How to Prevent Common Parapet Issues

Most flat roofs have a parapet. They bring with them many benefits:

  • They protect the entire roof system from wind-uplift
  • They can improve building aesthetics by making buildings appear taller and more uniform
  • They hide necessary roofing materials including drains and vents
  • They protect furniture and other objects from falling off the roof (If the roof is being used as a public space or terrace)

Parapets certainly have their uses. But, as great as they can be and as essential as they often are for flat roofs, they can cause problems.

If not fitted correctly and with the appropriate fixings, parapets can lead to serious damage to the roof, structure and façade. Fitted correctly, however, these issues can be avoided.

Here is how to prevent some of the most common problems with parapets.

1. Water ingress is getting in beneath my roof membrane

When water gets in beneath your roof membrane, it can cause bubbling, mould and rotting of the roof substrate. These issues can reduce the thermal efficiency of the insulation, causing damage to the roof structure and creating a damp atmosphere within the building, making it unsafe to live and work in.

To ensure the parapet wall is truly waterproof, ensure the membrane is dressed right over the parapet wall.

This can be done either by dressing the membrane to the edge of the parapet and terminating it with a roof edge trim or it can be done before a capping is applied.

Whichever method is chosen, an entire roof – if correctly dressed – will be covered by the membrane manufacturers guarantee, ensuring one of the most vulnerable areas of the roof is well covered.

Skip this step at your own risk: a ‘waterproof’ roofing membrane is only really waterproof if it has been installed with care.

2. Staining slowly ruining your building’s façade

The parapet is where the roof meets the wall. If water has nowhere to go, it can – and will – run down the side of your building.

We’ve all seen water-stained walls and there’s no denying it can completely ruin the look of a building: making it look shabby and run down.

It is therefore essential that – firstly, there is a slope on top of the parapet so water doesn’t pool and secondly, that a drip edge has been used to ensure that all water runoff from the parapet falls well clear of the building.

Extra points if the top of the parapet slopes away from the leading edge, keeping water off the parapet and allowing it to the drain via outlets on the flat roof.

3. I’ve got a leak!

Leaks can quickly ruin a parapet wall. They can ruin a whole building if left unfixed.

A small leak which has made its way into brickwork will freeze during cold weather and then thaw, breaking up the wall. Repeat this process over and over and you’ve got yourself a problem which is very costly to fix.

One of the best ways to eliminate the possibility of leaks is to dress membranes right over parapet walls, with roof edge trim along the outside edge of the parapet.

When membranes aren’t dressed to the edge of the parapet, capping is often the only protection the parapet has against the elements.

Not the best idea!

Joints between the lengths of parapet capping allow water to penetrate which results in a rotting, failing parapet.

Ultimately, you can prevent these issues by:

  • being careful during installation
  • using quality fittings and finishes
  • ensuring everything is well maintained by the building owner

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