How many roofing sheets do I need for a 10 perch house?

Land extent (perches) does not set the sheet count, the roof dimensions do. A typical single-storey house on 10 perches has a roofed footprint of roughly 11 m × 8 m. As a gable roof at 22.5° pitch with UPVC sheets, that works out to about 50–56 sheets after wastage. Enter your actual plan length and span above for an exact figure.

What is the effective cover width of a UPVC roofing sheet in Sri Lanka?

The effective (net) cover of a common UPVC/ASA corrugated sheet is about 0.98 m, the raw sheet is wider (~1.06 m) but a corrugation is lost to the side-lap. Metal tile-profile and fibre-cement sheets cover about 1.0 m each. The calculator uses effective cover, not raw width, so the count is right.

What roof pitch is recommended for corrugated sheets in Sri Lanka?

For corrugated UPVC, metal and fibre-cement sheets, most Sri Lankan builders use a pitch between 15° and 30°. Below about 10° water can back up under the end-laps in heavy monsoon rain; steeper than 30° wastes material and is only needed for a specific look. The default here is 22.5°.

How many purlins do I need per roof slope?

Count them by the slope length: rows per slope = slope length ÷ purlin spacing, rounded down, plus one for the eave purlin. At 0.6 m spacing a 5 m slope needs 9 rows. Multiply by the ridge length and the number of slopes for total linear metres of timber or box-bar. CIDA norms put purlin spacing at 0.6–0.9 m for sheet roofing.

How many roofing screws or hook bolts do I need per sheet?

Fasteners are counted per square metre, not per sheet, the norm is about 6 per m² (one at each corrugation crest along every purlin line). A 125 m² roof therefore needs roughly 750 screws or hook bolts. The tool multiplies your total slope area by 6.

Does the metric ⇄ feet toggle change the answer?

No. Switching between metres and feet only re-labels your inputs, the tool converts everything to metres internally, so the sheet, purlin and screw counts are identical either way. Sheet lengths stay in metres (with the feet equivalent shown) because that is how SL dealers list stock.

Why does the area cross-check show fewer sheets than the headline?

The headline uses the real layout, whole sheets per column, so the last sheet in each column is partly cut and counted in full. The area cross-check (roof area ÷ one sheet's coverage) ignores those per-column round-ups, so it lands slightly lower. That gap is normal; the layout count is what you actually buy.

Does this handle hip, gable and lean-to roofs?

Yes, gable (two slopes), simple hip (four slopes) and single-slope lean-to are all supported. Complex multi-hip, gambrel, mansard, dormer and curved roofs are out of this version. For clay or concrete tiles the coverage maths is different; this tool is for profiled sheets only.

Sri Lanka · Building

Sri Lanka Roofing Sheet Calculator

Find out how many roofing sheets your roof needs from its plan dimensions and pitch, plus ridge caps, purlins, screws and an optional rupee cost. Built for the UPVC/ASA, metal tile-profile and fibre-cement sheets sold in Sri Lanka. No signup, sources cited below.

By Induwara Ashinsana· Co-Founder, Ryzera TechnologiesUpdated Jul 11, 2026

How many roofing sheets do I need?

CIDA / SLS geometry

Roof type

Units

Quick presets

Building length (ridge direction)

Length of the wall the ridge runs along.

Building width (span)

Distance the roof spans, wall to wall.

Roof pitch

Slope angle in degrees (5–45°). SL corrugated roofs: ~15–30°.

Sheet length

Lightweight UPVC/ASA corrugated sheets (e.g. Amano). Effective cover ≈ 0.98 m.

Eave overhang (per side)

How far the roof projects past the wall at the eave.

Verge overhang (per end)

Overhang past the gable wall at each end.

Sheet profile

Cover 0.98 m · end-lap 200 mm

Purlin / batten spacing

Gap between purlins up the slope (CIDA: 0.6–0.9 m).

Wastage allowance

Cuts, breakage & offcuts. Gable ~7%, hip ~10%, lean-to ~5%.

Roofing sheets

52 before wastage

Roof slope area

125.5 m²

1,351 sq ft

Ridge caps

pieces

Screws / hook bolts

753

6 per m²

How the count is built

Rafter run (per slope)	4.6 m
Slope (rafter) length	4.98 m
Ridge length	12.6 m
Usable sheet length (after end-lap)	2.8 m
Sheet layout	13 cols × 2 rows × 2 slopes = 52
Purlins / battens	9 rows/slope · 227 m total
Area cross-check (A ÷ cover × usable length)	≈ 46 sheets

Purlin length is total linear metres. Purlins/battens stay in metres, timber is priced by the metre in SL.

slope = run ÷ cos(pitch)

Add unit prices (optional), estimate the total cost

Price per sheet

Price per ridge cap

Price per metre of purlin

Price per screw / hook bolt

Prices are yours to enter, nothing is fetched. SL roofing prices vary by dealer, colour and batch.

Sheet cover widths & end-laps from SLS 9 / SLS 723 and Sri Lankan manufacturer catalogues; purlin spacing, wastage and 6-screws/m² norms from CIDA/ICTAD. Ridge cap cover 1.8 m/piece. Estimator only, consult a qualified engineer for structural design.

