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What is Foundation Underpinning?

Mary McMahon
Updated May 17, 2024
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Foundation underpinning is structural support added to the foundation of an existing structure. Underpinning can be done for a number of different reasons, and is usually performed by a construction firm which specializes in foundations, and may specifically focus on doing underpinning work. While installing foundation underpinning can be costly and sometimes time consuming, it can be very important for structural integrity and safety, and may be required by law in some cases.

One common reason for foundation underpinning is damage to a foundation. Foundations can crack over time as a result of settling or poor construction. Foundations can also be damaged by events like severe weather. In these cases, it may not be necessary or possible to replace the foundation, but some extra support is needed, and underpinning is used to arrest the damage and stabilize the foundation so that the structure above will stay safe.

Underpinning is also done as a form of retrofitting when new information about a structure or the land it was built on emerges, or when the law changes. In earthquake-prone regions, for example, many older structures are not considered earthquake safe under the law, and they need to be retrofitted. Foundation underpinning might also be needed if soil conditions under a structure change or if the results of a soil test reveal that previous information about soil stability was wrong.

There are a number of different techniques which can be used for foundation underpinning. Usually, a structural engineer visits the site to examine the structure, and collects information about the surrounding soils and other topics. The structural engineer may recommend several different underpinning options which can be used to stabilize and support the foundation. Often, underpinning involves deepening and extending the foundation, sometimes with the goal of reaching bedrock for additional stability.

In some cases, a foundation contractor can accomplish foundation underpinning without disturbing the occupants of the building. In other cases, the building may need to be vacated for all or part of the work for safety. If foundation underpinning is required because a previous contractor did not install a foundation properly or information about the conditions at the site was falsified, the contractor or person who lied on the records may be liable for the cost of the retrofit. It may be a good idea to retain a lawyer in these cases to receive the best advice about how to proceed.

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Mary McMahon
By Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a AboutMechanics researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Discussion Comments

By drhs07 — On Jun 30, 2011

My family and I recently moved into a brand new house in a new housing community. The community was finished in 2007 and we are the first occupants of the home.

My wife and I thought that because our home was built recently, that it would be built to the safest standards. We were wrong.

We moved into the home two years ago, and last year I started to notice cracks growing in our driveway. Apparently, the soil that our house was built on is creeping. It turns out that the original builder did a sloppy job of laying the foundation. I did not want to risk the chance of having any more damage happen to the home, so I had the foundation underpinned.

Our contractor said we could take legal action against the original contractors for not building the house up to standard. We did, and after a lengthy process, we were reimbursed the amount we paid to get our foundation repaired and underpinned.

Even when you buy a new home, always have it inspected by a trusted contractor. If we had done this, we could have saved ourselves the trouble and bought a better built house.

By john1478 — On Jun 30, 2011

My husband and I recently had our foundation repaired and underpinned. We have a few trees surrounding our house, and their roots have grown underneath the foundation.

We first noticed a crack in the concrete of our garage floor. My husband had a contractor inspect the house, and he said that our trees were the cause of the problem.

I love trees, so when my husband wanted to have them removed, I pleaded and begged him not to. I love the shade that our trees give the house during the hot summertime. Although it would have been cheaper to uproot the trees, my husband let me have my way. We hired the contractor to underpin our foundation.

I think it was a win-win situation. I got to keep my beloved trees, and my husband got to ease his concern that our house was falling apart.

By dimpley — On Jun 29, 2011

You would be surprised at how much a little bit of underpinning can help to insulate a home. We bought an old home in the middle of winter with high porches and floors with the intention of renovating it to its former glory.

The idea was to work on the inside until things warmed up; that didn't exactly happen, though.

What we had not counted on was how cold the place was going to be until we got the bottom completely closed in. Yowsers! It was freezing in that house.

My husband figured out what the problem was quickly enough, and we only had one outrageous gas and electric bill to contend with before he had us pinned right up!

House underpinning is really important, though, for the energy efficiency of a home, particularly old and drafty ones.

By Testy — On Jun 28, 2011

I have worked in construction management for many years now. If there was one home improvement project that I would recommend every home owner to do, it would be foundation underpinning. It is amazing how much damage your house can withstand if it has a strong foundation.

I live in the surrounding hills of Los Angeles, CA. In the past few years, a number of homes have been destroyed or damaged due to landslides. Wild fires weaken the soil, and then heavy rainfall moves the soil. This land movement can be detrimental to the integrity of a house if it is not properly stabilized.

Thankfully, more people are warming up to the idea of underpinning their foundation. After the recent rainy season, business has been booming since people are openly recommending foundation underpinnings Although it is not the cheapest thing you can do to improve your house, it is probably the most important.

By Agni3 — On Jun 28, 2011

Many people use underpinning when they live in mobile or modular homes, as well. We used to live in a double wide mobile home and it was quite spacious and affordable in terms of payments.

We had a brick house foundation put in, although many people go with vinyl as well. The brick was supposed to set our double wide up to be considered as an actual stick built structure. That, we were told, would lower our insurance prices, which were utterly outrageous.

Unfortunately, our brick underpinning didn’t do that for us and we got out of that situation before we were upside down in the mortgage that we had.

However, I think that nice underpinning for non-mobile homes is supposed to increase the value quite a bit.

Mary McMahon

Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a...

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