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Flooring and Carpeting/Sagging-shaking wood floor...level joists.


Why would a wood floor sag if the joists are level?  The wood floor in our bedroom sags almost 3/4" in the center of the end walls.  The floor touches the baseboards on the sides of the room but progressively sags as it meets the middle on the ends of the room.  One end is worse than the other.  I have checked the joists in the basement and they are level.  Is this just a subfloor issue and is it something we should be concerned about?  Is it dangerous?  This is a rental home and I do not want to make a big deal about it if is not dangerous.  Side note...the floor shakes a lot.  Items on my dresser will wiggle and eventually fall off if you do not pay attention to them.  I feel like this situation has gotten worse over the past 3-4 months.  We have 2 babies in the house and would hate for something tragic to happen.  Thank you....worried mommy!  Shannon

Hi Shannon,

This is a tough question. How do you check level ...on the bottom of the joist or where it actually touches the flooring ?? In other words the top of the joist. And how long is the level you are using? Is anyone above , walking on the floor as you check?

I don't know the length or span of the joist and what is also called the unsupported span. Or distance between each foundation support.

It is quite possible that the floor itself and possibly the joist as well flexes or sags with weight. And it is possible that the supports are not level thus allowing the floor to sag. I suppose you could buy some long lengths of pipe or EMT (electrical metal tubing) connect them together and lay them on the supports and check level that way. Then return them for your money back. EMT is about 2.00 for 10 feet, connectors are roughly .89 ea.

I realize you are renting and all this may not be worth it. I really don't think there is anything tragic about to happen , but I can't be there to determine this. You might want a general contractor to have a quick look with estimate for repairs included. Many contractors will do a free estimate and tell you what the problem is.

It might just be a sub floor that is supposed to be 3/4" plywood and it's cheap 5/8" OSB or particle board instead??? If you can determine the type of subfloor and drill out a very small hole in an obscure corner, you can measure the depth of the drill bit descending into the hole. You might determine better what is going on , or add to your data base.

I have no idea if your landlord is willing to make repairs?? A true home inspection would cost money, but then you might be able to legally take some action if the house is deemed unsafe or unlivable.

Best Regards,


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20+ years flooring installation ...carpet,wood,tile and vinyl. Residential and commercial. I do not sell the products , just install what ever the shop / customer has purchased. I actually love seeing the finished project completed and it gives me great satisfaction to help others acheive that goal. If I don't know the answer I will say so, and then I will recommend another expert for you. I may even research the subject and answer to the best of my ability ...including links to my sources. I wish you all success Chris


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