Case Study 24-2: Priya and Marcus Chen-Williams — New Roof, Clean Slate

Background

Priya Chen-Williams is a nurse practitioner; Marcus is a software engineer. They purchased a 1963 single-story suburban ranch in an unincorporated county at the edge of a mid-sized Western city. The price reflected the condition: it was a genuine teardown-quality gut renovation. Everything was being replaced — not cosmetically updated, but fully.

The roof was no exception. The original 1963 built-up gravel roof on the main flat section and asphalt shingles on the low-slope gable sections had been patched repeatedly, and the last patch had itself failed. With the interior already gutted and the framing exposed, this was the ideal moment to address the roof system comprehensively, because everything under the roof was accessible, repairable, and ready to receive new construction.

Priya and Marcus worked with a local architect on the renovation. The roofing system decision was part of a larger design conversation that also involved energy performance, aesthetic goals, and long-term maintenance philosophy.

The Geometry

The ranch house had a complex roof: - A large central flat section (about 1,100 square feet) over the main living area - Two low-slope shed-roof sections at 2:12 pitch over the bedrooms on each side - A small steep (8:12) gable section over the entrance

The flat and shed sections required low-slope systems. The entry gable section could use steep-slope material. Three roof planes, three potential material approaches.

Options Considered

Their architect presented four scenarios, ranging from a "practical minimum" to a "premium performance" approach.

Scenario A: Standard asphalt on gable, TPO on flat, modified bitumen on shed sections Estimated cost: $22,000 Pros: Industry-standard materials, widely available for future repairs, moderate upfront cost Cons: Multiple material types to maintain, 15–20 year life on most surfaces, white TPO reflects well but modified bitumen is dark

Scenario B: Standing seam metal on all three sections Estimated cost: $38,000 Pros: Single material type, 50+ year life, excellent for snow shedding on slopes, no seams on steep section Cons: Very high upfront cost; the flat-section standing seam is technically possible but less common than membrane

Scenario C: Standing seam metal on gable, 60-mil TPO on flat and shed sections Estimated cost: $28,000 Pros: Best-fit material for each geometry (membrane for low-slope, metal for steep), 40–50 year life expectation, cool-roof reflectivity on TPO Cons: Higher upfront than Scenario A

Scenario D: TPO on all sections (including the 8:12 gable, using a tapered single-ply application) Estimated cost: $24,000 Pros: Single material type, simpler future maintenance Cons: TPO on an 8:12 steep slope is unconventional and not recommended by most manufacturers for residential applications; aesthetically inconsistent

The Decision Process

Priya and Marcus eliminated Scenario B (budget constraint — the premium was $16,000 over the practical minimum, and they had other renovation priorities) and Scenario D (the architect was uncomfortable with TPO on the steep gable application for both technical and aesthetic reasons).

They were choosing between A and C — a $6,000 difference.

The case for Scenario C:

The architect's analysis: "You're doing this renovation once. The framing is already exposed, labor is already mobilized, and access is already set up. The marginal cost to upgrade from TPO + modified bitumen to standing seam on the gable is mostly materials — you're already paying the scaffold and setup. And when you're re-roofing the gable section in 20 years, you'll be paying full labor costs again. The standing seam doesn't need re-roofing in 20 years."

Marcus ran a simplified lifecycle cost calculation: - Scenario A gable section (asphalt): $4,000 now + $5,500 (estimated future replacement in 20 years, adjusted for inflation) = ~$9,500 over 40 years - Scenario C gable section (standing seam): $9,000 now + $0 for 40 years (standing seam expected to last 50+) = ~$9,000 over 40 years

The lifecycle cost was essentially a wash on the gable section. And that assumed no premature failure, no emergency repair costs, and no disruption. The standing seam was actually the rational choice on a lifecycle basis.

The 60-mil TPO selection:

For the flat and shed sections, their contractor strongly recommended 60-mil TPO over 45-mil. The price difference was $1,200 for the full area. The contractor had experienced 45-mil TPO failures in their market in extreme heat conditions and would not warrant it; the thicker membrane was their standard.

The TPO was specified as a Carlisle Sure-Weld product installed by a Carlisle-certified installer, giving access to the manufacturer's 20-year NDL (no-dollar-limit) warranty in addition to the contractor warranty.

Execution: What Came Up

With the interior already gutted and framing exposed, the roofing contractor had something unusual: the ability to inspect and repair every square foot of decking from the inside. Three significant issues were found:

Issue 1: A 4-foot × 6-foot area of the flat section decking over what had been the kitchen had severe water damage — soft, punky OSB with black mold on the underside. The source was a long-failed skylight that had been patched with roofing cement for years. The skylight location was eliminated in the renovation design; the decking was replaced with new 3/4-inch plywood and the rafter in the corner had a small section of rot that was sister-framed (a new rafter sistered alongside the damaged one to restore structural strength).

Issue 2: The flat section had no edge detail — no parapet, no gravel stop, just shingles barely overlapping onto the flat membrane. Water had been wicking at this transition for years. The renovation included installing a proper aluminum gravel edge and TPO flashing detail that runs the TPO membrane up and over the edge.

Issue 3: Two rafters in the bedroom shed section had split at the bird's mouth cut (where the rafter meets the top plate) — likely from decades of moisture cycling. These were sistered and the split portions repaired with epoxy consolidant before the new decking went down.

None of these surprises were catastrophic — all were catchable and correctable because the interior was already gutted. Had the roof been replaced without the full renovation, issues 2 and 3 would likely have remained hidden and continued to deteriorate.

Outcome and Reflection

The final roofing cost was $29,400 — slightly over the Scenario C estimate due to the decking and rafter repairs discovered during work. Priya and Marcus considered this a reasonable outcome: the scope additions were legitimate, the pricing was pre-agreed on a per-unit basis, and the conditions found justified the repairs.

Their roof is now: standing seam Galvalume steel on the 8:12 entry gable (copper-penny color, a premium factory finish), 60-mil white TPO on the main flat section and shed sections, with full TPO edge detail, properly flashed penetrations, and no skylights (intentional — they replaced the skylight with a solar tube, which requires only a 14-inch circular penetration with an engineered flashing boot).

The architect's assessment at completion: "This is as close to a 40-year roof as you can get with today's materials. The TPO warranty runs 20 years; a renewal inspection and potential recoat extends it. The steel doesn't need attention until the paint system starts to fade in 30–40 years."

What This Case Illustrates

1. Geometry drives material selection. A single house with three different roof slopes may require three different material approaches. There's no single "best" roofing material — there's the best material for each specific application.

2. Lifecycle cost, not upfront cost, is the rational basis for decisions. Scenario C was more expensive at year zero but essentially equivalent over 40 years — and eliminated a future disruption and mobilization cost.

3. A gut renovation is the ideal time for structural roofing work. Conditions visible from inside that would normally require tear-off to discover — decking damage, rafter problems — were identifiable and addressable without additional cost.

4. Specification details matter. 60-mil vs. 45-mil TPO, Carlisle-certified installer, manufacturer warranty NDL — these are the details that transform "I have a new roof" into "I have a documented, warranted, properly specified new roof."

5. Eliminating penetrations reduces risk. The decision to eliminate the skylight in favor of a solar tube reduced the number of roof penetrations (from two skylights to zero traditional skylights), meaningfully reducing long-term leak risk.