Exterior walls are very exposed to the elements and whatever their type they are prone to moisture problems.
Siding and coverings, sealants and flashing, or special paints, are part of the first line of defense of the walls.
But there are other first lines, especially important in humid climates: large roof overhangs and ground and surface drainage systems.
How does moisture Enter the Exterior walls?
It's not easy to keep walls dry. There are various mechanisms through which moisture penetrates the walls.
Rain-driven water can enter walls trough cracks and penetrations, or because of flashing defects (roof flashing defects; missing and bad flashing around windows or doors and other junctures).
Liquid moisture can also enter the walls by capillary suction: capillarity is able to move water from the footing of the building to its roof! Without capillary breaks water around the foundation or in soils, or water that enters the siding, can move a long distance upwards, causing serious harms. Liquid water can move into the walls horizontally (through gaps in the siding, namely when the siding becomes saturated with rainwater), or flow downwards (after penetrating through openings in the chimney, skylights, shingles, etc), or travel up through the foundations and the ground (capillarity suction).
But that's not all.
Walls are also subject to air leakage - coming from warm interior ar and outdoor air. Air can penetrate the wall through small holes and cracks and condense on the wall sheathing.
And there is also water vapor (water invisible to our eyes, but present in the air people inhale and exhale), which can move through most building materials (vapor diffusion). Water vapor doesn't need cracks and holes to enter the walls, and condense on contact with colder surfaces, within the wall.
Preventing mositure in Wood frame walls
Wood frame type walls require comprehensive moisture protection. We list them below:
1) Roof overhangs, comprehensive ground drainage;
2) Moisture protection materials: water resistive barriers (WRB), air barriers (AB), vapor barriers (VB);
3) Rainscreens - to allow drainage and drying.
4) Capillary breaks - to stop upward moisture travel;
5) Proper flashing at all wall penetrations and junctures.
6) Proper siding and wall coverings
Implementing all these protection measures should be carried out with attention to detail.
Bad flashing, stingy overhangs, ill-designed rainscreens or ground drainage systems (or other poor construction details) will compromise the performance of the wall.Moisture and insulation
Insulation materials are not intended to prevent moisture. That’s not their role. The role of insulation is to control and prevent heat transfer (to or from outdoors) and to provide thermal comfort.
Preventing Moisture Problems In Masonry walls
Concrete is very water resistant, but this fact t doesn’t mean that it will not wick moisture. On the contrary.
Bricks do not leak, but they too can absorb lots of moisture; and if bricks become saturated, water will start overflowing and can enter the wall.
Most stones and standard CMU are also water-permeable (though the degree depends on their porosity). These masonry materials are a lot less airtight than poured or pre-cast concrete and solid clay brick.
Mortar also varies significantly in their composition, and mortar joints are common trouble moisture areas.
Be aware of these differences, and of the differences within each product. They have a big impact on masonry moisture issues.
Though more water-resistant than wood-frame walls, masonry walls are not free of moisture problems.
Like wood frame homes, masonry walls also require a 1) first line of defense (roof overhangs, ground drainage, proper paints and sealants...), a 2) drainage cavity (wall cavity types), 3) water resistant materials, including insulation materials (that's especially important in solid masonry walls, that is, walls without a drainage cavity) 4) capillary breaks (to prevent upward moisture suction) and 5) proper flashing of all wall penetrations and junctures.
See, for details:
Wood and Masonry Cavity drainage and Rainscreen Walls