My question is regarding engineered hardwood floor installation and expansion. If you are nailing down an engineered hardwood floor, how much does it really expand. Every single piece is nailed into a subfloor. I would presume that nothing is expanding or it would rip out the nails. If this is true, do you need to leave a gap around the perimeter of the room for expansion, like every instructional video and website I’ve read tells me to do.
Flagged for title fix.
ETA: done while posting.
They still swell and contract so you have to leave a bit of a gap.
Some people avoid nailing down for this reason. You are also swelling and contracting around the nails which can lead to widening of holes around the nails and future squeaking.
Where are you? Engineered flooring should move very little, but it matters if you’re in Florida vs Arizona…
I don’t think engineered wood expands much when it absorbs water, but solid wood certainly does. The idea that nails could resist that pressure is laughable. Wood wedges expanded by wetting them have been used to split rocks since the time of ancient Egypt. Much of the design of furniture, doors and other large wooden objects is to avoid cross-grain joints (where one side would expand and the other wouldn’t). That’s why most doors are frame-and-panel rather than having all the grain running in the same direction. If you try to stop wood movement by force (attaching it to a non-moving object with glue or mechanical fasteners), either the connection will fail or the wood will split.
Yes, you have to leave a gap around the perimeter of the room, just like every single thing you have read about it. Wood moves. Also it is really difficult to not leave a gap, it’s the job of baseboard to hide the gap.
In restoration we are constantly replacing damaged hardwood. Engineered hardwood is preferred by flooring vendors as it is less problematic and is available in larger formats not possible with solid hardwood. It still expands and shrinks with humidity changes and is ruined by water or extremes of humidity.
It is almost always nailed or cleated, but I did have one installation (out of hundreds I have been involved with) on a basement slab that was floating and just glued at the tongue and groove. Larger formats require glueing to the sub floor or glueing of the tongue and groove as well as nailing.
Even nailed and glued, wood moves.
OK, I get it. wooden floors do expand even if they are nailed down. I just need someone to explain to me now how that works. You have a 1/2 expansion gap that runs the perimeter of the room. if the floor expands, how does the board that is nailed down closest to the wall not get ripped out of the nails when it does expand 1/2 inch. hell, even it it expands 1/4 an inch, that still is a huge amount of movement for something that is nailed down. I would expect to see loose floor boards around the perimeter of every room that has nailed down hardwood floors after only a season or two in a somewhat humid climate.
my understanding is that we’ve been using hardwood floors for a minute now. and we’ve been nailing them down from the start. I just need someone to help me make the connection/visualization of how hardwood floors that are nailed down to a subfloor (that is in it self nailed down to the joists) not rip itself free of said nails when it expands.
The entire floor does not tend to move as a single piece, it’s the individual boards. This happens slowly, with quite a bit of force. If they are already tight, and they all need to expand a millimeter, they will press on each other with increasing force. Will the entire floor move 25mm, probably not.
In a large room the gap at the wall is likely not going to do much to release pressure in the middle of the room, but it is affective on the floorboards that are closer to the wall. Over shorter distances it is definitely a factor. Hallways, corners closets are especially vulnerable. The floor can and will buckle when the boards cannot move to accommodate expansion.
It’s easier to use a general rule than to try to get too specific. There is rarely an advantage to install tight to the wall. Sometimes they might install tight to kitchen toekick for instance, but it is still best practice to remove and reset the finish kick instead.
If humidity is controlled and stable in your home and the flooring is properly acclimated to local conditions there should not be much in the way of problems
I’m still not getting it. Lets say I live in an area with humidity, but still within the guidelines and regulations of the floor manufacture. They specify that there needs to be a 1/2 inch expansion gap along the walls.
If it’s a floating floor, I can understand how this works. The board in the middle of the room expands a little bit and pushes against it’s neighbor. That board also expands a little bit and also pushes against it’s neighbor. By the time this all reaches the wall, up to a 1/2 of an inch in wood expansion can happen and there needs to be room for that, thus the 1/2 inch expansion gap.
In a nailed down floor though, how is this even possible? neighbor pushing against neighbor will rip the nails right out of the subfloor along the perimeter of the room. But this doesn’t happen. Why?
Do the nails hold each board fast? If so, then why such a large expansion gap?
Am I missing something?
One thing to keep in mind: the subfloor.
If you nail or glue engineered flooring (commonly backed by “various species of wood chosen for dimensional stability, so that the entire sandwich becomes stable and more resistant to moisture, humidity or arid conditions.” SOURCE) to either a plywood or OSB subfloor, then the movement of the flooring will be approximately equal to the movement of the subfloor.
Which shouldn’t put nails at risk or break the bonds of glue.
Because plywood (and OSB) doesn’t move much (, either):
The average coefficient of hygroscopic expansion or contraction in length and width for plywood panels is about 0.0002 inch per inch for each 10 percent change in equilibrium relative humidity. The total change from oven dry to fiber saturation averages about 0.2 percent
And both plywood and OSB subfloors are occasionally installed with very small gaps:
You really can’t nail into concrete, so if you’re using a ply/OSB subfloor, then float, glue, or nail should be okay.
Keep in mind, though:
- Acclimate your flooring to its eventual location for a longer-than-you-think-you-should time. A moisture meter is handy for comparing the MC (Moisture Content) of the planks to that of the subfloor
- Be conscious of when you’re installing. If it’s your humid season (and you also have a dry season), then expect a small bit of contraction. If it’s your dry season (and you also have a humid season), then expect a small bit of expansion
- If you have conditioned space above your floor, but you have unconditioned space (eg, basement, crawl space) below your subfloor, then your tiny expansion issue can become a larger (but probably still insignificant) issue
Floating the floor can be wise in a building with wide humidity swings (or a big above/below the floor/subfloor swing in humidity):