How it works

Roofing quantities come from one piece of geometry and a handful of catalogued sheet dimensions. Every length you type is converted to metres first, so the metric and feet inputs always give the same answer.

Rafter run. For a gable or hip roof the horizontal run of one slope is span ÷ 2 + eave overhang. A single-slope lean-to uses the full span plus the eave.
Slope (rafter) length. The sheet runs up the slope, not across the plan, so slope = run ÷ cos(pitch). This is standard roof trigonometry, the same measurement CIDA/ICTAD BOQs use for roof area.
Columns across the ridge. columns = ⌈ridge length ÷ effective cover width⌉. Cover width is the net figure after the side-lap: about 0.98 m for UPVC/ASA and 1.0 m for metal tile-profile and fibre-cement, per SLS standards and manufacturer spec sheets.
Rows up the slope. rows = ⌈slope length ÷ (sheet length − end-lap)⌉. The end-lap (150 mm for fibre-cement per SLS 9, ~200 mm for profiled sheets) is the vertical overlap between stacked courses.
Sheets. Multiply columns × rows × the number of slopes, then add the wastage allowance for cuts and breakage, about 7% for a gable, 10% for a hip (more diagonal cuts) and 5% for a lean-to. The result is rounded up to whole sheets.
Ridge caps, purlins and screws. Ridge caps = ⌈ridge ÷ 1.8 m⌉ (cover per cap). Purlin rows per slope = ⌊slope ÷ spacing⌋ + 1 at the CIDA 0.6–0.9 m spacing. Fasteners = roof area × 6 per m², one per corrugation crest at every purlin line.

A hip roof has the same total slope area as a gable over the same footprint, so its sheets are estimated by area (roof area ÷ one sheet's coverage) with the higher hip wastage, because the diagonal cuts across its triangular faces make a plain column-by-row layout meaningless. As a credibility check the calculator always shows an independent area-based sheet count beside the layout count. Sheet cover widths and end-laps come from manufacturer catalogues (Amano, Melwa/Lanwa, Rhino/Ceylon) and the SLS dimensional standards; the spacing, wastage and fastener norms come from CIDA/ICTAD roofing practice.

Worked examples

Gable roof · 12 m × 8 m · UPVC/ASA · pitch 22.5°

Run = 8 ÷ 2 + 0.6 eave = 4.6 m
Slope = 4.6 ÷ cos 22.5° (0.9239) = 4.98 m
Usable sheet length = 3.0 − 0.20 end-lap = 2.80 m
Ridge = 12 + 2×0.3 verge = 12.6 m
Columns = ⌈12.6 ÷ 0.98⌉ = 13 · Rows = ⌈4.98 ÷ 2.80⌉ = 2
Sheets = 13 × 2 × 2 slopes = 52 → ×1.07 wastage = 56 sheets
Area = 2 × (12.6 × 4.98) = 125.5 m² · Screws = ⌈125.5 × 6⌉ = 753
Ridge caps = ⌈12.6 ÷ 1.8⌉ = 7 · Purlins = 9 rows/slope, 226.8 m total

Single-slope lean-to · 6 m × 4 m · fibre-cement · pitch 15°

Run = 4 + 0.5 eave = 4.5 m (full span, one slope)
Slope = 4.5 ÷ cos 15° (0.9659) = 4.66 m
Usable sheet length = 3.0 − 0.15 end-lap = 2.85 m
Ridge (top edge) = 6 + 2×0.3 = 6.6 m
Columns = ⌈6.6 ÷ 1.0⌉ = 7 · Rows = ⌈4.66 ÷ 2.85⌉ = 2
Sheets = 7 × 2 × 1 slope = 14 → ×1.05 wastage = 15 sheets
Area = 6.6 × 4.66 = 30.8 m² · Screws = ⌈30.8 × 6⌉ = 185
Purlins = ⌊4.66 ÷ 0.6⌋ + 1 = 8 rows, 52.8 m total

Hip roof · 12 m × 8 m · metal tile-profile · pitch 22.5°

Eave length = 12 + 2×0.6 = 13.2 m · Eave width = 8 + 2×0.6 = 9.2 m
Slope = (9.2 ÷ 2) ÷ cos 22.5° = 4.98 m
Area = 2 × 13.2 × 4.98 = 131.4 m² (same as a gable of this footprint)
Sheets by area = ⌈131.4 ÷ (1.0 × 2.80)⌉ = 47 → ×1.10 = 52 sheets
Top ridge = 13.2 − 9.2 = 4.0 m → ridge caps = ⌈4.0 ÷ 1.8⌉ = 3
Hip flashing = 4 × 4.6 × √(2 + tan²22.5°) ≈ 27.1 m
Screws = ⌈131.4 × 6⌉ = 789

Frequently asked questions

Sources & references

Sheet cover widths, standard lengths and end-laps are catalogued dimensions from Sri Lankan manufacturer/importer spec sheets (Amano ASA/UPVC; Melwa/Lanwa colour-coated metal tile-profile; Rhino/Ceylon fibre-cement) cross-checked against the SLS standards. Purlin spacing, wastage allowances and the ~6 fasteners/m² norm follow CIDA/ICTAD roofing practice. Last verified 2026-07-11. This is a quantity and costing estimator, not a structural design tool, consult a qualified engineer for rafter sizing, wind load and spans.

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