Lintels

Lintels outlined

The purpose of lintels is to provide carry the masonry above an opening in a wall, and transmit the load to the wall either side of the opening. Lintels must be used above doors and windows, as the frames alone are not capable of carrying the load.

High stress in masonry can be caused by narrow piers between openings, the width of these piers needs to be controlled. Refer to Technical Guidance Document A of the Building Regulations for more information and guidance. In cases where the lintel span is greater than 3m, design by an engineer may be necessary. The engineer used must be qualified by examination, be in private practice, and possess professional indemnity insurance.

The two most common types of lintel are:

1) Pressed metal lintels.

2) Precast composite lintels

Pressed Metal Lintels and bearing details

With regard to corrosion protection, end bearing, load, water ingress, load capacity, fire and thermal properties, the manufacturer’s instructions as set down in the appropriate agreement certificate should be adhered to while installing.

Typical minimum bearing and DPC requirements are illustrated.

Diagram C1 - Typical pressed metal lintel detail

Diagram C2 - Typical pressed metal lintel - span is less than 2.25m

Diagram C3 - Typical pressed metal lintel - span is greater than 2.25m

Manufacturer’s requirements should be checked for bearing conditions. Weep-holes must be provided at 450 mm centres where the outer leaf is brickwork or fair faced concrete.

Closing Cavities

Cavity barriers should be provided to fire stop around openings in cavity walls in accordance with the following:

  1. At the top of an external cavity wall (masonry or framed construction) including any gable wall.
  2. Vertically at the junction of separating wall and any such wall with an external cavity wall
  3. Above the enclosures to a protected stairway
  4. Around all openings (windows, doors, vents, service boxes etc.) in framed construction.

Where a separating wall meets an external wall, the junction should be fitted with a cavity barrier, or where no cavity exists, maintain the fire resistance of the separating wall, or in the case of external insulation systems a fire stop within the insulation in the plane of the separating wall.

Note:

The details shown below apply to detached houses.

Diagram C4 - Typical cavity closing details - metal lintel closer

Diagram C5 - Typical cavity closing details - plasterboard closer

Diagram C6 - Typical cavity closing details - cavity closer block

Diagram C7 - Typical cavity closing details - cill

Composite Lintels

Guidance outline

The guidance detailed below should be followed when designing and constructing composite lintels from prestressed concrete lintels acting together with solid block or in-situ concrete.

In a composite lintel, the prestressed lintel works with a zone of blockwork or in-situ concrete laid on top to provide support. The prestressed lintel, much like the steel in a reinforced beam, resists the tensile force while the blockwork resists the compressive force.

This is the where the terms ‘composite lintel’, ‘compression blockwork’ and ‘compression zone’ come from.

It should be noted that a lintel is deemed to have no strength prior to blockwork or in-situ concrete being built above it.

Table C1 - Typical prestressed lintel specification

Diagram C8 - Measurement of roof and floor spans for determining floor and roof loads

Requirements and Walling Materials

Lintels should be manufactured in accordance with I.S. EN 845-2 2003 + A1 2013 Specification for ancillary components for masonry – Part 2: Lintels.

Walling Materials

Concrete blocks: Should comply with EN 771-3: 2011 +A1 2015 Specification for masonry units Part 3: Aggregate concrete masonry units (Dense and light-weight aggregates).

Mortar: Should comply with EN 998-2: 2016 Specification for mortar for masonry - Part 2: Masonry Mortar. 1:1:6 Cement/lime/sand or 1:6 Cement/sand (with plasticiser).

In-situ concrete: Should comply with EN 206-1: 2016, Concrete: Part 2: Specification, performance, production and conformity. Characteristic cube strength 30 N/mm^2^.

Lintel bearing

150mm bearing required when lintel span is less than 1.5m; 200mm required where lintel span is between 1.5 and 3m.

Lintel bedding

At supports, bed lintels in mortar and where possible construct lintels so that they bear on full, solid blocks where possible.

Propping during construction

Until masonry or concrete above lintel has matured, lintel must be propped at no more than 1.2m intervals. Lintels must be propped at 1.2m centres (maximum) until composite masonry or concrete has matured.

Filling of mortar joints

Ensure all vertical and horizontal joints in the masonry in the composite lintel area are fully filled. In composite lintels, shell bedding is not allowed.

Placing of in-situ concrete

When placing in-situ concrete into the watertight shutter, ensure that the shutter is wetted before placing the concrete and also that the workability of the mix allows the concrete to be fully compacted and vibrated.

215mm hollow block walls

In the masonry area of composite action, solid blocks must be used.

Joist hangers, DPC etc.

In the area of the composite action no loads can be imposed by floor joists, joist hangers, DPC or any other ancillary components. DPC should be built outside the compression zone.

Diagram C9 - Typical DPC installation around lintels

Cavity walls

In order to avoid a cold bridge, each leaf of a cavity wall should be built on a separate lintel. In the area of composite action, provide wall ties at 225 mm vertical centres.

