Measuring timber windows for upvc replacements - problems

[utterlydiy]

I've decided to replace my timber framed widows with upvc units.

But my problem is where do I take a measurement as the house is timber framed with brick on the lower half and wooden cladding on the top half.

The window frame in all the rooms petrude by 5mm into the room, so if I measure a window frame overall then take away 10mm, that I assume is the size given for a replacement upvc casement. But then if I measure the same window on the outside of the house again the window petrudes outwards by 20mm, the dimensions are totally different. The underside bottom edge of the window frame on the inside of the room is lower than the underside of the outside cill, the height and width are not the same.

Where do I start??? Can anyone suggest where to look on the Web etc for info on how these type of houses are designed or constructed or more importantly how do measure these type of windows.

Thanks

 

[utterlydiy]

It might be easier for me to ask how do I measure a window for a replacement casement in a timber framed house.

 

[biffvernon]

Oh dear, another one determined to spoil the appearance of his house, reduce its value, and help mess up the planet by using uPVC. Just don't go there. Wood is much better.

 

[masona]

Yep, wood is a lot easier to treat as well with oil treatments etc

 

[joe-90]

Agree with the others, PVC is rubbish.

 

[utterlydiy]

Everyone is free to have their own choice.

So I'm free to make my own choice, which is UPVC.