It is recommended to apply cypress over standard sheathing material with maximum stud spacing of 16 inches on center. Where building codes permit, siding may be applied over unsheathed walls. A suitable building felt paper should be used as a moisture barrier behind cypress siding. Foil faced sheathings should not be used in hot & dry climates due to the excessive baking conditions that occur with the reflective heat. This can also occur when some house wraps are used and the cypress siding is applied directly to the wrap.
Foam and Foil-Faced Sheathings – Both rigid foam and foil-faced sheathings can be vapor barriers. Rigid foam sheathings, however, offer little or no resistance to sag caused by the weight of the siding on the nails. For application of cypress over rigid foam sheathing, use angular threaded ring shank nails long enough to penetrate at least 1 inch into framing members. For example, siding over 1-inch foam requires a 3-inch nail (10d).
Note: Cypress siding applied over foam sheathing may take on a wavy appearance if the siding is compressed by nailing with too much force.