QUOTE(dreamKrusher @ Aug 9 2009, 01:03 AM)
From my research, rockwool or cellulose insulation for roof is your best choice.
Painting those heat rejection coating will only be good for first few years until dust start to collect on the tiles or the paint fades.
Radiant barrier (google is your friend) isn't that good in my opinion, but you may wan to consider that too.
Then you can also have option to have second roof tiles installed under your 1st tiles. Check out Monier.
Can I conclude that insulate the roof is of priority and wall secondary?
I am looking for something effective, affordable and last long.
I may now concentrate to select the best materials for roof now.

Added on August 10, 2009, 6:39 pmQUOTE(PJusa @ Aug 9 2009, 08:54 AM)
easyperson,
please note: cellulose can also be used to insulate your wall. measure the temp from wall inside and ceiling inside to see which transmits more heat. most likely the roof but just to be sure measure it over several points during the day. temporay spikes dont mean its the main culprit.
then insulate the bigger one of the two first and check what you have to pay for the second one. my walls are thick and painted just white. they dont get warm. the windows did. so we replaced the windows with class A UPVC (insulated white alluminium will do too i guess) windows, double glazed and laminated with raybarrier. works like a charm. can have the sun shine on the wall brighten the room and the aircon doesnt even have to work to keep the room at 28°. nice and comfy

I can't afford to spend too much monies on other parts of the houses.
among the roof, wall and windows, i can only afford to do one
so I summarise the advices from all of you is THE ROOF !!

Added on August 12, 2009, 10:09 pmMy lastest finding is that the best treatment to west wall for anti heat purposes is to install timber panelling on it.
Timber is poor heat conductor and can be used to decorate the wall also.
Added on August 12, 2009, 11:49 pmQUOTE(PJusa @ Aug 9 2009, 08:54 AM)
easyperson,
please note: cellulose can also be used to insulate your wall. measure the temp from wall inside and ceiling inside to see which transmits more heat. most likely the roof but just to be sure measure it over several points during the day. temporay spikes dont mean its the main culprit.
then insulate the bigger one of the two first and check what you have to pay for the second one. my walls are thick and painted just white. they dont get warm. the windows did. so we replaced the windows with class A UPVC (insulated white alluminium will do too i guess) windows, double glazed and laminated with raybarrier. works like a charm. can have the sun shine on the wall brighten the room and the aircon doesnt even have to work to keep the room at 28°. nice and comfy

My latest finding is that the best treatment to west wall for anti heat purposes is to install timber panelling on it.
Timber is poor heat conductor and can be used to decorate the wall.
Whereas for roof insulation, I agreed with your choice to use TCL cellulose.
This post has been edited by easyperson: Aug 12 2009, 11:49 PM