Hot Tile Roof

[Swelters]

Insulation scams proliferate because the thermal behavior of roofs is a little tricky and few people, including sales people, have a clear idea of what is going on. I hope this helps a little.

Metal or tile roofs heat up to 40 or 50 C in the sun in Thailand. Metal doesn't get any hotter than tile, it just feels hotter to the touch. Both to you and any cat walking on the roof.

Proof: underside of tile roof in restaurant in Korat at lunchtime. Very uncomfortable even though the air temp is only 29 C.

The underside of both gets up to almost the same temperature as the outside, 40-50C.

The roof transfers heat to the space below two ways. First it just radiates, just like one of those reflective hot coil heaters radiates. You feel this radiation (especially on your head if you have little hair as in my case) regardless of the air temperature. It also heats up your bed, your floors, your wife, whatever.

The second way is by heating the air below the roof directly. This hot air heat tends to stay up high under the roof but local air currents develop after a while and you can't count on this "hot air rises" protection, after a while the air below will heat too especially if the room is closed. But if you've got a lot of ventilation, I mean a lot, the hot air will flow out your vents or get blown away through open windows or doors.

But the most immediate and discomforting heat comes from direct radiation, no amount of ventilation will help prevent this.

Lets move to a different part of the restaurant.

Amazing, much more comfortable! It's got a grass roof, there are several layers of grass up there.

Proof: the undersurface of the grass is not much higher than the air temperature. Hardly any radiation. As a bonus, the thick grass slows down the movement of heat to the air below, so if you've got even a little ventilation the heat will get wafted out of the room.

But wait, isn't grass a little dangerous for fire and also doesn't last long, maybe 2 years?

More on this if any interest.

Swelters

[neverdie]

Very Interesting. Tell me more, please

[stevehaigh]

you should add the obvious fix for a tile roof heating problem is to use insulation. home pro sell rolls of foam/foil insulation. remember the shiny side faces up. the R factor on this stuff isn't so high, about R11-18 usually. use 2 layers if you have the budget.

i've been wondering about using grass roof because it looks nice on the inside and is a good insulator and putting a tile roof on top for durability. and maybe some foil insulation inbetween the grass and tile.

the only downside i can think of is maybe rats, snakes, bugs etc. will move in. has anyone tried a grass/tile roof like this?

thx steve

[Swelters]

you should add the obvious fix for a tile roof heating problem is to use insulation. home pro sell rolls of foam/foil insulation. remember the shiny side faces up. the R factor on this stuff isn't so high, about R11-18 usually. use 2 layers if you have the budget.

i've been wondering about using grass roof because it looks nice on the inside and is a good insulator and putting a tile roof on top for durability. and maybe some foil insulation inbetween the grass and tile.

the only downside i can think of is maybe rats, snakes, bugs etc. will move in. has anyone tried a grass/tile roof like this?

thx steve

Thanks for the comments Steve, I'll put up more on this topic. But for now I need to say that the shiny side should be down on the foil. If you put the shiny side up, it will work at about 50% efficiency for a while, then become close to useless at dust collects on the top of the foil and it loses reflectivity. Most places this takes only a few months. Watch out, your contractor may be very insistent about putting shiny side up. He's wrong.

Why the shiny side down? Because though most people understand that shiny surfaces reflect heat, the hidden secret is that they also refuse to emit heat. So you can heat up a piece of foil to say 150 C and hold it up in front of your face and you will not feel a blast of heat. Paint the same foil black and you will feel the full force of radiation.

Also for the foil to work it has to have at least an inch or two of air space below it. Otherwise it will do nothing. So you don't want to lay it on grass or anything else. But I'm going to follow up with a case history.

Swelters

[johng]

Swelters.

I have been trying to understand this shiny side down thing for a while now..

please look at my drawing and tell me if my understanding is correct.

also an air gap is needed between the tile and foil or not ?

[Gerontion]

Interesting stuff, Swelters. Please post more.

[neverdie]

Interesting stuff, Swelters. Please post more.

Yes, interesting....I would have more confidence if he changed his nic to something like 'inoswelters' or something.

I thought my builder must have stuffed up when he put the shiney side down.....lol lucky i never got around to revving him about it.

Interestingly, its layers of clothing that keeps the body warm in the cold, as opposed to just one thick piece of clothing. I would imagine that if you had many layers of roof lining with small gaps between each layer then this would be very effective for keeping the room below cooler...... its actually the space in between double glazed windows that makes all the difference, not the so called thickness of the glass?

