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Question DetailsAsked on 10/22/2016

what does it mean when upstairs floor goes in when you step on it and pops back up?

In the upstairs bedroom, in the corner near my closet and bathroom, the floor creaks. It's as if the floor is popped up in that location. When you step in that area the floor goes down and pops up when you remove your weight. What could be the cause of this? who would you need to contact to examine and determine the problem?

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1 Answer


Assuming this is not the subfloor sagging because of rot under it (in which in most cases its recovery would be slow if at all, not "popping" right back up, could normally be one of several things:

1) if nailed-down flooring like hardwood strip, could be they missed an area in nailing - nail gun ran out and they did not notice it for awhile. Ditto if gluled-down - could have a missed area or glule is popping loose with age.

2) if a "floating" floor or in serious cases nailed-down with short nails, if they did not leave enough expansion space around the perimeter (commonly 1/8" bare minimum in hot humid conditions and normally more like 1/4-1/2" depending on humidity and temperature of the flooring) then as it expands with higher humidity and/or higher temperature (humidity normally has more effect) it can jam up against the walls and buckle up in the "field" areas - commonly as you walk around, the "bubble" will actually migrate across the floor visible to someone with their eye down to the floor. Solution in that case is recutting a gap around the perimeter - usually requiring removal of baseboard strip. This is a common problem with flooring contractors who do not check the manufacturer tables on humidity and temperature to determine the right amount of edge gap - also in cases where the baseboard is thin so a normal gap would be exposed to view and puosh up against the baseboard when it expanded. Also happens in air-conditioned houses (when flooring was installed) that then sit without air conditioning in hot humid conditions due to long power failure, A/C off while house is vacant, etc.

3) with snap-joint or glued flooring, sometimes the joint comes apart, making the flooring "wider" in the direction perpendicular to the planks - resulting in loss of expansion space per 4) above, or sometimes if the joint is totally separated the plank you step on can sink into the padding enough to cause this effect. Of course, in this case you would have visible gaps along the flooring joints.

4) rarely, if there is a water leak saturating the subfloor (usually up against a utility room or bathroom) the nails/screws will rust out or loosen up enough in the wet wood to pull free, making the subfloor sheathing or fastened-down flooring free to move up and down like you described. To determine whether the subfloor sheathing is moving or not, sometimes you can check right at the edge of the wall in the edge gap - see if the flooring or flooring and subfloor combined are moving up and down. Or sometimes (especially over unfinished areas like basement or crawlspace) look from below while someone walks on it. On second-story cases might take about a 1/2" inspection hole to look in from below with a fiber-optic camera - or sneak it in around a depowered ceiling light fixture box with the light fixture removed if one is near - avoids a visible hole to be patched if the fixtures base/cover ring is large enough to cover the inspection hole.

5) sometimes subfloor sheathing can do this just due to nails working loose from the joists underneath - due to wrong or too short a nails, or just working out from the subfloor flexing a bit as people walk on it, so it gradually works the nails out of the wood - the classic "squeeky subflooring" issue.

6) rarely, like in 4 above but without any water issue, sheathing or a levelling overlay may pop free if it was fasstened down improperly - using wrong type of or too short a nail for sheathing, or nails instead of screws for a thin levelling overlay like is commonly put down under sheet flooring, or using drywall/sinker screws instead of structural screws so the heads pop off in use.

7) even rarer but I have seen it in older homes near the ocean - salty air rusts out plain (ungalvanized) nails or screws so the subfloor or levelling overlay or nailed-down flooring comes loose.

8) rarer yet - sloppy framers put down a short sheet of sheathing so it did not reach the next joist, leaving an edge unsupported, which then sags when you walk on it. Most common around outside walls.

Contractor for this would be a Flooring contractor.

Answered 4 years ago by LCD

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