As you will see from this drawing, it is possible once your conservatory has been built for moisture to appear within your conservatory. This can be a particular problem if you have decided to plaster / render what was previously your outside wall - covering over the "weep" holes that usually exist above doors and windows. This situation is worst when you live in an exposed situation and experience driving rain. (Coastal situations / tops of hills)

Fortunately there is a solution to this. The solution is to insert a new cavity tray just above your conservatory roof level - thus diverting moisture above your conservatory roof rather than inside your new room. The following drawing illustrates.

It should be noted that inserting cavity trays when building conservatory additions is not yet considered the "norm". Often there are no particular problems, especially in sheltered areas. However it is wise to raise this issue with your installer/supplier. It should be something reviewed by every conservatory purchaser - at least if you make the decision it is not necessary you will now be fully in the "picture". Regrettably a lot of purchasers only find out about the problem when it happens.

Cavity trays are usually created in lead or can be bought "ready made" in plastic. Ask your supplier for advice.