This is a common question asked when placing an order for a loft conversion. We can only share our many years of experience on the use of both these products. Whilst wooden French doors may look more in keeping with your house, they have fundamental flaws which do not lend themselves to being a good choice for a loft conversion.
Traditionally, wooden exterior doors are designed to open outwards (excluding front doors). The reason they open out is due to the weathering between the door and frame. Rain water cannot ingress past the frame and into the building as the door will seal against the frame on the inside and send any water outwards. When you reverse this process, once rain water gets round the door, then there is nothing within the frame on the inside to re direct the water and so a leak will occur. French doors have to open inwardly on a loft conversion due to the local authority regulations. Wooden doors and windows also need a lot of maintenance as the effects from the elements greatly increase with a loft conversion. Our experience has seen lots of these doors falling within a matter of 12 months due to either rotting or shrinkage and it is also worth noting that this product came become draughty. For these reasons loft companies generally exclude these from whatever guarantee they issue.
UPVC comes maintenance free, leak free and draught free. This is achieved simply by the nature and design of the doors. They will have specially designed drainage points and pull in handle systems to seal out any draughts. Now that UPVC comes in many colours and wood effect graining, it is hard to tell that they are even made from UPVC looking up at them from the ground floor.