During the last few decades well insulated, rendered, unventilated and un-drained stud walls have been very popular in Sweden. Unfortunately this structure has shown to be sensitive to moisture. The problem is that moisture enters the structure for example in joints, un-tight connections to windows and doors and at fixing studs and wet the materials inside the stud wall and cause mould growth, which is known from experience from surveys of more that hundred buildings. The damages are never visible on the surfaces of the wall but are hidden within the wall. The only way to detect these damages is to measure the moisture conditions inside the wall. A national survey is carried through this year in order to determine the extent of this problem and the connection to local climates, point of the compass, frequency and direction of driving rain, design of connections, type of plaster (thin or thick) and insulation material (mineral wool or cellular plastic) etc. At the same time, a number of mock-ups of rendered stud walls with existing and new design will be tested in the laboratory. Additionally, theoretical calculations of heat and moisture conditions in these walls will be estimated. Finally, a principal guideline for measures in existing walls, measures in damages walls and suggests on alternative solutions in new walls will be drawn up. Ingemar Samuelson, SP Kristina Mjörnell, SP Anders Jansson, SP