going inwards, perhaps slowed by the insulation, ie Q-Block, but it is nevertheless going inwards).

Note here the inner insulation Qblock is only reducing the rate of heat flow, it is not stopping it.

To reduce this inward flow of heat you can do one of three things, you can reduce the amount of heat stored in the outer wall, or you can reduce the amount of heat passing across the air gap.

Reducing the heat stored in the outer wall can be done in several different ways.

Use lower thermal mass materials (wood cladding being an example) This has the effect that as soon as the sun goes off the wall it rapidly cools to the ambient air temperature. I’m sure we’ve all walked past a wall that is still radiating heat well into the late evening (that is a high thermal mass wall and not what you want on a house in a hot climate).

Color is important, painting your outer walls white will reflect heat rather than allowing heat to be absorbed.

Growing plants, creepers and trees to throw a shade on walls exposed to the sun reduces heat up take. Adding a screen near a wall does the same thing.

And then, making best use of the wall’s air gap, you can encourage airflow between the walls. Remember, the wall might reach 70DegC but the ambient air temperature is very likely to be lower than 32DegC.

To increase airflow, simply add vents at the bottom of the wall and allow the gap of the wall to continue right into the loft space. Then add a vent (or two) to the loft space and close up as many gaps into the loft as possible (especially under the eves).

Now as the roof heats up, hot air rises in the loft space and moves out through the vents, as it does so it draws cold air in through the vents at the bottom of the walls.

This air movement will strip heat from the outer walls and allow it to flow up through the roof vents.

Ideally you would use all these components together to create a system of insulation and cooling. But don’t forget to add bug screens to all the vents!!!

Why Insulation Systems and not Components?

You now have to give some thought as to how to insulate your loft. If, as is popular with Farang builds in Thailand, you add reflective insulation under your roof tiles, you are reducing the heat into the loft space and removing the driving force that is sucking air through the wall space.

So if you are using this wall space draught method, don’t insulate under your tiles, but do add loft insulation mats above your ceiling (I suggest at least 4inches of rock wool with a reflective surface underneath.

Of course if you are not using the cavity walls and air movement to cool the building then the reflective insulation under the tiles is not going to cause a problem with the insulation design of the house. And is a cheap effective way of keeping the roof space cooler. Though I would still add vents and loft matting.

Well done Guesthouse!

[GuestHouse]

I should add, I don’t like the idea of trapping air, it invites mould/mildew and is, I am sure, a cause of the increase in asthma in the west, where homes are so locked up against draughts these days that they become breading grounds for all manner of fungi and insects.

A healthy flow of air seems to me to be just that ‘Healthy’.

(Thank you Ilyushin )

[jumbo]

Thank you very much guys

It is not an easy matter as I expected and I will keep yopur advises in mind

I basically wqas just thinking that the insulation would keep out the heat in the same manner as it keeps out the cold. Obviously not.

With regards to double walls I was afraid for the nesting of bugs etc

I will think about it and discuss the issue and when I have a solution I might just ask your advise

Thanks agian for the information

J

[ilyushin]

Thank you very much guys

It is not an easy matter as I expected and I will keep yopur advises in mind

I basically wqas just thinking that the insulation would keep out the heat in the same manner as it keeps out the cold. Obviously not.

With regards to double walls I was afraid for the nesting of bugs etc

I will think about it and discuss the issue and when I have a solution I might just ask your advise

Thanks agian for the information

J

Jumbo,

Keep Guesthouse and myself informed of your selection and how well it works for you.

GH gave you some very helpful information which should be taken by anyone building in this part of the world.

I am always looking at the pros and cons of building materials in Thailand. Any input would be appreciated.

[ilyushin]

This is a nice URL for Thailand Insulations. I am sure there are lots more on advance searches.

[GuestHouse]

I’d take a look at some of the work being done by Australian Architects working on Tropical/Sub Tropical Design, some of it is outstanding.

I have a real gripe with a lot of what is being built in Thailand at the moment. Do an internet search of house designs and you’ll soon become aware that much of what is being offered in Thailand is a direct copy of designs from the US – Tropicalized by simply changing the background greenery to palms and Banana trees.

[ilyushin]

I’d take a look at some of the work being done by Australian Architects working on Tropical/Sub Tropical Design, some of it is outstanding.

I have a real gripe with a lot of what is being built in Thailand at the moment. Do an internet search of house designs and you’ll soon become aware that much of what is being offered in Thailand is a direct copy of designs from the US – Tropicalized by simply changing the background greenery to palms and Banana trees.

Agreed GH, I did a trip ( fact finding mission) to eastern Australia and found that they are more in tune with materials and designs that will meet the proper housing solutions for places like Thailand.

