Facility Metrology & Roof Measurements
High-resolution satellite metrology calibrated at 0.2757 meters/pixel (0.9044 feet/pixel) was used to compute the exact dimensions of the Zigma Corporation industrial sheds:
💡 Simple Explanation: What is the Difference Between "Ground Area" (39,785 sq. ft.) and "Actual Roof Surface" (46,670 sq. ft.)?
When Zigma Corp orders "40,000 sq. ft. waterproofing", they are referring to the flat ground floor size of the building. But when applying waterproofing, you actually need 46,670 sq. ft. of material. Here is why in plain words:
This is what you see looking down from space or measuring the flat concrete floor on the ground (Length × Width). A flat building shadow of ~40,000 sq. ft.
The roof is not a flat concrete slab. It has two things that add extra surface:
• The Roof Slopes (Tilted 'V' Shape): Rainwater must slide off, so the roof is angled, making it longer than the flat floor.
• The Asbestos Sheet is Wavy (Corrugated): If you flatten all the curves (waves) of the sheet, it is 15% longer than a flat line! Because hot bitumen and tarfelt must be pressed into every single wave, the real surface area to paint and waterproof is 46,670 sq. ft.
| Structural Section | Length | Width / Span | Plan Footprint | Actual Roof Surface (Slopes + Wavy Curves) | Critical Roof Features |
|---|---|---|---|---|---|
| Eastern Main Bay (Stitching & Tarpaulin Division) | 303 ft (92.4 m) | 95 ft (29.0 m) | 28,785 sq. ft. | ~33,600 sq. ft. | Sloped corrugated asbestos roofs (inverted 'V' shape), rotary whirlybirds, central valley junction |
| Western Bay & Machine Extension (Extrusion Hall) | 102 ft (31.0 m) | 108.5 ft (33.0 m) | 11,000 sq. ft. | ~13,070 sq. ft. | Houses Gurucharan India extrusion tower, elevated ridge monitor vent |
| Total Main Facility Shed Roof | -- | -- | 39,785 sq. ft. | 46,670 sq. ft. | Exact match to commercial inquiry (38,000 – 40,000 sq. ft.) |
| North Access Courtyard (Loading / Staging) | 131 ft (40.0 m) | 54 ft (16.5 m) | 7,074 sq. ft. | -- | Interlocking pavers, truck bay access for material delivery |
Figure 1: Satellite Metrology & Bay Layout
Overhead layout showing the 303 ft x 95 ft East Bay, 108 ft x 102 ft West Bay, and 303 RFT Central Valley.
Figure 2: True-Color Satellite Architecture
High-resolution confirmation of the red-and-grey tiled courtyard (truck unloading yard) and twin multi-gable corrugated roofs.
Figure 3: Ground View vs. Rooftop Alignment
Courtyard view of twin gables aligned with rooftop turbine ventilators and neighbouring sheds.
Figure 4: Forensic Roof Condition Audit
Highlighting shattered AC sheets held by loose bricks, tarpaulin patches, and corroded J-bolt washers.
Scientific Material Selection: 2.5 mm vs 2.0 mm vs 1.5 mm
Waterproofing corrugated Asbestos-Cement (AC) industrial roofs is governed by mechanical, thermal, and chemical physics. In Howrah’s humid industrial climate, where summer roof temperatures reach 65°C to 72°C, membrane selection determines whether the system lasts 10 years or fails within 6 months.
| Membrane Thickness | Reinforcement Core | Tensile & Tear Resistance | Thermal Fatigue & Ridge Behavior | Suitability for Zigma Roof |
|---|---|---|---|---|
| 1.0 mm – 1.5 mm STRICT NO |
Paper / Rag / Light glass tissue (Type 1) | < 250 N / 50mm (Very low) | Differential thermal expansion tears sheet along corrugation peaks within 3 months. Chars under 180°C hot bitumen. | Strict Failure. Completely unviable for industrial roofs; guaranteed monsoon leakage. |
| 2.0 mm (Standard Oxidized) HIGH RISK / MARGINAL |
Lightweight Hessian or thin scrim | ~400 - 450 N / 50mm | Bitumen cover layer is under 0.6mm per side. Micro-cracking exposes raw jute threads, causing rot and delamination. | Not Recommended. Standard 2.0mm felt will fail within 2–3 seasons unless heavily modified. |
| 2.5 mm – 3.0 mm (IS 1322 3G1) RECOMMENDED STANDARD |
Heavy Woven Jute/Hessian Core (≥230 g/m²) | ≥ 700 N / ≥ 500 N (High backbone) | Bridges substrate hairline cracks. Absorbs 180°C hot bitumen without deformation, forming a solid monolithic membrane. | Proven Gold Standard. 8–10 year design life when protected with solar reflective aluminum paint. |
What Would It Take to Make 2.0 mm Work?
