Can i ask? Is it a metal roof or tiles roof?

Usually metal roof, then alu foil is insufficient. You will need insulation material like glass or stone fibre (some comes together with PU).

If a tiles roof, what it does is to increase the heat resistance value. If you are planning to put woven foil, i doubt it will have any benefits that will create impact. However, if is a bubble woven.foil, if does help. Just google - roofing insulation or search under Monier tiles roof system.

And confirm.. if there is a leakages... u wont be able to determine it. Its applies for both types of roof.

Hope this helps.

This post has been edited by stanck: May 18 2020, 03:34 PM

Putting zinc sheet under roof tiles. Hmm, thats got to be something new... to put it honestly, i am not a roofing expert as my experience more on insulation.

Usually a double metal roof system, its quite a good and guarantee that u ensure that u wont have leakages. Even if the top layer is rusted (max lifespan for quality one is about 25 years), you can alway change the top deck.

However for roof tiles is different due to the fact that they need to sit on purlin. ( google metal roof purlin). So how do u secure the zinc sheet?
So if you refer to Monier Malaysia system, u will notice that they only add the aluminium bubble foil to create a system either for reflection of UV or air circulation movement. If u look carefully on their architecture drawing, this foil do not touch the roof tiles, so it has a gap for air movement and to reflect UV.

If the contractor plan to install a metal zinc below the roof tiles ( let just say it legit, and the roof truss and frame can support it), then why install the aluminium foil sheet?

Having a sheet of metal itself already, u wont be able to identify the leakages.
But what i can say, if the contractor is able to do it... there is on thing guarantee... pencuri tak boleh masuk.