Cavity walls consist of two skins of masonry separated by a gap (cavity). When rain falls onto the outside skin, it becomes damp and after prolonged rain it becomes completely saturated. (It's the gap between the two skins that prevents the dampness transmitting to the inside skin of your home.)

When a new conservatory is attached to an existing cavity wall, what was an original outside wall of your property is now a wall inside your conservatory. Therefore this wall will remain a damp wall under usual circumstances.

If you propose to use the conservatory as an extension and living area of your home, the Building Regulations contain specific reference to keeping parts of the structure dry and free from damp. You should therefore consider whether you wish this original outside wall to be damp-proofed?

Cedar Home Improvements can fit preformed cavitrays into the wall above the roofline, to prevent the penetrating rain from causing dampness.

Cedar Home Improvements recommends that a cavity tray is fitted to all properties of 15 years of younger due to the increased porosity of materials used in modern housing construction.