If Zigma Corp requests 2.0 mm thickness, standard oxidized felt cannot be used. It can only work if upgraded to:
- APP Polymer Modification: Increases membrane elongation to >35% so it can flex without tearing.
- Non-Woven Polyester Core (≥160 g/m²): Rot-proof synthetic core instead of organic jute.
- Heavier Bitumen Underbed: Increase hot bonding bitumen to 1.6–1.8 kg/m² to compensate for reduced felt thickness.
- Note: APP polymer-modified 2.0mm membrane costs more per m² than traditional felt, making IS 1322 3G1 (2.5mm–3.0mm Hessian) the most cost-effective solution.
Comprehensive Bill of Materials (BOM)
Materials calculated for a 39,785 sq. ft. plan footprint, incorporating a 1.15 corrugation expansion factor, 10% lap allowance, and double-ply valley gutter reinforcement:
| Item # | Material Description | Standard / Specification | Technical Function | Gross Quantity Required |
|---|---|---|---|---|
| M-01 | Hessian-Base Bitumen Tarfelt | IS 1322 Type 3 Grade 1 (2.5 - 3.0mm) Roll size: 1.0m x 20m |
Primary waterproofing membrane; tensile reinforcement bridging substrate fractures. | 235 Rolls (1m x 20m) (~50,525 sq. ft. gross) |
| M-02 | Industrial Blown Bitumen | IS 702 Grade 85/25 or 90/15 Packaged in 200 kg steel drums |
Hot-melt bonding matrix (1.2 kg/m² underbed + lap sealing); forms a seamless monolithic seal. | 12.0 Metric Tonnes (60 Drums of 200 kg) |
| M-03 | Penetrating Bituminous Primer | IS 3384 (Solvent-based penetrating) Packaged in 200 Liter steel drums |
Cold-applied base sealer; penetrates porous, chalky asbestos to ensure 100% bitumen adhesion. | 1,500 Liters (7.5 Drums of 200L) |
| M-04 | Commercial Fuel (LPG Cylinders) | 19 kg Commercial Red Cylinders (Indian Oil / Bharatgas / HP) |
Fuel for high-output bitumen melting boilers and handheld lap-torching burners. | 24 Cylinders (19 kg each) |
| M-05 | Solar Reflective Aluminum Paint | IS 9862 (Bitumen-compatible aluminum) Packaged in 20L sealed containers |
UV shield and heat reflection; lowers roof temperature from 68°C to ~48°C. | 700 Liters (35 Cans of 20L) |
| M-06 | Bitumen Sealing Mastic Putty | Heavy-duty rubberized bitumen mastic | Flashing pyramid collars around all J-bolt stems and filling deep valley fissures. | 250 Kilograms (5 Cans of 50 kg) |
| M-07 | Replacement AC Corrugated Sheets | 6mm thick, 10 ft length, matching corrugation | Replacing fractured, shattered sheets currently weighed down by bricks (Photo 6). | 35 Sheets |
| M-08 | HDG J-Bolts, EPDM Cup Washers & Nuts | 8mm x 150mm Hot-Dip Galvanized | Re-anchoring loose roof sheets to existing angle-iron purlins prior to waterproofing. | 500 Sets |
Work Breakdown Structure (WBS)
Safety Mobilization & Under-Truss Catch Netting
Rig 4,000 m² of certified safety catch netting beneath purlins inside the shed to protect stitching workers and machinery. Deploy steel lifelines and crawling boards.
Debris Clearing, Brick Removal & AC Sheet Patching
Remove loose bricks, tarpaulins, and moss under water mist. Replace 35 cracked AC sheets with new 6mm matching corrugated sheets anchored securely.
J-Bolt Anti-Rust Treatment & Mastic Pyramid Collars
Wire-brush rusted bolt shanks, apply zinc-phosphate primer, and form 30mm bitumen mastic pyramids capped with 150x150mm felt bibs.
Cold Bituminous Primer Penetration Coat (IS 3384)
Apply continuous coat of solvent primer across 46,670 sq. ft. developed surface area. Allow 24 hours to penetrate porous asbestos.
Hot Blown Bitumen Application & Hessian Tarfelt Rolling
Pour molten Grade 85/25 bitumen at 180°C (1.2 kg/m²). Unroll IS 1322 3G1 felt into hot bitumen, maintaining 100mm end and 75mm side laps.
Central Valley Gutter 2-Ply Heavy-Duty Waterproofing (303 RFT)
Apply 2-ply reinforced treatment extending 300mm up both slopes with staggered seams to withstand monsoon standing hydrostatic water.
Solar Reflective Aluminum Protective Topcoat (IS 9862)
Apply leafing aluminum reflective paint (0.15 L/m²). Reflects >75% of solar rays, preventing bitumen embrittlement and cooling the shop floor.
Transparent Direct Quotation (Zero Contractor Margin)
Direct Base Cost Policy
This quotation reflects pure at-cost wholesale procurement rates from Burrabazar (Brabourne Road / Posta, Kolkata), direct truck freight to Jalan Gate 1, optimized theka labor, and equipment rental. No contractor profit margin has been added.
Comprehensive Sq. Ft. Rate Breakdown
Exact breakdown of the ₹ 39.76 / sq. ft. (Excl. GST) base cost into its 9 major technical components on the 39,785 sq. ft. plan area:
12.0 MT (60 Drums) of IS 702 Grade 85/25 bitumen applied hot at 1.2 kg/m² underbed plus lap flood-sealing.
235 Rolls (1m x 20m) of IS 1322 Type 3 Grade 1 felt (2.5–3.0mm) with heavy woven jute core (≥230 g/m²).
10-man piece-rate theka gang covering ~3,500-4,000 sqft/day in 14-16 days. High productivity, zero idle wage leakage.
1,500 Liters of cold solvent primer conforming to IS 3384, penetrating chalky asbestos cement to prevent delamination.
700 Liters of IS 9862 leafing aluminum paint reflecting >75% of solar rays, preventing bitumen embrittlement.
24 commercial 19kg LPG cylinders for melting 12 MT of bitumen and torching laps, plus torches and safety gear.
2 tar melting boilers for 16 days (reduced from 25 days) plus 4,000 m² certified under-truss fall-arrest safety nets.
35 replacement 6mm AC sheets for cracked zones, 500 sets of HDG J-bolts with EPDM washers, and 250 kg bitumen mastic.
2x 10-Tonner truck trips from Burrabazar to Jalan Gate 1 (@ ₹5,000/trip), Burrabazar loading coolie, and rooftop hoisting.