Edited February 14, 2009 by neverdie

[Crossy]

This shiny side up/down thing always confuses me, physics was never my best subject

Should it not be "shiny side INTO the roof space" whether it is under the tiles or on top of the ceiling. Reduces radiation into the roof space when under the tiles, reduces absorbtion into the room when placed above the ceiling.

Either way plenty of roof ventilation can only help, can't it?

Would placing insulation/foil both under the tiles and on top of the ceiling be even better or is my aging thought process faulty?

Edited February 14, 2009 by Crossy

[GungaDin]

Good topic, Sweaty, oops, sorry, Swelters.

More please.

[Artisi]

Shiney side down in all locations as explained by swelters -

"Why the shiny side down? Because though most people understand that shiny surfaces reflect heat, the hidden secret is that they also refuse to emit heat. So you can heat up a piece of foil to say 150 C and hold it up in front of your face and you will not feel a blast of heat. Paint the same foil black and you will feel the full force of radiation."

Conventional wisdom says to also put thick insulation under the tiles or on the upper side of the ceiling or both - sure this will slow the heat build up into the house but unfortunately it also stops any transfer of heat from the room into the roof space and inhibits the release of heat out of the building as the outside temp drops during the evening / over night.

For Thailand the best solutiuon is a metal roof, reflective insulation under with correct air space ( shiny side down) good ventilation of the roof space - wide verandahs and cavity wall constuction or light weight walls with reflective insulation (shiny side facing the inside of the house).

There is a wealth of information on the internet if you wish to search it out.

[Swelters]

This shiny side up/down thing always confuses me, physics was never my best subject

Should it not be "shiny side INTO the roof space" whether it is under the tiles or on top of the ceiling. Reduces radiation into the roof space when under the tiles, reduces absorbtion into the room when placed above the ceiling.

Either way plenty of roof ventilation can only help, can't it?

Would placing insulation/foil both under the tiles and on top of the ceiling be even better or is my aging thought process faulty?

Don't worry, the emissivity thing confuses everybody, it's not an everyday obvious experience. Foil on the top of the ceiling, shiny side up, which you suggest as an alternative, would redirect the radiation back up to the underside of the tiles, which is good. But the effect would be short lived because of the accumulating dust problem and consequent loss of shine. Especially if there is good ventilation which would bring in more dust. Ironical!

I'm going to develop this subject further in subsequent posts.

In regard to the magic "space", it needs to be on the shiny (down) side of the foil, in other words don't lay the shiny foil on a surface. With the foil right under the roof, it's fine, even helps more, if there is also little space above the foil too.

But you will get rid of the radiation problem even if the foil is actually glued to the underside of the roof. This is what they do in some places like Houston Texas, where the underroof is plywood (asphalt shingles on top). This means that you could actually use ordinary supermarket foil, glue it to the underside of the tiles before you put 'em up. Trying to drape big sheets of roll foil or that bubble stuff over roof joists and purlins, then put up tiles over this is dangerous and not fun. Funny to see the Houston builders making a big thing of this simple expedient, blathering on about how this was learned from "space science." You just can't keep the sales guys out of this business.

Swelters

Edited February 14, 2009 by Swelters

[BillyBobThai]

Swelters, this is the type of information I was looking for when I asked for help on my roof design. Thanks. I just built a room on the top floor of the in-laws house. The ceiling is wood framing with sheetrock/drywall, with glass insulation with foil on both sides. It made a big difference.

My question is, would the foil be better just below the roof with an air space, or placed on top of the ceiling, or both?

[Swelters]

Swelters, this is the type of information I was looking for when I asked for help on my roof design. Thanks. I just built a room on the top floor of the in-laws house. The ceiling is wood framing with sheetrock/drywall, with glass insulation with foil on both sides. It made a big difference.

My question is, would the foil be better just below the roof with an air space, or placed on top of the ceiling, or both?

I hadn't got to blanket insulation yet, but in short I think you did it right.

Swelters

[stevehaigh]

thanks for correct my mistake. i googled roof insulation for hot climates and found several sites that confirm that shiny side down is best and the air gap is necessary

http://www.taunton.com/finehomebuilding/ho...rms=61678,61866

http://www.yourhome.gov.au/technical/fs48.html

http://www.coolmetalroofing.org/elements/u...aseStudy_13.pdf

http://www.radiant-barrier.org/

i installed shiny side up on my house but its between the rafters and is sloping at about 45deg so i'm hoping the dust doesn't build up too much. i should check periodically and try blow it out with a shop vac or something.

steve

[MeetJohnDoe]

Why doesn't anyone plant a "living" grass garden on their roof...like the new California Academy of Sciences roof in San Francisco. I guess in their case, they mainly want to keep the heat in (coldest winter he ever spent was a summer in san francisco a famous writer once said) but wouln't it also work in reverse...to keep heat out or cool airconed air in?

