Question about tongue-in-groove flooring

[Mike Stelts]

I'm told that tongue-in-groove flooring should be set back from walls and float on a slippery underlayment to allow for wood movement. What I don't understand is how can the wood move when it's nailed to the floor every 12" on every plank and there's no space between each board. This allows for contraction, but not expansion. What am I missing?

Thanks in advance for helping me with this riddle.

[Steve Demuth]

Well, the wood is going to expand and contract with moisture changes, nailed down or not. The force developed by the absorption of water in wood is very substantial. The question is where the expansion will go. Because the nails go into the flooring and subfloor at an angle, the expansion will be almost entirely in the direction of the tongues. When the wood shrinks, it tends to shrink in place, which is what causes the flooring to become less tight over time. If you screw it down sufficiently to keep it from moving, it'll still expand, but by forcing the wood to cup. Large expanses of wood flooring may need expansion joints to accommodate the expansion and prevent cupping.

[Ron Citerone]

Well, the wood is going to expand and contract with moisture changes, nailed down or not. The force developed by the absorption of water in wood is very substantial. The question is where the expansion will go. Because the nails go into the flooring and subfloor at an angle, the expansion will be almost entirely in the direction of the tongues. When the wood shrinks, it tends to shrink in place, which is what causes the flooring to become less tight over time. If you screw it down sufficiently to keep it from moving, it'll still expand, but by forcing the wood to cup. Large expanses of wood flooring may need expansion joints to accommodate the expansion and prevent cupping.

Very well explained Steve!

[Holmes Anderson]

Steve Demuth is correct. The small gaps hidden by the baseboard are typically enough to prevent solid wood flooring from expanding into the drywall or bottom board of the stud wall during the humid months. Tar paper can be used to provide a slippery underlayment for the floorboards to smoothly expand and contract. If you nail the hardwood flooring directly to the subfloor then the hardwood flooring is more likely to pop as it expands because of friction with the subfloor. You can chalk joist lines on the tar paper and drive long nails at the chalk lines rather than randomly to get better holding and reduce squeaking.

[Mark Bolton]

The expansion issues common now are basically a CYA for the industry that are now fast-tracking materials and installers needs to go fast. Hardwood floors have been installed for decades in homes captive between baseboard. Most of the homes built in the 50's, 60's 70's that had hardwoods were installed AFTER the base went in, and were installed dead tight to the base. This hogwash about installing your base over top of the hardwood is a modern day HGTV incantation just like tiling before cabs, hardwood before cabs, burying expensive hardwood and tile beneath cabinets that will never be seen because its simply cheaper (labor) than installing around obstructions. There are endless justifications for this like "if I change my layout down the road the flooring will be there"... the bottom line is your the wasted flooring under the cabs will never match the worn, faded, exposed, so its a cop out.

Then you take into consideration that in many (most) locations the captive hardwood installed for 40 years was installed in poorly conditioned homes (perhaps no AC, no dehumidification) and now we are installing hardwood in homes that may never, or only rarely, open a window. They remain closed and conditioned 100% of the year. They are dehumidified in the summer and humidified in the winter. The need for extreme allowance of expansion and contraction is completely unnecessary because nothing in the space will see more than a low single digit change in RH.

If you needed 1/4" gap around a hardwood floor all those floors installed in the 50's, 60's, 70's, and 80's, would either be buckled off the floor or would have such enormous gaps they would be torn out. You can walk in beautiful 50-60-80 year old homes with captive floors that will of course show some gap but they are still beautiful.

The 1/4" gap rule is mainly because a floor is likely going to expand after install... its never going to shrink because it will come out of the kiln, wrapped, shipped, drier than the final resting place.

We never gapped floors and we never landed base on top of tile or hardwood. Its a cheap out option. Base on top of tile or these "scraped" or v-groove hardwoods leaves nasty gaps beneath the base that trap trash and crap and look horrible over time.

Go into a 50+ year old school and look at a gymnasium floor that has been fixed in place for its entire life. There lies your answer.

[Ed Aumiller]

Agree with Mark Bolton...
Put down over 800 sq ft in my house over 40 years ago.. downstairs bath is oak flooring nailed to sub-floor... no problems whatever...
Put same in my son's house 17 years ago... no problems..
Just refinished floors over 70 years old in a house we fixed up for our daughter... there was no problems there (except where a CAT had stained the floor)....

