Low Slope Steel Roofing - the Winners in Life Cycle Cost Analysis

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An independent assessment of the life cycle cost for various low slope roof systems revealed that steel roofing had the longest life span, no leaks due to material failures, and the lowest overall maintenance cost.

These are the results of a study conducted by Ducker Research Company1 for the National Roofing Contractors Association (NRCA). The purpose of the study was to compare three commonly used types of low slope roofing systems (2:12 roof slope or less) from the standpoints of service life, maintenance cost, and overall life cycle cost.

The study looked at the following three different roofing types:

1. Metal (mostly unpainted coated steel roofs)
2. Built Up Roofs (BUR) - modified bitumen, asphalt
3. Single ply membrane (EPDM/PVC/TPO)

Four different building categories were surveyed:

1. Office/Bank
2. Retail (store, mercantile)
3. Manufacturing (industrial, warehouse)
4. Institutional (education, healthcare, hotel/motel)

Based on 41 plus interviews with building owners and managers, 36 case studies of roofing systems were selected from the western, northern and southern regions of the United States. In all, twelve case studies were evaluated on each of the three roofing types. Steel comprised the vast majority of the metal roofing systems.2 Most of the roofs were installed between 1981 and 1994; roof areas varied from 4,000 to 750,000 square feet with the average being approximately 92,000 square feet. The expected service life of steel roofing was determined to be 40 years – 17 years longer that Built Up Roofs and 20 years longer than Single Ply systems (see Figure 1).

Life Cycle Cost: All relevant aspects of low-slope roofing were considered: roof design, number of layers, sheet gauge, standing seam or through-fastened, insulation type and thickness, installation systems (i.e. seamed, ballasted, etc.), labour, balance of systems (i.e. venting, parapets, etc.), geographical effects, life span and additional items relating to the full life cycle, as well as the original installation cost.

Steel roofing has two characteristics that the other two roofing materials do not:

1. Steel is a non-porous material and under some conditions requires no underlayment to keep the building dry
2. Steel is easily engineered to withstand increased gravity and wind loads

Service life, durability and life cycle cost are considered the most important criteria in the selection of roofing type, according to building owners. While the majority of buildings had experienced roof leaks, none of the steel roofs had leaked as a result of material failure. By comparison, 30% of the Built Up Roofs and 56% of the Single Ply roofs experienced leaks resulting from material failure.

Furthermore, owners of buildings having steel roofs reported having little or no regular maintenance performed on their roofs. The leaks reported on steel roofing were a result of contractor installation problems. Regardless of roofing type, failure to achieve a quality installation is the primary reason for roof failure. (see Figures 2 and 3)

The service life of a roof will vary by system type and it is critical to apply the average annual cost across the full life of the roof system as illustrated in Figure 4. The Ducker Research study also identified that roofing material quality heavily impacts the overall life cycle cost (e.g. greater level of maintenance activities). In this regard, steel roofing and Built Up Roofing were more consistent across all four building categories.

Conclusion:
The Ducker Research Company study showed that the life cycle cost of a metal roof is significantly less than BUR and Single Ply roofing. Steel roofing had the lowest maintenance costs and had, on average, a 17+ year greater lifespan than the other two roofing systems. The study also concluded that
building owners believe that service life and life cycle costs are the most important factors in roofing material selection and overall, metal roofing is by far the best option based on its lowest life cycle cost. Add to this the fact that steel roofing is 100% recyclable, has industry leading recycled content and easily qualifies for LEED Canada certification.

Click here to download Fact Sheet 21: Low Slope Steel Roofing - the Winners in Life Cycle Cost Analysis