can this be installed directly on top of existing sheathing that has sprayfoam on the underside or does the old sheathing have to be stripped off?

Hi Steve, Installing ZIP System OSB directly over existing sheathing that has spray foam on the underside is generally not recommended. Here's a breakdown of key considerations: Moisture Concerns: The spray foam on the underside of the old sheathing could trap moisture between the old and new layers, potentially leading to mold, rot, or degradation of the materials over time. It's important to ensure that there is proper ventilation and no moisture accumulation in that gap. Structural Integrity: If the existing sheathing is in good condition and properly attached to the framing, it may provide additional strength. However, the condition of the sheathing must be assessed. If it's compromised (e.g., damaged or weakened by moisture), it would be better to remove it before installing the new ZIP System OSB. Compatibility of Layers: ZIP System OSB is typically designed to be installed directly on the framing, with attention given to the way seams are sealed. If you're installing over existing sheathing, you would need to ensure that the seams of the new board are properly sealed, and the system's integrity isn't compromised by the additional layer. Manufacturer's Instructions: It's always a good idea to refer to the ZIP System installation instructions and any guidance specific to layering over spray foam. Some manufacturers may recommend stripping old sheathing for optimal performance and to avoid complications with air or moisture management. Building Codes: Depending on local building codes, there may be regulations on the maximum number of layers of sheathing or other materials that can be used. You should check with a local building authority to ensure compliance with standards. In summary, while it's technically possible in some cases, installing ZIP System OSB over existing sheathing with spray foam on the underside is not a best practice. It’s safer and more effective to remove the old sheathing to ensure proper installation, structural integrity, and moisture management. Thank you, Abigail