Compare a roof replacement over its full service cycle
A low headline quote can become expensive when it omits removal, waste haulage, access and lifting, decayed deck repair, underlay, insulation, flashings, gutters, professional review, or disruption. This calculator places up to three actual proposals on one scope and one roof-area basis. It then compares initial cash, fifteen-year and thirty-year lifecycle present value, equivalent annual cost, renewal dates, and service-life sensitivity.
No Korean national-average price, material-specific standard life, or automatic recommendation is prefilled. Roof geometry, access, existing layers, substrate condition, product grade, warranty, location, and disposal requirements can materially change both price and service life. Copy verified figures from each contractor proposal. The optional synthetic example is fictional and demonstrates the workflow only; it is not a market benchmark.
This is a cost-planning aid, not an engineering, legal, asbestos, leak-diagnosis, permit, or contractor-selection service. Obtain site-specific advice before demolition or structural work.
When this calculator is the right tool
Use this page when the project removes and replaces the roof covering as a system: metal sheet or panel, clay or concrete tile, asphalt shingles, or another quoted assembly. It can include the deck or frame, membrane or vapour layer, insulation, flashings, ridge, gutters, waste, access, professional services, and business or occupancy disruption.
A flat-roof coating or membrane-only renewal belongs in the separate rooftop waterproofing lifecycle calculator. A leak investigation belongs in the leak detection and repair calculator. This boundary prevents a membrane maintenance cycle from being compared as though it were a full roof-covering replacement.
Appropriate decisions
- Whole-covering replacement on pitched, low-slope, or complex roofs
- Like-for-like comparison of three itemised contractor proposals
- Trade-offs between a lower first cost and fewer future renewals
- Budget planning for deck repair, insulation, access, and disruption
Decisions outside the model
- Structural capacity or adequacy of an existing roof frame
- Leak source, hidden decay, or hazardous-material diagnosis
- Whether a product is suitable for a particular exposure
- Permit, filing, asbestos, warranty, or legal-liability determinations
Build one comparable roof area
Measured slope area
Choose measured sloped area when the surveyor or contractor has already measured the actual roof planes. The pitch percentage is then informational and is not applied a second time. Add a waste and overlap percentage only when the quotation basis requires it.
Horizontal projected area
Choose horizontal projected area when the available figure is a plan-view footprint. Pitch percentage is rise divided by horizontal run, multiplied by one hundred. The calculator converts that projection using a simple slope factor and then adds the selected cutting, overlap, and waste allowance.
slope factor = square root of (1 + (pitch percent / 100) squared)
comparison area = input area × slope factor × (1 + waste percent / 100)
This is a geometric planning shortcut, not a quantity survey. Valleys, dormers, cross-gables, curved surfaces, multiple slopes, parapets, penetrations, eaves, and product module dimensions can make actual ordering area different. A complex roof warning means that the displayed area should be replaced with a measured take-off before contracting.
Enter each proposal on the same scope
Area-based work
Enter the combined roof-material and installation unit cost per square metre. The model multiplies it by the comparison area. If labour, accessories, or fastening are separate in one proposal, combine only the items that truly scale with area or move them into an appropriate fixed-work field.
Fixed work and contingency
Enter removal, disposal, access and lifting, deck or frame repair, underlay and waterproofing, insulation, flashings and drainage, and professional review separately. Contingency applies to the construction subtotal. Initial disruption is kept outside that construction amount so a business owner can see contract cost and economic cash exposure separately.
Service cycle
Use the service life stated for the actual proposed system and site conditions, not a generic product headline. Renewal cost percent represents the share of the initial construction cost expected to recur at each future full replacement. Annual inspection and maintenance is charged in every year of the horizon. Renewal disruption is charged at each renewal event. Confirm the service life only after its basis, maintenance conditions, and warranty exclusions are understood.
