Large Timber Cladding Projects: A Guide for Contractors

A cladding job on a single extension and a cladding job across a large building share the same material, but the risks are different. Larger projects magnify small mistakes: a wrong profile, a mismatched batch or a missing fire certificate can stop work across hundreds of square metres.

This guide is for contractors, architects and specifiers planning larger timber cladding packages. It covers the points that most often need attention. It is general guidance, not a substitute for your own design team or building control.

Start with the specification

Settle these before you ask for prices:

• Species or product type. Cedar, larch, Thermowood, charred, painted or Accoya all behave and look differently. See our external timber cladding range.
• Profile. Tongue and groove, shadow gap, shiplap, featheredge or rainscreen. The profile affects cover width, so it changes the quantity you need.
• Finish. Natural, oiled, stained, painted or charred.
• Orientation and fixing. Horizontal, vertical or diagonal, and visible or secret fix.
• Fire requirements. Covered below.

A clear written specification gives every supplier the same basis for pricing.

Measuring and quantities

Cladding is usually sold by the linear metre or pack, but projects are drawn in square metres. Convert using the cover width of the profile, not the full board width. Then add a waste allowance for cuts, corners, openings and defects. The right allowance depends on layout, so agree it with your installer.

Order a little over what you need in one go. Reordering later can bring differences in colour or grain, particularly with natural timber.

Natural variation and batches

Natural timber varies. Western Red Cedar, larch and Thermowood all show colour and grain differences between boards, and between deliveries. On a large elevation:

• mix boards from several packs as you fix them
• avoid stopping and starting with a new delivery mid-elevation
• hold back a few packs of the same delivery for repairs

Samples help set expectations, but they show only a small piece. Our timber samples are a useful start, and a site meeting can help with scale. Painted and charred boards are more uniform in colour than bare timber, but are still made from a natural material.

Fire performance

On larger buildings, fire is often the deciding issue. Building Regulations set requirements for external wall materials, and these depend on the height, use and distance from boundaries of the building. We cannot give you a requirement for your project. Your approved inspector or building control body can.

What we can say in general:

• Untreated timber cladding is combustible.
• Fire retardant treatment can improve reaction-to-fire classification.
• The classification applies to a specific species, thickness and treatment, backed by a test report.

Our HR Prof fire treatment page says that factory-applied treatment comes with a fire treatment certificate that can be presented to building control, and recommends checking the classification report against your species and application. See fire retardant cladding and our fire-safe timber guide. Always confirm the current rules for your building height and type with building control before you specify.

Moisture, ventilation and detailing

Good detailing matters more on big elevations because repeated errors repeat everywhere. In general terms:

• Allow a ventilated cavity behind external cladding so air can move and the boards can dry.
• Keep boards clear of the ground and of horizontal surfaces where water sits.
• Use a suitable breather membrane and insect mesh at ventilation openings. We list cladding insect mesh.
• Seal cut ends where the species or finish calls for it. Our finishes and treatments range includes an end sealer.
• Use fixings that suit the species. Cedar in particular can stain with the wrong metal, so use stainless steel fixings.

Follow the cladding manufacturer’s installation guidance and your designer’s details.

Bespoke and painted elements

Large jobs often need something non-standard: a particular profile, bespoke corner or colour. Bespoke or painted orders take 5 to 7 working days. Read about bespoke profiles and plan these early, since drawing sign-off tends to be the slow step.

Ordering and delivery

For larger packages, talk to us about:

• the total quantity and any phasing across the programme
• delivery points and site access, including vehicle size and unloading arrangements
• storage on site, with boards kept flat, off the ground and under cover

Our website prices include VAT and UK delivery. For a large order, ring us on 0161 504 0011 with your specification and we will talk you through the options.

Maintenance and long-term cost

Specifiers and clients increasingly ask about upkeep. Natural cedar weathers to grey without treatment, while oiled or stained boards need re-coating over time. Painted and charred finishes have their own maintenance needs. Include the maintenance plan in your handover. Avoid quoting years of life unless you can back them with a warranty or manufacturer data.

A short checklist

1. Specification written and agreed
2. Fire requirement confirmed with building control
3. Samples approved by the client
4. Quantity calculated from cover width, with waste allowance
5. Bespoke or painted items ordered early
6. Delivery and storage planned
7. Fixings, membranes and trims included in the order

Trends to watch

Regulation is the trend most likely to affect a large project. Building Regulations guidance on external walls and fire safety has changed in recent years and may change again, so check which provisions apply to your building type and height with building control at design stage.

In general terms, expect clients to ask for documented fire performance, clear maintenance plans and early sample approval.

FAQs

Can you supply cladding for commercial projects?

Contact us with your specification and we will tell you what we can supply.

Do you provide fire certificates?

Our fire treatment product page states that a fire treatment certificate is issued with factory-applied treatment. Ask us about the scope for your species and project.

Can I order samples for a client sign-off?

Yes, free samples are available for many products.

Can you visit the site?

We offer site meetings.

Talk to us about your project

Send your drawings for a quote, arrange a site meeting or call 0161 504 0011.