Parapet Cappings
Cappings are flashings used to cover the top of a parapet wall to protect the wall from the ingress of moisture. As leaks in parapets are often not immediately noticed and can result in damage to the structure if not quickly detected, good design, installation, and maintenance of parapet caps are important.
Parapcap Expansion Provisions
To maintain the integrity of laps, adequate expansion joints must be provided as per this table.
| Parapet flashing design | Expansion joint positioning |
|---|---|
| Fixed aluminium | Every 6 m |
| Clip-fixed aluminium | Every 12 m |
| Fixed steel | Every 12 m |
| Clip-fixed steel | Every 20 m |
| Internal and external corners | Within 2 m of each corner. |
The corner of the wall is a fixed point for the capping, and as thermal movement can only occur in one direction away from the corner, an expansion joint should be provided as shown for length in either direction exceeding 2 metres.
Clip-fixed parapet are preferable where leaks will cause damage to the structure as having free provision for expansion will reduce the amount of stess on the joint fastneners.
Fixed cappings must not be fastened to the structure through the top of the capping, but can be fixed on one or both vertical legs by one of three methods. Having a clip fastened outer edge will minimise rippling of the face but will not allow the free movement of a clip fastened option.
- The capping is fastened to the parapet on both sides using screws with embossed washers through oversized holes.
- A continuous cleat is fastened on the exterior face of the wall with an open hem at the drip for ease of application. After the exterior face of the capping is hooked to the cleat, the capping on the interior side is secured to the parapet using fasteners with embossed washers through oversized holes.
- Intermittent clips are fastened to the exterior face of the wall at 600 mm centres. All cleats and clips should be accurately aligned by string line during installation
Instead of chasing into the wall or using a faced-sealed flashing, the preferred detail is to cover the inside of the parapet wall with vertical ribbed metal or other cladding material, used in conjunction with an apron flashing and parapet cap. (See Vertical Cladding (Parapet Flashing and Detail)
Parapet Cap Slope
Parapet cappings that follow the slope of the roof do not require any fall across its width, but transverse parapet cappings must have a positive slope of onto the roof side to avoid ponding and encourage free draining. This slope should be 3 – 5°. Parapet cappings wider than 300 mm can fall both ways, with the drainage slope provided on each side.
- Log in to post comments