How the lifecycle calculation works
Roof replacement lifecycle outputs and calculation basis| Output | Basis | Horizon |
|---|
| Initial construction | Area work + fixed work + contingency | Year 0 |
| Initial cash requirement | Initial construction + initial disruption | Year 0 |
| Lifecycle present value | Initial + maintenance + renewals + disruption − residual value | 15 and 30 years |
| Equivalent annual cost | Present value converted to a level yearly amount | KRW/year |
| Life sensitivity | Thirty-year PV at 80%, 100%, and 120% of entered life | 3 cases |
Future maintenance and renewal costs first grow by the entered nominal escalation rate. Each future amount is then discounted to the base year with the entered nominal discount rate. Renewal events occur at whole multiples of service life strictly before the end of the fifteen-year or thirty-year horizon. A renewal exactly at the horizon is not charged because it begins the following ownership period.
When residual service value is enabled, the model deducts the unused straight-line share of the last installed roof at the horizon. This is an analytical credit, not a forecast of sale price, scrap value, tax value, or an amount a buyer must pay. Equivalent annual cost uses the capital-recovery factor when discounting is positive and simple division by years when the rate is zero.
A worked check with transparent numbers
Assume 100 square metres, KRW 10,000 per square metre, no fixed work, no contingency, a five-year confirmed service life, KRW 100,000 annual maintenance, one-hundred-percent renewal cost, zero escalation, zero discount, no disruption, and no residual value. Initial construction is KRW 1,000,000.
The fifteen-year horizon contains renewals in years five and ten. Two renewals cost KRW 2,000,000 and fifteen annual maintenance charges cost KRW 1,500,000, producing KRW 4,500,000 lifecycle cost. The thirty-year horizon has renewals in years five, ten, fifteen, twenty, and twenty-five, producing KRW 9,000,000. Equivalent annual cost is KRW 300,000 in both horizons.
Initial construction
KRW 1,000,000
15-year lifecycle
KRW 4,500,000
30-year lifecycle
KRW 9,000,000
This deliberately simple case is suitable for checking a spreadsheet or the visible output. Real results differ because the model may escalate future amounts, discount them, add disruption, and deduct remaining service value.
Step-by-step workflow
- Standardise geometry. Select measured slope area or projected area, enter pitch and waste only where applicable, and reconcile the resulting square metres to every proposal.
- Set common economics. Use one base year, contingency, nominal escalation, nominal discount rate, and residual-value policy for all enabled proposals.
- Transcribe the quotes. Separate area work from removal, disposal, access, deck, underlay, insulation, drainage, and professional-review amounts.
- Record disruption. Keep initial and future renewal disruption separate from the contractor construction price.
- Verify future assumptions. Confirm service life, renewal percentage, maintenance, warranty, and any conditions that shorten coverage.
- Close every scope question. Mark an item confirmed only when the proposal states whether it is included, excluded, provisional, or separately priced.
- Read the scenarios together. Compare initial cash, fifteen-year and thirty-year PV, renewal calendars, annualised cost, and the eighty-percent-life downside case.
Ten quote-scope checks
Removal
Overlay or full removal, number of existing layers, and hidden-layer pricing
Waste
Sorting, hazardous materials, weight, haul distance, tipping, and extra loads
Access and lifting
Scaffold, edge protection, crane, road use, weather protection, and occupied areas
Frame and deck
Opening-up allowance, unit rates for decay or corrosion, and approval before extras
Underlay
Product, laps, joints, penetrations, vapour control, ventilation, and terminations
Insulation
Material, thickness, thermal bridges, existing insulation, and excluded energy analysis
Flashings and drainage
Eaves, ridge, abutments, valleys, gutters, outlets, and accessories
Professional scope
Design, structural review, filing, inspection, fees, and response to corrections
Tax basis
Whether VAT, statutory charges, and third-party fees are included or additional
Warranty
Product and workmanship periods, exclusions, transfer, maintenance, and claim process
Decision scenarios
Older detached home: metal versus tile
A tile proposal can have a higher first cost but fewer renewals if its site-specific service life is supported. It can also require structural-load review or additional deck work. Enter those items explicitly rather than burying them in the unit price, then check whether the thirty-year ranking survives the eighty-percent-life case.
