Why 3/8-1/2 inch gap at walls?

Reply

  #1  
Old 01-12-08, 01:07 PM
Member
Thread Starter
Join Date: Jan 2008
Posts: 1
Why 3/8-1/2 inch gap at walls?

Most instructions I have seen say leave 3/8 to 1/2 inch gap between 3/4" hardwood floor and wall to allow for expansion. How can there be that much expansion if the boards are nailed to the subfloor and the subfloor does not have that much room to move. If this is the case, then it seems the quarter round would have to be nailed to the baseboard and not the floor to allow the floor to slide underneath it. Could it be that this is just an urban legend?
 
Sponsored Links
  #2  
Old 01-12-08, 01:36 PM
HotxxxxxxxOKC's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2006
Location: USA
Posts: 8,044
There is no myth. Wood does expand, and the manufacturers test how much it expands with each wood species.

You only need the quarter round trim if you do not remove your basemboards.

Remove the baseboards if you want a cleaner look without adding the quarter-round.

Manufacturers will not warranty your floor if you do not follow their gap specifications.
 
  #3  
Old 01-12-08, 01:58 PM
Gunguy45's Avatar
Super Moderator
Join Date: Dec 2007
Location: USA
Posts: 20,956
gap

btw 1/4 round or shoe should always be nailed to the baseboard, not the floor.
 
  #4  
Old 01-13-08, 11:48 AM
Join Date: Nov 2000
Location: Austin, TX
Posts: 5,074
Do a little research on wood swelling..

There is not a fastener made, that will keep wood from swelling, increasing in dimensions.
 
  #5  
Old 01-15-08, 09:44 AM
Member
Join Date: Jan 2008
Posts: 13
Yes, you need the gap

Originally Posted by dpaden View Post
Most instructions I have seen say leave 3/8 to 1/2 inch gap between 3/4" hardwood floor and wall to allow for expansion. How can there be that much expansion if the boards are nailed to the subfloor and the subfloor does not have that much room to move. If this is the case, then it seems the quarter round would have to be nailed to the baseboard and not the floor to allow the floor to slide underneath it. Could it be that this is just an urban legend?
Yes, wood EXPANDS and SHRINKS based on environmental factors like humidity and temperature.

The example below applies to laminate, hardwood, etc.

Here's an example: You have some laminate flooring, and the boards are 7 inches wide. In HUMID conditions, that wood (width-wise) will expand by say, something like one one-hundredth of an inch per board. That's common, and almost impossible to detect on its own. And of course, it's not much!!!!!

BUT-- Let's say you have a nice licing room, and let's call it 20 feet long. And now let's do the math: 20 feet is 240 inches. And in 240 inches, you'll end up with about 34 boards of flooring wide. As each of those boards "expands" one one-hundredth of an inch in the summer (0.01 inch), the TOTAL expansion across the room is 34 of those-- or, 0.34 inch. Whoa - that's pretty close to .0375 (3/8ths of an inch).
 
  #6  
Old 01-15-08, 04:29 PM
Join Date: Nov 2000
Location: Austin, TX
Posts: 5,074
Casey, you have the idea, but lets put this into real world stuff.

The interior of some homes can get to nearly 70% humidity in the summer times, with the greenhouse effect we have now from sealed tight homes. Then winter time and the heater running you get 30%, and sometimes lower humidity.

Right??

Now lets take a 5" wide plain sawn red oak plank.

It is winter time and the wood is brought in and acclimated for weeks(in that 30% humidity) The wood is installed tight at the low moisture content of 6%. Everything look sweet till May, and a cupped appearence starts. Come July, and the flooring has tented/bucked, taking doors and cabinets with them, along with pushing walls off the anchors. The flooring moisture content is checked, at it reads, 13% moisture content, about right for 70% humidity. Ahh, lets give them a break... Lets say 60%rH and the wood reading 11% moisture content. A 5% gain in moisture content, from the time of installation, right???

Lets do the math... All wood species has what is called the shrink/swell cofficient.
This is the amout that species of wood shrinks/swells, per inch width, given 1% rise in moisture content.

The math... Read Oaks S/S cofficient is .00396.

We have a gain of 5% moisture content... 5 x .00369 = .01845.

Now we have a 5" wide board 5 x .01845 = .09225

Each 5" board swelled .09225.

Say a room only 10 feet wide. That would be 20 rows of 5" boards right? 20 x .09225 = 1.845"

So, in that room, the floor almost gain 2" in dimensions!!!!!!!!!!!!!


Where is it going to go, but up. Tented & Buckled.
 
  #7  
Old 02-10-08, 06:25 PM
Member
Join Date: Jan 2008
Posts: 8
So to add on to this one...if I am installing a 2 1/4" x 3/4" oak hardwoods and my house is dry given the winter, am I ok leaving 1/2" gap around the perimeter? My largest run will be 17' and my narrowest would be a hallway of 3.5' (with which I running length-wise).

Thanks.



Originally Posted by Carpets Done Wright View Post
Casey, you have the idea, but lets put this into real world stuff.

The interior of some homes can get to nearly 70% humidity in the summer times, with the greenhouse effect we have now from sealed tight homes. Then winter time and the heater running you get 30%, and sometimes lower humidity.

Right??

Now lets take a 5" wide plain sawn red oak plank.

It is winter time and the wood is brought in and acclimated for weeks(in that 30% humidity) The wood is installed tight at the low moisture content of 6%. Everything look sweet till May, and a cupped appearence starts. Come July, and the flooring has tented/bucked, taking doors and cabinets with them, along with pushing walls off the anchors. The flooring moisture content is checked, at it reads, 13% moisture content, about right for 70% humidity. Ahh, lets give them a break... Lets say 60%rH and the wood reading 11% moisture content. A 5% gain in moisture content, from the time of installation, right???

Lets do the math... All wood species has what is called the shrink/swell cofficient.
This is the amout that species of wood shrinks/swells, per inch width, given 1% rise in moisture content.

The math... Read Oaks S/S cofficient is .00396.

We have a gain of 5% moisture content... 5 x .00369 = .01845.

Now we have a 5" wide board 5 x .01845 = .09225

Each 5" board swelled .09225.

Say a room only 10 feet wide. That would be 20 rows of 5" boards right? 20 x .09225 = 1.845"

So, in that room, the floor almost gain 2" in dimensions!!!!!!!!!!!!!


Where is it going to go, but up. Tented & Buckled.
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes
'