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A growing gap in a wood floor spells structural trouble

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Q: There's a growing gap on one side of the wall that divides the living and dining rooms in my 60-year-old split-level home. Do I need a structural engineer, an architect or someone else?

Kensington, Md.

A: Improper installation sometimes leads to gaps in flooring — just a cosmetic issue, albeit a frustrating one. The pictures you sent appear to show something more serious. The floor looks as though it is sinking where it passes by the wall between your living and dining rooms. A structural engineer is best equipped to assess what is going on.

“Something’s wrong. You don’t end up with a big crack unless something’s moving,” said Ryan English, an engineer at BE Structural (866-682-2693;, a structural engineering firm based in Wormleysburg, Pa., that offers services in several areas nationwide including the Washington region.

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English said there is no way to tell from a couple of snapshots what might be causing the problem in your house. A structural engineer needs to visit and crawl around in the attic and the basement or crawl space and assess the evidence.

It’s similar to what happens when someone shows up at a doctor’s office and isn’t feeling well but doesn’t know why. The doctor looks and feels and asks questions while mentally running through various scenarios. The doctor rules out some possibilities and puts others on a shortlist. Then, even if there isn’t enough evidence for a firm diagnosis, the doctor should be able to recommend what tests are likely to tease out an answer.

“We’d look at the ceiling, the flooring, the basement or crawl space to diagnose why this is separating,” English said. “We don’t destroy anything — we just poke around and make a visual inspection.”

It’s possible the soil has settled or there is a problem with the foundation of your house. Or a critical floor joist or beam might be weaker than it once was. Termites might have tunneled through the wood, or dry rot, a type of fungus, could have sapped the wood’s strength. Or a clueless plumber might have cut holes in the wrong place for pipes. A past owner might have taken out a key support post to open up more space in the basement. The culprit could even be an environmental factor, such as an earthquake or an especially high windstorm, English said.

BE Structural charges $500 to $1,000 for an initial diagnostic visit, depending on how far an engineer needs to travel, English said. The company has engineering employees in numerous locations.

Rusty Swindoll, technical adviser for the National Wood Flooring Association (800-422-4556;, also looked at the pictures you sent. Improper installation of wood flooring can result in gaps, but that probably doesn’t explain your situation, he said. Based on the age of your home and the look of the floor, you seem to have a traditional wood floor, made of natural wood boards that have interlocking tongue-and-groove edges and are nailed to floor joists. On this type of floor, gaps sometimes open up between the boards in the winter, when indoor, heated air tends to be especially dry. The gaps then close up in the summer, when the air is more humid. In your case, though, the gaps aren’t between the boards, just at that dividing wall.

Edge gaps are more likely with newer hardwood floors made of multi-layer material that’s installed as a “floating floor,” where pieces click together or are glued together but aren’t fastened down. With a floating floor, installers have to leave a gap at all edges so the flooring can expand and contract as temperature and humidity change. They cover the gap with quarter-round molding fastened to just the wall so the flooring underneath can still move in and out as needed.

Detailing around doorways gets tricky when a floating floor is involved. Adding quarter-round molding there would look odd and get in the way of a door closing. So, instead, flooring installers are supposed to trim the bottom of the molding and fit the flooring underneath. But the expansion gap still needs to be there. If the molding isn’t thick enough to cover the gap and still hide the edge of the flooring, some of the expansion gap can become visible in dry weather.

In your case though, the gap shows up on the side as well as the front of the room divider wall. “Darn, it looks like the floor has dropped,” Swindoll said. That’s not a flooring issue but a structural issue, he added. “The first place I would go is to a structural engineer.”

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