When a hot roof surface is suddenly cooled by rain the pressure in the area between the vapour barrier and roof covering can fall below atmospheric.
Flat lead roof build up.
The fixing of lead sheet is carried out in many different ways all of which are dependent on the particular application.
For instance a lead bay on a roof with a pitch of up to 3 degrees differs in the arrangement and position of its fixings when compared to the same bay on a higher pitch.
Some carry warranties of up to 20 years approaching those for sloped roofing.
Correctly laid lead roof greyfriars roofing note the height of steps between bays the rolled joints and adequate overlaps problems.
Others would treat even steeper pitches as flat roofs.
The basic construction of a flat roof starts with roofing timber that is laid across two upright items usually two walls.
The definition of a flat roof according to bs 6229 is having a pitch less than 10 o to the horizontal however some in the industry would consider up to 15 o as their definition of a flat roof.
Fortunately modern materials for covering flat roofs have improved considerably over the past two decades.
Should the ceiling below also have downlighters the vcl could be seriously damaged and therefore virtually useless.
They require a root barrier to stop the plants interacting with the waterproofing beneath and a flat roof in particular requires a drainage layer to retain water.
Lead is commonly used for flat roofs because of it s long life and ability to be formed to fit many positions lead must be laid and formed correctly to achieve this long life however.
Coupled with some edging features to stop the vegetation leaking away this makes a green roof build up quite.
Warm flat roof fully packed with insulation to prevent any condensation build up.
However there is a lot more to them than a normal flat roof.
More about lead as a building material.
Investigative work carried out on warm roofs covered in lead has shown that in rare instances moisture can also be introduced by the development of sub atmospheric pressure in the roof space.
Having a manual for warm flat roof construction with details and a summary of rules to follow helps.
Given that the specially selected insulation layer is loose laid it will require ballasting to guard against wind uplift or floating in wet conditions.
When building a flat roof it is vital that a degree of falls is built into the construction to ensure rainwater run off.
Where insulation above the roof void allows the air underneath to stay warm avoiding condensation but also allows for an air flow should one be deemed to be required through the joists.
In a cold roof build up the vcl normally ends up on the underside of the joists or rafters and is punctured many times when covered over by the internal finishes.
The vcl in a warm roof.
This can lead to underside corrosion.
