Yikes! I have Gaps in My Hardwood Floors
It’s nearly winter. That means that your hardwood floors are about to show cracks between the boards. If you’ve moved into a new house, these cracks could cause alarm. How could your brand new hardwood floors crack?
Gaps between boards, or cracks, if you will, are not the result of the wood floor failing or falling apart. They are the result of the wood planks shrinking as the relative humidity goes down and the wood floor loses moisture content. The air in the summer has a higher relative humidity than in the summer. This lets the wood flooring absorb moisture and swell. So usually gaps between boards go away in the summer. Then those gaps reappear in the winter as the humidity goes down again.
If your builder had installed the floors with too little moisture content at the time of installation, when the relative humitidy went up, the boards would have nowhere to swell or expand and they would push against each other causing the planks to cup and possibly rise. Flooring must be installed to allow this seasonal swelling and shrinking.
If you have standard, 2 1/4″ wide flooring, you should not have gaps wider than the thickness of a business card. However, sometimes two or three boards will stick together and move as a unit. This would produce one crack the width of the thickness of three business cards instead of three cracks, each the with the thickness of one business card. This would be considered normal. If you have cracks wider than that, chances are the floor was installed with too high a moisture content.
If your flooring consists of wider planks, your gaps will be proportionately wider. The wood will shrink the same percentage, but the actual dimension of the crack will necessarily be wider. Planks twice as wide will produce gaps that are twice as wide.
Engineered flooring shrinks less than solid wood flooring. This is because engineered floor has a solid wood surface, but the underlying wood is actually plywood. Plywood is dimensionally more stable because it is assembled with the wood grain of each layer running ninety degrees to the layer above and below. Wood shrinks across the grain and not much with the grain. So one layer reisist the shrinkage of the neighboring layer. If you want wide plank floors, take a hard look at engineered flooring. It will remain much more dimensionally stable than solid wood planks, yet the surface, the part you see and walk upon, will be identical to the solid plank.
Filling the gaps is merely a temporary cure. When the wood swells again as the season changes, chances are the filler will be squeezed out. My recommendation is to look around at older houses and observe the gaps in those floors. It’s likely you looked right past those blemishes and maybe even viewed them as part of the “patina of age” and thought they enhanced the charm of the house. Your house will develop it’s own patina and grow more charming every season if you let the nature of wood take its course. Your wood floors are a natural product that abides by the laws of nature. Swelling and contracting with moisture content is the natural behavior of wood.
I always welcome comments. Please feel free to post a comment and share your experience with the rest of us.
Tags: hardwood floor, house design, Wood, wood flooring
November 25th, 2009 at 2:56 pm
You really can save a ton of money buy installing your wood floors yourself. Most installers in my area charge at least $2 a square foot for installs. It is not that hard and the nail gun can be rented for like $40 per day.
November 25th, 2009 at 5:05 pm
Yes, you can save quite a bit of money if you are handy and have the patience to install the floor correctly. By the way, I was the architect for Mannington Mills executive office building expansion and the company fitness center. I designed those buildings about 25 years ago. They are a first class company.
December 16th, 2009 at 10:38 pm
Bill,
Your post was helpful. It is December, and we just had 5″ wide engineered hardwood floor planks installed in our home. We’ve noticed that there are several places in the floor where there is at least a business card gap at the seam where two board ends come together. Do you think this was intentional to account for summer expansion? The reason I ask, is that this spacing is not uniform across the floor. Most of the board ends come together at a tight seam.
Thanks,
Jason
December 16th, 2009 at 10:54 pm
Jason – Good question. The gaps in the flooring I was referring to occur along the long edges of the boards. Wood shrinks and expands in a perpendicular direction to the grain. Wood shrinks very little, if at all, in its length (with the grain.) So there should be no noticeable gaps at the ends of the planks. The gaps you have are probably a result of the planks not being installed tightly enough. It sounds like you have a legitimate complaint with your flooring installer.
