Bay window movement problem.

[Wiiispa]

Our 1930's bungalow has 2 bay windows topped with gable ends that come out of a hip roof. Around 20 years ago the Windows were replaced with UPVC by the previous owner (mother-in-law) At the time there was some comment by the installers about the replacements not being structural. I'm assuming that the original wooden windows may have had some Structural element because there has been some movement of the windows resulting in roof leakage and internal gaps (5mm) appearing around the tops of both bays.

I'm trying to persuade the other half that this is the case and that remedial action needs to be taken to prevent further movement. But she can't see it and just wants me to mend the roof.

I see this as wasting my time unless I can effectively stop further movement of the bay gable ends. The roof consists of 4x2 rafters covered in 3/4 boards, felt and then tiled. The valleys have lead flashing.

I need to figure out how to tie the gable ends to the existing roof to prevent movement in future. Adding structural strength to the windows would prove difficult without replacing them again which will be expensive ....

Oh and the roof tiles are marked as Marley RD 80705 which I am struggling to match.

 

[^woody^]

How do you know that the issue is caused by the windows and is not either rotation of the bay due to foundation movement, or roof spread?

Likewise, a one off movement or ongoing?

Your other half may well be right to be skeptical to your prognosis.

 

[Wiiispa]

I would have thought that foundation movement would result in cracks in the render around the bays themselves. There is none. The roof could well be spreading, as one of the former owners decides to remove diagonal internal bracing beams from the loft space and place them vertically to gain some room for a botched conversion. This has resulted in the roof visibly bowing and cracked ceilings inside where the joists were not upgraded to take the extra load transferred to them. However, the ends of the rafters outside the walls do not have any Fascia/Soffits fitted and are painted. There is no visible sign of movement here either. The only visible signs internally and externally are those above on both bays which is why I've made that diagnosis. The gaps have widened over the years to the 5mm that I can see now.

Also, the windows themselves do not appear to have moved either, with external silicon and trims still intact. There is however some movement of the trim along the tops of the windows which again points to the whole of the roof part of the gable above the bay having dropped slightly.

 

[^woody^]

Masonry is flexible and a 5mm gap at 2500 height, does not mean there will be a visible gap or crack in a bay panel lower down.

Pictures would help a lot.