In this building survey series we cover flashings – flashings form an important part of building survey reports.
Flashings are used to weather junctions, such as to valley gutters or at the abutment of parapet walls and chimney stacks, these being a number of the most common flashing points. You will also see flashings on upstand details where say a flat roof meets a parapet wall.
There are three principal types of flashing used in the UK, the most common generally being a use of sheet lead, the second being a specialist valley tile which is used for valley gutters and the third being a cement mortar fillet, which is simply a mortar detailing. In terms of flat roofs and upstand details abutting flat roofs, this can commonly be a mineral felt detail. Mineral felt is generally limited to use on flat roofs rather than chimney, parapet or pitched roof flashings.
Lead is often the best flashing in terms of providing a weatherproof detail, but also in terms of longevity. However, it is also the most expensive.
Valley tiles are a good option where valleys require weathering and you want a seamless aesthetic across the roof.
In terms of the mortar fillet detail, this is often the least preferable option, but also is the cheapest option. A cement fillet detail is often found around the chimney and pitched roof abutment, but it is very much a brittle detail and will have very little longevity.
The use of lead if well maintained should give in excess of sixty years plus in terms of longevity.
Of course, on all flashings, the workmanship and detailing is absolutely key to achieving weather tightness and longevity.
Flashings are important in that they are the weatherproofing detail at the junction of different materials and often at the junction of difficult angles. Therefore, these are inherently weak spots in the structure for potential water ingress to occur. They are often neglected details.
Flashings are fully detailed and covered in our Building Survey reports.