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Technical Information

Hi-Therm Lintel Psi 0.06 W/m·K

Fig. 1 - Hi-Therm Lintel
Hi-Therm Lintel

A hybrid of Glass Reinforced Plastic (GRP) & Galvanised Steel

When combined, these two materials form the ultimate in lintel design.
Psi 0.06 W/m·K

Acier leads the way with the development of a completely unique lintel range to address the thermal requirements of new building regulations.

The benefits
  • GRP has very low thermal conductivity and therefore when used to support the outer leaf in cavity wall construction, cold bridging is significantly reduced.
  • Galvanised steel, which has a much higher load bearing capacity than GRP, is used to support the heavier load on the inner leaf of the cavity wall.
  • DPC is not required with the Hi-Therm Lintel
Key Performance Features
  • Outperforms all other lintels on Thermal Performance.
  • Outperforms even stainless steel for corrosion resistance.
  • Outperforms Stainless steel on price.
  • DPC is not required with the Hi-Therm Lintel

Building regulations require that lintels should be assessed for their effect on the thermal performance of a building. Thermal performance of a lintel is expressed in terms of Psi Values (ψ) i.e. linear thermal transmittance.

The thermal performance of the Hi-Therm Lintel has been evaluated by the Building Research Establishment (BRE) and achieved a Psi value of 0.06 W/m·K.

Psi Comparison Chart

To help understand the immense thermal benefits of the GRP lintel it must be compared to other lintel types.

Lintel type comparison table

BRE (Building Research Establishment) Logo

Testing of Acier's Hi-Therm Lintel was carried out by the BRE (Building Research Establishment) using Physibel's thermal analysis software TRISCO which complies with BS EN ISO 10211-1. The modeling follows the requirements of the BRE conventions document BR497.

Fig. 2 - Example Section: 90 - 105mm cavity
(also available to suit wider cavities)
An example Hi-Therm Lintel
Standard Load
Standard Load (HT/S 100) table

For information on Hi-Therm lintels to suit other applications please contact our technical team.

Heavy Duty Load
Heavy Duty Load (HT/HD 100) table

Standard Lintel Technical Info

Typical Construction Detail - See Figure 1 and Figure 2 below

Acier Lintels Unique Patented THERMAL BREAK PLATE explained:

This plate is unique in that it enhances the stiffness and structural capacity of the lintel yet performs thermally similar or better than lintels with no bottom plate.

Fig. 1

The Linear Thermal Transmittance for a Acier lintel in a typical cavity wall (see Fig. 1) Ψ = 0.26 W/m-k*

*Acier Lintel S/K-90 @ 2400mm Long Modelled by Building Research Establishment.

Acier HD/K-90 lintel range fitted with thermal break plate achieves same ψ value.
In carrying out the thermal modelling, Physibel Trisco software (version 11) was used.

Fig. 2

The Linear Thermal Transmittance for a Acier lintel in a typical cavity wall (see Fig. 2) Ψ = 0.3 W/m-k*

*Acier Lintel S/K-90 @ 2400mm Long Modelled by Building Research Establishment.

Acier HD/K-90 lintel range fitted with thermal break plate achieves same ψ value.
In carrying out the thermal modelling, Physibel Trisco software (version 11) was used.

THE DEFAULT (accredited) VALUE FOR THE Acier LINTEL IS 0.30 W/m-K

The Acier lintel incorporates a patented Thermal Break Plate which is perforated, but in addition has a unique castellated design that bridges the cavity along only 15% of its length. This ensures a low effective thermal conductivity for the plate of only 17 W/m-K. Thus Acier's unique Thermal Break Plate, when used in a range of typical cavity wall constructions, results in Linear Thermal Transmittance values of between 0.25 and 0.30 W/m-K.

Effectively Acier's unique Thermal Break Plate enhances the structural performance of the lintel whilst placing the lintel in the more favourable default category; Psi = 0.30 W/m-K


The loading tables in this brochure are the result of testing at the group’s premises under the supervision and direction of the British Board of Agrèment.

All tests were carried out in accordance with BS 5977 Part 2 1983 and BS EN 846–9:2000 and relate to the strength and torsional stiffness of lintels to sustain total uniformly distributed loads.

