A simple 'Cavity Affected Zone' model is proposed to describe the influence of the interfacial pore fraction on the average interfacial crack propagation energy in a brittle porous interface. It is based on the assumption that each cavity is surrounded by a perturbed interface zone along which the fracture energy is locally different from its reference value in a perfect plain and planar interface. Consequently, when the interface pore fraction is increased, a two-step sequence of regimes is predicted for the measurable overall interfacial fracture energy. This simple but flexible description is found to be consistent with two different recent examples of experimental adhesion measurements. It is expected to be helpful in analysing detailed mechanisms of crack growth and practical adhesion in porous or patterned brittle solid/solid interfaces. (C) Koninklijke Brill NV, Leiden, 2011