Final answer:
The increased cost is a notable negative aspect of the protected membrane roof due to the need for more materials and a complex installation process.
Step-by-step explanation:
A negative aspect of the protected membrane roof (PMR) is that it can involve an increased cost. The PMR systems typically require more material and a more complex installation process, as insulation is placed on top of the waterproofing membrane, protecting it from the direct effects of the elements. This can lead to both higher material costs and labor expenses. However, while PMRs do offer advantages such as improved durability and easier maintenance, the initial investment is significant and may be a deterrent for some building owners.
Because the insulation is on the outside, installation of a PMR can be more complicated and potentially more costly than more traditional roofing systems. Furthermore, PMR systems require diligent maintenance to keep the insulation dry and ensure the roof's longevity.