Questionss On Hardwood Underlayment And Expansion

newtofloor

Looking at doing a hardwood project on the second story of of a townhome and have a few questions. The wood is 0.71" thick Brazilian Walnut.

1) Underlayment Barrier/soundproofing
I've got conflicting information on what kind of underlayment to use. (This would be on top of 3/4" plywood.) Some say use rosin/felt/tar paper as it won't trap moisture. Others say to use a moisture barrier. Which is correct? As indicated, this is a second story room, so it is not over concrete. (Unless you count the ceiling below, which is wonder board with radiant heat installed in the ceiling (I have no idea as to why this was done, other than it might have been the trend in the lat 70's until someone realized that heat rises.) If the climate matters, the location is about a mile from the Ocean in Southern California, so there is humidity.

2) Sound proofing.
Can it be done with hardwood? Is there an underlayment that will dampen the sound. Worried about sound transferring in both directions. Don't want sound from below (like stereo) moving up more than it has to, and don't want footsteps above to be any louder than necessary. I get the impression that there isn't much a a way to dampen hardwood. Comments?

3) Expansion
Am planing on nailing or stapling (this wood is HARD! Not worked with this before. Do the pneumatic staplers work without damaging the wood in the process? Issues with it splitting? Otherwise would look to drill with a carbide bit, and then use finishing nails) this down to the 3/4" subfloor. For this wood, after anchoring (screws or nails in wall edge) the initial run, one then nails/staples the tongue to the subfloor. (The perimeter for expansion is something else that I see conflicting requirements for. I've seen 1/4" to 3/4". Manufacturer says 1/2" so I'll go with that.) But, what I don't understand is how the expansion works. I mean, if it is a floating floor, then I can see that. But, if every piece is nailed/stapled to the subfloor, then how can it expand? It would have to fight against the staples/nails on ever single other board in the entire floor.

In fact, as the initial run is anchored with vertical screws or nails, there should be almost no expansion there as the shear forces against the nail/screw will fight that. So the only expansion is the other direction, and that is to the staples/nails that are at a 50 degree angle that favors pulling the nail/staple out of the subfloor. In fact, that angle should push the hardwood out and UP AWAY from the subfloor. Is this how it should work?

And I have no idea how the side to side expansion should work, as that is not favored by the side angle/shear of the staples/nails.

[Is this really an issue as isn't there an inverse relationship between the hardness of the wood (as indicated, this stuff is HARD) and the hydroscopic properties? (ie, the harder the wood, the less porous, the less moisture absorbtion, the less expansion.) Imagine this won't expand as much as other woods. Just curious on this one.]

Thanks in advance for any and all input!

Mike Finley

Yea hah, you got yourself some Ipe there!

Is this prefinished or unfinished?

I've used Ipe on outside decks and that stuff does shrink. I'm not sure if there is any correlation between the Ipe used for outside decking and the stuff used for interior flooring, but man does that stuff shrink! The rule of thumb doing Ipe decking is set it with 1/16 gaps because after it drys out you will have 1/4 gaps. That's on 6 inch wide 3/4" thick stock.

newtofloor

Yea haw, indeed.

Prefinished. And it it narrower than yours (3 11/16th").

I also don't know about interior vs exterior (never thought of it for a deck. must be something to look at), but as this is prefinished T&G, I'm hoping it won't shrink that much.

Add to that, it is winter (well as much of one as SoCal gets anyway) so the humidity on average is a tad lower now (73% vs about 82% average in summer) so I would think it would be a bit of expansion if anything.

trimguy

I've been doing hardwood floors for about 12 years now, in New England, mostly custom installations, including mixed species ( oak w/ walnut border, walnut w/ maple border, etc.) To answer your questions, in my opinion,
1) underlayment- rosin paper is the standard here, unless the manufacturer specs. something different.
2) sound-proofing- there isn't much, short of lifting the sub-floor and insulating between the joists.
3) expansion- if the flooring is nailed to the subfloor it is not a "floating floor". No matter how many nails you put in the board the wood is still going to expand and contract with the differant moisture levels throughout the year.(we're talking very small amounts on each board in normal conditions).But over the entire room, if you don't leave that expansion gap on the edge the floor could buckle. The wood is going to move it needs a place to go. Most of the movement takes place across the grain of the wood (width of board). You don't need to screw the first row of boards(if the first row can't move with the rest of the floor, you've effectively moved the wall in 3+ inches.)
1/2" expansion joint on all walls should be plenty, if this is what the manufacturer calls for that's what they want for warrenty purposes.

Good luck, and remember everytime you put a piece of flooring next to a wall, the flooring wants to move where is it going to go if it can't go horizontaly? only direction left is up. Not a pretty sight (buckled floor)

kneel_eh!