The loading tables shown for the L1 (where noted), L1/E, L5 and L11 lintels are the results of testing in accordance with BS 5977 Part 2 1983 and BS EN 846–9:2000, taking into account composite assistance from the surrounding masonry, this masonry should be of good quality (in accordance with BS 5628).

A lintel should not exceed a maximum vertical or horizontal deflection of 1/325 x the effective span, when subject to the safe working load.

Load ratio 1 - applies to loads with an inner to outer leaf ratio of between 1 :1 and 3 :1. This ratio is normally applicable to lintels that support:

  • Masonry
  • Masonry and timber floors

Load ratio 2 - applies to loads with an inner to outer leaf ratio of between 4 :1 and 19:1. This ratio is normally applicable to lintels supporting:

  • Constructions with concrete floors
  • Eaves applications

The L1 profile has been subjected to two fire tests by:

  • The fire research station, Boreham Wood.
  • The Warrington Fire Research Station.

In both cases one hour fire rating was achieved with the load successfully supported 48 hours later. Further details available on request.


The service life of lintels will be equal to the life expectancy of the building when installed with a flexible DPC and within the humidity and condensation conditions normally experienced in habitable buildings.

Lintels conform to the requirements of BS EN 845–2:2003 for corrosion protection, workmanship and materials. Acier lintels are rated by the Housing Association Property Mutual as satisfying the ‘35 years to first maintenance’ durability rating, laid down in the ‘HAPM Component Life Manual’.

Galvanised lintels - lintels are fabricated from galvanised steel to BS EN 10142 1991 Specification for continually hot dip zinc coated low carbon steel sheet and strip for cold forming: Technical advisory conditions, grade Fe P01 G, with a coating type Z600 giving a minimum coating weight (triple spot test) of 600g/m2; including both sides but with a minimum yield stress of 250 N/mm2.

Stainless steel - All Acier lintels can be manufactured with stainless steel.
Stainless steel lintels and expanded metal lathing are formed from Austenitic Chromium Nickel Steel to BS EN 10088-2 1.4301 (304S15) and require no additional corrosion treatment.
Higher grades of stainless steel can be supplied on request - BS EN 10088-2 1.4401 (316S31).


For the lintels to perform to the quoted loading figures and to meet the durability expectations included in this brochure, the following information MUST be adhered to:

  1. Lintels damaged in transit should not be used.

  2. Check the correct lintel is being installed.

  3. All bearing areas should be prepared using full bricks/blocks or padstones.

  4. Lintels should be installed with a minimum 150mm end bearing at both ends, be fully bedded on bricklaying mortar and levelled both longitudinally and horizontally. When limited end bearings are unavoidable, check with Acier technical office for suitability.

  5. Open back lintels should be filled with masonry in accordance with BS 5977 and a full block built in through the end bearing and allowed to cure before continuing building.

  6. The inner and outer leaves supported by the lintel should be raised together to avoid excessive eccentricity of loading. Masonry above lintels should be allowed to cure before applying floor or roof loads, if this is not achievable, temporary support in the form of props should be used.

    NHBC guidelines propose no greater than a 1m span for props during construction.

  7. When installing concrete floor units or other heavy components, care should be taken to avoid shock loading. Temporary support in the form of props is advisable if there is a limited amount of masonry to the outer leaf. Pre-cast floor units should be laid on a mortar bed to avoid load concentrations at high points in the masonry. Floor units should not be dragged into position.

  8. Point loads should not be applied directly to lintel flanges. Lintels should have a minimum of 150mm masonry between the flange and the application level of any form of loading.

  9. In accordance with BS 5628 and NHBC requirements, all external wall lintels MUST be installed with a flexible damp proof course with the exception of those adequately protected by an eaves overhang or similar form of protection. Stop ends should be provided as specified by BS 5628 Part 3 1985 and the NHBC to avoid moisture entering the cavity near the reveals.

    Proprietary stop ends should be used or alternatively the DPC should extend to the edge of the front toe and 50 - 150mm beyond the end of the lintel (depending on coursing) to allow formation of an integral stop end at a suitable perp joint. Weepholes should be used in the external masonry leaf to drain moisture away from the cavity. A minimum of 2 weepholes should be provided for each lintel, generally at 450mm centres. Weepholes can be formed with proprietary weep vents or by leaving perp joints open.