See: http://www.calacademy.org/ (let the graphic load to see the roof)

http://www.calacademy.org/academy/building/

[Cuban]

> Why doesn't anyone plant a "living" grass garden on their roof...

Weight is one factor - watering is a second.

If you have a large office building then the roof surface area per occupied unit space is lower and so the cost is reduced per unit. Also of the 'green' buildings that I have seen using the live grass approach, they tend to have a whole system that uses waste water to irrigate the roof spaces as well as having the roof lawn/garden accessible to the occupants as useful space rather than just a roof. (The one I saw was a university.)

I like the idea of using dead grass, thatch is the expression I believe, either as a thick layer 10-15cm or simple sheets of woven grass (20 baht a time at the local seller) would reduce the exposure of your tile/sheet roof from the sun but as mentioned above fire would be a concern if I were sleeping under it.

Treatment of dried grass is possible (Fireproof with a solution of 10 to 20 parts of potassium carbonate, plus 4 to 8 parts of ammonium borate in 100 parts of water.) but I would want to experiment first. Not sure how such treatment would last exposed to strong UV here, it eats up plastics pretty quick.

One house I saw a few years ago during hot season has a solid hose fixed on to the roof that fed a constant supply of water running across the surface creating a warm pool of water in their garden. Not sure if this is ideal from a health safety point of view - thinking of legionnaires disease type bacterial growth.

Mixing both ideas might offer a better level of safety.

[johng]

From www.radiant-barrier.org

You do not have to install the aluminum foil with the shiny side up. Most products have one shiny side and one dull side. This finish look is created in rolling mills during the process of making the aluminum sheeting. Radiant Barriers work by reflecting infra-red energy so the aluminum foil would work just the same if both sides were dull.

doh now thats confused me again...they are saying it doesn't matter if shiny side is up or down or even not shiny at all

who to believe ??

[Swelters]

From www.radiant-barrier.org

You do not have to install the aluminum foil with the shiny side up. Most products have one shiny side and one dull side. This finish look is created in rolling mills during the process of making the aluminum sheeting. Radiant Barriers work by reflecting infra-red energy so the aluminum foil would work just the same if both sides were dull.

doh now thats confused me again...they are saying it doesn't matter if shiny side is up or down or even not shiny at all

who to believe ??

Safest thing is never believe anything insulation sales people tell you. Few understand the basics. This quote is absolutely wrong, the foil will not function as a radiant barrier unless it is shiny.

Swelters

[TomBrown]

Safest thing is never believe anything insulation sales people tell you. Few understand the basics...

Swelters

I was looking at insulation in the shop yesterday and noticed that the rolls of 75mm thick fiberglass covered with aluminium were really squashed down / packed tightly to fit into the packaging bags. I've read that squashing down the installation reduces the effectiveness, wouldn't the claimed R value be less then?

Many companies seem to be favouring the 10mm thick foil-foam-foil solutions, can they really be effective at maintaining the cool inside the living space and the hot outside, or is this another marketing / sales pitch with little substance?

As most of the insulation options available are now covered with shiney foil at 95% - 100% aluminium as a radiant barrier, the question is what to have as an insulation material and how thick, this particularly is what I'm interested in.

Can't wait to read more on the subject from you Swelters, but as our house is already build with no aluminium foil or insulation, I'll have to wait eagerly for the attic floor solutions.

[Swelters]

Safest thing is never believe anything insulation sales people tell you. Few understand the basics...

Swelters

I was looking at insulation in the shop yesterday and noticed that the rolls of 75mm thick fiberglass covered with aluminium were really squashed down / packed tightly to fit into the packaging bags. I've read that squashing down the installation reduces the effectiveness, wouldn't the claimed R value be less then?

Many companies seem to be favouring the 10mm thick foil-foam-foil solutions, can they really be effective at maintaining the cool inside the living space and the hot outside, or is this another marketing / sales pitch with little substance?

As most of the insulation options available are now covered with shiney foil at 95% - 100% aluminium as a radiant barrier, the question is what to have as an insulation material and how thick, this particularly is what I'm interested in.

Can't wait to read more on the subject from you Swelters, but as our house is already build with no aluminium foil or insulation, I'll have to wait eagerly for the attic floor solutions.

Don't worry too much if you missed the foil solution, there are other ways to go, I'm going to follow up on this.

The 10 mm bubble foil is ok, but not much better than the plain foil. The R value claims are mostly lies for this product. It doesn't really have its own R value, it can be said to have an R value only when used as part of a sandwich of things.