| Cost Component Category | Physical Scope / Basis | Amount Excl. GST (₹) | Rate Excl. GST (Plan) | Amount Incl. 18% GST (₹) | Rate Incl. GST (Plan) |
|---|---|---|---|---|---|
| 1. Primary Waterproofing Sheeting | 235 Rolls IS 1322 3G1 Hessian Tarfelt | ₹ 4,11,250 | ₹ 10.34 / sq. ft. | ₹ 4,85,275 | ₹ 12.20 / sq. ft. |
| 2. Hot Bitumen Matrix Coating | 12 MT (60 Drums) Blown Bitumen 85/25 | ₹ 6,00,000 | ₹ 15.08 / sq. ft. | ₹ 7,08,000 | ₹ 17.80 / sq. ft. |
| 3. Direct Site Labor (Theka Gang) | Piece-rate contract gang (~16 working days) | ₹ 1,40,000 | ₹ 3.52 / sq. ft. | ₹ 1,65,200 | ₹ 4.15 / sq. ft. |
| 4. Penetrating Bituminous Primer | 1,500 Liters IS 3384 Solvent Primer | ₹ 1,35,000 | ₹ 3.39 / sq. ft. | ₹ 1,59,300 | ₹ 4.00 / sq. ft. |
| 5. Solar Reflective Aluminum Finish | 700 Liters IS 9862 Aluminum Paint | ₹ 1,22,500 | ₹ 3.08 / sq. ft. | ₹ 1,44,550 | ₹ 3.63 / sq. ft. |
| 6. Fuel & Consumables | 24 LPG Cylinders + Torches + PPE | ₹ 55,200 | ₹ 1.39 / sq. ft. | ₹ 65,136 | ₹ 1.64 / sq. ft. |
| 7. Site Equipment & Safety Netting | 2 Tar boilers (16 days) + safety nets | ₹ 51,000 | ₹ 1.28 / sq. ft. | ₹ 60,180 | ₹ 1.51 / sq. ft. |
| 8. Structural Repairs & J-Bolt Detailing | 35 AC sheets + 500 J-bolts + Mastic | ₹ 47,000 | ₹ 1.18 / sq. ft. | ₹ 55,460 | ₹ 1.39 / sq. ft. |
| 9. Transport, Freight & Hoisting | 2 Truckloads Burrabazar → Jalan Gate 1 | ₹ 20,000 | ₹ 0.50 / sq. ft. | ₹ 23,600 | ₹ 0.59 / sq. ft. |
| SUBTOTAL BASE (EXCLUDING GST) | Direct At-Cost Net Base | ₹ 15,81,950 | ₹ 39.76 / sq. ft. | -- | -- |
| ADD: GST @ 18% (SAC 9954) | Works Contract (100% ITC Claimable) | ₹ 2,84,751 | ₹ 7.16 / sq. ft. | ₹ 2,84,751 | ₹ 7.16 / sq. ft. |
| TOTAL PROJECT VALUE (INCL. 18% GST) | Gross Invoice Amount | ₹ 18,66,701 | ₹ 46.92 / sq. ft. | ₹ 18,66,701 | ₹ 46.92 / sq. ft. |
Burrabazar Wholesale Sourcing Directory & Strategy
Prepared specifically for Balaji Hardware & Agrico to procure every material in the 40,000 Sq. Ft. Bill of Materials (BOM) at the lowest wholesale cash rates across the Burrabazar, Brabourne Road, Netaji Subhas Road, Canning Street, Ezra Street, Posta, and Howrah trading hubs.
Burrabazar distributors quote assuming 30-day credit. By offering instant RTGS / Cheque clearance against delivery challan, demand a 2.5% to 3.5% Cash Discount. On a ₹ 13.15 Lakh material outlay, this saves ₹ 35,000 – ₹ 42,000 instantly.
For 12 MT (60 Drums) of Bitumen and 235 rolls of Tarfelt, do not allow dealers to route via their Burrabazar godowns. Demand direct dispatch from the Haldia refinery / Dankuni warehouse straight to Jalan Complex Gate 1. Saves ₹ 10,000 – ₹ 14,000 in double-handling.
• Burrabazar / Posta: Bitumen, Tarfelt, Primers, Solar Paint, Fasteners.
• Howrah Kona Expressway (5 km away): Source 35 replacement 10ft AC Sheets locally to eliminate bridge transit breakage.
• Domjur Gas Depot: Order commercial LPG locally to bypass Vidyasagar Setu hazmat police checkpoints.
• Tarfelt Weight Test: Weigh 5 random rolls. Genuine IS 1322 3G1 must weigh 45–48 kg per 20m roll. Reject if under 40 kg.
• Bitumen Test: Check refinery batch test cert for Grade 85/25 (softening point 80°C–90°C).
• Paint Leafing: Test brush stroke; aluminum must rise to form a mirror-like silver foil within 60 seconds.
