Design of Parapet As Per British Standards - Materials and Construction Details

Materials for Parapet Construction

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1. Bricks and Blocks for Parapet Construction

Bricks and Blocks Dense aggregate concrete blocks to BS EN 771-3 are normally sufficiently frost resistant for use in UK locations. F2, S1 or F2, S2 clay bricks to BS EN 771-1 are recommended in order to minimize the risk of frost attack. Under some circumstances F1, S1 or F1, S2 clay bricks to BS EN 771-1 may be used.

2. Mortar for Parapet Construction

A mortar mix of 1 part Portland cement, ½ part lime and 4½ parts sand (a 1: ½:4½ cement: lime: sand (CLS)) is recommended for use in parapet walls constructed from F2, S1 or F2, S2 bricks. If the wall is built with concrete blocks it is likely to be rendered and a 1:1:6 CLS mortar should be acceptable. If the wall is constructed from F1, S1 or F1, S2 bricks use 1: 1: 6 CLS. 

BRE Digest 362 provides further information about building mortars. The choice of sand is very important in ensuring a good bond between the units and the mortar. BRE recommends the use of a well graded building sand with a low fines content. 

3. Damp Proof Courses and Cavity Trays for Parapet Construction

Damp proof courses and cavity trays must have good bonding properties to the masonry

4. Cappings and Copings for Parapet Wall Construction

Use frost resistant copings to BS 4729, or other copings to BS 5642. In all instances, copings must include an adequate overhang and include a drip. Capping and copings should be capable of being mechanically fixed to the parapet wall. A number of manufacturers produce suitable systems, including preformed metal and GRP capping. Render should not be applied to the upper surface of the capping or copings on parapet walls.

5. Joint Sealants

Joint sealants should be selected according to BS 6213.

Design of Parapet As Per British Standards - Materials and Construction Details

Construction guidelines for Parapet Wall Construction

Stability of Parapet Wall Construction

Wherever possible, parapet walls should not be free standing; they should incorporate returns at each end or be tied into adjacent structural elements. To ensure that parapet walls are as stable as possible, wall ties must be used at the following centres in them: horizontal spacing - 450mm; vertical spacing - 225mm. Where panels are structurally isolated because of the presence of movement joints, slip ties should be incorporated across the joint. The positioning of the slip ties must not affect the subsequent sealing of the joint.

Masonry for  Parapet Wall Construction

Follow accepted good workmanship practice guidance given in BS 5638-3 and BS 8000-3. Use bricks frog up, finishing the mortar pointing with a bucket handle profile. Use stainless steel wall ties. If there is to be a render finish (usual with blockwork), ensure that the joints are raked back by 10mm to 12mm prior to applying the render to provide a good key; with brickwork, do not render both faces of the parapet wall as this is likely to extend the periods during which the wall will remain damp. When applying render, dampen the masonry to reduce the initial dewatering of the render. Protect new masonry from rain, frost and wind.

Positioning of Slip Ties for  Parapet Wall

Slip ties should be used whenever a parapet wall abuts an adjacent structural element and across any movement joints that are incorporated in its construction. The slip ties should be made from stainless steel. Three slip ties should be positioned through the height of the wall, and at third points, but not at greater than 225mm vertical spacings. The upper tie should be positioned in the mortar bed of the course below the DPC. 6The remaining ties should be positioned ⅓ and ⅔ of the distance from the cavity tray to the upper slip tie.

Loading for Parapet Walls

Parapet walls will be subjected to wind loads. Wind loadings should be calculated according to the procedures in BS 6399-2. Where the parapet wall is also to act as a safety barrier the appropriate horizontal loadings should be calculated to BS 6399-1. Procedures for designing masonry for particular loadings can be found in BS 5628-1. 

Allowing for Movement for Parapets

Movement joints must be incorporated at appropriate intervals, BS 6093. The spacing of the movement joints in the parapet walls should mirror those in the walls directly below them, where they are present. 

Jointing For Parapet Walls

Joints should be designed according to the procedures described in BS 6093 and sealed according to the procedures described in BS 8000-16.

Content Source and Copyright: Guidance document on parapet walls BD2452 – Safety of Masonry Parapets

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