Ask any installer what customers complain about a year after installation, and the answer is rarely generation. It is leaks. Forty anchor holes through a waterproof layer, a blocked drain and one monsoon are all it takes. This lesson covers how to keep the roof dry, how to keep the terrace usable, and how to check a structure before the modules go on.
Before you drill
- Fix existing leaks first. Note them in the survey (module m02) and agree who repairs what before work starts.
- Plan the timing. In Mumbai, Kochi or Goa, avoid drilling a roof in the weeks before the monsoon unless sealing can be completed and cured. Sealants and coatings need dry surfaces.
- Know the waterproofing system: brick bat coba, cementitious coating, membrane or elastomeric paint. Use sealants and patch materials compatible with it; ask the waterproofing applicator if in doubt.
- Map drains and slopes. Flat roofs fall towards rainwater outlets, often at about 1 in 100. Structure base plates and pedestals must not dam that flow.
Sealing every penetration
At each anchor
- Drill, clean and set the anchor (lesson 4).
- Before placing the base plate, apply sealant to the hole mouth or under the plate as the method statement says.
- After tightening, run a continuous bead of sealant around the plate edge and cap the nuts and studs.
- Patch the waterproof coating around the plate, lapping at least about 150 mm onto the existing coat, in two coats.
Use sealants rated for outdoor UV exposure and movement (polyurethane or MS-polymer types are common) and compatible with the roof coating. Ordinary silicone from a hardware shop often does not bond to cementitious coatings and peels within a season.
Pedestals
If the design uses PCC pedestals, cast them on a cleaned, primed surface, tie them into the slab, chamfer the top edges, and carry the waterproof coat up their sides. Sharp pedestal edges crack the coating; chamfers do not.
Cable penetrations
Where DC or AC cables go down through a slab or wall, use a sleeve with a downward bend outside (a "drip loop") and seal the sleeve. Never leave an open conduit pointing up at the sky.
Terrace use under and around the array
The structure type was chosen with terrace use in mind (lesson 1). Finish the job so that use is safe:
- Headroom: on walk-under structures, keep at least the agreed clear height everywhere, including under bracing and cable trays. Paint low points in a contrasting colour.
- Sharp edges: fit end caps on cut rails and channel ends at head and shin height.
- Walkways: keep the agreed clear paths to tanks, doors, drains and the cleaning tap.
- Water point: provide a tap or hose route for module cleaning.
- Clothes lines and storage: agree where they go so lines are not tied to module frames or rails.
- Children and parapets: do not create a "ladder" of structure members next to a low parapet.
Structure inspection checklist
Do this after the structure is complete and before modules go on. Fixing a structure under modules is slow and risky.
| Check | How | Pass |
|---|---|---|
| Layout | Tape from parapets and between rows | Matches drawing, setbacks and row gaps |
| Alignment | String line along the front purlin | Straight within a few mm over the row |
| Tilt | Inclinometer on rafters | Design tilt ±1° |
| Plumb and level | Spirit level on legs and purlins | Legs vertical; purlins level along the row |
| Bracing | Visual against drawing | All braces fitted and bolted |
| Bolt torque | Torque wrench on a sample; all bolts marked with a torque stripe | As per design or fastener maker |
| Anchors | Pull test on a sample; visual on all | Proof load held; sealant complete |
| Coating | Gauge at random points; check cuts and holes | Thickness as specified; zinc-rich paint on any site cut |
| Fasteners | Visual | Correct grade (SS304/SS316) and washers |
| Clamp positions | Mark module clamp zones on purlins | Purlins located to suit the module's clamping zones |
| Earthing bonding | Bonding jumpers across sections | Continuity confirmed (module m06) |
| Waterproofing | Visual at every plate; water test where required | No gaps; drains clear |
| Housekeeping | Sweep | No drill dust, metal swarf or packing left on the roof |
Metal swarf from drilling rusts within days and leaves orange stains on the roof and on module glass. Sweep and magnet-sweep before you leave.
Worked example: material and time check for a 4.95 kWp Pune job
- Legs: about 2 per kWp, so 10 legs; 4 anchors each = 40 chemical anchors
- Sealant: about one cartridge per 6 legs (Sunlectric rule) gives 10 ÷ 6 → 2 cartridges, plus one spare
- Drain fall check: over a 6 m run to the outlet at 1 in 100, the slab should drop about 60 mm; confirm the new pedestals sit clear of that path
- Pull test sample: for example 3 of the 40 anchors, chosen at rear legs where uplift is highest
- Cure time: check the resin sheet for the day's temperature before torquing; in a 35 °C Pune afternoon it is usually much shorter than on a cool morning
Key points
- Repair existing leaks and plan around the monsoon before drilling.
- Seal every anchor with compatible, UV-rated sealant, patch the coating with a 150 mm lap, and keep drains and slopes clear.
- Use chamfered, slab-tied pedestals with the waterproof coat carried up their sides.
- Make the terrace safe: headroom, end caps, walkways, water point and agreed clothes-line spots.
- Inspect the finished structure with a checklist before modules go on, and keep records and photos.
Check yourself
- Why should you avoid ordinary silicone sealant on a cementitious waterproof coating?
- Name three things to check on a structure before mounting modules.
- Why sweep up drilling swarf the same day?
Answers
- It often does not bond well to cementitious coatings and peels within a season, letting water in.
- Any three of: alignment, tilt, plumb and level, bracing, bolt torque, anchor pull test and sealing, coating at cuts, clamp-zone positions, earthing bonding, drainage.
- Steel swarf rusts within days and stains the roof and module glass, and can damage the waterproofing.