Thermally Broken Insulated Lintels, Are They Worth It?

Insulated lintels are not a new idea. We’ve seen them used on residential and commercial projects for some time, and they are a regular part of building spec these days.

Thermally broken insulated lintels take things a step further, reducing heat transmission to a default lintel psi value of 0.5 W/mK, which is almost zero. Whether you need to go this low depends on the overall heat loss SAP calcs for the rest of the building.

When margins are tight, cost considerations can sometimes make the decision for us.

How Much Does a Thermally Broken Insulated Lintel Cost?

At first sight, a thermally broken insulated lintel is not going to look like the cheap option, but you need to see it in context. The area above the head of a door or window has been identified as a key area for heat loss and allowing extra in the budget here could save money elsewhere.

An extra heavy-duty insulated lintel without a thermal break can sometimes be about half the cost of a fully thermally broken version. However, the additional cost of the thermal break could be absorbed by lowering the specification of the cavity wall insulation.

Top Tip: Cavity Wall Savings

If you are at the pre-start stage with a client, talk to your (or their) architect about the options. By specifying thermally broken insulated lintels the cavity wall requirement could be reduced from 150mm to 100mm.

It’s the swings and roundabouts approach. On an average new build house with 8 – 10 doors and windows, the average additional cost of thermally broken insulated lintels could easily be offset in this way.

Image Source: Catnic.com

Why Does a Thermally Broken Insulated Lintel Matter?

New houses and extensions are currently subject to the requirements of an SAP (Standard Assessment Procedure). It was originally set up to work out how much energy will be required to heat and light a house to normal comfort levels.

It uses information on U-values of materials used, any renewable energy systems, airtightness, and other efficiencies. One way that new buildings can fail an SAP is in the ‘performance gap,’ which is the difference between expectation and the quality of the installation.

Installing a thermally broken insulated cavity lintel over a window or door head will reduce heat transfer to almost zero in these locations. It may help by giving a builder a broader margin of error, in some cases, and reduce the risk of SAP failure.

Top Tip: Picture It!

Insulation is one of the key things that a building inspector will want to see, so make sure you photograph everything. Most inspectors are reasonable people. If you call them out before you close up around the first window or door opening, they will likely be happy with a set of photographs for the rest of them.

Check out Wade’s easy guide to Part L photographic compliance.

Can You Use Two Lintels Instead?

The short answer is yes, of course you can. Depending upon the load, or the aesthetics you could use two separate steel, or concrete lintels, and insulate between the inner and outer leaves with a cavity closer at the head.

The obvious issue straight away is that you will need to double the number of lintels and lintel specifications on a job. The next issue is one of time. It’s not recommended that lintels are installed on an inner and outer leaf at the same time.

Using a one-piece cavity lintel saves time as you can raise lifts at a similar rate. A cavity lintel often has a cavity tray built in too, as well as being an effective cavity closer at the head.

One lintel can do the job of four other items: external lintel, internal lintel, cavity tray, and cavity closer!

What is a Thermal Bridge?

With improvements in the insulating performance of cavity wall, loft, and under floor insulation products, the focus has turned to areas where heat can bridge the gap. It has been estimated that today almost 30% of heat loss from a new building can be accounted for by thermal bridging.

A thermally broken insulated lintel minimises the potential for any heat loss in this area. The cavity is closed securely by the insulation at the head of the opening. If there is a cold bridge, providing a spot for heat to transfer easily, there may be future problems with condensation, or mould.

A regular insulated steel lintel will still perform well, as part of SAP calculations, as long as robust details have been adhered to elsewhere. Even if an insulated steel lintel has been installed properly there will still remain a small thermal bridge in the steel, across the cavity from one leaf to another.

5 Top Reasons to Go for Thermally Broken Lintels

• Minimal thermal bridging delivering high-performance energy savings
• Potential cost savings on other thermal envelope elements
• Time savings on specifying and installing multiple items
• Cost savings on specifying and installing multiple lintels
• Future proofing a build ahead of the 2025 Future Homes Standard changes to the  UK building regulations

The main reason to select a thermally broken insulated lintel is simply the fact that it is often the best build product for the job.

Apart from anything else, a single-piece cavity wall lintel is structurally superior to a two-part, twin-lintel job. It delivers much better stability between the inner and outer leaf, especially in areas of high loadings where extra-heavy-duty performance is required, i.e. at gable ends, etc.

If in doubt consult a structural engineer or talk to one of our professional team at Wade today.