Basement Wall with rigid insul in middle
Basement Wall with rigid insul in middle
(OP)
I'm an Architect and I am questioning putting 2" of rigid insulation in the middle of a basement wall.
Is this a good detail for insulating a basement wall?
It seems to me that in areas where there is lateral pressure on the wall due to expansive soils this would not be good because it would make the wall weaker.
Is this a good detail for insulating a basement wall?
It seems to me that in areas where there is lateral pressure on the wall due to expansive soils this would not be good because it would make the wall weaker.






RE: Basement Wall with rigid insul in middle
1. Is the wall reinforced?
2. What prevents you from putting foams against exterior wall face?
RE: Basement Wall with rigid insul in middle
If you need it where shown, it will want to 'float' when you place concrete and you will require ties going through the insulation to connect the inner and outer concrete portions.
Dik
RE: Basement Wall with rigid insul in middle
However, this is not a typical system.
Some insulation is rigid enough (40 psi or 60 psi rated) such that it wouldn't be compressed by the lateral earth pressures, but without adequate shear ties, the wall is very weak in bending as you essentially have two, thin sections trying to do the work of one thick section.
RE: Basement Wall with rigid insul in middle
Richard A. Cornelius, P.E.
WWW.amlinereast.com
RE: Basement Wall with rigid insul in middle
"but without adequate shear ties, the wall is very weak in bending as you essentially have two, thin sections trying to do the work of one thick section"
So my next question would be if say this was a 10" thick wall with 2" of foam in the middle and adequate shear ties
will this wall function as a 10" wall without the middle insulation...
RE: Basement Wall with rigid insul in middle
Now half of the wall is cold, half is warm, how to avoid coedensation?
RE: Basement Wall with rigid insul in middle
The answer to your question is that if you can provide adequate webs across the cavity to make the two wythes act together, the wall would be almost as strong as a 10" solid wall. But achieving that linkage is not easy.
RE: Basement Wall with rigid insul in middle
I agree with hokie. - the composite ties we used on a previous project worked fine. But the system, as I said before, is not "typical" so you will struggle with contractors knowing how to construct it all properly, and inspectors that will have concerns since its not in the code.
RE: Basement Wall with rigid insul in middle
Puzzle #1 - Usually, bearing rarely controls in wall like this, however, just for the sake of argument, unless the foam (2") has the same bearing capacity as the wall material (8" total), how the sandwiched 10" wall has the same capacity as a solid 10" wall?
Puzzle #2 - Obviously the sandwiched wall relies heavily on the shear reinforcement with little, or no, contribution from the wall material, as general theories do not cover this type of application, we can only provide estimate/design through test results.
On top of difficulty in construction, any problem would be very difficult to correct. For this reason alone, I will stay away for now.
RE: Basement Wall with rigid insul in middle
Puzzle #2 - You are correct that a sandwich wall panel using some type of shear tie is not as common...but the concrete tilt panel industry uses these all the time. The mechanics of it aren't that difficult. What is the main challenge is understanding how the stiffness of the shear ties affects the flexural stiffness of the wall ties. Also knowing what that tie stiffness is can be tough to determine - requiring, as you suggest, testing.
RE: Basement Wall with rigid insul in middle
Thanks for the excellent explanations. But, I am still in doubt, and hesitate to place an equal sign between these two applications without further information as you have put into assumptions in making the comparison.
Of course, my doubt and hesitation are purely based on lack of understanding of the mechanics and its behaviors. And, I don't see it is a cost effective, or better, solution to conventional method.
But I do agree extensive testing can make up for the lack of understanding.
RE: Basement Wall with rigid insul in middle
RE: Basement Wall with rigid insul in middle
RE: Basement Wall with rigid insul in middle
RE: Basement Wall with rigid insul in middle
The detail has no obvious advantage over the normal practice of placing insulation on the exterior face of the wall after the concrete has cured for a while.
BA
RE: Basement Wall with rigid insul in middle
1. A conventional cast in place wall with drain tile around the footings and 2" extruded polystyrene on the exterior. This will give you a hard wall on the interior.
2. Insulating concrete forms (ICFs) with drain tile are also an alternate. For details you can go to the Reward site or any of the major sites that provide complete technical information and suggested details.
It all depends on the criteria, use and finish requirements.
Dick
Engineer and international traveler interested in construction techniques, problems and proper design.