Sagging floor joist

           Sagging floor Joist: Common Causes

If you live in an older home, lets say pre-1970, and you are noticing a sag in your floor, then take a look at these pictures I’ve included in this post for the most common root of the cause. These pictures are good examples of what happens when a worker (usually a plumber or HVAC installer) gets in a hurry and does not care about the long term effect of weakening a floor joist by notching or cutting it.

saggy floor joist cause picture


I see floor joists notched most often by someone trying to get a plumbing waste line through the joist for a toilet flange. I would like to think a professional plumber would have been able to prevent the need to drill or notch large holes through the floor joist by simple foresight and planning where to run the main waste (drain) line.

saggy floor joist cause

Depending on the “live load” (weight bearing downward) and the span of the floor joist- together determine, how soon a noticeable sag in the floor joist will appear.   All of these pictures are from the last two consecutive homes I have been renovated.  In other words, this is a widespread problem!

Keep in mind residential construction was not regulated by way of city building inspectors until the early 1970’s.  It was only then that Cities started requiring structural engineering, and plan checks before a building permit will be issued.  This is one of the biggest contributing factors that helped improve the overall quality of homes that were built.  It was not just left up to the skill and knowledge of the general contractor to decide  to why many older homes have settling and structural issues. two most recent homes I have been working on.  some of the most recent hack jobs I have seen.  But unfortunately, I come across floor joist that have been completely cut out.  Completely compromising the integrity of the floor.  Over time everything starts to droop and


Saggy joist in floor

I am not sure why the person even bothered to leave the sliver of wood below the heat register.  Did he think that would do something? This floor was already undersized and framed completely wrong.  The floor became completely ruin and unsafe after this main structural member.  Its really amazing this floor did not completely drop out from under someone walking across it!


Saggy floor joist picture

Look at the bottom of this beam.  Can you see how far down the left side has dropped?

This structural beam supports not only the floor above, but a bearing wall on the main floor and the roof above that.  This beam originally rested in a small beam pocket on the foundation wall.   Over time the back of the house settled enough that the foundation tilted away and the beam slipped out and the whole kitchen floor sagged a couple inches from one side to the other.

So to fix the sagging floor, we had to lift the beam back up to level and put a post under it for support.

The first step in all sagging floor joist repairs is to find the root of the problem.  Only then can you remedy the situation.  Two common solutions include what is called “sistering up” joists, which simple means add another floor joist to the side of the sagging floor joist, or using a beam and posts to provide support under the sagging joist.


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