The first question one of our home inspection customers asks when we tell them that a house is built with concrete block that has been sided over with some other material is “Well, how do you know that?” The thickness of the exterior wall and position of the window in the wall tells the story. An exterior wall of a block house is significantly thicker than a wood frame home and the windows are inset in the openings, like in the photo above of a block house sheathed with vinyl siding. Windows in a frame house are set near the front surface of the wall.

    Why would somebody take a perfectly good concrete block house with an extremely durable stucco finish and cover it over? There are three reasons we can think of. One is devious, another is sensible, and the third is gullible:

• Devious - We have inspected several block houses over the years with severe structural problems, either due to settlement or spalling concrete, that have been wrapped in siding to conceal the structural cracks in the wall. That’s our big concern in this situation. The wall itself is no longer visible and we have to look at the floor and attic around the walls for evidence of structural distress; however, ultimately, it is necessary to disclaim the concrete block wall because we simply cannot see it.
      The seller of a house we inspected years ago in Key West had added “decorative” siding just over the top area of the block wall where the concrete tie beam is located. Luckily, the tie beam spalling was so severe that it was visible from the attic at the top of the beam and nobody was fooled. To learn more about concrete spalling, see our blog post What is concrete spalling?
• Sensible - If a homeowner of an older CBS house builds a large addition with wood frame walls, it makes sense to cover the original block walls with the same siding used for the addition, because It ties everything together and often modernizes the look of the house.
• Gullible - This summer we inspected a home whose seller was a older woman that had been sold an aluminum siding package 25 years ago by a glib salesman from a national home improvement company. The sales pitch was that it would be low maintenance and “you’ll never have to paint your house again!”
      Actually, the existing paint finish on the stucco was nearly as durable and much more impact resistant, plus the metal siding had already been painted once since it was installed. If you saw the 1987 movie Tin Men, starring Richard Dreyfuss and Danny DeVito, about the rivalry between two high-pressure aluminum siding salesmen in 1960s Baltimore, you’ll understand how this could have happened. The structure was perfectly fine, as far as we could tell; but, again, it was necessary to disclaim the condition of the block wall in our report because we could not see it.

    So we suggest looking extra carefully at a block house that has been sided over and realizing that you are taking on the additional risk of a concealed problem by buying it, but do not automatically assume the worst. Also, because houses in the same neighborhood tend to have similar problems, especially ones in a development that were all built within a few years of each other and by the same contractor, it can be a good strategy to look at nearby houses that have not had siding added for additional insight.

    Also, see our blog post What are the pros and cons of aluminum siding?

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To learn more about exterior walls and structures, see these other blog posts:

• What is the average lifespan of a house foundation?

• What causes vertical cracks in fiber cement siding planks?

• What causes raised white lines of residue on a block wall that are crusty and crumbling? 

• What is the difference between soil subsidence, heave, creep, and settlement? 

• How much ventilation is required for the under-floor crawl space of a home? 

• What causes stair-step cracks in a block or brick wall?

• What causes a horizontal crack in a block or brick wall? 

• How can I tell if a diagonal crack in drywall at the corner of a window or door indicates a structural problem?

• What causes the surface of old bricks to erode away into sandy powder? 

• What are the pros and cons of concrete block versus wood frame construction?

• Should I buy a house with a crawl space? 

• Why is my stucco cracking?

• There's cracks running along the home's concrete tie beam. What's wrong? 

• What would cause long horizontal lines of brick mortar to fall out?

• How do I recognize serious structural problems in a house?

• What is engineered wood siding?

• Should I buy a house with structural problems? 

• What are those powdery white areas on my brick walls?

• What causes cracks in the walls and floors of a house?

• How can I tell if the exterior walls of a house are concrete block (CBS) or wood or brick?

• What are the common problems of different types of house foundations? 

• What are the warning signs of a dangerous deck?

• How can I tell whether my house foundation problems are caused by a sinkhole or expansive clay soil?

        Visit our EXTERIOR WALLS AND STRUCTURE page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.