The damage has occurred in walls designed with a “single-layer sealing ” on a wooden frame wall that has been insulated with polystyrene or stiff mineral wool directly on exterior plaster boards with paper coating or chip boards applied on the wooden frame wall. The polystyrene/mineral wool is then coated with so called thin plaster. It has become evident that this type of design is extremely moisture-sensitive because it is very difficult for the moisture entering such a wall to dry out.
The cause of the moisture problem
There are several causes for this moisture problem. During construction, weather conditions may be rainy or moist, in which case moisture can be trapped in the construction. There may also be leaks resulting from punctured plaster with inadequate sealing around windows and doors, as a result inadequate window sills etc. Installations of sun shades, balconies and electrical fittings may also let in moisture, which has nowhere to go, resulting in mould problems in the walls’ organic materials. On a building site, it is practically impossible to create a completely tight wall surface protecting against water penetration.
This outer wall design was originally developed in Germany as a method for additional insulation of existing brick houses. In Germany, experiences with this system have been positive. However, in Sweden, this design has been adopted and used on wooden frame walls. When applying this design for wooden frame walls, the risk of damage from moisture in an unventilated wall design was not taken into consideration. A large number of losses have now occurred as a result of this design.
Contractual Guarantees and Liabilities
In May 2007, the problem received much media attention. SP, The Technical Research Institute of Sweden had arranged a conference on this topic in Borås with approximately 300 participants from the building industry. After the very extensive package of information given at this conference, which gained much media attention, the entire building industry in Sweden had been made aware of the problems.
Usually, these faults and thereto related damages are discovered during or after the defects liability period. According to the standard contracts used by the Building Industry in Sweden, AB 04 and ABT 06, the contractors are liable for loss or damage occurring during the defects liability period. According to the respective contract, the contractor who is liable for faults and errors is also liable for damage to the contract work as a result of any such faults and errors.
The defects liability period is five years with respect to the contractor’s work. According to AB 04 and ABT 06 in cases where a fault or error can be proven to be the consequence of negligence from the contractor, he is also liable for any essential fault or error that becomes evident after the expiry of the contractual defects liability period. A contractor who is liable for faults or errors is also liable for loss or damage to the contract works caused by such fault or error. An essential fault or error is an error that affects the owner’s possibility to use the building or structure for its intended purpose or a fault or error that affects the building’s future existence. Moisture in a wall construction will lead to microbiological growth and possible rot. This must be considered as an essential fault or error. When it comes to negligence, gross negligence is not required in order to establish contractual liability. Hence, the contractor will according to the contract be liable for in principle all faults or errors.
Compensation for loss or damage
After receiving such a broad attention at the conference in Borås in May 2007, the entire building industry has been made aware of the current problems. According to If’s policy wordings for Contract Works indemnity will be paid for unforeseen physical loss or damage to insured contract works. However, the fault or error itself being design, material or workmanship is excluded and only any possible consequential loss or damage can be indemnified.
As this type of façade problems have received such broad attention within the Building industry in Sweden, the consequential loss or damage can no longer be considered as unforeseen. If will therefore no longer indemnify loss or damage caused by this type of façade design.
Monitoring the moisture status
Property owners with this type of façade design in their houses should monitor the moisture status in the buildings’ exterior walls to minimise the risk of any damage or problems due to moisture.
- Thick or thin plaster
- Stiff insulation of cellular plastic or mineral wool that has been attached to a board (3)
- Plaster board, plywood, chip board, mineral fibre board or equivalent
- Wooden frame, often crossing with heat insulation in between
- Air and moisture insulation, often polythene foil 0.2 mm
- Internal board, usually of plaster board
Damage usually occurs in the exterior board (3) and the outer parts of the wooden frame construction. Water leaking into the structure, for example, around not tight connections, is absorbed by the board (3) or runs down the front or back of the board – downwards, inwards and also laterally. If a glue spatula with teeth is used when applying the glue to the board, the water can run sideways along the tracks created in the glue. Once the structure has become damp, it takes a long time for the moisture to dry, which is why the measurement can be performed practically at any time.
Image 11: Plastered wooden frame wall with ventilated facade board.
Plaster
Moisture resistant board
Ventilated Air Core
Wind-proof board
Wooden frame
Mineral wool
Egon Stenberg
