What is the average lifespan of a house foundation?

Wednesday, June 13, 2018

Determining the life expectancy of something that is buried in the ground is tricky business. The variables include the amount of rain that soaks the ground, fluctuations of the water table below it, creeping tree roots,  severity of temperature fluctuations—and specifically freeze/thaw cycles, movement of soil due to geological or site drainage conditions, concentrated loads at points along it, and the composition of both the soil and foundation materials. 

    All these things make a lifespan generalization risky, so a range rather than a specific number is the best we can do. These numbers are based on estimates published by the International Association of Certified Home Inspectors (InterNACHI), a study by the National Association of Home Builders (NAHB), and our own experience over the years.

FOUNDATION TYPE                    AVERAGE LIFESPAN YEARS 

Concrete Footing..............................100 to indefinite   

Thickened Edge Concrete Slab........100 to indefinite 

Concrete Piers and Grade Beam......70 to 100          

Treated Wood Piers...........................40 to 75           

Concrete or Brick Pier on Grade.......50 to 80  

Stacked Concrete Block on Pad.......25 to 50 

Here are some problems that can shorten the life of a foundation:

  • Sinkholes - There are three major types of sinkholes: 1) solution sinkholes, 2) cover subsidence sinkholes, and 3) cover collapse sinkholes. The first two types sink slowly over time. It’s the cover collapse sinkholes, which usually fall down abruptly and dramatically, that are on the evening TV news.  Our blog post What are the warning signs of a sinkhole? outlines what to look for.
  • Clay soil - Although a sinkhole is the most feared underground defect, clay soil is the more common one. The elasticity of clay causes it to shrink during dry spells, then swell during seasons with heavy rains. The swell/shrink cycle causes the ground under a home built over a layer of clay soil to heave up and down. Several of these wet/dry cycles, if they are extreme, can fracture a foundation, with corresponding cracks running up the walls.
        Determining whether structural cracks in a home are due to sinkhole activity, clay soil, or erosion, is complicated. Engineering experts sometimes reach different conclusions about the cause of a structural problem when examining the same home. To learn more, see our blog post What is the difference between soil subsidence, heave, creep, and settlement?
  • Trees near the foundation - Most people know that tree roots growing under a home can heave the foundation but, because roots remove so much water from the ground, they can also cause soil shrinkage and foundation settlement. See our blog post How can trees damage a house? for more.
  • Concrete spalling - Spalling is caused by moisture penetrating the layer of concrete covering the reinforcing steel in concrete footing, foundation pier, or grade beam. Over time, the steel begins to rust inside the beam and, because rust is slow but very powerful expansive process, cracks appear at the surface over the reinforcing steel. It‘s a progressive deterioration, because the open crack allows more moisture to accelerate the corrosion--formally known as ferrous oxide scale--which opens the crack further. Eventually small chunks of concrete begin falling out and, if left without repair long enough, structural failure follows. 
  • Poor site drainage - Rainwater draining around a house or under it on a sloped site can erode and expose the foundation, eventually undercutting it. The ground around the foundation should slope away from it on all sides for best drainage. A long-term plumbing leak in the ground under a home can also cause foundation problems.
  • Wood rot - Certain types of wood, like cypress, have a surprisingly long lifespan when set in the ground as a foundation and can remain structurally sound for 100 years or more. But sometimes rot sets in early, with a curious result. When we were working in the Florida Keys years ago we occasionally came across homes constructed entirely of cypress lumber, named “Moody Mansions” by their builder during the 1980s. Fast-forward 25 years, and the outside layer of buried cypress log piles had rotted away and loosened, although the interior wood was still sound. So the piles had a little wiggle room around them and, when you walked across the house from side to side, there was a definite feeling of being on a ship at sea. The floor shifted ever-so-slightly under foot—a disturbing sensation. Many of the Moody Mansions ended up with a replacement foundation of concrete piers, while some homeowners just found it an amusing idiosyncrasy. The defect negatively affected the value of the homes, however.
  • Brick pier deterioration - Freeze damage of wet brick and a problem called “rising damp” can cause brick foundation piers to begin to crumble. For more details, see our blog post What causes the surface of old bricks to erode away into sandy powder?

    Go to our blog post What are the common problems of different types of house foundations?  for more on foundation defects. Also, see our blog post How accurate are the average life expectancy ratings of home components? Are they actually useful? to learn more about life expectancy ratings.

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

 What is the minimum depth below ground of the foundation of a house, for either monolithic thickened edge slab or stemwall footing?

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? 

 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 structural problems in a retaining wall? 

 What is engineered wood siding?

 Should I buy a house that has had foundation repair? 

 What is a "continuous load path”?

 Should I buy a house with asbestos siding?   

 How can I tell if cracks in the garage floor are a problem or not? 

 What do you look for when inspecting vinyl siding?

 Why is housewrap installed on exterior walls under the siding? 

 How do I recognize serious structural problems in a house?

 Why did so many concrete block homes collapse in Mexico Beach during Hurricane Michael? 

 How can I tell if the concrete block walls of my house have vertical steel and concrete reinforcement?

 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 warning signs of a dangerous deck?

• What are the code requirements for installing manufactured stone on the exterior of the wood stud wall of a house?

   Visit our EXTERIOR WALLS AND STRUCTURES and LIFE EXPECTANCY pages for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles. 

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