Wooden structural floors can come with unique problems

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This article was published 14/07/2018 (2723 days ago), so information in it may no longer be current.

Question: We have wooden structural basement floors in our home, which was built in 1999. We also had the home built on piles. We have noticed in one area, against the back of the house, that the floor has heaved, and also some lower spots in one area, only. I looked under the floor in the crawl space and all is dry. My next step is to pull back the carpet and replace the warped plywood. I am curious as to how this might happen.

— Linda R Burndorfer

Answer: Problems with wooden structural floors in homes are fairly common, and may be because of either workmanship or moisture related issues. Pulling up the carpet may be the next step in diagnosing your problem, but hiring a registered home inspector (RHI) or structural engineer to physically inspect the crawl space will also likely be required.

Wooden structural floors are a fairly recent method used in our area to prevent common cracking and heaving of concrete basement floor slabs. These work well to allow a warm, straight floor for the lower level of the home, below grade, but may also be subject to unique issues. Some early versions of these floor systems had crawl spaces which were too shallow, and the joists or manufactured I-joists were too close to the soil in the crawl space. These were subject to moisture damage, with some sustaining minimal rot, while others had major issues with damage and crushing. Most builders have found solutions to these issues, but if your bumps are around the perimeter of the floor, then that is the likely cause. Partial tearing up the subfloor may be needed for a complete diagnosis and repair, but crawling under the floor may yield some answers.

Since your home was built almost 20 years ago, the joists in your floor may be manufactured I-joists. This excellent product works well for many applications, but is not well suited to damp crawl spaces. I have seen several situations where they crush or buckle from moisture damage, because of their design with a thin middle of OSB. It would be a good idea to look into your access hatch and see if you have I-joists, which may increase the urgency for inspection and repair.

Diagnosing a problem with the heaving floor sheathing in your structural wood floor may be possible by pulling up the floor coverings if it is minor, but will likely require further inspection from the crawl space to fully see the extent of the issue. Calling an RHI for this more detailed look may be warranted before committing to any costly repairs.

Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and the past president of the Canadian Association of Home & Property Inspectors — Manitoba (cahpi.mb.ca). Questions can be emailed to the address below. Ari can be reached at 204-291-5358 or check out his website at trainedeye.ca.

trainedeye@iname.com

It can be difficult to determine whether a report and quote for repairs from a contractor is fair or not. Unfortunately, there are also a limited number professional engineers that even want to do these types of inspections. For that reason, calling an experienced RHI may be your first course of action to figure out whether you have a serious problem, or a more minor one.

The best-case scenario for your buckled floor is telegraphing of the subfloor sheathing. That complex sounding issue is simply a lifting of the sheathing at the joints or seams. This can happen at the interlocking tongue and groove edges of the sheathing, or between square cut joints. This may occur from shrinkage or movement in the joists, loosening of the fasteners holding down the plywood or OSB or high moisture levels. If you have any moisture leaking into the lower level crawl space or foundation, for any reason, it could cause these joints to swell, creating the heaving you are seeing.

At the other end of the spectrum is rot and moisture damage to the joists themselves, below the sheathing. If the joists have rotted enough to lose some of their structural integrity, they may start to sag or crush, leaving other areas higher and giving the illusion of heaving. This may only be fully evaluated by pulling up the carpet and portions of the subfloor and probing the framing, but may also be identified by probing the wood from the crawl space below. Unfortunately, this often occurs because the soil is too close to the bottom of the joists, leaving little space for an inspector to crawl into and reach. Inspection from the hatch, or further into the crawl space, will determine whether this evaluation is possible, or not.

Since your home was built almost 20 years ago, the joists in your floor may be manufactured I-joists. This excellent product works well for many applications, but is not well suited to damp crawl spaces. I have seen several situations where they crush or buckle due to moisture damage, due to their design with a thin middle of OSB. Many builders have gone back to using real wood joists, or even pressure treated wood, in crawl spaces to avoid structural damage if the crawl space gets wet. It would be a good idea to look into your access hatch and see if you have I-joists, which may increase the urgency for inspection and repair, if they are present.

Diagnosing a problem with the heaving floor sheathing in your structural wood floor may be possible by pulling up the floor coverings if it is minor, but will likely require further inspection from the crawl space to fully see the extent of the issue. Calling an RHI for this more detailed look may be warranted to get a truly independent viewpoint, before committing to any costly repairs.

Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and the past president of the Canadian Association of Home & Property Inspectors — Manitoba (cahpi.mb.ca). Questions can be emailed to the address below. Ari can be reached at 204-291-5358 or check out his website at trainedeye.ca.

trainedeye@iname.com