How can I level a hump in my floor?

Answered by Jeffrey Anderson ~ December 16, 2013 ~ No Comments

In my 100+ year old house we have an uneven bump in our floor from one basement jack that is too high. We plan to install laminate flooring upstairs but want to level the floor first. How can we lower the jack safely?


Jeffrey Anderson

Danielle, the first thing I would say is that if you don't have a lot of experience as a DIYer, this is a project that might require the expertise of a general contractor -- not necessarily to install the flooring, but to level the existing floor. The jacks or columns that support the floor are structural components. Doing something to them that might adversely affect their structural integrity could damage the house and might even create a safety hazard.

How high is the hump? Is it something that could be cured by using a power sander on the subfloor? If so, that's a chore that can normally be handled by a homeowner without too much trouble. Just make sure to constantly check the trouble spot with at least a four foot level while sanding or you're liable to end up with a dip where there was a hump. If the hump is ¼ inch or less, I would give sanding a try before resorting to adjusting the jack.

However, if the hump is over ¼ inch, adjusting the jack or jacks might be the best option. There are several types of columns or jacks commonly used to support floor systems. If you have a non-adjustable pipe column that is causing the hump, adjusting it will almost definitely require a contractor. These types of columns normally sit on a pier below the concrete slab and are welded or fastened in another fashion to the above beam.

Some pipe columns can be adjusted and can be identified by a threaded rod extending out of the top of the column that is attached to the top plate. However, even these should be adjusted by a general contractor. If your home is over 100 years old and has never been renovated, there's a good chance there may be wooded jacks or columns supporting the floor system. This type would be the easiest to adjust as they can often be trimmed with a saw. Before removing the offending column, the floor should be temporarily supported at the column location with sturdy framing lumber. Once the column has been trimmed and reinstalled, the temporary support can be removed.

Determining how much needs to be trimmed can be done by taking measurements across the subfloor upstairs using a string line and level. However, if sanding isn't an option, I strongly recommend that you get a contractor involved.

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