[chownah]

I’d take a look at some of the work being done by Australian Architects working on Tropical/Sub Tropical Design, some of it is outstanding.

I have a real gripe with a lot of what is being built in Thailand at the moment. Do an internet search of house designs and you’ll soon become aware that much of what is being offered in Thailand is a direct copy of designs from the US – Tropicalized by simply changing the background greenery to palms and Banana trees.

GuestHouse,

I've been reading your posts and it interesting. What you say makes some sense but I've got some hesitation about adopting what you have said. I would like to discuss some things with you here but if I can find some of this information on the internet then I can avoid asking questions needlessly. Can you provide a link or suggest some keywords to use when searching for the type of information you provided?

One thing that I've noticed is that to compare the heat buildup on white sand to the heat buildup on a wall is a bit misleading. In the tropics when the sun is high and the heat is soaring the sun is shining almost perpedicular to the sand on the ground but it will only be striking the wall at a slight angle so the amount of insolation intercepted by one square unit of horizontal surface will be much much higher than one square unit of verticle surface during the middle part of the day. Walls do get hot when the sun shines on them and a good design will provide maximal shade to avoid this...I am just wanting to add some perspective to the heating of the walls which I think you have over estimated....maybe I'll take some temperatures to see...but I have wide eaves (1.5 metres mostly) so most of my walls don't get direct sunlight in the middle of the day.

Chownah

[GuestHouse]

Chownah, I don't have direct links to the concept I have outlined, it is the basis of a design I am working on - The design itself is based in basic thermodynamic principles - I'm aproaching the problem of heat and cooling as one of an 'Engineered System'.

What you say about angles of light on sand and walls is generaly correct, and the use of large eves is a factor to reduce radiated solar heat on walls is a good technique to apply - Also fitting with local architectural norms.

But be careful of surroundings, I have a friend who (for reasons only known to him and his wife), tiled the yard of his house. The resulting reflection of sun light onto his walls and through doors and windows made the house inhabitable during the day and for some time after sun set.

Do also be aware that sun angle does change during the year.

I've found this Tropical House Design Issues which discusses issues but does not provide all the answers.

If you want to do an indepth read on heat and materials then I'd recommend Easop and McConkey 'Applied Thermodynamics' - Longman Press.

What is absolutely clear is, the techniques and methods applicable to a house built in temperate climates are not directly applicable to a house built in the Sub Tropics

I'm working on designs which address consumption of energy and other resources, I hope to achieve a design that requires no AC at all.

But the proof of the pudding and all that..

Edited August 26, 2006 by GuestHouse

[londonthai]

I have heard about white colour external walls exposed to sun - what about internal walls? Painting them dark/black would allow the heat to escape out

[Rimmer]

You can, but be careful as I have seen many applications where the application of insulation and building methods is patched together wrongly – If you are designing a house you should consider how the insulation works as a ‘system’ rather than individual elements.

Example: Double wall insulation.

BIG SNIP

Now here’s a problem. The outer wall has a thermal mass, once hot it will stay hot until it radiates it’s heat to its surrounding. If you trap air in an insulating layer between the outer layer and the

inner layer, you will allow that to heat up and pass the heat into the inner core. (Even if the inner core is insulated, the heat is going inwards, perhaps slowed by the insulation, ie Q-Block, but it is nevertheless going inwards).

Note here the inner insulation Qblock is only reducing the rate of heat flow, it is not stopping it.

To reduce this inward flow of heat you can do one of three things, you can reduce the amount of heat stored in the outer wall, or you can reduce the amount of heat passing across the air gap.

Reducing the heat stored in the outer wall can be done in several different ways.

Use lower thermal mass materials (wood cladding being an example) This has the effect that as soon as the sun goes off the wall it rapidly cools to the ambient air temperature. I’m sure we’ve all walked past a wall that is still radiating heat well into the late evening (that is a high thermal mass wall and not what you want on a house in a hot climate).

Color is important, painting your outer walls white will reflect heat rather than allowing heat to be absorbed.

Growing plants, creepers and trees to throw a shade on walls exposed to the sun reduces heat up take. Adding a screen near a wall does the same thing.

And then, making best use of the wall’s air gap, you can encourage airflow between the walls. Remember, the wall might reach 70DegC but the ambient air temperature is very likely to be lower than 32DegC.

To increase airflow, simply add vents at the bottom of the wall and allow the gap of the wall to continue right into the loft space. Then add a vent (or two) to the loft space and close up as many gaps into the loft as possible (especially under the eves).

