Sagging Floors over a Crawl Space

Sagging Floors over a Crawl Space

Sagging Floors over a Crawl Space

Monday, October 22nd, 2012 by Clint Cooper

What causes sagging floors over a crawl space?

Sagging floors are not only a nuisance, but can leave you wondering how much longer the floor will be able to support the weight of everything on it! So what created the problem?

1. Existing block or brick columns are spaced too far apart.

When a crawl space is built, block or brick (sometimes even wood) columns are located throughout the crawl space to support the weight of the structure above. If those columns are spaced too far apart, the beam or girder can become overloaded and sag between the columns. When the girder sags, so does the floor above it.

2. Weakened floor joists and girders due to moisture and wood rot.

Because crawl spaces are often unsealed from the earth, excess moisture and humidity is a problem. And what happens to wood when it has been exposed to moisture and humidity? It begins to rot, get moldy and become weak. Yuck! The weakened girders and floor joists are unable to continue supporting the weight above, and the floor above the crawl space becomes bouncy, soft, and may begin to sag.

3. Existing columns settle due to weak soil

Soil can cause a lot of problems, and it is no different here. Weak soil can cause the existing columns in the crawl space to sink or settle, often creating a gap between the top of the column and the bottom of the girder it was supporting. Once the column settles, then the girder sags and the floors above sag. It’s a chain reaction.


- Sloping floors, sometimes creating a gap between the floor and the interior walls

-cracks in interior walls and door frames out of level, caused by a wall sinking along with the floor

-gaps between existing columns and girders in the crawl space

-Evidence of moisture, wood rot, and compression of the floor joists in the crawl space.

What NOT to have done. and why!

Concrete Columns- What is it? Concrete footings are poured throughout your crawl space. After the concrete footings cure, concrete blocks are stacked on top of the footings, and sometimes with mortar placed between the blocks. after the mortar cures, shims are placed between the uppermost concrete block and the girder.

Why might people choose this? It’s a common solution and concrete seems strong.

Why this doesn’t work. Not only is this solution time consuming due to all the waiting for concrete and mortar to cure, but it is also not adjustable. As the concrete column later settles into the soil below, additional shims may need to be added. In other words this isn’t a long term solution. If the existing concrete columns in your crawl space aren’t working, why would new ones?

Sagging Floors over a Crawl Space

What is it? A temporary jack is used to lift the girder to make room for the shims. Shims are then pushed between the existing column and the girder. The temporary jacks are removed.

Why might people choose this? It’s cheap and easy.

Why this doesn’t work. You get what you pay for. Additional shimming is only a temporary fix, and you will find yourself repairing damages again and again and again.

Light-duty jack post

What is it? A concrete block is laid on top of the soil, and a light-duty jack post is set into place. The light-duty jack post is then tightened to fit against the girder.

Why might people choose this? A light-duty jack post can be purchased at the local hardware store and installed by the homeowner. There’s nothing like a do-it-yourself project.

Why this doesn’t work. Do you want anything referred to as «light-duty» stabilizing your sagging floor? Light-duty jack posts can hold very little weight, are difficult to adjust, and don’t address the most important problem- the weak foundation soils below.


Leave a Reply