Hybrid PERSIST model with ICF?
Curious about people’s thoughts on using the PERSIST model on ICF?
I know that ICF manufacturers will laud the benefits of ICF’s air tightness due to the concrete, but that doesn’t seem to account for instances where multiple building materials are being used, much less the several hundred feet of block joints.
For example, take an ICF wall where there is a stick frame on top…if we wanted to keep a single exterior plane (ie, a wall with no overhangs or lips), short of framing the stick wall out so so that the sheathing is flush with the ICF foam and then applying the PERSIST style WRB, this would mean adding about 6″ of rigid foam to reach something around R30 to the stick frame…but this now also means that the ICF wall (in keeping with a single plane) is now its R20ish + the rigid foam of R30…which is simply overkill and a waste of resources.
So what to do then? Do you frame out the stick wall so that it is a hybrid PERSIST in sort? With both external insulation on the exterior and then also some cavity insulation? This would be very similar to the ICF in respects to where the insulation sits if we put an airtight WRB on it.
Are we going to run into issues with a hybrid PERSIST model that incorporates some form of cavity insulation in addition to the external insulation?
Put another way, you might be able to ask the question like this: what issues are builders going to run into by applying Grace I&WS to an ICF structure, followed by additional exterior foam such as with the PERSIST model?
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