Foil Roof Insulation

[stevejones123]

The standard recommendation for hot climates is to have a light roof (tiles or asbestos cement sheeting + tiles) so that heat is rapidly dissipated.

Secondly the roof should obviously be ventilated, with ventilation both at the bottom and the top (normally there will be enough gaps for this to happen without any special effort needed).

The next important part is that you should have a ceiling. The point is that you want to trap the heat in the space between the ceiling and the roof. You then place the insulation on top of the ceiling, not the roof itself.

In India and Sri Lanka the standard method of insulation is tar sheet (that is a bitumen sheet). This is placed on top of the ceiling and then aluminium foil, shiny side up, is placed on top of that to reflect heat back up. Now temperatures are generally lower than in Thailand (where I live around 28-30 degrees all year round) so it is possible that the tar sheet is not the answer for Thailand, but the general principle of ceiling + insulation + aluminum foil holds true.

The other thing that needs deciding is whether you are going to have air conditioning or not. If you are not then you want the ceiling to be high (eleven feet is about right) as hot air rises. If you're using air conditioning then you will want a low ceiling (eight to nine feet) as you want to cool as small a volume of air as possible.

Obviously some of these choices will have been made for you.

[Swelters]

The standard recommendation for hot climates is to have a light roof (tiles or asbestos cement sheeting + tiles) so that heat is rapidly dissipated.

Secondly the roof should obviously be ventilated, with ventilation both at the bottom and the top (normally there will be enough gaps for this to happen without any special effort needed).

The next important part is that you should have a ceiling. The point is that you want to trap the heat in the space between the ceiling and the roof. You then place the insulation on top of the ceiling, not the roof itself.

In India and Sri Lanka the standard method of insulation is tar sheet (that is a bitumen sheet). This is placed on top of the ceiling and then aluminium foil, shiny side up, is placed on top of that to reflect heat back up. Now temperatures are generally lower than in Thailand (where I live around 28-30 degrees all year round) so it is possible that the tar sheet is not the answer for Thailand, but the general principle of ceiling + insulation + aluminum foil holds true.

The other thing that needs deciding is whether you are going to have air conditioning or not. If you are not then you want the ceiling to be high (eleven feet is about right) as hot air rises. If you're using air conditioning then you will want a low ceiling (eight to nine feet) as you want to cool as small a volume of air as possible.

Obviously some of these choices will have been made for you.

Many good ideas here, but I offer some differences.

SteveJones proposal is almost identical to the approach used in the US in places like Houston Texas which are close to Bangkok in discomfort. Some exceptions follow.

By "light roof" you can mean either light color (white) or light weight, and they are both great. I don't know if I'd like the appearance of a white (exterior) roof but if it's ok with you you can buy special paint to do the job. This reflects much of the solar heat back up into the sky. By light weight, you want to have a roof light enough so that you can lift a square meter of it. If you can't, you are building something that has the potential to store heat into the evening (for example a four inch concrete slab will toture you for hours)..

Put the foil shiny side down on the underside of the roof tiles or (in US plywood underroofing.) You can just glue the cheapest foil on the underside, or use those rolls of foil they sell in building supply stores. This takes care of the radiant heat, about 40 percent of total. Upward facing foil on the top of the ceiling will work fine until it picks up dust, which wont be long in Thailand.

If you ventilate the "attic" space vigorously, for example an air change every minute, you will prevent heat buildup in the attic space. But this requires either a big exhaust fan or a lot of natural open (but screened) louvers, both upwind and down. (figure typical afternoon wind velocity of say 5 km/hr).

More likely you will go with or supplement with more insulation on top of the ceiling, should be at least 6 inches and prefereably more. I can't imagine that a tar sheet would do the slightest good in this application, but maybe they have some kind of thick tarry stuff that is light and full of air. Fiberglass or some other fluffy substance is what you want, just buy the stuff they sell at HomePro.

To keep it simple, you don't need the ceiling, you can just go with the thick fiberglass or whatever right under the roof. You can spray paint the shiny underside of the fiberglass insulation if you don't like looking at shiny brand names, the shiny surface isn't really necessary if the thickess is enough. I've seen this done with off-white color, the insulation held up to the ceiling by wire or cord and it looks pretty good, sort of a cool loftish look. If the insulation delivers an R value of about 10, you will bring the ceiling temp down to room temp (within about a degree) and the heat delivered will be only about 10 watts per square meter, about the same as a single light bulb in the room.

Better yet, build your house under a big tree, and forget all this.

Then all you have to worry about is the amount of heat and vapour you and the Missus generate in bed (discussing the family budget).

[chownah]

I think that the tar sheet is the moisture barrier.

Chownah

[tartempion]

We moved to our new house in Januari 2007 and first results are 5C less in house versus outside.

In late afternoon I mesure 36C in the shadow outside and 30C inside.

We rented a house around Udon Thani for one year and there it was the other way round: average 5C MORE inside the house.

Our house is a bungalow 120sqm ground level.

We spent 15k on foil under roof tiles and 15k on "Stay Cool" fiber mats bought at Home Mart.

STill will need to evaluate results in hot months (March to May)

Edited February 17, 2007 by tartempion

[fxm88]

My material has only one foil side; should the foil face the roof?

No. In attics, single-sided radiant barrier material should be installed with the foil side facing down. Even if you use a double-sided radiant barrier material, it is best to install it at the rafter level so that the bottom side faces the attic airspace and will not collect dust. This may run counter to our intuitive feel for "how things work," but it does work, and work well.

To understand how it works, remember the two properties of aluminum foil from our Thanksgiving turkey and light bulb analogies; foil reflects radiant energy very well but does not radiate heat well. It does not emit heat to the cooler surfaces around it.

If you install a single-sided radiant barrier with the foil side facing up, the aluminum will (for a time) reflect the thermal energy radiated by the hot roof.

If you install a single-sided radiant barrier with the foil side facing down, the aluminum simply will not radiate the heat it gains from the roof to the cooler insulation it faces.

At first, a single-sided radiant barrier will work equally well with the foil facing up or down. However, over time, dust may accumulate on the surface of foil facing up. The dust will reduce the radiant barrier effect by allowing the foil to absorb rather than reflect thermal radiation. However, a radiant barrier with the foil side facing down will not collect dust on the foil and will continue to stop radiant heat transfer from the hot roof to the insulation over the life of the installation.

Source: http://www.fsec.ucf.edu/en/publications/ht...ex.htm#foilside

[pumpuiman]

I used the spray on foam for my home in Isaan. I did the entire roof topside, and the roof over the kitchen and bedroom on the first floor (just barely visible in pic)

Had a company from Bangkok come to do it.

I don't have the paperwork handy, but I believe the entire cost was around 60,000 baht.

Impressed the hel_l out of the village, seeing guys in spacesuits working on the roof!!

Edited February 17, 2007 by pumpuiman

[Sakeopete]

I'm having foil placed under my roof tiles on the 2 story house we are having built. I found a couple grades of roofing foil, we took the best one. I also found that you can get the sheet rock for the ceiling with foil on it. Its about 90 Baht more/sheet I beleive so I'm going to use it as well. Will not know the results for a while but will post any when the house is done.