Floating Walls in Basement


  #1  
Old 11-15-00, 08:58 AM
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I have just bought a house near Boulder Colorado. Local building code requires that all walls in the basement be "floating walls". This means that they are attached to the floor joists of the 1st floor, but not directly attached to the cement basement floor. This allows the floor to move up and down without destroying the floor above.

This web page is the only information that I have been able to find on the subject:
http://www.toolreviews.net/home/qand...atingwalls.htm

I have a few questions:

#1) How should I do the trim around a door so that a door can move up and down, but the door casing will still be covered by the moulding?

#2) The previuos owners finished part of the basement and did not float the walls, is there any EASY way to cut off the bottom of the walls and make them float? Cutting off the wall is easy, but how do you attach a new bottom plate to the wall since there is no room to nail?

#3) Should I even worry about floating the walls? The house is 18 years old and there are no cracks in the basement walls or floor so obviuosly the floor hasn't moved up and down any in the past.

If anyone has experience with this I would appreciate any tips you can give me.


Thanks,

David
 
  #2  
Old 11-15-00, 04:34 PM
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If you don't float the walls, it's a gamble. You get to choose your level of risk.

Go to the Carnegie library just west of Broadway on Pine street, ask for the expansive soils map. You can find your property on it and see how expansive your soil is. This might give you some idea of the risk you are taking.

Expansive soils cause more dollar damage in the U.S. than all other natural disasters combined. And heaving soils may crack neither the walls nor the floor. Lack of cracks is no evidence that the floor isn't moving up and down. There are many examples of houses with no basement floor movement for 20 years, and then it starts moving. Subtle changes in the drainage pattern in your neighborhood can cause large changes to your home.

Good luck.
 
  #3  
Old 11-16-00, 03:40 AM
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Actually the answers to your questions are very simple. No need to visit libraries and have parking problems. To cut loose your internal basement walls which are attached just take a reciprocating saw with a 12" metal blade, and run it between the bottom sill and the floor. You walls are only attached in a few places. Very easy to do.
Now your door. At the bottom of the door, just make a cut to the side of the frame just above the threshold. this will detach your door frame from your threshold. This is very common in garages. Usually they install the frame first, then cut. Good Luck
 
  #4  
Old 11-16-00, 08:04 AM
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Jack, please don't make fun of my answers. I believe I provided useful information, as did you. Our answers complement each other. We answered different questions.
 
  #5  
Old 11-16-00, 08:57 AM
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Thanks for the info. John, you have me sufficiently worried that I will go ahead and fix the existing basement walls.

If I cut off the bottom of the existing basement walls, Isn't it a bad idea to just leave the bottom of the walls free? Won't the interior walls move around and crack the dry-wall if they aren't supported at all on the bottom? (ie: if someone pushes on the wall it will move)

I guess there really isn't any way to anchor the walls without taking off all of the dry-wall. At that point, I might as well just tear down and rebuild the walls.


The part of the basement that the previous owners finished has a bathroom with a shower insert. Is a special way to run the plumbing to the shower so that it can also move with the floor?


 
  #6  
Old 11-16-00, 02:58 PM
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Now that I have you worried, let me mitigate this worry. I know of many basements in Boulder without floating walls and that have no problems -- but there are horror stories as well. As I say, it's just a risk.

There are two kinds of basement floors that do not require floating walls. Please check to see if you have one of these.

(1) A structural slab. Although this looks like a regular slab-on-grade, it is really a floor suspended above the ground with voids underneath. I really don't know how to tell you how to figure out if you have this.
(2) A engineered wood floor. If you basement floor is wood (fairly common in new development along the front range of the Rockies), you never need floating walls.

I hope you have one of these two kinds of floors. If your house was built in the last ten years, you have a chance. If your house was built longer than 10 years ago, it's pretty unlikely.

On your existing walls, you may find it easier to tear them down rather than try to figure out how to float them in place. But you may be able to saw off the bottom 4.5 inches of the wall, and install a new sole plate by swinging the wall over a little. But the problem you may discover is that the wall is not attached to the joists above with sufficient strength to hang.

Check with your neighbors and find out if they put in floating walls. Another key thing to check is the stairs themselves -- are they floating?

Good luck.

[This message has been edited by John Nelson (edited November 16, 2000).]
 
  #7  
Old 11-18-00, 11:40 PM
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I say frame it like the rest of the basement. After 18 years you would have some inkling as to how the soil was reacting. I also assume that the area you live in has completed it's development, so dont cause youreself the headache. Somewhere down the road(years and years) you will probably have some cracking but if you do a quality job you shouldnt have to worry.
Most house's have soil movement. I have some problems here in Kansas City. I would say it is from a piss poor job more thatn anything and a little rock putty and paint good as new.

[This message has been edited by timmy (edited November 19, 2000).]
 
  #8  
Old 11-19-00, 09:17 AM
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The danger we're talking about here is not merely cracking. Basement floors sometimes rise 8" or more, with tremendous force. The danger we're talking about is lifting the house off its foundation. The foothills of the Rocky Mountains are famous for expansive soils. The risk is not the same from neighborhood to neighborhood, and the degree of expansive soils has already been mapped out -- I see no reason not to make the minimal exertion of effort of looking at the map.

But I tend to agree with the thought that if the floor hasn't moved in 18 years, the risk that it will move in the future is small (although not zero).
 
  #9  
Old 11-19-00, 06:40 PM
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So, let me ask you a stupid question John. I have never heard of this before,and I am trying to visualize it. The floor may rise 8",and the walls are still vertical only not fastened to the basement floor. The wall's run perpendicular to the floor joists in places. Soooo if the floor rises and the wall is still in between it and the floor joists above shouldnt it still lift the house? The floating of the wall would only be beneficial for small movements of the soil, correct.
I agree though wouldnt hurt to check the map.
 
  #10  
Old 11-19-00, 07:43 PM
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Yes, if your floor rises 8 inches, you're in trouble even with floating walls. A floating wall typically only handles a rise of 1.5 to 2 inches, which is enough for all but the most severe cases. If you want to, you can make the wall handle 4 inch rises -- I've seen walls with this much allowance. The diagram mentioned in the first post of this thread illustrates a wall that can handle 3 inches. Once you find out how expansive your soil is, you can choose how much to allow for.

[This message has been edited by John Nelson (edited November 19, 2000).]
 
  #11  
Old 11-20-00, 07:54 PM
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I am not making fun of anyone's answers. I tell it like it is. I am a builder and have been for 30 years. Also a civil engineer. I have been involved in building more $1 million dollar plus houses in colorado then you could imagine. If the code says floating walls, it means floating walls. I told the proper way to solve the problem. If the home owner wishes to do something different thats ok. But as a FORUM MODERATOR, I have to say follow the codes. End of story, Turn the page.

[This message has been edited by Jack the Contractor (edited November 21, 2000).]
 
  #12  
Old 12-08-00, 05:58 AM
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Thanks for the help. I just finished adding a couple of walls and two doors to the basement.

I decided to leave the existing (non-floating) walls as-is but I floated the walls that I added. Most of the walls that the previous owner added stop 2" short of the joists on the top and are only tied into the joists in a few places, so they are floating in a sense, just not the way that I would have done it.



I did not know how to handle the doors, so I just ran them all the way to the floor. I figure that if the ground heaves the door frame will not be strong enough to cause major structural problems on the 1st floor. Worst case is that I have to replace a door or two which is a risk I can live with.

-David
 
 

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