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What is a Thermal Break?

A thermal break is an insulating material inserted between two structural elements to prevent or minimise heat transfer into or out of a building. A cavity lintel that is thermally broken is a perfect example of a thermal break in practice.

A cavity closer helps to stop heat transfer between a cavity and a window or door frame. The insulation fitted to the inner leaf of a masonry wall is, at its most basic, a thermal break.

YBS Easi-Close Multi Width Cavity Closer 50mm to 100mm x 2.4m

YBS Easi-Close Multi Width Cavity Closer 50mm to 100mm x 2.4m
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Cavalok Multi Width Cavity Closer 2.4m

Cavalok Multi Width Cavity Closer 2.4m
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The key is to reduce thermal conductivity wherever an opportunity presents itself. In a building with balconies, very often there is an insulating pad set between flanges as a thermal break, where the balcony is bolted to the main structure.

What Does Thermally Broken Mean?

The term thermally broken sounds like something you wouldn’t want in your new building. Perhaps it’s better understood as thermally interrupted?

A thermal bridge may be something that has been discussed as being a problem. Thermal bridging is defined as something that heat can transfer through without interruption.

Breaking that bridge by design with thermal break materials can stop, or at least slow down, heat loss out of a building. Installing a thermal break at strategic points, and closing off bridging points, is what a thermally broken detail is all about.

Why is a Thermal Break Important?

Thermal breaks are important as they can contribute to the overall sustainability of the building under construction. The new measures that require a BREL (as-built Building Regulations Energy Label) and an EPC (Energy Performance Certificate) rely on the consistency of insulation in vulnerable areas such as openings and wall junctions.

Without ensuring there are satisfactory insulating materials in place in critical positions, such as reliable thermal break materials, the assessor may require additional insulating materials to be installed before sign-off is achieved.

The rules that complicate compliance with Part L energy use Regulations actually give a contractor and designer some leeway in building construction. You may not require thermally broken lintels, as long as the cavity insulation is deep enough, or has the right U value to counter it.

What Are the Benefits of Having a Thermal Break?

There are several benefits of installing thermal breaks in a building wherever it is possible to do so, least of all compliance with building regulations (which you have to comply with regardless). A thermal break helps save energy and save money over the longer term, making it advantageous to the end user of the building.

Energy Efficiency

thermal energy efficiency chart house

The clearest benefit is energy efficiency. Reduction of heat transference through a building means that the temperature indoors is easier to maintain at a reasonable level. The homeowner is not paying to heat the outdoors!

Lower Running Costs

The less heat escapes from a building, the lower the heating bill will be. It’s not even close to rocket science. It has been proven that insulating lofts, wall cavities, and the area below the slab pay dividends, so ensuring all these areas join up to make an efficient thermal envelope is just common sense.

Better Building Liveability

A high level of insulation continuity means a more comfortable and consistent indoor environment can be maintained. With a lack of cold spots transferring heat out of a building, it is easier to manage temperature indoors whatever the weather outdoors.

Better Building Performance

Increased efficiency leading to better comfort levels for the building occupants will mean that the equipment used to heat or cool the space does not have to work as hard. With thermal breaks minimising heat loss, plant such as boilers, heat pumps and the like will last longer.

Indeed, if a building interior is also not subject to wide changes in temperature then it too will take longer to deteriorate.

Control of Condensation

Using thermal breaks ensures better control over cold spots where there may be a risk of condensation. With properly installed weep vents at lintels, many condensation issues that can arise in cavity walls are solved.

Condensation occurs when warm air comes into contact with a cold surface, so insulating a steel plate, or putting a barrier between the inner and outer leaf of a lintel will minimise moisture that can cause mould or rot.

How Can I Incorporate a Thermal Break in my Building?

Thermal breaks are being developed in many ways in the construction industry with innovative designs tested and regularly coming to market. Replacement uPVC and metal windows have long incorporated thermal break technology in their design.

Here’s a selection of some of the products that are easily incorporated in your next Part L compliant build.

Thermally Broken Lintels

A regular cavity lintel is one continuous piece of folded, galvanised steel, with a leaf each for the internal and external masonry. It will usually have foam board insulation, the standard is expanded polystyrene, already fitted between the two leaves below the sloping part of the lintel that deflects water out of the cavity.

Catnic TS90/100 Standard Duty Thermally Broken 100mm Cavity Lintel

Catnic Standard Duty Thermally Broken (Part L Compliant) 100mm Cavity Lintel TS90/100
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Catnic TH90/100 Heavy Duty Thermally Broken 100mm Cavity Lintel

Catnic TH90/100 Heavy Duty Thermally Broken (Part L Compliant) 100mm Cavity Lintel
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thermally broken lintel is one that is discontinuous, but still one item. Two steel leaves are bonded together with a section of expanded polystyrene sandwiched between them. The twin pieces of steel still do the same job as a regular lintel except that they incorporate a thermal break.

The cavity insulation should be installed on top of the lintel to allow continuity of the building’s thermal envelope. The front metal leaf of the lintel is angled in such a way that it can act as a partial cavity tray when the insulation does not fill the entire width of the cavity.

Cavity Closers

Cavity closers have been around for a while now and are gradually getting better regarding specification and usability. Fitted properly, so that the insulation remains continuous, and buts up properly at the corners of an opening, they are a very effective thermal break.

Insulating Shims and Wall Ties

To slow conductivity, thermal shims that fit between a masonry wall and a steel wall tie, with a high compressive strength are sometimes specified when very high thermal performance is required. Ancon makes a shim with a low conductivity rating of 0.3 W/mK.

Their Teplo wall tie is made from low-conductivity basalt fibres and is ideal if your target is net zero!

Thermal Break Fixings

When you are fitting insulation to a wall the fixings of choice will be a plastic compound material that are drilled and tapped into place with a hammer. Sometimes called hammer-set fixings, these can be augmented with either a metal or other compound material screw or nail.

Covered with an insulating cap, any material that could contribute to a thermal bridge is isolated at either end, literally thermally broken, twice. Fischer’s Termo range of insulation fixings is a good example of efficient thermal break fixing.

Thermally Broken Windows

Aluminium, steel, and uPVC windows have been supplied with built-in thermal breaks for some time. The frames are usually insulated between the inside and outside to reduce heat transfer. The biggest issue with windows and doors is the glass portion, it’s true, although glass technology has improved considerably in recent years.

The update Part L of the Building Regulations means that the requirement for thermal performance for windows has increased from 1.6W/m2K to 1.2W/m2K. For manufacturers, this will mean improving the performance of their insulated window frames.

fitting thermally broken windows

Part L and Thermal Breaks

As part of the Part L Building Regulations, a contractor has to provide evidence of thermal breaks, detail the material used, and record any specific labelling such as will be found on double-glazed windows, cavity closers or thermally broken lintels.

Extra Help

Why not download our Prompt Sheet to help point you in the right direction for what to photograph, and when. The photographic records for Part L on any project should be pre-agreed with the designer, however, in all cases, the requirements will likely include the items included on our checklist.

If you have been asked to supply and install energy-efficient thermal breaks, thermally broken lintels, or other products to enhance compliance with the regulations, do not hesitate to get in touch.

Our team is here to help you get the best products at the best prices as conveniently as possible. We deliver kerbside across the UK, saving you time, and saving you energy too!
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