Sagging floor joists

garojOctober 16, 2008


I have a house in RI built in 1956 that seems to have been built like a tank in most respects, but lately it seems that the floor has sagged in one quarter of the house. The only changes that have occurred have been a rather heavy bunk bed put in and, more recently, two large skylights. It is a ranch. I'm wondering if this could be perceptual but my whole family seems to notice it. There are no cracks in walls, though one small one in the ceiling is newish. Under the house (the basement is a 4 foot crawlspace) there is a noticeable sag over a span of about 20-30 feet.

Could changes to the roof when the skylights went in have any effect?

Is an LDL beam of some sort a simple solution?

Thanks. I can post photos if that helps if I can figure it out.

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it depends on what was used for the joist and if any have broken/rotted. since you have a 4ft crawlspace it would not be that difficult to get a contractor in to check it out and tell you what you need to do.

my stepdads childhood home(he still has it as a 2nd home) did the same thing a few years back. turned out some sort of bettle(NOT termites) was eating the joists and he had to have 3/4 of teh joists replaced in teh house. a couple areas they simply braced up and resupported from below. but most of the house was so bad they were amazed the floor had not collapsed.

    Bookmark   October 16, 2008 at 1:35PM
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Photos might help.

The LVL ( laminated veneer lumber ) is used mainly to span a distance without any support. Not a problem in your crawl space to install support poles. You should be able to visibly see the joist problem if any. A heavy bed could start a sagging problem. A car service jack works great to jack the joists back into position...and then add supports

    Bookmark   October 16, 2008 at 1:39PM
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Inspect the joists before you do any thing.
Main floor loads are 40 pounds per square foot (PSF) live load, and an additional 10 PSF dead load.

It is usually very hard to load up to the 50 PSF total load.

The entire span of the joist must be loaded to reach the limit, and even then you would need to load the entire floor since bridging and flooring allow joists to share loads.

    Bookmark   October 16, 2008 at 7:55PM
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I would definitely get a well recommended inspector, or structural engineer in to really find out what's going on. All the guessing in the world won't actually tell you if something is wrong or in imminent danger of collapsing, and you need to know.

    Bookmark   October 17, 2008 at 6:52AM
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Thanks. The joists span 15' and the nice bow starts at about 3-4 feet out from the center beam in the house, directly under the wall that is in the hallway above it. Then they go back up to the outside wall of the house. I will probably just use an LVL where the wall is (i.e., 3-4 feet out from the center beam) and jack it up an inch or so and leave it at that. I have photos but don't see how to upload them and I don't see a HELP page. You can email me at for the photos if you would have opinions.

    Bookmark   October 21, 2008 at 8:54AM
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