Installing French Doors into new opening

[welshcottage]

Hi all

I'm sure this has been answered numerous times, I have used a number of searches but cant quite answer my questions so apologies in advance!

We own a older cottage which has a 1970's extension on the back, I am installing new 4ft French doors into this. We have a trusted builder, where he will do some of the more skilled work but then I will pick up the remaining work, so for this project, the builder is cutting the opening adding the lintels to the exterior with cavity tray(cavity wall, breese block) in line with building regs etc, but up to myself to install the door. I have installed windows before but not from a new opening, so my questions are around sealing the new door:

I can seal the window with chalking/sealants etc, how do I seal the top, should I add flashing

If I am using flashing should I use all the way round?

How do I address the gap between the cavity?

All other thoughts tips etc appreciated?

 

[BeyondHomeImprovements]

Hi there,
If the wall already has dpm on the back of the outer skin you really need to extend it round into the new opening and seal the doors to it from threshold to head inside
You want the doors to open right back against the walls so position them with 25mm ish of reveal showing on the outside then gun from frame to wall.
At the head, seal from the frame to the drip tray so water can still escape.
Providing the dpm is properly extended into the new opening you could just brick/block up the cavity!
Cheers