[Mike Stelts]

Thanks everyone. I guess the moral of the story is to believe what you see, rather than what you read, or try to correlate with installing a table top onto its frame or a panel in its door.

I will be replacing chopped up flooring in a 160 year-old house, so I'll do exactly what they did - drive cut nails into the joists at the same distance from the edge of the board as the rest of the house, assuming I want the outside of tree down, because nails are near the edge. I'll install it tight with the same molding detail underneath to "hide" the gap. One difference: I don't have the patience to use a wooden rounding plane to add the detail.

[Holmes Anderson]

Thanks everyone. I guess the moral of the story is to believe what you see, rather than what you read, or try to correlate with installing a table top onto its frame or a panel in its door.

I will be replacing chopped up flooring in a 160 year-old house, so I'll do exactly what they did - drive cut nails into the joists at the same distance from the edge of the board as the rest of the house, assuming I want the outside of tree down, because nails are near the edge. I'll install it tight with the same molding detail underneath to "hide" the gap. One difference: I don't have the patience to use a wooden rounding plane to add the detail.

Perhaps, but do you really know what they did 160 years ago? Was their flooring as dry as yours? What month did they install the floor? If you install your kiln dried low moisture content flooring tight against the molding in the dry winter months then please report back to us in the humid summer months when the boards reach max expansion. Just saying, 160 years ago they probably installed flooring with a much higher moisture content than yours and probably in warmer, more humid months of the year, and those things can make a big difference, which is perhaps why very old flooring is more likely to have gaps than cupping and crowning from lack of expansion space.

[Mike Stelts]

Having no idea what was done in 1860, my intention is a summer install using rough-sawn, air-dried pine which is waiting in the barn. I'm planning to let it acclimate in the house before preparing it for install. Hopefully, this is good enough... we'll find out.

[Holmes Anderson]

Having no idea what was done in 1860, my intention is a summer install using rough-sawn, air-dried pine which is waiting in the barn. I'm planning to let it acclimate in the house before preparing it for install. Hopefully, this is good enough... we'll find out.

Well that is definitely a different scenario than installing kiln dried flooring against molding in the middle of winter (assuming your winters are cold and dry). But why the question about T&G? All the rough pine floors I've seen are just edge butted.

[Richard Coers]

Having no idea what was done in 1860, my intention is a summer install using rough-sawn, air-dried pine which is waiting in the barn. I'm planning to let it acclimate in the house before preparing it for install. Hopefully, this is good enough... we'll find out.
I don't know what species of pine you are talking about, but won't pitch pockets and weeping knots be an issue if not heated high enough to set the sap? I found out that storing wood in a barn is an open invitation for powder post beetle infestation. Watch for frass around the pile.

[Mark Bolton]

I don't know what species of pine you are talking about, but won't pitch pockets and weeping knots be an issue if not heated high enough to set the sap? I found out that storing wood in a barn is an open invitation for powder post beetle infestation. Watch for frass around the pile.

Agreed on setting the pitch. Without setting the pitch that could wind up being a sticky mess for an eternity.

[Mike Stelts]

My question about floor movement was general interest. Sorry for creating confusion by shifting to a different flooring topic. The existing floors are tongue-in-groove (see picture of separated boards). I have 16" 5/4 white pine in the barn, spraying for beetles when I see frass. Thanks for advice about the pitch; I'll experiment first.
468337

[Steve Demuth]

Go into a 50+ year old school and look at a gymnasium floor that has been fixed in place for its entire life. There lies your answer.

I live and walk on a 100 year old QS white oak floor every day (our home is a converted one room schoolhouse). It was installed with a gap, covered by baseboards, and you can, when we've had things off for remodeling, see where it expanded about 1/8" or so over time. And to be sure, it has plenty of gaps between boards at this point, from the many expansion-contraction cycles.



The 1/4" gap rule is mainly because a floor is likely going to expand after install... its never going to shrink because it will come out of the kiln, wrapped, shipped, drier than the final resting place.

It's never going to shrink to much less than what it is when installed. But it will shrink back from whatever expansion occurs, assuming there are humidity changes in the home. The woodwork in our house goes between about 10% in the dead of winter, to about 16% in the middle of summer (I've measured it). To be sure, we don't keep a climate controlled home - wood heat in the winter, and air conditioned in the summer for maybe 25 days total in any given year.

