I'm using Heat-Away. http://www.gpgmt.com/solutions.htm
Can't recall exact price, I remember it was pretty expensive, per roll. RM 600 maybe?

I wouldn't say you will notice a 7C drop in temperature. It's more towards preventing your ambient temperature from increasing too much due to the sun's ray. I have climbed above the ceiling into the roof cavity during mid-day ( during my Unifi installation ), it doesn't feel that hot inside. Usually, without a thermal shield it would be incredibly hot like a sauna.

It won't magically cool your house, if that's what you expect. It would, however, make your aircond work less, hence save you money. If you use an IR thermometer and measure the temperature of your ceiling during midday, you will probably get temperature of about 30C, whereas without any thermal shield, it's probably 40C or so.

Foil type of thermal insulation is usually installed between roof truss and batten. It follows the gradient of the roof, hence does not sit on top of the ceiling. Other insulations may sit on top of the ceiling. Usually they cut holes where the downlights protrude.

Yes, it's possible, just more troublesome. They can climb into the roof cavity and staple the foil to the bottom of the roof trusses. Another option they will propose is laying the foil down flat on top of the ceiling, like how they do with cellulose insulation.

I thought Monier's Radiant Barrier is usually installed following the gradient of your roof, either above your roof truss or just underneath it. So you can still go inside your roof cavity through the manhole at the ceiling. If there's something wrong with the roof tiles, you would fix it outside of your roof. The barrier won't get in the way.

It helps, a little. Doesn't do much to stop radiant heat, which is primary cause of heat in a house here. Also, if you turn on airconditioning at night, and wind is blowing, cold air will get sucked out from your room.

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Added on May 25, 2012, 11:51 amActually, MOST terrace house should come with this side partition, known as the firewall. It helps prevent fire from spreading.

This post has been edited by wdarke: May 25 2012, 11:51 AM

Looks similar to Heat-Away. Double sided alu foil with bubble wrap in the middle.

I use Heat-Away. I think they are all effective in their own ways. Heat-Away sits on top or just underneath the roof truss, while CoolBatts and TCL sits on top of your ceiling board. CoolBatts/TCL would be better if you constantly aircondition your house, as it thermally insulates the ceiling board too. Use both types for maximum effectiveness