Masonry walls can be strong and very durable, and also airtight and moisture-resistant. But this doesn’t mean that masonry walls are impermeable to moisture, or that they can’t be leaky.
Besides, masonry walls also need high levels of insulation.
Masonry materials do not provide any significant insulation. Insulation is critical for home comfort.
Making walls with dense concrete is not the same as making them with bricks or with CMU (Concrete Masonry Units). Similarly, using using porous CMU is not the same as using dense CMU blocks.
Be aware of these type of differences, and also to the differences within each masonry product.
Pay special attention to the density of the masonry. Typically, the higher the density, the more water resistant, airtight and strong the masonry wall will be.
Many masonry walls use a single line of oversized block or brick as the structural part. It's a way of saving money, by eliminating components of the cavity and double-wythe walls.
But to be effective, single-wythe walls have to be carefully built.
These walls must be extremely airtight, and blocks should be integral water repellent, or have a repellent coating.
Issues such as flashing and weep systems, or control joints (to allow masonry to shrink and grow with changes in temperature), or water resistant rigid insulation and full head joints, are of the outmost importance
Solid cavity walls
Many modern two-wythe cavity walls have become “solid” walls; in other words: traditional cavities are now fully-filled with a water-resistant insulation material (mineral wool...).
This design has obvious risks, in rainy climates.
To minimize the risk os moisture, walls have to be built with water-resistant and dense materials. Reducing moisture migration to a minimum is critical, as it is a comprehensive sealing and flashing strategy.
Even concrete walls should be protected. All potential trouble areas - particularly around windows and doors, or at the intersection of the floors and ceilings with the exterior walls… - should be properly sealed.
The use of waterproofing products is obviously helpful, but are not a panacea or without disadvantages.