Velux Roof Window Flashing - Ken's Guide
House roofing generally comprises the combination of a number of
materials and surfaces aimed at maintaining a barrier between
inside the house and the external weather. The hardest weather
element to control is water since water is particularly invasive.
Roof flashing is generally used as the final barrier against water
penetration.
Flashing comprises the intersections and terminations of roofing
systems and surfaces to prevent water penetration.
Roof flashing is generally installed around roof windows
valleys, chimneys, eaves, rakes, skylights, ridges, and at roof to
wall intersections. In all cases, effective flashing should resist
all three drivers of water penetration: gravity, surface tension
and wind pressure. As a result, flashing materials must be durable,
low maintenance, weather resistant, able to accommodate movement
and maintain compatibility with adjacent materials.
Roof flashing materials generally fall into one of two
categories: membrane or sheetmetal. Commonly used roof flashing
materials include aluminium, copper, lead-coated copper, lead,
stainless steel, galvanized steel, zinc, and Galvalume.
Roof Window
Flashings
As mentioned, flashings are required for roof windows. Roof
window flashings come in grey aluminium as standard to
match the window profile, with the options of copper, titanium
zinc and coloured aluminium.
Choosing the right flashing for a roof window requires three
questions to be answered:
- What is the pitch of the roof, ie. the angle of the roof's
slope?
- What is the existing roof made of? Eg. is the roof made of tile
or slate?
- How thick are the existing roof tiles?
The following table breaks the decision down into simple
components:
