If window frames are thinner than the width of the wall, does it matter whether PVC windows are fitted with the frame flush to the outside wall, flush to the inside wall, or in the middle ? Wooden windows seems to be fitted with the frames flush to the outside wall.Thanks.

We built two houses here. Both houses have PVC windows flush to the outside wall, so water won't accumulate on the sill. Also, don't be shy with the caulk.

Whats this, cowboys corner?

Whatever option you choose, they will be OK as long as they are well sealed.

Most houses built here only have 100mm walls and rendered inside and out I assume yours has been built in this way.

If the frame is flush the inside wall make sure you fit a drip window sill, same for a centre fix and also a head sill.

If you are flush with the outside it will depend on whether the type of build frame you have is flush itself or has window openings protruding, the later could cause a problem in driving rain unless you put a window canopy over the frame position.

In the west where we have stick build houses , the windows are nailed to the sheathing and a molding is nailed around them sealed with caulking Here in Thailand where the walls are made from block and the windows are set in the block , the windows should have a return, Usually 1/3 of the wall thinnest return is adequate, with the window sill rendered at a downward slop for the water to run out. And a 2/3 of the wall thickness return in the inside for architectural detail.

It's more of a design/desired appearance thing, but when recessed they can form a bird landing/droppings and dirt/snow/etc accumulation area. Of course when made flush to the outside wall the inside ledge can become an accumulation point for nicknacks.

I have seen houses where the windows were inconsistently placed, some were lined with the outside of the wall other with the inside of the wall. Not the best option in terms of design or aesthetics.

At our moo baan, all the uPVA windows are set flush with the inside wall, not the outside. The outside windowsill has a slight downwards slope for water drainage. Ours have been in for 10 yeas now and not a single problem with either the windows themselves or any water ingress.

Am building a new place currently & again using uPVA windows & sliding doors as they've been just so reliable & again on the advice of our builder (I asked the specific question), the windows are again set flush with the inside wall.

As other posters have mentioned, be as generous as you can with the sealant!