Like trim-guy says the floor IS going to expand. Make sure u leave at least 1/4 inch all the way around and undercut door jambs. What are the manufacturers recommends for install? If you follow them you should be ok but rely also on your experience!
As for insulating the floor, I have used 'spray foam'. Use a hole saw and drill 2" holes between the joists and shoot it in. Make sure you drill enough holes for the insulation to expand or your next project is gonna be drywalling the ceiling downstairs!!!

__________________
'Just cuz I'm paranoid, does'nt mean everyone's not out to get me !!!

Donedat

This might sound fishy, but on the second floor you don't really need paper. Check with the manuf. instructions. If you have questions, open a box and get the instruction sheet out. There is usually 1-800 number for technical assistance.

Have fun

__________________
I admit...I don't know everything...but don't tell my kids I told you.

justin savage

do not screw down your starter row ,like the others said this will not allow that end to move and could cause the floor to buckle.ipe is extremely hard and dense but it will move with moisture and seasonal changes.there is a product called the floor muffler that will help with sound.justin

newtofloor

Happy Thanksgiving all!
Thanks for the comments so far.

Trimguy -
Sorry. Wasn't clear here. I meant to say that I can see how, as opposed to a nailed down floor, something like a floating floor could expand. Wasn't suggesting that nailing down hardwood made it floating.

kneel_eh! -
Good idea about using spray foam with holes. Trimguy suggested insulating there, and the hole cutting idea seems a bit quicker.

Donedat -
Manufacturer's sheet says paper, allowing it to breath. But hear enough conflicting info that... well, that's why I'm here asking. Didn't know if there are other concerns above and beyond what the manuf. recommends.

Justin Savage -
I checked the Floor Muffler. Sounds like a good idea, but it is a moisture barrier.
From their FAQ:
So I guess it is not a good idea.


All --
(correct me here if my summary is off base or missing something)

Underlayment, Moisture
A moisture barrier does two things: Keep moisture out, and keep moisture in. From your comments, it seems the value of keeping mositure out (on the second floor) isn't as import as NOT keeping the moisture in (letting it breath).
I'm going to venture a guess that the recommendations I got (before posting here) for a barrier are from people that mainly have experience with/thinking only of installing on concrete (with plywood overlay), where is it more important to keep moisture from reaching the floor from the concrete, than to let the moisture in the floor out. So it just boils down to which side of the barrier will have a higher moisture content?

Underlayment, Soundproofing
Consensus seems to be between the joists is the only option for hardwood.
I note that some high rises require soundproofing, and that natural cork is used as it allows the wood to breath. Anyone used cork? Curious here...

Expansion
I will go ahead and do the 1/2" regardless, but was curious as there was such a difference in opinion. (kneel-eh! - will remember undercut door jambs. thanks!)

The "don't anchor the first row" issue
(and just to be clear, not to question all of your sage advice, but I'm trying to wrap my head around all of this )
It occurs to me that the staple/nail/whatever at a 50% angle in every board to either side of a given board either fights expansion or allows it.
Going back against the staples to the first row, it would seem to me that the resistance provided by the staple (it would either have to be driven down more or be bent backward, and then multiply that by every single other staple between the board in question and the first row) would be much greater than the single anchor nail in the first row.

So, as the wood expands, the path of least resistance for the entire floor is AWAY from the first board to the other wall.

Maybe a diagram might help.
(EDIT: nope. doesn't help at all. The web page takes all of my spaces out between the lines. Anyone know how to make it so more than one space doesn't get compressed down to one space? If someone can tell me, I'll come back and add them later. Well, I hope the idea gets across without the diagram.]



|   &nbsp/ / / /
| / / / /
| / / / /
----------------------------------------------------------------- Subfloor
Nail/ Staple Staple Staple Staple
Screw

<------ Force this Direction pushes against the staple
and down into subfloor.
THUS, the combined force of expansion plus
the guide of the metal run through floor
and subfloor at a 50% angle results in movement
this direction
/
/
|/_


Path of least resistance
-------> Force this Direction pushes WITH the staple
and up AWAY from the subfloor.
THUS, the combined force of expansion plus
the guide of the metal run through floor
and subfloor at a 50% angle results in movement
this direction _
/|
/
/



So, does this not mean that

A) one should allow for more expansion on the tailing end?
and
B) does this not eventually push the floor away from the subfloor and pull out the fasteners on this end? (as it is easier to pull out the fastener than it is to bend it)


Or am I just entirely over-thinking this?
(I do have a tendency to do that and am working on too little sleep as is... reminds me I have a turkey to check on...)

Thanks for your comments!

justin savage

sorry about the floor muffler there is one just like it that is sound deadening i will try and find the name (thougt that was it) havent used it in awhile.The wood will move more toward the tongue ,but if you fasten the first row tight then the rows in the middle may bind and cause buckling.Its like pushing a car by hand down the street 1 car by itself ok- 3or4 cars in a row you cant do it -the only problem is with wood it will keep pushing in the form of buckling or the sides of the wood will crush then the wood goes back to normal and oops big gaps.hope this helps.justin