January 6th, 2010 at 11:34 pm
Bill, we had 5″ engineered dark wood floors installed in Oct. Now in cold January, we see gaps along a slight rise or fall near the floor joists. We are very alarmed. The installers supposedly evened out a small dip in the floor from water damage with a tarpaper like material stacked in layers under the wood. The floors have creaked and been noisy since the installation. The floor guys said this was normal and that they would “settle”. We could live with the clicks, but can’t live with seeing the subfloor through the cracks. Our hardwood is a very dark santos red so the cracks really show. Can the floor people correct this?
Thanks,
Sandy
January 7th, 2010 at 10:24 am
Sandy – There may be several things that might be going on here. I’ll try to cover each. Hopefully one will apply to your situation.
All wood flooring will shrink and expand with the season. If you live in a very cold climate, the wintertime humidity level will be very low and the wood will shrink a lot. The wider the planks, the wider the gaps will be. Wood shrinks most across the grain and not in the long direction. But engineered flooring should shrink far less than solid wood planks. That’s because the direction of the grain in each ply (layer) of the engineered flooring is oriented in a different direction and the cross grains stabilize each other. If your gaps are very wide, a quarter inch or more, and don’t close up in summer, that is surprising and might indicate a structural problem.
If you have numerous gaps wider than a quarter, that could be considered excessive. This could have been the result of the flooring being installed when its moisture content or the moisture content of the subfloor was too high. If you can actually see the subfloor, that is totally unacceptable. Are you actually seeing the subfloor or might you be seeing the unfinished tongue in the tongue and groove joint between the boards? Try sticking a business card into the gap and mark how deep it goes. Then compare it to the thickness of the wood flooring to see if it goes to the subfloor. If it does, I’d say your installer owes you a new floor. There is no remedy other than replacement.
If you are actually only seeing the tongue and groove joint, the gap is no more than the thickness of a quarter, and the gap closes up in the summer then it could be considered to be “normal.” Dark floors show the gaps much more readily than light floors since the light, unfinished wood in the joints contrasts sharply with the dark surface finish.
You don’t want to fill the gaps with wood filler. This will only be squeezed out in the summer. One suggestion would be to stain the wood within the gaps the color of the finish. You could use an artist’s brush and carefully dab in stain deep in the joint. Tape off both sides of each joint before you do this to keep from getting stain on top of you surface finish. It’s a painstaking process and it won’t cure the gaps, but they wil not be as visible.
Sometimes the structure of a house will shrink enough to cause seasonal gaps in wood flooring. This usually results in one or two significant gaps located above primary girders or where an addition might have been built on to an existing building. I have a spot in my wood kitchen floor that shows a gap each year. It’s right over a girder. You see this often in older houses. It’s just the house “breathing” with the seasons and reminding you it’s built with wood, an organic material.
I hope this helps. Good luck and let us know what the resolution ends up being.
February 3rd, 2010 at 8:11 pm
Bill, Your posted reply on Jan 8th was very helpful. I have a New Home that was completed in August 2009 and I now have gaps in my hardwood also. They Run the length of my house everywhere that there is a girder. Some gaps are bigger than a quarters width. I also have some gaps against the grain on the long axis of the planks. The wood is 2 1/2 solid oak (not pre-finished)
My question is, why do the gaps manifest over the girder and not uniformly throughout the remainder of the floor? Also will the usage of my gas fireplace cause an unusual amount of “drying out” of the planks and cause larger gaps?
February 3rd, 2010 at 10:35 pm
Joe – I’m not certain why it happens there, but I have a theory. Every piece of wood in a house shrinks when it loses moisture. Most of the shrinkage occurs perpendicular to the grain. But there is still some shrinkage parallel to the grain (the long dimension) of the wood. The floor joists can shrink a little bit over their length. They usually have a lapping joint over the girders. They are not one continuous board from one side of your house to the other. So I believe what happens is the joists pull apart as they shrink a little. The movement occurs at this lapping joint. Since it is also the location of plywood seams for half of the sheets of plywood in the subfloor, it is more susceptible to movement than other spots.
