Standard Lintel Technical Info

MATERIAL

Keystone Lintels are manufactured from Z1 grade galvanised steel to BS 2989: 1982 (BS EN 10327: 2004) with a zinc coating type G600 (H3) giving a minimum zinc coating of 600g/m2 (including both sides).

In accordance with BS5977: part 2, 1983 (BS EN 845-2: 2003) all cut edges are treated with a corrosion resistant paint.

THERMAL PERFORMANCE

Typical Construction Detail - See Figure 1 and Figure 2 below

Keystone 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 Keystone lintel in a typical cavity wall (see Fig. 1) Ψ = 0.25 W/m-k*

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

Keystone 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 Keystone lintel in a typical cavity wall (see Fig. 2) Ψ = 0.3 W/m-k*

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

Keystone 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 Keystone LINTEL IS 0.30 W/m-K

The Keystone 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 Keystone'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 Keystone'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

QUALITY

Keystone Lintels are manufactured to the highest quality and are continually assessed by the BSI to ensure our quality assurance systems comply with BS EN ISO 9002: 1994. The ‘Keystone People’ are also a highly trained and motivated workforce.

Our manufacturing premises have been approved as a N.V.Q. Training Centre and the company has also received the Investors In People Accreditation.

STRUCTURAL PERFORMANCE

The Keystone Lintel range have safe working loads shown in each applicable loading table, taking into account the differential loading arrangements which are common to traditional cavity wall construction.

Differential Load: 3:1 ratio, 75% load on inner leaf.

Differential Load: 19:1 ratio, 95% load on inner leaf.
Lintel Types HD/K, S/K-50 (215WIL), S/K-70 (215WIL), S/K-90 (215WIL), S/K-110, S/K-130, S/K-150, SB/K, T/K, SL/K, RB/K, TJ/K, TW/K, INT/K, SW/K, IB/K, CFS/K, X/K, EL/K-50, EL/K-90 have been tested as a composite unit with surrounding masonry, built in accordance with BS5628. These composite units have been tested in accordance with the requirements of BS5977: part 2 1983.

TESTING

BBA - Extensive testing has been carried out on the Keystone range of lintels. The lintel testing procedure and Agreement Board assessment is carried out under the direct supervision of Dr. David O’Connor BSc, C.Eng, MIStrut E, MICE, Lecturer, Dept of C.Eng, University of Ulster.

Fire Test - The Keystone S/K & P/K lintel ranges have been subjected to fire tests at the Warrington Fire Research Station and have achieved a one hour fire certificate by successfully supporting their imposed load for 48 hours after the tests.

Durability - The service life of lintels shall be the same as that anticipated for the building within which they are used, when used in conjunction with a flexible D.P.C. and where the normal humidity and condensation levels of a habitable building exist. The Keystone Lintel range complies with the technical requirements of the Housing Association Property Mutual (HAPM) with appropriate adjustment factors.

INSTALLATION

Lintels should be installed with a minimum end bearing of 150mm bedded in mortar, levelled along its length and across its width. With cavity walls, both leaves should be raised together to avoid excessive eccentricity of loading and be allowed to cure before applying floor or roof loads. Blockwork is permitted to overhang the lintel flange by a maximum of 25mm. Point loads and concrete floor units should not be applied without prior consultation with our Technical Department or a Structural Engineer. Care should also be exercised in the selection of lintels for each application with regard to wall construction, cavity width and loads applied.

COSHH - All components and materials in our products are considered as non-hazardous to health under normal conditions of use as determined by COSHH Regulations 1994.

Due care should be taken when lifting and handling lintels with regard to weights. A table of weights for individual lintel types is available on request. For further information contact our Technical Department.

A cavity tray should be installed over all openings in external cavity walls.