Flat & Low-Slope Roofing

Flat and low-slope roofing systems serve a critical role in North Dakota's commercial and residential construction. Modern flat roofs are not truly flat—they incorporate a slight slope to promote drainage—but they require specialized membrane systems designed to provide continuous waterproof coverage without the overlapping shingle approach used on steeper pitches. B&C Northern Construction installs three primary flat roofing systems: EPDM rubber, TPO thermoplastic, and modified bitumen. Each system has specific strengths suited to different applications and budgets. EPDM (ethylene propylene diene monomer) is a synthetic rubber membrane that has been used successfully in cold climates for over forty years. Its exceptional flexibility allows it to accommodate the extreme thermal movement that occurs on flat surfaces in North Dakota's climate. TPO (thermoplastic polyolefin) membranes are heat-welded at seams, creating monolithic waterproof barriers that are especially resistant to chemical exposure and UV degradation. Modified bitumen systems use torch-applied or self-adhered multi-layer construction that provides redundant waterproofing. Ponding water is the primary enemy of flat roofing systems. Even minor depressions in the roof surface can trap snowmelt and rain, accelerating membrane degradation and eventually causing leaks. Our installations include careful attention to slope and drainage, using tapered insulation boards to direct water toward roof drains and scuppers. We also install overflow drains as secondary drainage in case primary drains become blocked by ice or debris.

Insulation is a critical component of flat roofing performance in North Dakota. We install rigid polyisocyanurate insulation boards in multiple layers with staggered joints to eliminate thermal bridging and achieve the R-values necessary for our extreme heating climate. Tapered insulation systems serve double duty by providing both thermal resistance and the positive slope needed for reliable drainage. The insulation layer also protects the structural deck from the extreme temperature swings that cause expansion and contraction stress, extending the life of both the deck and the membrane above it. Our flat roof assemblies typically achieve R-30 or higher, significantly exceeding minimum code requirements and delivering meaningful energy savings over the life of the system.

Maintenance is essential for maximizing the service life of any flat roofing system in western North Dakota. We offer annual maintenance contracts that include debris removal, drain clearing, seam inspection, and membrane condition assessment. Catching a small seam separation or puncture during a routine inspection costs a fraction of repairing the water damage that results from an undetected leak migrating through rigid insulation and into the building interior. Our flat roof clients in the Williston area receive priority scheduling for seasonal inspections in late fall before freeze-up and again in spring after snowmelt, the two most critical maintenance windows for flat roofing systems in our climate.