Extension doorway & moisture ingress

[daggermark]

My house has a single-story side extension, with lead flashing installed where it joins the house.

The house itself is timber-frame with brick skin & cavity. The extension simply has studwork fixed to the (previously external) brick wall.

There is a doorway from the main house into the extension. This has been achieved by installing a steel into the existing brickwork. Plasterboard has then been fitted to the top reveal, such that it bridges all the way from the house timber frame to the extension studwork.

The problem here is that any failure of the lead causes water to run down the outer face of the brickwork, landing on the door reveal and leaking into the extension.

What other measures, if any, could be taken to protect against this? As both sides of the wall are now 'internal', a cavity tray could only divert water one side or the other.

 

[Alastairreid]

sounds like you have no cavity trays.

 

[daggermark]

That is correct. Where should the cavity trays go in this situation though? Surely they can only divert water into the extension, into the house, or into the existing cavity of the house. None of these seem correct?

 

[Alastairreid]

the cavity tray diverts any penetrating water back outside through weep vents.

 

[daggermark]

Ah I see, something like this?

 

[Alastairreid]

They would be installed above the lead apron.

 

[Alastairreid]

Thats it.

 

[daggermark]

In this configuration though, it is still the lead which is the sole protection against moisture entering where the extension meets the house, running down the outside of the brickwork which is now inside the extension?

The reason I ask is because the lead has failed twice in about 10ish years, meaning an annoying redecorating job after!