Cinderblock Walls in San Carlos CA Homes: Robust but Beware of Moisture Problems

Cinderblock Construction

While there are not many homes in San Carlos CA with cinderblock walls, they do still exist – mostly east of the El Camino Real in the Clearfield Park neighborhood. If you happen to be looking to buy one of these homes, there are some things to consider.

Robust but Difficult to Remodel

These homes are built with slab foundations, that a cement floor on top of dirt. So, doing remodels where you want to move wastewater (sewer) plumbing is a major pain. You need to jackhammer the floor to expose the sewer lines and cut trenches to connect your new location to the sewer main running through the house. Remember, you’re jackhammering inside your house, this will be messy! You may also be limited in flooring choices. Some slabs get moist so wood flooring may not be the best option for you, a nice vinyl plank might be best?

The advantage to cinderblock walls is termites will not eat them! You do still have wood ceiling joists and rafters. So, you’re not 100% invincible against termites or dry rot, but you certainly are better off compared to standard wood structures. Cinderblock walls like stucco can also crack due to soil shifting, especially if those walls are not reinforced. These walls are also a major pain to remove.

Moisture Problems

However, for me the worst thing about cinderblock construction is the propensity for condensation inside the home. The cinderblocks can transfer the cold from the outside through to the interior walls in the winter. Those super cold walls will then condense any moisture inside the home on their surface. Kind of what happens to the outside of a glass filled with ice, condensation builds up on the outside of the glass.

The more airtight the house is, the worse the moisture problem can get inside the home. This is because in the winter that cold air is quite dry, but you’re trying to keep your house warm, so you close everything nice and tight and moisture from cooking, hot showers, breathing, etc. begins to build up in the house.

The humid environment then allows for condensation to build up on the cinderblock walls. Then if you got a piece of furniture against a wall where it doesn’t get much light or airflow. That’s a perfect recipe for mold/mildew to start growing on the wall and nearby wood/cloth furniture. Of course, the last thing you want is mold inside your home, it can lead to all types of serious health issues.

You have to treat the interior of a cinderblock home like they do basements back east. This means installing at least 1″ thick foam board to insulate the cinderblock walls, then furring out over the foam and finally installing sheetrock over that. The insulation should prevent the sheetrock walls from getting cold enough to allow moisture in the air to condense out. Mold/mildew should not grow in dark, low air flow spaces if moisture is not present. Do this and your San Carlos CA cinderblock should be warmer inside and not suffer from moisture issues. Something else that helps is having a good, forced-air furnace; the air circulation helps keep the walls dry.