[Mark Bolton]

It's never going to shrink to much less than what it is when installed. But it will shrink back from whatever expansion occurs, assuming there are humidity changes in the home. The woodwork in our house goes between about 10% in the dead of winter, to about 16% in the middle of summer (I've measured it). To be sure, we don't keep a climate controlled home - wood heat in the winter, and air conditioned in the summer for maybe 25 days total in any given year.

No doubt. I lived most of my life in an unconditioned home with wood auxiliary heat in the winter. Brutally dry, no active humidification (occupants, showers, farts, burps, cooking and bathing). Strip oak hardwood throughout captive between base (last board scribed, back beveled, and driven against the base dead tight, finish nailed, and filled). Re-finished the floors when sold, looked better than a bowling alley.

Granted these were standard narrow (2 1/4") strip oak floors, no underlayment. full basement/concrete foundation. 50+ years old as of this date.

Wider boards of today, lesser quality wood being harvested, faster processing and installation, but even today I live in an uninsulated masonry home hardwoods everywhere. The wildest MC swings imaginable, captive floors. Its not to say to be reckless but this HGTV brainwash is just that, a brainwash.

[Ole Anderson]

I just put down 800 sf of floating stranded bamboo click and lock flooring. Of course they wanted an allowance around the perimeter for expansion. I installed it in mid winter with 30% indoor humidity. I undercut the entire dry wall perimeter and installed it basically flush with the drywall, leaving a 1/2" underneath for expansion. I measured an offcut, approximately 5"x5" with my digital calipers at 30% humidity at install and again in the summer at 50% indoor humidity. Not more than a few thousandths difference in size across 5". Two thousandths across a 14' floor (33 boards) is less than an eighth of an inch. I left an inch.

[Mark Bolton]

I just put down 800 sf of floating stranded bamboo click and lock flooring. Of course they wanted an allowance around the perimeter for expansion. I installed it in mid winter with 30% indoor humidity. I undercut the entire dry wall perimeter and installed it basically flush with the drywall, leaving a 1/2" underneath for expansion. I measured an offcut, approximately 5"x5" with my digital calipers at 30% humidity at install and again in the summer at 50% indoor humidity. Not more than a few thousandths difference in size across 5". Two thousandths across a 14' floor (33 boards) is less than an eighth of an inch. I left an inch.


Of course manufacturers have to allow a massive safety factor for anything from poorly acclimated/not acclimated materials, tropical climates, and 300 miles of other variables they are trying to cover their butts on. A good one I remember clearly was helping a local shop with setting a bunch of cabs in a home (other shop had had surgery and was on low power) and went to this large home where the homeowner wanted to use all kinds of local/off the property material. Had cabs made by other shop from old heavily weathered barn wood that was cleaned of grit and dust, shipped to a drying facility, kiln dried, then shipped to the other shop for cabs. Similarly flooring was all locally sourced random with full thickness (3/4") Vgrove T&G hickory. Stained and pre-finished a local millwork shop.

While there for initial batch of cabs the mountain of flooring was staged in the great room and the homeowners were carrying on about how long they wanted to acclimate the hardwood to the space. Heat on (end of winter). 8 weeks minimum I believe was the plan. Went back again to help with the kitchen cabs into the space and setting them and all the flooring was in and they had painted the walls and done a lot of other door and trim finishing. Warm damp spring rains were setting in. Every single window in the house was open with warm damp air blowing through the house because the homeowners didnt like the smell of the paint and finish. The home was left window open for days likely pouring who knows how much moisture into the structure, drywall, flooring, etc..

No makey a lot of sensey. But manufacturers have to cover their butts for scenarios far worse than that. Ive only seen one or two wood floors in my live tent due to expansion. The most common scenario is someone installs a prefinished floor super tight hoping for the floor to remain tight and then they are upset when all the gaps appear. Whether the floor shrunk or expanded, jacked itself apart, and then shrunk, who knows.

Bottom line if you want super tight it better be narrow strip, installed raw, sanded and finished old school. Either that or clip/glued together floating.

[Ron Selzer]

Have seen numerous gym floors being laid new and older floors repaired due to water damage
New/replacement floors every 5th strip install a gap using flat washers. Some have special underlayment with rubber? cushions installed. High traffic areas with lots of play that gap vanishes.
old floors with severe water damage will tent up, run fans into the wall with baseboards removed to get air under floor. most times the floor will settle back down. some floors have been bad enough over lots of years to have sections cut out and replaced
Ron