Polycarbonate for roofing & glazing
Polycarbonate for roofing & glazing
What it is
Customers often ring up asking for multiwall (also called twinwall) polycarbonate roofing — the hollow, ribbed sheet used on carports and patios. We don’t stock that. We supply solid (monolithic) polycarbonate sheet — the clear, one-piece sheet. This guide is how to turn that enquiry into a sale of the sheet we actually carry, and how to pick a thickness that won’t bow.
flowchart LR
A[Customer asks for multiwall roofing] --> B[We supply SOLID PC sheet]
B --> C[Confirm framing/purlin spacing]
C --> D[Pick thickness so it stays flat]
D --> E[Quote Opal or Grey Tint for QLD]Solid sheet vs multiwall — what to tell the customer
- Solid PC is virtually unbreakable — a strong selling point over glass and multiwall for hail-prone SE QLD.
- It’s optically clear (or Opal / Grey Tint) rather than hazy and ribbed.
- It’s heavier, so it needs the framing or purlins closer together to stay flat. That’s the main thing to work through with them.
Solid sheet is not a like-for-like swap for multiwall on widely-spaced purlins. If the customer has a roof with purlins far apart and wants a light infill, flag it — they may need a thicker (heavier, dearer) sheet or extra battens. Tell Daniel if you’re unsure.
How to pick a thickness so it doesn’t bow
Solid polycarbonate will visibly bow between supports if the framing is too far apart. The spacings below are an unverified staff rule of thumb for flat glazing framed on all four edges — read the note underneath before using them, and do not give them to a customer:
| Thickness | Max support centres before it bows |
|---|---|
| 3 mm | ~350 mm |
| 4.5 mm | ~450 mm |
| 6 mm | ~550–600 mm |
| 8 mm | ~700 mm |
| 9.5 mm | ~800 mm |
| 12 mm | ~950 mm |
- Ask the customer how far apart their purlins / battens are.
- Match that spacing to the table and pick the thickness at or above it.
- Typical patio purlins are 600–900 mm apart — at that spacing 6 mm will bow, so recommend 9.5–12 mm, or tell them to add battens to bring the centres in.
Where these numbers come from — read before you quote them
They have no approved source. This table’s only provenance was the PIM Chat system prompt, and that prompt’s front-matter named this document as its own source of truth — the two cited each other and neither cited a manufacturer datasheet, a test, or a recorded shop observation. Nobody knows who measured them or under what conditions.
So they are staff rule-of-thumb only: a starting point for a conversation,
never a figure to give a customer, put in a quote, or design a roof against.
openspec/changes/business-context-fabrication-architecture classifies them as
SHOP_OBSERVED / RULE_OF_THUMB, promoted to VALIDATED only once someone
re-observes rows against the stated four-edge condition and records who, when
and what they saw.
PIM Chat can no longer state any support-spacing figure (removed 2026-09-14) — it asks for the spacing and hands the question to the supplier’s engineering data or the customer’s builder. Do the same. What is safe to say is the qualitative shape: solid PC bows between supports, and spacing, thickness, orientation and span all change how much.
Always tell the customer to confirm the wind classification for their address and that HB Plastics does not certify structural design — their builder or engineer signs off the roof.
Regional climate — SE QLD
- Wind: SE QLD is AS/NZS 1170.2 Region B (non-cyclonic, but higher wind than inland Region A). Most low-rise sites are N2–N3. Confirm the exact classification for the street address.
- UV: All our PC sheet is UV-stabilised — essential for the QLD sun.
- Heat & glare: Suggest Opal or Grey Tint to cut transmitted heat and glare; Clear for maximum light.
- Thermal movement: PC expands and contracts with roof heat — fixings need oversized holes and must not be over-tightened, with expansion gaps.
Common questions
- Do we sell twinwall/multiwall roofing sheet? — No. We sell solid polycarbonate sheet. Offer that instead (see “What it is”).
- What thickness for a patio roof? — Ask the purlin spacing. At the usual 600–900 mm, go 9.5–12 mm so it doesn’t bow; 6 mm is only good to ~550–600 mm.
- What colour for a QLD patio? — Opal or Grey Tint to reduce heat and glare; Clear if they want maximum light.
- Can we say it will pass wind loads? — No. Give the sheet spec and colour, but the roof structure and wind sign-off is the customer’s builder/engineer.
Who to tell if it breaks
If a customer needs a genuine multiwall roofing product, or a structural span sign-off, escalate to Daniel or ask in #whats-new before quoting.
Derived from: HBPlastics-PIM/product-master-worker/lib/pim-chat-agent.js. If this looks wrong, the source changed — update the source and re-generate, don’t just patch this page.