I believe it's hot because one of the wall face sunlight during afternoon to evening. Heat trap in the wall will be released at night.

Have ventilation, use a suction fan to suck out hot air. Ventilation fan does not use much electric as air con.

if you have money to invest. The best bet will be an insulator. I got a contractor to build this some time ago.

On the wall that face sun light, they assembled a frame consisting of made of wood laid vertically. aluminium can be use as well. In the empty spaces, heat insulator can be placed. if not leave empty, air also can act as an insulator. Before you put up the wooded / gypsum / artificial concrete. You can have additional heat reflector pasted at the board facing inside to reflect heat.

Last time i did not do both heat reflector / physical insulator. Still the temperature reduce to an acceptable range.

The greenest way. Grow a tree to block of the afternoon sunlight.

If you were to put aircond do not put at the wall facing the afternoon sunlight. avoid placing the compressor at the same wall too,

Good luck!

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Added on June 4, 2011, 10:53 amrefer here! http://en.wikipedia.org/wiki/File:Hallway_insulation.jpg

Thermal Foil insulation.

You can contact Roxul. They have a system to cold 5 deg down.

Thermal insulation is critical as the heat will not go away. I installed insulation material and I could take nap in the afternoon with the moderate fan on.

To be really effective, laminate window film to window too.

how bout take cold shower b4 u sleep

hang some wet cloths in your room...

open your room door , dont close it...

It shows that your roof is badly insulated. Your condition is same as mine, mine is three storey house, The top floor is super hot in the afternoon, the living room is probably 2-3c colder than the top floor. You can practically feel the difference in temperature, downstairs and upstairs. It's like walking into a sauna room in the afternoon.

can try install a turbine ventilator..

to extract the heat out from the space between ur ceiling and roof

or install a ceiling ventilation fan to remove the warm air from the room and keep a circulation of air to keep the temp down..

air from bottom house raise up due to the ceiling ventilation fan and the air is extracted to the ceiling and the turbine ventilator take the hot air out from the attic/space between ceiling and roof...

u want better install thermal insulation material.. and if got some extra money to spend around wash and repaint the roof to white/silver shade..

maybe what you can do is to get ventilation holes for your wall (the lower the better, then get electric ceiling ventilation fans..... then have your roof install the "mushroom" thingy....