On the squashed down issue, I just bought a bunch of that stuff, supposed to be 4 inches, I'll open a bag and see if it springs back.

Swelters

[Gerontion]

A question or two for you Swelters (if you don't mind): Do you think reflecting foil and venting is sufficient for a roof in Thailand? What is the recommended number of air changes per hour? If you were building a house, is this (foil and venting) what you would do or is there something else?

[tjo o tjim]

Insulation is really a black art. The ratings are originally based on heat loss calculations, not heat gain as dominates Thailand.

For a roof, the main goal is to keep the temperature of the outermost surface as close to the outside air temperature-- to minimize the radiant heat gain. The keys to this are light (or reflective) colors and minimal thermal mass.

[thatguy]

on where the foil should be,

the side toward the living space.

[fremmel]

Swelters, a good series of posts. Like many, when I first saw foil "insulation" I couldn't believe it would actually do anything and thought it was just a marketing ploy. Then I did a little research, started using it, and now I know that it really does work.

In the house I just built I laid it under the tile battens, shiny side down. The house has a conventional attic with flat sheetrock ceilings and I put 4" of fiberglass batts on top of them. The eaves are 1 meter wide and vented and there are vent stacks in the roof. This has worked great. Even during bright sunny days the attic space doesn't get all that much hotter than the outside air. And with the ceiling batts essentially none of that heat enters the living space.

We're in Issan and have only been in the house about 5 months so we haven't seen the real hot season yet. And, I put in double block exterior walls with 2" of fiberglass in between so it's kind of hard to separate the insulating effects of the walls from the roof. But the net effect is that, so far, on hot days the air inside the house has been enough cooler than the outside air that we actually keep the windows closed when it's hot outside. Last week I measured the outside temperatures at 35 to 36 degrees but inside it never got above 27 to 28 degrees. I'm sure there won't be as much difference as the nights get warmer and the mass of the house doesn't get as much chance to cool down at night. So, sooner or later we'll have to start using the ACs but so far we haven't needed them.

I think I saw the same article you mentioned from the University of Florida. http://www.fsec.ucf.edu/en/publications/ht...31-01/index.htm Very worthwhile reading for non-beleivers. I thought 15% power saving was kind of low but then I noticed that these houses started out with R-9 to R-30 attic insulation. So for the typical Thai building method with no insultation the power savings should be a lot more.

[GungaDin]

Swelters,

a good topic and good, informative posts by all.

Thank you.

[Swelters]

Swelters, a good series of posts. Like many, when I first saw foil "insulation" I couldn't believe it would actually do anything and thought it was just a marketing ploy. Then I did a little research, started using it, and now I know that it really does work.

In the house I just built I laid it under the tile battens, shiny side down. The house has a conventional attic with flat sheetrock ceilings and I put 4" of fiberglass batts on top of them. The eaves are 1 meter wide and vented and there are vent stacks in the roof. This has worked great. Even during bright sunny days the attic space doesn't get all that much hotter than the outside air. And with the ceiling batts essentially none of that heat enters the living space.

We're in Issan and have only been in the house about 5 months so we haven't seen the real hot season yet. And, I put in double block exterior walls with 2" of fiberglass in between so it's kind of hard to separate the insulating effects of the walls from the roof. But the net effect is that, so far, on hot days the air inside the house has been enough cooler than the outside air that we actually keep the windows closed when it's hot outside. Last week I measured the outside temperatures at 35 to 36 degrees but inside it never got above 27 to 28 degrees. I'm sure there won't be as much difference as the nights get warmer and the mass of the house doesn't get as much chance to cool down at night. So, sooner or later we'll have to start using the ACs but so far we haven't needed them.

I think I saw the same article you mentioned from the University of Florida. http://www.fsec.ucf.edu/en/publications/ht...31-01/index.htm Very worthwhile reading for non-beleivers. I thought 15% power saving was kind of low but then I noticed that these houses started out with R-9 to R-30 attic insulation. So for the typical Thai building method with no insultation the power savings should be a lot more.

You have done your homework and seems to me you have done it exactly right. You've got a fair amount of thermal mass in the walls but the insulation sandwich there will slow the delivery of heat so your aircon should keep up easily. If you can keep them shaded with plantings that will help a lot.

Unless you've got a light-colored roof (such as the Bluescope steel light colors) your roof is probably getting hot as hel_l but you don't care because the heat cannot get down in significant quantities and what does gets wafted out the vents. So the heat is just getting radiated back up into that blue Isan sky.

