Timber Frame Insulation Options – Your Guide to Insulating a Timber Frame House

There are plenty of different routes to properly insulating a timber frame house and multiple ways to deliver the requisite performance in a timber-built home. “PIR insulation is still the bread and butter for most of our projects,” says Simon. Frame Technologies’ standard 140mm-deep wall panel features 100mm of PIR, vapour control layers (VCLs), an internal insulation lining (from 20mm to 100mm thick), battens and the internal plasterboard finish.

“This approach gives a strong balance in terms of performance, value and panel thickness,” Simon adds. It’s worth remembering that great thermal efficiency from thinner wall profiles is one of the original selling points of timber building systems, as it can translate into more internal living area.

“Our most popular timber frame wall system achieves a U-value of 0.15 W/m²K,” says Paul Newman, self build director at Potton. This combines a 90mm thickness of PIR insulation within the panels (made up of studwork, sheathing and a vapour control layer) with an additional 50mm internal lining. “We don’t go deeper than this with the internal layer, as follow-on trades will need to nail or screw through the lining to get a fixing,” says Paul.

Ecologic SIPs has two variants of its structural insulated panels. The 172mm-thick Eco +Plus version features 150mm of recyclable EPS insulation for a wall U-value of 0.18 W/m²K. For roofs, the spec is 222mm (with 200mm of integral EPS) and an internal layer of YBS SuperQuilt insulation, sandwiched between two battens, which takes the U-value to 0.11. “We use an I-joist spline where the roof panels join, giving a more continuous run of insulation versus systems that use a solid timber spline,” says Mike.

Potton offers several SIPs options, too, with the most common a 142mm-thick panel plus an internal or external lining to achieve the desired performance. The 170mm system is more typically used for roofs, largely because its extra depth means it can span further. This makes it even easier to achieve vaulted ceilings (whether on top of a SIPs or timber frame walling system). “We tend to steer people towards SIPs if they want Passivhaus,” says Paul.

With oak frame construction, the insulation isn’t part of the core structure in the same way. Instead, it’s provided through encapsulating panels (which could be pre-insulated timber or SIPs). “Think of it like an insulation cladding system, running all the way around the outside,” says Tim Crump, founder of Oakwrights.

“You erect the frame, and then crane the wall and floor panels into place.” Oakwrights’ WrightWall system combines 140mm of Rockwool inside the studs with 50mm of Kingspan as an internal lining (or 75mm if it’s for the roof). The lining can be increased if you want better performance – or you can go for the WrightWall Natural system (more on this in a moment).

What Are the Timber Frame Insulation Upgrade Options?

Each manufacture offers a range of certified systems and performance points. Insulation-wise, it’s about beefing things up either with a thicker lining (often the first port of call, depending on required U-values), higher-performance product or a deeper core of timber frame insulation within the panel. Of course, the timber frame insulation spec must go hand-in-hand with addressing factors like cold bridging and thermal performance – which all comes back to holistic system design.

In general, the walling system is the main area where the total insulation depth can flex. This is because the Building Regs notional dwelling already recommends a high-spec U-value of 0.11 W/m²K for roofs (as opposed to 0.18 for walls). For instance, EcoLogic’s Eco Premium is a 222m-deep panel with 200mm of integral EPS insulation, achieving 0.14 W/m²K for the walls, while the system’s roof spec remains at 0.11.

This 268m² self build showcases some of the key benefits of SIPs. The SIPS@Clays install used 142mm-thick panels with 50mm of extra insulation on the inside face of the walls, and 100mm on the roof

Most Oakwrights customers who want to upgrade their insulation opt for WrightWall Natural, which has a 240mm core of either Warmcel or woodfibre insulation. “I think they tend to go this way because they’re already thinking more environmentally in general,” says Tim. Between panels, a neoprene gasket provides the first airtightness layer, with Siga tapes backing that up, and a membrane connecting up from the slab to the panel. The windows are installed in the workshop, for even greater control over the timber frame insulation’s performance.

Naturally, adding more insulation will put the price up – although many self builders feel it’s worth a modest uplift for lower long-term energy bills. “You might spend between £2,000 and £2,500 upgrading from a system that hits a U-value of 0.18 W/m²K to one that achieves 0.10 W/m²K,” says Simon. “It’s peanuts, really! Most clients want to get the fabric as good as they can get it first, and then add renewables like heat pumps and solar panels later.”

Oakwrights’ WrightWall Natural systems is used to encapsulate its oak frame buildings, combining natural insulation with airtightness measures to deliver a low-energy home

All three of Frame Technologies’ systems can be specified to hit a range of performance goals. Its gold-standard option is TechVantage T, which uses a split wall construction: two 90mm studs fitted with glasswool, mineral wool or natural insulations, with a 90mm separation between them. The cavity is packed with insulation, too, creating a thermal bridge-free timber frame construction that delivers U-values from 0.13 to 0.09 W/m²K.

If you want to get to Passivhaus, it’s common to switch to an external insulation lining rather than an internal layer. “The advantage of this is that you cover the floor zone and eaves, which gets rid of those long thermal bridges,” explains Paul from Potton. It does, however, require a thicker layer of insulation to eliminate the risk of condensation (not such an issue with internal linings). “External insulation is usually done with a very high-performance product,” he continues. “You also can’t use PIR or phenolic insulations below ground, as they’ll get waterlogged and degrade.”

What Are the Sustainable Timber Frame Insulation Options?

There are a number of great sustainable and high-performance timber frame insulation options entering the mainstream. “Many people we work with are moving towards more natural options, such as recycled cellulose and woodfibre,” says Tim. “These create a breathable wall system that will capture carbon, contributing towards net zero targets.”

Natural insulations also provide greater density than standard products, which can add thermal mass (helping to maintain an even internal temperature) and improve sound performance – although they will generally require a thicker wall profile.

Using lower-carbon materials is perhaps the next piece in the eco home puzzle. Frame Technologies’ TechVantage S and T, for instance, both accept natural and breathable insulations (teamed with a woodfibre external sheathing board) and are designed to achieve U-values down to 0.10 W/m²K.

“We’re seeing a shift towards people starting to look at alternative and natural options,” says Simon. “Just be sure you’re specifying readily-available products. Some natural insulations may be more difficult to get hold of than others, which could add cost to your self build project.”

If your focus isn’t strictly on natural products, glasswool and Rockwool are both mainstream options, manufactured to high quality standards and – like cellulose (Warmcel) – capable of supporting a breathable, healthy internal living environment. The up-and-comer, though, looks to be woodfibre – as evidenced by insulation giants Kingspan taking a 51% stake in German manufacturer Steico last summer.

Some products offer other sustainability benefits. “We use EPS because it’s recyclable,” says Mike. “Any offcuts are repurposed, such as for sections under windows, or turned into briquettes on site with our EPS compactor, and donated to a recycling firm. We’ll even come and collect panels for recycling if they’re damaged on site.” Ultimately, whatever insulation you choose, with a timber building system, you’re investing in a high-quality product that will deliver ongoing energy and carbon savings over the building’s whole life.