A guide to insulation and vapour barriers with timber frame cladding

As a staple of eco-friendly construction, the number of properties with timber frame cladding is on the rise. Renewable, thermally insulating, and undeniably beautiful, there is a lot to love about timber. But how does this exterior feature work with the rest of your building frameworks, such as your insulation and damp-proof membranes? We will answer that in this guide, giving you a more well-rounded understanding of how your timber frame cladding slots into your wider construction.

Where Cladding & Membranes Are Installed

Your timber frame cladding will be the outermost layer of your property, but there is a lot going on beneath the surface. Directly behind your cladding, you will have a ventilated cavity. This is a must to keep air circulating and allow moisture to escape, preventing your timber boards from rotting.

Behind this cavity lies the water-resistant membrane, which stops external moisture from entering the structure while still allowing internal vapour to escape. Further inward, you will find the insulation layer, fitted within or around the structural frame to minimise heat loss.

Together, these layers work to keep your property warm, protect it from damp and ensure comfortable interiors.

Your Options for Timber Frame Cladding Insulation

There is no one-size-fits-all approach when it comes to insulation behind timber cladding. Typically, you will choose from three types of insulation:

Rockwool and mineral wool

Rockwool is a brand of wool insulation which is very popular in UK properties, with excellent thermal conductivity of just 0.035 W/mK. You can also find other varieties of mineral wool, all of which are renowned for their excellent water resistance, which keeps damp and mould at bay while warming your property. These wools offer good fire resistance, which is a must when aligning with building standards.

Polyisocyanurate (PIR)

This is a rigid foam insulation, installed as boards behind your cladding ventilation cavity. They are a lot narrower than other options, making them ideal for slimmer walls, while still providing fantastic insulation (they have a super low thermal conductivity of 0.02 W/mK!). The only thing to be wary of with PIR is that it can reduce breathability, making moisture control essential for timber cladding that lasts.

Phenolic

Phenolic insulation delivers some of the best thermal efficiency available, achieving very low U-values with exceptionally thin boards, which makes it attractive for high-performance or space-restricted builds. However, it is more expensive than other options and requires professional installation to ensure breathability in your building.

Your Options for Vapour Barriers

When looking at vapour barriers, the most common option is a traditional polyethylene vapour control layer (VCL). This is a robust, durable sheet that works well at blocking moisture, while being an affordable choice for most projects. Do note that your VCL sheet needs to be carefully sealed around any joints to perform effectively.

Your other option is to go for an intelligent vapour membrane. This changes its permeability depending on humidity levels: it tightens in winter to keep vapour out and opens in summer to let trapped moisture escape. This makes it particularly useful in properties with timber frames and timber cladding, where breathability is so crucial to the longevity of your wood.

Whilst we don’t sell the vapour barriers themselves, we can supply you with durable timber cladding for your project. To learn more, speak to our team about our vast range of cladding timbers, including Western Red Cedar, Larch, Douglas Fir, Oak, Red Grandis, Thermowoods, and a plethora of tropical hardwoods.

Buy Sustainable Timber Frame Cladding

If you are installing timber cladding, we can help. Start by choosing sustainable timber cladding boards from EcoChoice, where all our timber is sourced from FSC or PEFC-certified woodlands. Then chat with us about how best to install your cladding and bring your property to life.

Get in touch to start your timber cladding order.