I like moving non-conditioned air and a certain sense of connection with the outside, and for that reason don't like the new American style housing which is so sealed that it feels like being in a coffin and promotes unhealthy accumulation of unwanted gases. It also promotes excess use of aircon which of course is the real purpose of it all, an invention of the devil's corporate culture that outwits the environmentalists at every turn. But you've got it so you can open up the house if you want and skip the aircon except when you want.

There is only one beneficial thing that your rural neighbors have with their plain tin roofs. With night skies dropping to 5 deg C or lower, their roofs get cooler than the air by 3-4 degrees so they get free aircon at sundown, paid for by sauna-like conditions in the daytime. But in the end there is a certain native genius to this, too. They sit under their houses, chatting and gossiping with the neighbors, not sitting alone in a room on the internet like I do. This is very good for their mental health, prevents the isolated brooding that we northern folk are prone to. As you can see from the photo, my wife likes the local kids to gather around and "being available" assures plenty of visitors. But this gets into the interesting subject of village social life, perhaps another post.

Thanks for your post, most informative.

Swelters

[fremmel]

I like opening the windows and feeling the breeze too. That's what we did in the cool season and hopefully will be able to do in the rainy season. In fact, I laid out the house and windows so that I have pretty good air flow along both axes of the house. But for the next 2 or 3 months I think we'll have to shut the house during the day. Right now we open the windows at night and point the fans to bring in the cooler air. But the last few days the clouds and heat haze have started to build up so the nights aren't cooling off as much and the house doesn't have as much chance to cool down.

So... I'll probably have to turn on the ACs before too long, at least during the day. The ceiling and wall insulation should help with that. To try to minimize solar gain I built the house only 2 rooms wide and oriented the long axis pointing east and west. The west wall just has the master bedroom, bath, and a small storage room since we don't use those rooms in the late afternoon. With all the insulation I'm expecting the load on the AC's to be pretty light so I just put in 9K BTU units, even in a 25 sq meter room. I hope I'm wasn't too optimistic. If the thread's still active in April I'll let you know how it worked out.

[pete_r]

I was looking at insulation in the shop yesterday and noticed that the rolls of 75mm thick fiberglass covered with aluminium were really squashed down / packed tightly to fit into the packaging bags. I've read that squashing down the installation reduces the effectiveness, wouldn't the claimed R value be less then?

[...]

[...]

On the squashed down issue, I just bought a bunch of that stuff, supposed to be 4 inches, I'll open a bag and see if it springs back.

Swelters

I've started to install 4" fiberglass under the tiles last year (haven't quite finished yet - having to cut some to the right size to fit the roof space). The fibers do spring back when the rolls are opened and laid into place.

[Goinghomesoon]

So Swelters what have you found works best in your traditional Thai house? After abandoning expensive modern tiles we are back to traditional clay tiles for our place. Looking up at the tiles butts seems preferable to looking up at silver reflective surfaces, but we do want to be as cool as possible. We have allowed extra big windows, large sized vents in each end of the roof cavity and trees as near as possible. The plants will come after construction finishes...anything else that Thai farmers haven't already discovered?

[Swelters]

So Swelters what have you found works best in your traditional Thai house? After abandoning expensive modern tiles we are back to traditional clay tiles for our place. Looking up at the tiles butts seems preferable to looking up at silver reflective surfaces, but we do want to be as cool as possible. We have allowed extra big windows, large sized vents in each end of the roof cavity and trees as near as possible. The plants will come after construction finishes...anything else that Thai farmers haven't already discovered?

Plants grow quickly, esp banana trees.

Tiles are going to be the same thermally, though your small tiles may allow more ventilation. You're going to suffer in the daytime, best you can do if you have to be inside is open everything up so you get air change every few minutes, and have some kind of roof sandwich with air in it--for example I'm looking up at teak planking which looks very nice and now, at 10 pm in Bangkok, is 30 C same as floors and walls and still a degree or so warmer than outside. But my wood windows are closed because by this time of night, and certainly later, the humidity outside is building up when at 30 you really need a bit of sweat to dump your body heat so humidity is a killer.

But my wife has some Isan lullaby on the CD and the woman is pretty good and I,m happy enough to be here and not back in some California tract house ever again. Over time things like "comfort" and "luxury" mean less to me and their absense does not detract from happiness as most of the non-westernized Thai well know. Drink more water.

I finally broke down and put in an old aircon unit and I may turn it on for a while to dry things out a bit and my wife does turn it on when she occasionally hangs around the house in the daytime.

Actually mosquitos are more of a problem than heat, they are devilishly clever at getting by all screens and traps.

Swelters