More and more we are using engineered floor joists that come in very long lengths. One of the advantages of this is they can actually run from one side of the house to the other. Combining that advantage with the fact that engineered lumber is not as prone to shrinkage ad “dimensional” lumber, and the chance for cracks is greatly reduced.
I don’t think that using your gas fireplace will further dry the wood and exacerbating the shrinkage. Actually, one of the byproducts of burning gas is water vapor. So it is actually adding a bit of moisture to the air. Dry air problems in winter come from taking cold air that can hold fewer grains of moisture than hot air, and heating it up. Although the air has the same amount of grains of moisture, the relative humidity goes down. The larger the difference between the outside air temperature and the indoor air temperature, the more the relative humidity will drop when it is heated. Your gas fireplace won’t “dry” the air any more than your furnace will.
Furnaces have to heat the air to a higher temperature than the room actually needs because there is a loss of temperature as the air is sent through the ductwork and delivered to the room. Because of this “over-heating,” the air in the house ends up dryer than it would be if you used a radiant heat system, such as an in-floor radiant system or good old fashioned radiators. The radiant systems only need to heat up the air just enough to make you comfortable. Thus they do not dry the air as much.
The only cure for dry air in winter is to humidify it. Humidifiers are tough maintenance problems, sometimes. They tend to clog, grow mold if not cleaned regularly, and they can leak. I’ve had the best luck with steam humidifiers. A good humidifier will go a long way toward keeping the moisture content up in your wood and reduce those cracks.
February 4th, 2010 at 6:12 pm
Bill, Thanks for the reply!
February 11th, 2010 at 5:30 pm
wood under my carpets? There is a large lump under my carpets that honestly feels like a metal rod about 4 feet long, which raises the carpet about 1/2 an inch in a 4 foot straight line. Could this be wood planks under the carpet that have swelled from moisture? Not sure what is under the carpets. You seem to be the expert on wood flooring, could this be possible? Does it sound like something that wood, or plywood might do? Any information would be helpful, thanks!
February 12th, 2010 at 10:22 am
Jim – It sounds like one edge of the plywood sub-flooring or underlayment has warped upward. Plywood is four feet by eight feet in size. If one edge has pulled loose, it could rise like this. Sometimes you can nail it back down by driving finish nails (nails with tiny heads) right through the carpet and into the wood. Because the nails have small heads, they slip right through the carpet and don’t stick up. But this solution is usually only a temporary fix. Finish nails don’t have a lot of holding power and even if they did work to pull the plywood back down, they can pull loose easily and the problem may return.
The best solution is to have the carpet pulled back, screw the edge of the plywood down and/or grind off the ridge, and re-stretch the carpet. If you don’t fix this soon, you will develop a worn spot on the carpet and even when you fix the issue underneath, the carpet will still show a line. Good luck.
March 1st, 2010 at 6:17 pm
Bill,
My house is 3 years old was built using 3 each 2″ x 10″ nailed but not glued girder running left and right with 2″ x 10″ floor joist on ledger strips spanned 15′ 7″ of Southern Pine running front to rear. Our 3 1/4″ white Oak strip flooring seperates over 1/4″ during the months of December thru April and closes completely in May (we can fit 5 dimes in the crack in places). The subfloor was laid and the seam is over the girder and the installers also changed the floor direction with an unglued spline over the same seam over the girder. I believe this created an expansion joint over the girder. The floors were not acclimated before installation and the HVAC unit was not running when installed. Do you have any suggestions on how to correct the seperation problem?
I believe that the OSB subfloor should have spanned the girder. I am not sure if the seasonal movement is in the floor joist or the subfloor sheeting, I do not think it is the Oak floors but what they are attached to. We do have the normal small cracks throughout our floors. By the way we are located in South West Virginia.