Now as the roof heats up, hot air rises in the loft space and moves out through the vents, as it does so it draws cold air in through the vents at the bottom of the walls.

This air movement will strip heat from the outer walls and allow it to flow up through the roof vents.

Ideally you would use all these components together to create a system of insulation and cooling. But don’t forget to add bug screens to all the vents!!!

and loft matting.

BIG SNIP

That is VERY interesting and informitive.

I am using Q-Con to build and maybe have the situation you describe. How do feel about air bricks bottom and top of the outer wall as it's too late for me to leave a cavitiy at the top in to the loft.

Any suggestion about how far apart to place them if you think would be OK as well.

[GuestHouse]

How do feel about air bricks bottom and top of the outer wall as it's too late for me to leave a cavitiy at the top in to the loft.

Any suggestion about how far apart to place them if you think would be OK as well.

I think anything that helps move the air through your cavity wall will help, but do be aware of insect and pest problems. So grills/Insect Mesh is essential.

I thking air vents every two or three meters ought to help, staggering them from top to bottom will force the air to move across the wall

Like this (hopes this comes out

===.............===................=== Top Vents

.........===...............===..............=== Bottom Vents

Edited August 26, 2006 by GuestHouse

[GuestHouse]

I have heard about white colour external walls exposed to sun - what about internal walls? Painting them dark/black would allow the heat to escape out

Heat travels from Hot to Cold (actually when a heat difference exists it tries to level the difference)

The amount of heat transmitted in radiation is a function of temperature, you and I don't radiate a lot of heat (not compared to the sun), so there is no practical gain in adding dark walls inside the house, and there is two very practical reason not too.

Firsly light rooms will reflect light a lot better, so you need less artificial light and/or need less window area to get a light room - Both these can be very significant sources of heat in a house.

Then there is the psychology - we feel warmer in dark rooms than we do in white or light blue, light green rooms.

So the dark colours risk tricking you into thinking you are warmer than you actually are.

[Thaddeus]

I have heard about white colour external walls exposed to sun - what about internal walls? Painting them dark/black would allow the heat to escape out

Heat travels from Hot to Cold (actually when a heat difference exists it tries to level the difference)

The amount of heat transmitted in radiation is a function of temperature, you and I don't radiate a lot of heat (not compared to the sun), so there is no practical gain in adding dark walls inside the house, and there is two very practical reason not too.

Firsly light rooms will reflect light a lot better, so you need less artificial light and/or need less window area to get a light room - Both these can be very significant sources of heat in a house.

Then there is the psychology - we feel warmer in dark rooms than we do in white or light blue, light green rooms.

So the dark colours risk tricking you into thinking you are warmer than you actually are.

I'm no expert on thermodynamics.... but I can pass on one thing from experience..... I chose some very dark parquet 'look a like' ceramic tiles for the living room (because they looked nice) this means that I have to keep the main front doors closed until the afternoon, otherwise they spend from sunrise to noon just soaking up heat and then the rest of the day just giving that heat off.

One thing that I have always found curious is that the hong nam is the coolest room in the house (not using any aid like a pad lom or air-con of course).... when the power has failed, which has a tendency to happen, especially during a large thunderstorm, we have even slept in there..... has that got anything to do with the size of the small window?

[tutsiwarrior]

I’d take a look at some of the work being done by Australian Architects working on Tropical/Sub Tropical Design, some of it is outstanding.

I have a real gripe with a lot of what is being built in Thailand at the moment. Do an internet search of house designs and you’ll soon become aware that much of what is being offered in Thailand is a direct copy of designs from the US – Tropicalized by simply changing the background greenery to palms and Banana trees.

GuestHouse,

I've been reading your posts and it interesting. What you say makes some sense but I've got some hesitation about adopting what you have said. I would like to discuss some things with you here but if I can find some of this information on the internet then I can avoid asking questions needlessly. Can you provide a link or suggest some keywords to use when searching for the type of information you provided?

One thing that I've noticed is that to compare the heat buildup on white sand to the heat buildup on a wall is a bit misleading. In the tropics when the sun is high and the heat is soaring the sun is shining almost perpedicular to the sand on the ground but it will only be striking the wall at a slight angle so the amount of insolation intercepted by one square unit of horizontal surface will be much much higher than one square unit of verticle surface during the middle part of the day. Walls do get hot when the sun shines on them and a good design will provide maximal shade to avoid this...I am just wanting to add some perspective to the heating of the walls which I think you have over estimated....maybe I'll take some temperatures to see...but I have wide eaves (1.5 metres mostly) so most of my walls don't get direct sunlight in the middle of the day.

