Old House Remodeling: Raising A Slightly Sagging Floor

By Bruce W. Maki, Editor

Words Of Warning:

Raising sections of a house can be dangerous. Read our disclaimer. We know of no instruction book on house-raising. 

If there are any rules to this practice they are:

• Go slow. An old rule of thumb is lift only 1/8 inch per day, or face consequences of broken plaster and drywall, even cracked structural members.
• Spread out the load. Jacks are made from steel and iron. These materials can handle tens of thousands of pounds per square inch of contact bearing stress.  Common framing lumber can only handle about 625 pounds per square inch of compressive stress. (See footnote 1) Bottle jacks can develop enough force that, if applied to a small area can easily exceed the 625 psi allowable stress. Therefore, it is crucial that the load be spread out with appropriate materials, typically heavy gauge steel plates.
• Listen to the structure. I wish I could demonstrate for you what I witnessed in one of my college engineering labs. We used a big testing machine to destroy various building materials: wood, concrete, and steel.  Concrete and steel make virtually no noise before they fail (break), but wood is different. When a large piece of wood is placed under extreme stress, it makes a tremendous racket. It snaps, it crackles, it pops. And loud. We tested wood beams to destruction, and it was a rather long process, perhaps three or five minutes. The wood fibers break a few at a time, not all at once. My experience is that wood-framed structures make a heckova lot of noise before they fail. This fact can be employed when raising buildings. Small sounds will be heard, most of them (I believe) are from wood members rubbing on other wood members where they are nailed together.  Over the years I have learned what sounds to expect when lifting a house, they are similar to the creaking and groaning sounds made by a house during a very strong windstorm, just a little louder and a lot more frequent.

Getting Started:

Our first step in raising the floor was to attach a 4x6 beam to the underside of the floor joists.  We used a pair of ordinary rafter ties, attached with screws, to hold the beam in place while we got the jack and columns ready.

This photo shows the 4x6 beam used to spread the lifting force to all of the floor joists. The rusty-red column on the left is a lally column with a threaded adjustable base. The post on the right is a heavy-duty lally column we use for lifting with the 12 ton hydraulic jack.

The bottom of the right-hand post in the above photo. We use a piece of 1/4" steel plate under the jack, to distribute the load to the wood cross-beams. These cross-beams are in two layers: double 4x6 posts on the bottom and an old 6x6 post on top. This helps spread the load across the floor.

If the above cross-beams were not used, there is a serious chance that the jack would literally "punch-through" the floor.  But even more likely, the lower floor will deflect as the jack is raised.

The lally columns must bear on a solid surface. These columns come with a pair of thin steel plates, to help spread the forces to the wood to avoid crushing the wood fibers. In my opinion, many of these steel plates are barely adequate. We have a nice collection of cup-shaped plates from previous projects. It does not take much to bend some of these flimsy plates.

It pays to be a pack-rat.  Over the years I have gathered quite a few chunks of heavy steel plates, 1/4" and thicker. These come in handy when lifting houses.

The top of the lally column has a metal plate. Without this, the steel tube would slice right through the wood. Danger! Later, when a column like this is removed, the top plate can easily fall on the head on the person who is unscrewing the threaded base. We always have a helper stand on a ladder and steady the column and catch the loose plate before it cracks someone's noggin. Or, we secure the plate with duct tape. (Look in the big photo above)

Our pride and joy. On top of the hydraulic bottle jack is a nice scrap of 1" thick steel plate. Now that's heavy metal. This little chunk weighs about 15 pounds. We need this piece of steel to transfer the force from the small top of the jack to the larger column. We have used 1/4" steel plate for this, and bent it dramatically. (but that was from lifting a major section of a two-story house)

As the right-hand end of the beam is lifted, a lally column is placed nearby and adjusted so it fits tightly. There are flat spots on the threaded base to allow a wrench to turn it.

Note that there is a risk of the jack tipping over, allowing heavy parts to fall from up high. Make sure that the jack is resting on a stable base, using shims if necessary. 

Lifting a floor (or a part of a house, or a whole house) is an iterative process. We cranked up the jack about 1/8 inch while simultaneously tightening the lally column.  We did this for each end of the beam until the floor was raised a little more than 1/4". We checked the floor upstairs with a good level.

In this case, we were sistering floor joists, but the process is the same for other tasks such as:

• Raising a sagging floor and installing a supporting stud wall. The wall can be built parallel to the temporary beam. A good foundation is necessary.
• Raising a floor, right below an interior wall, that is sagging from all that weight. A permanent lally column can be installed.
• Raising a structure (such as a garage) to repair the foundation or sill plate. The beam can be used to lift up on the roof trusses (as close to the ends as possible) or the columns can lift the top plate of a wall.

After all the repairs are made, the hydraulic jack is raised a bit, the lally column is removed, and the jack slowly lowered to let the load bear on the new structure.

There are larger bottle jacks available, such as a 20 ton unit, but we have been able to do all of our lifting jobs around this old two-story house with the 12 ton jack.

Copyright © 2000, 2005  HammerZone.com

Written April 6, 2000
Revised January 11, 2005