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Forum topic by Chuck posted 02-12-2011 02:31 AM 1758 views 0 times favorited 25 replies Add to Favorites Watch
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Chuck

88 posts in 2663 days


02-12-2011 02:31 AM

Hi All,
I’m going to be installing hardwood flooring, and while one normally posts such projects over on Homerefurbers, my question is really about the nature of wood.

I’m using standard nail-down 2 1/4 by 3/4 strip oak. The manufacturer says to leave 3/4 of an inch gap around the perimeter of the room to allow for wood movement. Makes sense. But here is where I get confused:

Lets say that during the course of the year the humidity fluctuates such that each strip changes by 1/64 of an inch. As wood moves accross the grain, 2 1/4 becomes 2 17/64. Now lets say there are 32 rows of wood, making a total expansion of 1/2 inch. Everything is peachy, right? Well lets focus for the moment on a strip in the center of the room. It moves 1/64 and pushes against the strips on either side. The strips on either side expand 1/64 plus the amount the center strip pushes them. Then the next two outer strips each expand 1/64 plus the two aformentioned strips. This goes on until the strips on the very outside have to move a full 1/2 inch. But all the strips are nailed to the floor preventing them from moving that much. I suppose an obvious solution would be to create expansion gaps every 10th row or so, but i have never seen any such thing on hardwood floors.

So how does this work? My worst fear is a buckling floor and everyone will think I have zero handyman skills (including wife and kids) and I’ll look like a horse’s ass.

I know someone out there has the brains and experience to solve this. And yes, I do spend my time thinking of such things.

-- Chuck, Washington D.C.


25 replies so far

View ScottN's profile

ScottN

261 posts in 2142 days


#1 posted 02-12-2011 02:46 AM

I have a kitchen and dining room that I did with a hardwood floors about 10 years ago and still looks like new…Love it.. I kept the wood a 1/2” from the walls and kept the boards tight using a floor nailer.

-- New Auburn,WI

View Julian's profile

Julian

880 posts in 2988 days


#2 posted 02-12-2011 03:35 AM

The floor will only expand and contract across the grain and not lengthwise. I always leave 1/4 to 1/2” gaps and make sure the wood is well acclimated to the house. This along with a whole house humidifier will leave you with a very stable floor. Just make sure to staple the floor every 6” and all will be fine and squeak free.

-- Julian, Park Forest, IL

View Jack_T's profile

Jack_T

623 posts in 2494 days


#3 posted 02-12-2011 06:13 AM

Just make sure you leave the wood in the house for at least two weeks before you install it. The boxes should be open during those two weeks.

-- Jack T, John 3:16 "For God so loved the world that he gave his only Son, so that everyone who believes in him might not perish but might have eternal life."

View Jesse 's profile

Jesse

105 posts in 2325 days


#4 posted 02-12-2011 09:56 AM

I am not gonna wrack my brain around your math, but I will offer you this to help you do your calculations.

You already understand that wood will expand most significantly across the grain; however, in the case of hardwood flooring, this expansion isn’t going to be equal for each board. Only the perimeter boards are likely to show any expansion because air needs to circulate around a board for humidity to have much impact. This is why when you stack lumber you sticker the stack. Without the stickers, the wood will dry and absorb moisture unevenly causing it to warp. In the case of hardwood flooring, the center portion of your room will allow the least amount of air to circulate. Under the flooring you have plywood, then some form of vapor barrier to restrict humidity changes on the underside. Then when the boards are nailed down you have them flush against each other. The top of the flooring is either pre-finished or will be sealed after installation. So your only weak point ( humidity change wise) is the perimeter. Nothing you can do about those areas so you add an expansion area between the flooring and the wall.

Personally, I’ve used 1/2” gap because it is easier to cover up with trim molding and haven’t had any problems. Then again, I use central air when it’s hot and heater when it’s cold, so my home’s humidity doesn’t change drastically.

DO let your flooring acclimate to your house ( not the garage) for reasons that should be obvious now.

Finally, If the flooring does buckle it is probably because someone spilled a liquid on the flooring and never cleaned it up. That would cause a a swelling of the wood in an area of the flooring that doesn’t have the ability to expand or release that moisture. ( As explained above) If this were to happen, you get to lecture and accuse others while keeping your handy-man status in tack.

