Roofing Slate Lead Times: The Week-by-Week Breakdown That Saves You a Delayed Roof

Part of the Roofing Slate Guide's Buying & Importing section — the scheduling half of the puzzle whose inspection half is covered in the pre-shipment inspection checklist and the breakage story in Understanding Breakage Allowance.

Let me start with the number that made me want to write this down. I'm the man who puts the dates on the orders — twelve years in shipping schedules, most of them with slate and stone, and the single most common sentence I hear from a buyer is "I need the slate by mid-September." The second most common is the one that follows it, a week later: "Wait — you can't do it by then?"

Here's the thing nobody says out loud: lead time isn't a promise the supplier makes, it's the distance between today and the day a block of stone became a roof. The stone has to come out of the mountain, get split, cut, dried, packed, shipped, and unpacked again. You can't hurry a wet slate out of its drying yard — you can only watch it dry. So let me give you the honest, week-by-week version of that distance, the numbers I use in my own quotes, and the four questions that turn "8 weeks" from a number into a plan.

And yes, one more thing before we go: I'm going to keep saying weeks rather than a single number, because anyone quoting a single lead time is quoting a number they haven't had to defend yet.

The Short Answer: The Week-by-Week Breakdown

Here's the honest shape of a standard order — size, spec and colour already settled, no custom shapes, going by sea in a 20ft container:

Total: about 10–12 weeks from order to your site, with the factory side (production + drying + packing) about 5–6 weeks and the shipping + clearance side about 4–6. The sea leg is the flexible part of the sum — the factory side is the honest one. Put a calendar with real dates on it, not a number, and you'll see the slack your quote actually carries.

Stage 1 — Confirmation: the Week That Isn't a Week

The order is not "placed" the day you click send; it's placed the day the deposit is in and the batch is allocated. Two things quietly eat the first week: the bank transfer clearing, and the factory waiting until they have a production run that fits your volume rather than starting a saw for a single order. A 20ft container (roughly 1,300 m² of 6–8 mm standard) fits naturally into a batch; a 300 m² order may wait a few extra days to be grouped, and that's not slowness, it's economics — the alternative is a line that stops between every order.

What you can do this week: settle the spec, the batch reference and the payment terms before the PO is signed. A two-day delay at confirmation is the cheapest to make up; a two-day delay at the port is the most expensive.

Stages 2–3 — Production and Drying: the Weeks That Can't Be Rushed

The production stage is the heart of the lead time, and it has a natural floor: the CNC and cutting lines work in batches, and each batch has a rhythm of splitting, trimming, dressing and 100% individual inspection. A 1,000 m² order doesn't double in a week because the line is a physical machine with a cycle time, not a photocopier. The how slate is made guide walks the process; here's what matters for your schedule: the line doesn't care that your roof is waiting.

Then comes the stage most buyers never see and no supplier can sell: drying. A freshly split and cut slate carries water in its micro-structure; loaded damp, it carries the water into the micro-cracks, the water freezes on the first winter, and the tile splits along a line nobody saw — the same chain the water absorption article explains in detail. The rule we work to: moisture content under 0.5% at the time of packing, measured on the stacking face of a packed tile, not on the first tile of the crate that has been airing for two hours. In dry weather the slate can reach the gate in a week; in monsoon season it can take two — and no "rush" on your order changes the weather. When you hear a factory quoting "two weeks drying" in the monsoon, that's not padding, that's physics. That's the single most important reason lead time stretches between May and August.

I'll be straight with you: the factory that quotes a lead time without a drying gate is either drying in a kiln (fine, that's honest and it costs money) or shipping wet (that's the one that comes back in year two, and it's the one the inspection guide warns about). The factory QC guide holds the gate and keeps a lab record of it. The pre-shipment inspection checks it on your side.

Stages 5–6 — Booking, the Sea, and the Port: the Weeks Everyone Thinks Are the Factory's Fault

Once the slate is packed, the schedule leaves the factory and moves to the sea. This is the part of the calendar most buyers can't see, and where the delays multiply in ways nobody controls:

• The booking. A 20ft container is booked when the factory has a confirmed volume — and in peak season, bookings are 2–4 weeks out. Space on the vessel is not guaranteed; a booking is a request, not a reservation. The factory can only book what it has, and what it has arrives at the port on the week the ocean sailing happens to be.
• The port. Slate goes to the port, gets consolidated and customs-cleared, then waits for the vessel. The crate standards and the arrival inspection are the two parts of the trip that are fully in the buyer's and the factory's control — the ocean leg is in nobody's.
• The transit itself. The ocean leg from a Chinese port to a UK or European port usually runs about 25–40 days — call it 3–5 weeks — and then your port, customs and the final truck add another week or two. A US West Coast run is similar; a US East Coast or an inland delivery adds days. The square metres per container page shows why this is a 20ft world for slate — weight, not volume, drives the numbers.
• The final hop. Port to roof: customs at your end, haulage, and the receiving check can add 1–2 weeks you'll want in the plan. This is the stage where "the ship was on time" meets "the container sat in the yard for a week."

