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Patriciax1

Wood Basement floor

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Can anyone tell me how the create a foundation with a wood floor joist system. The floor joist will sit on a pwf 2x4 (flat) sitting on the footing with the rim joist fastened to the ICF wall. 

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More info needed.  Got a section detail?

 

And describe "pwf."

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Something like this?

 

What have you tried -- what's not working?

 

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I have no idea where to put the information in for that kind of floor. I have tried several things but I'm obviously missing something.

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Try thinking about the foundation as this part.

 

ct1.thumb.png.576135b093bef3d6e92a5f39f9d7a3f7.png

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Is this a proven method up there in Canada?  Never seen this before, esp. when I know the footing has to be pretty deep because of frost.  What keeps the joist from getting wet (besides a layer of vapor barrier), and what about the back pressure of the soil pushing against the joist (from all directions)?  I def. not schooling anyone here for sure, but I really never seen this before.. very curious on how this works and stands up to time.  

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In Colorado, along the front range from Colorado Springs all the way up to the Wyoming border, the soils are not stable, and a well-built house has its footings bearing on pilings that go to bedrock.  Little screw pilings, but they do the job.

 

The basements get what is called a "structural floor," exactly as this is being discussed here.  A 60-mil membrane, think "Stego," some airspace, and a framed floor, with any required beams being steel and intermediate bearing points for the beams being piling-supported.

 

Houses there, if built with the basement being slab on grade, have a wall base detail that permits the bottom plate to move as much as 2.5 inches up or down, which the bentonite soils can do.

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Guess I need to get out more huh...  never had to design on rock or earth that moved so much. 

 

1 hour ago, GeneDavis said:

move as much as 2.5 inches up or down, which the bentonite soils can do.

This blows my mind. 

 

Thanks Gene.  

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16 hours ago, mtldesigns said:

Is this a proven method up there in Canada? 

It is a proven method as a solution to regional issues relating to the availability of ready-mixed concrete (very rural areas, the far north, etc). In its conception, it is part of a PWF (Permanent Wood Foundation) system that utilizes a pressure treated wood-frame foundation wall often on a gravel footing, and pressure treated wood floor on wood sleepers, raised above the level of excavation. It is part of a comprehensive foundation design system that clearly lays out the specifications to provide a structurally sound and well insulated foundation that uses no concrete.

As it relates to the OP, it is an odd choice of construction assemblies, to choose a concrete foundation wall and footing, with a wood-frame basement floor, however that's not to say it doesn't have some benefits. Some of which could be:

  • a more level and true floor surface, especially beneficial for interior partition framing as well as cabinet installation and plumbing fixture installation
  • a warmer basement floor
  • a floor that can be less subject to internal heaving due to expansive clay soils (if present)
  • easier construction in winter, as temporary heating and insulating and covering would not be required as it would for a concrete slab
  • eliminates concrete slab cracks telegraphing through a tile finish

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16 hours ago, mtldesigns said:

What keeps the joist from getting wet (besides a layer of vapor barrier)

In this type of construction, there would be a significant airspace below the wood-framing. The 'vapor barrier' (6mil poly) would be serving as a soil gas barrier as well as a moisture barrier and would be on top of coarse gravel fill (the poly must be sealed, and weighted down and / or protected from damage). The coarse gravel fill would be on top of the excavation which, at least in theory, should be sloped to a central location to facilitate the installation of a sump pit which would be connected to a storm sewer or sanitary sewer and which could contain a sump pump if excessive groundwater is present. The coarse gravel fill allows incidental water to flow freely through it, reducing water pressure buildup and of course, it also allow soil gases, like Radon, to move through the gravel substrate and be expelled from the building by means of a soil gas vent.

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8 hours ago, robdyck said:

In this type of construction

I'm always interested in how other systems are used and the why.. that was an excellent Rob!  Thank you. 

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