  10. Masonry should not overhang any flange by more than 25mm.

  11. The lintel toe must project beyond the window/door frame and it is recommended that a flexible sealing compound is used between the underside of the lintel flange and the frame to avoid moisture penetration.

  12. When the underside of a lintel is exposed, its appearance can be enhanced by the addition of lintel soffit cladding, supplied in white and brown, or by the application of a good quality etch primer and paint after installation.


To help ensure optimum performance and economy from lintel specifications, Acier provide a free expert advisory service, the service includes:

  1. Preparation of lintel schedules from drawings supplied.

    These drawings should include the following information if future revisions to the specifications are be avoided:

    1. Plans including dimensions (1:50 scale preferable)

    2. Elevations (1:50 or 1:100 scale)

    3. Sections (1:50 scale preferable)

    4. Floor joist layouts or PC concrete floor layouts and loadings (1:50 scale preferable)

    5. Roof layout, showing positions of girder trusses etc. (1:50 scale preferable)

    6. Any other relevant information, such as steelwork layouts etc.

  2. Provision of lintel location drawings.

  3. Provision of structural calculations for Building Regulation approval. We reserve the right to supply these only in reply to a written request from a Building Control Authority or upon the receipt of an order/letter of intent.

  4. Advice on the use of lintels in uncommon situations such as reduced end bearings, point loads and the like.

  5. Design and detailing of special lintels, see special lintel page 29.


Total UDL - This is the safe uniformly distributed load and indicates the total design load spread evenly along the length of the lintel including an approximate safety factor.

British and European Standards

Acier lintels are designed to meet all relevant standards: for manufacture BS 5977 Part 2:1983 and BS EN 845–2:2003; for galvanised steel BS EN 10142 1991 Specification for continuously hot dip zinc coated low carbon steel sheet and strip and for stainless steel BS EN 10088-2 1.4301 (304S15) cold rolled stainless alloys.

Agrément Certificate No 97/3343

The BBA have assessed the following lintels which are covered by the certificate: L1/S 50, L1/S 75, L1/S 100, L1/HD 50, L1/HD 75, L1/HD 100, L1/XHD 50, L1/XHD 75, L1/XHD 100, L1/S WIL 50, L1/S WIL 75, L1/S WIL 100, L1/HD WIL 50, L1/HD WIL 75, L1/HD WIL 100, L1/XHD WIL 50, L1/XHD WIL 75, L1/XHD WIL 100, L1/ST 50, L1/ST 75, L1/ST 100, L1/ST HD 50, L1/ST HD 75, L1/ST HD 100, L1/ST XHD 50, L1/ST XHD 75, L1/ST XHD 100, L1/S WOL 50, L1/S WOL 75, L1/S WOL 100, L7/50, L8/50, L9, BOX 75, BOX 100, BOX 140, BOX 200, L5/50, L5/75 and L5/100.

Quality Control:

Manufacturing facilities and quality control systems at Cwmbran have been successfully assessed by the British Standards quality inspectorate and the company has been awarded a Quality Assurance certificate to BS EN ISO 9002.

Hazard Identification
  • There may be a risk of cuts from sharp edges or projections.
  • Structural products must be installed in accordance with their specific instructions to prevent the risk of failure.
Handling, Storage & Disposal
  • Handling of materials must comply with the Manual
  • Handling Operation Regulations 1992.
  • Protective gloves should be worn when handling or cutting material to prevent injury from sharp edges.
  • Some products may have a film of mineral cutting fluid after manufacture, therefore carry out personal hygiene including proper washing of hands after contact.
  • Where structural products are to be removed from an existing installation, care must be taken to ensure that the procedure followed does not compromise the loading/installation restrictions applicable to the products.
  • No special disposal requirements, subject to local restrictions.

We are not aware of any risk to the person, arising from chemicals or any other substances present on or in our products.

Part L Compliance

Following numerical analysis, the British Board of Agrément has concluded that Acier’s steel lintels with continuous base plates do comply with the cold bridging requirements of Part L of the Building Regulations.


The expanded polystyrene core used in Acier Lintels has an ozone depletion potential of zero.

Part Of The Keystone Group