Add it all up and you'll see why "8 weeks" is the optimistic end of the honest range, "10–12" the realistic one for the first order, and "13–16" the honest one for custom — and any of them can slip by a week or two when a vessel moves and the calendar finds out.

What Changes Lead Times — the Two Levers That Actually Move the Number

You can't compress the drying, but you can compress two things that sit next to it: the confirmation and the sea. And there are three genuine levers that move the number one way or the other:

• Standard vs. custom. A slate from the standard 500×250 / 600×300 range in stock sizes is a production run away; a custom size or a colour-only spec adds cutting and a re-check cycle, and the quote honestly goes to 13–16 weeks.
• Stock vs. made-to-order. If the factory carries ready-stock of your size and batch, the order jumps to the front of the drying stage — 2–4 weeks off the calendar. That's the honest reason "in stock" and "made to order" quote differently.
• Peak season. Container space and sailing frequency tighten between about now (autumn) and the Chinese New Year shutdown. A booking in October has a different wait than one in March. The Chinese New Year factory holiday — usually a week or two in January or February — shifts everything by that amount, and "after the new year" in a quote is a date, not a delay.

If you can only buy one thing for your schedule, buy the stock check: ask the supplier which sizes they keep in ready stock, and let the calendar know it.

Custom Sizes and Special Colours: The 13–16 Week Plan

When the size or the colour isn't in the catalogue, the schedule changes shape. A custom tile means: cut from a block with the custom dimensions, dress the edges, check the holes and the nibs against a drawing, dry to the gate, then the same crate-and-container journey as a standard one — but each custom stage runs at a custom pace, because the tooling and the run-size are set up for this order alone. A run of 2,000 custom tiles is a different cost and calendar than a run of 20,000.

The honest range for a custom order: 13–16 weeks from confirmation to your port, and a roof on site maybe another 1–2 after that. If your custom spec involves a colour match to a heritage roof, add the sample-approval loop (the sample approval process explains the sealed sample that guards the whole batch) — that's a step a standard order never sees, and it earns a week of its own.

The Calendar Method: The 4 Real Questions That Turn "8 Weeks" Into a Plan

Here's the bit I really want you to take away. A supplier's lead time is the end of the story; the plan is the beginning. Ask the supplier, at the quoting stage, the four questions that build the calendar:

1. When does production start — on PO, or on the deposit? The answer defines "week zero." If it's "on the deposit," the week your bank is slow is a week your roof is slow.
2. How many crates does the order make, and is the batch guaranteed in one run? A 1,300 m² order split into two batches means the second batch doesn't start until the first one is done — a calendar with a seam in the middle.
3. What is the drying policy in the current month? Monsoon drying is 2 weeks; dry-season drying can be 1. The supplier who can't answer this doesn't know the weather or the yard — both are a warning.
4. What is the sea leg, and what does the port do to it? The FOB date is the factory's delivery; the arrival date is the vessel's, plus a customs window that belongs to your side. Ask for the "to the port" and "to the roof" split, and put the difference in your contract line.

Then build it on paper. Week 1, confirmation; weeks 2–5, production; weeks 5–6, drying; week 7, packing and the pre-shipment inspection; weeks 8–11, sea; week 12, port and haulage; week 13, the receiving check. That's the honest 12-week calendar for a standard 20ft order — and when you see it on paper, you'll see why the answer "8 weeks" never lands a roof on time, and why the range "10–12" is the one a planner can actually defend.

And here's the one thing I'll insist on — build the calendar before the order, not after. The week you find out the supplier "can't do mid-September" is the week you could have been two weeks earlier with a plan. A lead time you can't plan around is just a date you'll miss.

How to Use This in a Real Order — the Checklist

Before you send the PO, put these four lines on the order form:

• The split. State the "ready to ship" (FOB) date and the "arrival at your port" date separately — not one number that means both.
• The batch guarantee. "Whole order in one batch, batch number stated in the test report and the packing list" — the calendar can't slip on a seam that doesn't exist.
• The drying gate. "Moisture content below 0.5% at packing, with the record on the packing list." — this is the line that makes the calendar honest.
• The inspection step. "Pre-shipment inspection before the container leaves, report and photos to the buyer." — the PSI checklist is the plan you run on the day the container is sealed.

Put the calendar up on the wall the day you confirm, mark week 8 in red, and let the supplier's weeks speak for themselves. The roof you're putting on is going to be there for 100 years — the 12 weeks that get it there are the cheapest part of the whole job.

Frequently Asked Questions

Related Reading

• Pre-Shipment Inspection Checklist — the inspection day that keeps the week-8 seal honest
• How Many Square Metres Fit in a Container? — the container maths that fixes the order size and the shipment calendar
• How to Compare Roofing Slate Quotations — the incoterm and the freight line hidden inside every quote
• Roofing Slate MOQ Explained — the volume that decides whether the container waits on a full load
• Samples and Sample Approval Process — the sealed sample that adds its own two weeks on a custom colour