Chownah

for those of you that want to design your own cooling system do a google on ASHRAE. This is the bible for HVAC designers internationally and includes tables for thermal conductivities for insulation materials, factors to include for exposed and shaded walls, expected median wet and dry bulb temperatures internationally, loads of good reference material. They may offer some of their expertise on the internet for free...check it out.

Don't be daunted by all the engineering jargon...just remember that the basic relationship is Q = UAdT...the U factor is where all the conductivities and the of the correction factors for sun exposure, etc come in. You can get all that from the tables in the back. Given an arrangement (that you can control when building a new house) the Q = relationship will give you a handle on the A/C that you need to install to maintain a selected inside temperature and choose your A/C capacity accordingly.

All these calculations are computerised so that if you were really serious give a consultant your house layout drawings and indicate the materials and they would tell you what you need for A/C to maintain a selected inside temperature. Alternately, select a desired indoor temperature and the computer can select the materials for construction for you and indicate the required A/C power required. There might already be something on the internet that you can use in this regard.

loadsa stuff on the internet...check it out...

[londonthai]

if we put at least 4 inches of loose rock wool on the ceiling won't it be too heavy? Wouldn't be better to use rock wool boards? And what about putting them instead of internal walls as well?

[Chang_paarp]

if we put at least 4 inches of loose rock wool on the ceiling won't it be too heavy? Wouldn't be better to use rock wool boards? And what about putting them instead of internal walls as well?

If your ceilings have a problem with only 100mm of rock wool you will have a lot of other problems with the design of the house, the ceilings will be the least of them . In spite of its name it is not that heavy per metre square.

[londonthai]

in many traditional thai houses there is no ceiling - recently only they started to use the cheapest possible option of alluminium frame filled with panels (that kind of ceiling you see in offices). Good wood is heavy and expensive and they opt for the easiest. What about rock wool boards as ceilings? Are they available anywhere in thailand?

Edited August 26, 2006 by londonthai

[chownah]

I think that allowing outside air to flow through the cavity of a double wall system may be counterproductive in some cases. In the case where the wall is fully shaded then its outside surface will be the same temperature as the outside air. If air IS NOT allowed to flow throught the cavity then the heat's travel from outside to inside is inhibited by the two walls of the system and the cavity between them. If air IS allowed to circulate in the cavity then the warm outside air will tend to make the temperature in the cavity the same as the warm outside air and the result will be that the heat's travel is inhibited only by one of the walls of the two wall system. So you can see that if the warm air is allowed to circulate inside the wall cavity the result is an easier path for the heat to travel inward.

This is assuming that the wall is fully shaded....I think that full shade on all exterior walls should be a highest priority for energy efficient construction in tropical climates....large eaves....moveable awnings and roll down exterior curtains...strategically placed trees and shrubs...proper house orientation...etc.

Chownah

[chownah]

"......................

One thing that I have always found curious is that the hong nam is the coolest room in the house (not using any aid like a pad lom or air-con of course).... when the power has failed, which has a tendency to happen, especially during a large thunderstorm, we have even slept in there..... has that got anything to do with the size of the small window?

The small window means that very little sunshine will enter the bathroom so this will certainly help to keep it cooler. If your bathroom is always cool, I bet that the sun never shines on its external wall...or if it doe it probably only shines there for a brief time.....is this right?

Chownah

[astral]

Coming from the UK I am used to the idea of big windows to catch every bit of sun.

In Thailand we need the opposite, as Chowna mentions.

Smaller windows, trying to avoid west facing walls,

big eaves to provide shade and big trees in the garden for the same reason.

[COBBER]

Guesthouse, Great posting. Love your concept. The only part that worries me a little bit is the 4 inches of medium above the ceiling. I would have thaught that as hot air rises you would be better to let the heat escape through the ceiling , rather than creating a barrier to retain it.

Ceiling insulation to reduce heat works well in places like Alice Springs and Arizona where the outside temperature can varie from 0 degrees overnight to 50 degrees during the day.

My thaughts are that ceiling insulation would only be beneficial if your concept is to retain what you have rather than your concept where you are trying to maximise the ventillation.

[GuestHouse]

I think what needs to be understood, and going back to what I said earlier, is we must consider insulation as part of the designed 'System'.

It is clear from what everyone says here that that insulation can work for the design or against it.

Chownah's post is a good example where a fully shaded area behaves differently than an unshaded area.

What I'm getting at is the addition of insulation needs to be considered within the whole design.

------

COBBER

I think you'll find that the temperature in a Thai roof space (no matter how it is insulated) is very much higher than the room below. The issue becomes heat being radiated into the room. Not heat in the room being radiated out.

For keeping rooms cool I plan to use air flow - Next posting on this subject.