March 2nd, 2010 at 10:43 am
Ken – It sounds like you have the “Perfect Storm” of floor cracks. You are correct in thinking that changing the floor direction right on top of the girder and then having a seam between the sheets of subflooring does create a natural expansion joint over the girder. Now all the little cracks gang up in that spot. To compound the problem, it sounds like the flooring was installed when it had the highest moisture content and was the most swollen. When you say that the installers changed directions for the hardwood at that point, do you have flooring that runs parallel to the floor joists? If so, this is a big mistake. that leaves many planks of the wood flooring supported only on the subfloor. Wood flooring should always be installed perpendicular to the framing below so the planks span from joist to joist. The only way to install it parallel to the framing is to install additional blocking between the joists to support the wood planks.
I doubt that the OSB board it the culprit. It does not expand as much as regular pieces of wood. That’s because it does not have a directional grain. If some strands want to shrink in one direction, opposing strands resist the shrinkage. This is the same principle in plywood. It shrinks a little bit, but not nearly as much as your floor planks will. If the wood flooring planks had straddled the girder, you would have less of a problem. If the installers had not created such an effective expansion joint over the girder, you would have had numerous smaller cracks between several of the other planks. Instead, you see all of the shrinkage of each of the planks manifested in one spot.
As for a cure, this is a tough one. I talked with my friend, Bill Campbell at Select Forest Products to get some expert advice. Here’s what we came up with. If the flooring is installed parallel to the joists on one side of the girder, I would first recommend installing solid, 2×10 blocking beneath it at 24″ on center to support the floor better. If you have a crawlspace beneath this floor, you might want to have that crawlspace sealed. This will stabilize the humidity and the seasonal floor changes will be less. You need to check the moisture content of the wood floor before doing any repairs. Your builder or a wood flooring installer will have a moisture meter. Check the size of the crack when the flooring is at an 8% moisture content. That’s when you can fill the crack. My guess is that when the crack completely closes now, the moisture content in the floor is more like 10%. So i’m suggesting making hte repair when the floor is at an optimal, mid-range moisture content.
To do the repair, remove the first piece of flooring running parallel to the crack and replace it with a wider piece of wood. This new piece should be cut with a vertical grain (a quarter sawn or rift sawn piece). That way it can absorb the compression if the flooring expands some more. It should not cup when the floor expands, but it might rise slightly in the middle of the summer if the humidity is really high. Gluing it in place is a great idea, too. In the winter, if the moisture content of the floor drops below 8%, you may still see cracks, but they should be much smaller than what you are experiencing now. One other suggestion is to keep the humidity in the house higher in the winter months. This would mean installing a humidifier. For those, I would recommend a steam type humidifier. They are easier to maintain and seem to work better.
I hope this helps.
March 3rd, 2010 at 4:34 pm
Bill,
The strip flooring is installed perpendicular to the floor joist with the flooring running left and right, what I mean is the male part of the strip flooring on the rear of the house points to the rear and the male part for the front flooring is pointing to the front of the house. The two female grooves join over the girder and are joined with a spline that is not glued.
Do you think it would be better to remove enough strip flooring and sub flooring to span the girder 4′ on each side and then replace the flooring.
I am on a crawl space and intend to seal it up, I have been advised by a HVAC company a humidifier is not possible on our system, I’m not sure why.
Ken
March 4th, 2010 at 12:16 pm
Ken – I see what you’re saying now. Yes, you do have a perfect expansion joint.
Altering the subfloor so it spans the girder will certainly help. When you replace the portion of wood flooring, try to use vertical grain pieces to reduce the shrinkage. Also, be sure the moisture content in both the wood flooring and subfloor are around 8% when you install them. There is no way to totally eliminate seasonal cracks. But you should be able to greatly reduce the problem you now have.
Now I’m curious why the HVAC company says you can’t put in a humidifier. I don’t know what sort of system that would be. If you send me the particulars on your system, including the kind of ductwork you have, I’ll do a little checking and see if I can confirm or refute what they are telling you.