Leaking roof seal against wall

[dcjones]

Timber framed conservatory to rear of house, roof replaced with twin wall roofing sheets, but as I have provided a timber "walk way" against the wall to give access to guttering and also to act as a fire escape from the second floor. With the winter weather hitting the rear of the property water is entering the conservatory.

The walk way has two layers of mineral felt, and lead flashing into the wall. The felt is under the flashing against the wall.

The walk way does overhand the twin wall so water is not entering along this joint.

Water runs down the joists from the wall of the property - so some how water is getting under the walk way - any suggestions to rectify.

Thanks

[Perry525]

Is the building in an exposed position?
How steep an angle is the roof?
What usually happens is that the rain is blown up the roof and under the flashing.

[dcjones]

The rear of the property gets the full blast of the weather during the winter.
The walkway does not have a steep angle.
The roofing felt runs up and behind the lead flashing for approx 2 inches. I used the widest lead flashing available on the market, and sealed any overlapping joints with lead mastic.

There is a good 3 inch overhang where the polycarbon roofing sheet meets the cross joist running the length of the building. Could it be that the rain is being driven up the polycarbon roof, this part does have a steep run off. The leaks are along this cross joist.