Modified bitumen roofing systems usually require a suitable underlayment to provide an extra layer of protection against moisture, improve overall waterproofing, and help with roof longevity. The underlayment can be a self-adhering membrane, synthetic roofing felt, or an insulation board depending on local building codes and manufacturer recommendations. This layer acts as a secondary defense beneath the modified bitumen sheets, protecting the roof deck from water infiltration due to wind-driven rain or ice dams. It also helps the top layers adhere better and can reduce thermal shock by balancing temperature changes. If you want to do simple DIY checks, look in your attic or ceiling space after heavy rain for any signs of water stains or dampness, which might indicate problems with the underlayment or flashing. Make sure your roof deck is dry before installation, and confirm that the underlayment is installed smoothly without gaps or bubbles that could trap moisture.
Knowing when to call a professional roofer is important because improper underlayment installation can lead to costly damage. A contractor will ensure all components are code-compliant and compatible with the modified bitumen system you choose, especially since warranties often depend on following these guidelines precisely. When speaking with a roofing contractor, ask, “What type of underlayment do you recommend for my climate and roof structure, and how will that choice affect my warranty?” Also inquire, “How do you handle ventilation and moisture control in combination with the underlayment to prevent future problems?” These questions help ensure your roof will perform well and that any warranty claims won’t be jeopardized by installation shortcuts or incompatible materials.