Comparing Manufacturers, Primary Distributors, and Wholesale Traders to identify the Best Value Sourcing Choice.
| Item # | Material / Scope | Quantity | Option A (Brand Mfr) | Option B (Stockist) | Option C (Local Market) | Selected Best Value Option | Target Rate | Total Budget |
|---|---|---|---|---|---|---|---|---|
| M-01 | Hessian Tarfelt (IS 1322 3G1) | 235 Rolls (1m x 20m) | STP Limited (Lyons Range) ₹ 1,780 / roll |
Tiki Tar (Brabourne Rd) ₹ 1,720 / roll (3% CD) |
Canning St Godown ₹ 1,650 / roll |
Tiki Tar / STP Project Desk | ₹ 1,750 / roll | ₹ 4,11,250 |
| M-02 | Blown Bitumen (IS 702 85/25) | 12.0 MT (60 Drums) | IOCL Terminal (Posta) ₹ 51.00 / kg |
Eastern Bitumen (Posta) ₹ 49.50 / kg |
Local Blenders (Howrah) ₹ 45.00 / kg (High Risk) |
Eastern Bitumen Syndicate | ₹ 50.00 / kg | ₹ 6,00,000 |
| M-03 | Penetrating Primer (IS 3384) | 1,500 Liters (7.5 Drums) | STP Shalitex Primer ₹ 105 / L |
Tiki Tar Tikiprime ₹ 98 / L |
Ezra St Paint Hub ₹ 88 / L |
Ezra St Chemical Hub (200L drums) | ₹ 90.00 / L | ₹ 1,35,000 |
| M-04 | Commercial LPG (19 kg Cylinders) | 24 Cylinders | IOCL Kolkata Depot ₹ 1,820 / cyl + toll |
Indane Depot (Domjur) ₹ 1,780 / cyl |
Local Retailer ₹ 1,900 / cyl |
Indane Agency (Domjur Depot) | ₹ 1,800 / cyl | ₹ 43,200 |
| M-05 | Solar Aluminum Paint (IS 9862) | 700 Liters (35 Cans x 20L) | STP SilverShield ₹ 220 / L |
Berger / Asian Stockist ₹ 195 / L |
Ezra St Leafing Paint ₹ 170 / L |
Ezra St Wholesale Paint Market | ₹ 175.00 / L | ₹ 1,22,500 |
| M-06 | Bitumen Sealing Mastic Putty | 250 kg (5 x 50kg cans) | STP ShaliMastic ₹ 65 / kg |
Tiki Tar Mastic ₹ 60 / kg |
Canning St Stockist ₹ 52 / kg |
Canning Street Stockist | ₹ 54.00 / kg | ₹ 13,500 |
| M-07 | Replacement AC Sheets (6mm, 10ft) | 35 Sheets | Everest Depot (Taratala) ₹ 890 / sheet + freight |
Everest (Kona Expressway) ₹ 820 / sheet |
Local Yard ₹ 860 / sheet |
Everest Stockist (Kona Exp, 5km) | ₹ 820 / sheet | ₹ 28,700 |
| M-08 | HDG J-Bolts + EPDM Washers | 500 Sets (8mm x 150mm) | Brand Fasteners ₹ 13.50 / set |
NS Road Fastener Hub ₹ 10.00 / set |
Local Hardware ₹ 12.00 / set |
Premier Fasteners (NS Road) | ₹ 10.00 / set | ₹ 5,000 |
| M-09 | Plant: Tar Boilers & Safety Nets | 2 units + 4,000 m² Nets | Kolkata Rigging ₹ 62,000 lump sum |
Howrah Foreshore Depot ₹ 51,000 lump sum |
Informal Riggers ₹ 45,000 (No safety cert) |
Howrah Foreshore Scaffolding | ₹ 51,000 | ₹ 51,000 |
| M-10 | Freight & Rooftop Hoisting | 2x 10-Ton Trucks + Winch | Stand Trucks ₹ 6,500 / trip |
Posta Lorry Syndicate ₹ 5,000 / trip |
Local Pickups ₹ 5,500 / trip |
Posta Lorry Syndicate (Strand Rd) | ₹ 10,000 + Hoist | ₹ 20,000 |
| TOTAL DIRECT PROCUREMENT BASE OUTLAY (ZERO CONTRACTOR MARKUP) | Net Base: | ₹ 15,81,950 | ||||||
Interactive Margin & Billing Simulator
Use this tool to add your desired trading markup over the base direct cost (₹ 39.76 / sq. ft. = ₹ 15,81,950) and dynamically compute your final client billing rates:
(100% ITC claimable by Zigma) + ₹ 3,27,464