Stucco as an exterior finish works well- if done properly. The unfortunate reality is that it VERY rarely is. One thing that is important to define is that stucco is a reservoir cladding. This means it soaks up water like a sponge, and slowly dries/evaporates. This is true of most any masonry cladding (brick, stone), but is especially true with stucco. This isn’t a problem, provided the following is true:
- A ventilation space behind the stucco is critical. It allows the stucco to dry to the front or back. There are numerous ways to achieve this.
- An air tight high quality waterproofing membrane against the buildings sheathing is important, especially in a climate like the one where we are, Winnipeg. Weather changes from one extreme to another, and all cladding leaks. With stucco, not only does it unavoidably leak bulk water, it holds it up against the buildings sheathing over, and over, and over again. With most buildings these days being sheathed with osb, this is especially problematic.
- Proper flashing methods MUST be used, especially at roof to wall intersections.
Stucco is used heavily, especially on the sides and backs of buildings because it is very cost effective when compared to other cladding options. It is important to note though- if done properly, it no longer has it’s cost competitive advantage.
If we want to make our buildings last, promote healthy indoor air quality, become more energy efficient, and more sustainable- we need to completely re-think the way we deal with exteriors on residential wood frame construction buildings. This includes changing the way stucco is applied.