View Brit's profile

Brit

6716 posts in 2305 days


#5 posted 02-12-2011 04:25 PM

Chuck, I’d really hate people to think you don’t have any handyman skills so I’d like to underline what other have said about allowing the wood to aclimate to the room where it is going to be laid (2-3 weeks). I know this is a pain if the room is being used, but trust me this is VERY important. Some time ago, I studded out a summer house at the end of my garden. I used Tongue and Groove all around the bottom half of the walls. I didn’t allow it to acclimate (or acclimatize as we English would say). It looked great when I put it up, my wife painted it (still fine) and a couple of months after it started shrinking. Now I have 1/4” to 3/8” gaps in between some of the boards and no easy way to fix it. Don’t make the same mistake I did. My handyman reputation and my pride took a lot of stick over it. We live and learn.

-- Andy -- "I saw the angel in the marble and carved until I set him free." (Michelangelo)

View Chuck 's profile

Chuck

88 posts in 2663 days


#6 posted 02-12-2011 06:49 PM

This has been tremendously helpful and I feel much more confident. For at least one more project my 5yo daughter will think I can do anything.

-- Chuck, Washington D.C.

View tbone's profile

tbone

273 posts in 3147 days


#7 posted 02-14-2011 06:55 PM

While it’s true that wood will expand across the grain, it’s also true that wood will shrink across the grain. I think that’s why most of us here would leave just a half inch around the perimeter. That should allow for wood movement in either direction without your floor popping out from under the shoe molding.

-- Kinky Friedman: "The first thing I'll do if I'm elected is demand a recount."

View eaglebkh's profile

eaglebkh

6 posts in 2133 days


#8 posted 02-14-2011 10:39 PM

I don’t think Chuck’s question has been answered. How can wood that is nailed down move 1/2”? Even 1/4”? It has always stumped me when I watch Tom Silva help someone install hardwood flooring and he tells the homeowner about the importance of leaving a 1/2” gap just as he nails in the last plank 1/2” from the base board. Is that last plank really going to move 1/2”? If it did, the nail would bend or shear. So either the floor or the nail is not following the rules…

-- Brandon

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tbone

273 posts in 3147 days


#9 posted 02-14-2011 11:13 PM

Brandon, I think Jesse did a good job of answering the original question. The perimeter is the only real issue. The 1/2 to 3/4” gap is there not ONLY for possible movement of the flooring plank, but also to accommodate any imperfection along the wall—maybe not straight or out of square—and maybe even the movement of the wall itself due to environmental factors or foundation issues.

-- Kinky Friedman: "The first thing I'll do if I'm elected is demand a recount."

View dpark's profile

dpark

13 posts in 2121 days


#10 posted 02-14-2011 11:43 PM

I’m with Brandon on this. I’ve been very confused at the 1/2” border that supposed to be necessary for floor movement. If we’re only concerned about the wood on the perimeter, then there should be no need for anything close to 1/2”. 1/8” should be more than enough. Wall straightness is a separate issue, and could be addressed in other ways.

If I’m laying down hardwood flooring, and I have perfectly square walls, would I be fine laying down hardwood and leaving only 1/8 or even 1/16 around the perimeter? If not, why?

View tbone's profile

tbone

273 posts in 3147 days


#11 posted 02-15-2011 06:17 PM

Maybe the best answer is that if you don’t follow the manufacturer’s instructions, you will void the warranty if there is ever a problem on down the road.

-- Kinky Friedman: "The first thing I'll do if I'm elected is demand a recount."

View dpark's profile

dpark

13 posts in 2121 days


#12 posted 02-15-2011 07:11 PM

I suppose that’s true at least. It’s not very intellectually satisfying, but the warranty is a pretty big reason to leave the gap.

I found this discussion of the same topic: http://www.bt3central.com/showthread.php?t=15183

There they are claiming that the entire floor will expand, and the nails will flex to allow this. All this makes me think a flexible glue might be a better long-term solution. Nails that get pulled and pushed with the wood movement will eventually loosen permanently.

View Brit's profile

Brit

6716 posts in 2305 days


#13 posted 02-15-2011 09:08 PM

Chuck, have a read of this article. There are other links at the bottom of the page that you might also find useful.

http://www.hardwoodinstaller.com/hardwoodinstaller/expansion.htm

-- Andy -- "I saw the angel in the marble and carved until I set him free." (Michelangelo)

View Chuck 's profile

Chuck

88 posts in 2663 days


#14 posted 02-16-2011 03:46 AM

Thanks,
I’m going to do more research and get to the bottom of all this. Although I believe there is no way those nails will give. They have barbs to keep them in the wood.

-- Chuck, Washington D.C.

View drewnahant's profile

drewnahant

222 posts in 2552 days


#15 posted 02-16-2011 04:02 AM

First off, let me say that I have no clue how to answer this one, but I think it is awesome that in this huge knowledge base, and in my online research, nobody seems to have a real answer to this which makes sense, except for the warranty, the “because I said so” solution”. I’m definitely going to have to watch this forum.

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