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Property Surveying Blog

April 29, 2019

Typical Roof Defects

Written by Sadek Miah

In this Blog post I will be discussing typical roof defects and some of the causes.

A roof has many functions, however the most important of all is to protect the building beneath from weathering.

In order for a roof to fulfil its function it should meet certain criteria. These criteria points can be seen below;

  • Strength – It must be capable of supporting its own weight as well as any additional load such as rainwater, snow, plants, debris etc.
  • Stability – The roof should be designed so that it is not to be moved or movable or cause instability throughout the rest of the building.
  • Durability – The materials used should be capable of lasting a considerable amount of time without becoming defective.
  • Weathertightness – This can be considered as one of the most important as the roof must prevent moisture penetration.
  • Thermal Efficiently – This may not be seen as important as the aforementioned points however, in recent years thermal efficient materials are used to enhance the function of a roof for completeness.

When discussing roofs we often consider the importance of it and how vital this part of the building is in comparison to the rest of the other elements of a building. It is probably considered as the most important element of a building except for perhaps the foundations. This is because a poorly designed or defective roof inevitably has an adverse effect upon one or more elements elsewhere in that building.

There are a number of reasons why a roof may be defective; It can occur from the early stages such as poor design and construction to poor maintenance. Roofs can also become defective due to other defective elements of a building such as a failing load bearing wall.

Typical Roof Defects 

Slipped and broken tiles/ Tile Delamination

This is quite a common issue found in defective roofs. It is usually caused from weather conditions. Heavy winds and storms can slip tiles out of place or even damages them. Rainfall can corrode nails that are holding slate tiles in place which may consequently displace the tile leading to further damages to the timber it is fixed to or internally. This is usually a quick fix as single slipped/broken tiles can be replaced.

Blocked Valleys and Gutters

Valleys and gutters can get blocked with leaves and debris. This can cause overflowing into the eaves of the building or into ceiling cavities. You may notice that where the blockage has occurred there is likely to be mirrored water damage internally if left untreated for a considerable amount of time. Again, this is relatively cheap and quick to fix as you just need to clear the blockage.

Lichen and Moss Growth

Lichen and moss can grow on surfaces of roofs, especially if it is situated in a damp and shaded position, overhung by trees. If lichen and moss growth is present on roof coverings then it is a good indication of high levels of moisture. This may in turn cause or contribute to damp and humidity issues internally as lichen and moss holds in moisture which works against the function of the roof covering as it is meant to help water flow freely down the slopes, valleys and into the gutters on a pitched roof.

Roof Sagging

Excessive weight load on a roof is one of the most common reasons as to why roofs sag. Every roof is designed to withstand a certain load and if exceeded this may cause the roof to sag. Properties originally made with slate and clay tiles were able to withstand the load of the tiles. Sagging in roofs typically occurs when tiles are replaced by concrete tiles as the previous tiles typically reached the end of their life expectancy and concrete tiles were quicker and easier to install. However, they were considerably heavier than slate and clay tiles which caused rafters to bow and in turn causing sagging. This is a common problem in recent years once concrete tiles were more predominantly used. A solution to this is to reinforce the roof timbers with additional purlins and struts.

Flat Roof Pooling

Roof pooling or ponding is quite a common occurrence with flat roofs. It may seem harmless but over a substantial amount of time this can have adverse effects on buildings.

Any unevenness in the covering may prevent free flowing drainage which can lead to ponding. This may cause roofs to sag, increase the likelihood of leaks, provide a suitable habitat for the growth of moss and deteriorate roof coverings which weaken much faster in the presence of water. One of the reasons this may also occur is if a roof pitch is not aligned properly. This means that this needs to be resurfaced once aligned correctly. Ponding can attract insects and larvae which can also attract birds. This may cause birds to peck away at the roof covering which can cause further damage to fabric based coverings.

Roofs are an essential part of all buildings and it is important to ensure that it is maintained properly to increase the longevity of roofs and their coverings. If you feel that you may have a defective roof or something developing into an issue then feel free to give one of our surveyors a call and we will be happy to advise.