Operating shop: construction disruption
Two proposals with the same contract price may have different access plans, durations, weather exposure, and renewal disruption. Enter only incremental economic loss that the project causes, such as unavoidable contribution-margin loss, temporary relocation, or special protection. Do not enter gross revenue as though all of it disappears permanently.
Low quote with blank scope lines
A zero insulation, flashing, or disposal amount can mean included, reused, excluded, or forgotten. Leave its scope box unconfirmed until the contractor answers in writing. The calculator will display the arithmetic but will not declare that proposal the lowest ready lifecycle option.
Korean legal and technical context
Sources were checked on August 23, 2026. Building Act ID 001823, master text 273437, effective February 27, 2026, defines the roof frame as a major structural part in Article 2 and establishes permit and filing frameworks in Articles 11 and 14. The Building Act Enforcement Decree ID 002118, master text 288339, effective July 28, 2026, includes adding, dismantling, or repairing or altering at least three roof frames within the major-repair definition in Article 3-2. Application depends on the actual work, building, scale, exceptions, and competent authority, so this calculator never determines permit or filing status.
Demolition may require a separate asbestos process. Occupational Safety and Health Act ID 001766, master text 283449, Articles 119 and 122 address asbestos surveys and qualifying removal work. The Asbestos Safety Management Act ID 011384, master text 276749, effective October 1, 2025, also contains building-asbestos survey and disclosure provisions. Do not treat general waste allowance as an asbestos-removal quote. Obtain the required survey and a compliant site-specific proposal before entering that cost.
Scope labels reference the Korean Construction Specification family listed by the Ministry of Land, Infrastructure and Transport CODIL system: KCS 41 56 01 general roofing, KCS 41 56 02 clay and cement tiles, KCS 41 56 04 metal tiles, KCS 41 56 05 asphalt shingles, KCS 41 56 07 metal sheets, KCS 41 56 08 metal panels, and KCS 41 56 14 accessories. These classifications help compare descriptions; the calculator does not test specification compliance.
Present-value and equivalent-annual-cost structure follows general lifecycle-cost practice described in NIST Handbook 135e2025, published August 2025. The handbook does not supply Korean roof prices or guaranteed material lives here. Every price and life used in the calculation remains a user-entered proposal assumption.
Frequently asked questions
Should I confirm a scope item priced at zero?
Yes. Zero can mean included at no separate charge, reuse, owner-supplied, excluded, provisional, or simply missing. Record the written answer before treating the quote as comparison-ready.
Does no renewal within thirty years prove that an option is best?
No. Its life may be unconfirmed, and initial or maintenance cost may be high. Review the thirty-year present value and the eighty-percent-life downside case together.
Does residual value predict a higher sale price?
No. It deducts only a straight-line unused-service share at the analysis boundary. It does not predict property appreciation, buyer value, tax value, or scrap proceeds.
How should I choose escalation and discount rates?
Apply one internally consistent nominal basis to all proposals. If no organisational benchmark exists, rerun reasonable combinations and keep the assumptions with the decision record.
Can I use this for a flat roof?
Yes when the project replaces the complete covering and related layers. Use the rooftop waterproofing lifecycle calculator when the decision concerns only a coating or membrane renewal.
Does the lowest result endorse a contractor or product?
No. Ranking is limited to complete user-entered cost assumptions. Quality, safety record, solvency, programme, references, warranty enforceability, specification, and contract risk need separate review.
Turn the result into a safer quote review
- Reconcile area, tax, removal depth, deck allowance, accessories, and warranty across all enabled proposals
- Attach opening-up unit rates, photo approval, weather protection, and stop-work rules to the contract
- Resolve structural, asbestos, leak, and authority questions with qualified parties before demolition
- Check that cash remains affordable when life is twenty percent shorter than the stated base case
Bring three actual proposals, transcribe each line, and use the missing-scope list as a written request for clarification. A defensible decision is usually the option whose scope and downside remain manageable, not merely the smallest unqualified headline number.