IMPORTANT NOTE

Within the compression zone, in the blockwork course never leave out or cut out any openings for services above the prestressed lintel.

Assumptions with respect to design and load

Timber floor loads

The following design guidance is applicable for use for domestic dwellings with timber floors up to 3 storeys.

NOTE: This guidance does not cover lintels supporting concrete floors.

Design table assumptions

The following assumptions have been made when preparing the design tables detailed throughout this section:

Timber floor loads without partitions

Self weight of floor - 0.30 kN/m^2

Imposed load - 1.50 kN/m^2

Total floor load - 1.80 kN/m^2

Timber floor loads with partitions

Self weight of floor - 0.30 kN/m^2

Imposed load - 2.50 kN/m^2

Total floor load - 2.80 kN/m^2

Applied floor load on lintel

Table C2 - Applied floor load on lintel

The applied load in the table above is calculated as the total floor load multiplied by half the floor span.

Pitched roof loads

The following design guidance is applicable for use for simple plan domestic roofs with timber floors up to 3 storeys.

Roof construction

Timber trusses are used in modern roof construction to spread the roof load to the supporting walls, the table below details the roof load to be applied in these situations. In traditional roofs, struts and purlins are incorporated to spread some of the load to internal walls. In cases like this, reduce the loads given in the table below by a third.

Note: No reduction can be made if there are no purlins.

Table C3 - Applied roof load on lintel - up to 45 degree pitch

The applied load in the table above is calculated as the relevant roof load multiplied by half the roof span.

Assumptions made in assessing dead and imposed loads in roof construction:

Dead load on slope

Concrete tile roof – self weight: 0.68 kN/m^2;

Fibre cement slate roof – self weight: 0.25 kN/m^2

Dead load on plan

Ceiling ties: 0.25 kN/m^2

Imposed load on plan

Roof pitch 0° to 30°: 0.75 kN/m^2;

Roof pitch 30° to 45°: 0.75 to 0.0 kN/m^2

Due to the fact that for increasing pitch the imposed load decreases sufficiently to balance the increasing dead load, the roof load can be simplified up to 45 degree pitch. For concrete tiled roofs, load is 2.0 kN/m^2 and for fibre cement slated roofs the load is 1.6kN/m^2.

Masonry composite lintels in cavity walls

Table C4 - Composite lintels of masonry in cavity walls

Diagram C10 - Typical window head detail - ground floor - masonry lintels in cavity walls

Diagram C11 - Typical window head detail - first floor - masonry lintels in cavity walls

Masonry composite lintels in 215mm walls

Table C5 - Composite lintels of masonry in 215mm walls

Diagram C12 - Typical window head detail - ground floor - masonry lintels in 215mm walls

Diagram C13 - Typical window head detail - first floor - masonry lintels in 215mm walls

In-situ concrete composite lintels in cavity walls

Table C6 - Composite lintels of in-situ concrete in cavity walls

Diagram C14 - Typical window head detail - ground floor - in-situ concrete lintels in cavity walls

Diagram C15 - Typical window head detail - first floor - in-situ concrete lintels in cavity walls

In-situ concrete composite lintels in 215mm walls

Table C7 - Composite lintels of in-situ concrete in 215mm walls

Diagram C16 - Typical window head detail - ground floor - in-situ concrete lintels in 215mm walls

Diagram C17 - Typical window head detail - first floor - in-situ concrete lintels in 215mm walls

Dormer Roof Construction

Lintels directly below roof level in a dormer roof construction are required to support floor loads as well as the roof loads; floor loads should also include partition loads where relevant. A dormer roof refers to roof construction where the roof space is used as living space.

Calculate the additional load imposed by the floor of the dormer using Table C2, then add this to the roof load (which is taken from Table C3) and use the sum of the two to calculate the depth of composite lintel required.

For dormer roofs, the reduction for cut roof construction in Table C3 is not allowed.

*Diagram C18 - Measurement details for roof and floor spans - dormer construction *

Important Note:

  1. In the area of composite action, only use solid concrete blocks or bricks.

  2. In the area of the composite action no loads can be imposed by floor joists, joist hangers, DPC or any other ancillary components. DPC should be built outside the compression zone.

Table C4A - Composite lintels of masonry in cavity walls

Cast In-Situ Reinforced Concrete Lintels

Use Table C8 in any situation where case in-situ reinforced concrete lintels are being used. Table C8 gives guidance regarding ope span.

Table C8 - Cast in-situ reinforced concrete lintels

Diagram C19 - Cast insitu reinforced concrete lintels

Metal Support Angles to Outer Leaf

Use Table C9 for guidance where metal angles are used to provide support to the outer leaf. Table C9 gives guidance on ope span and angle dimensions to be used.

Table C9 - Metal support angles to outer leaf

Stainless or galvanized steel metal lintel angles may be used in accordance with the manufacturer’s recommendations with regard to loading and span.

Diagram C20 - Metal support angles to outer leaf