General Information
When designing and installing lead sheet, due consideration must be given to the following areas:
Physical and mechanical properties of lead sheet
-
Contact with Other Materials
- Bossing and welding methods
- Jointing methods
- Support and fixing methods
- Prevention of corrosion
Rolled lead sheet to BSEN 12588:1999 is commonly used on all types of modern and historic properties for:
- Flashings to abutments on flat and pitched roofs
- Weatherings to ledges and cornices
- Damp proof courses and cavity trays
- Linings to parapet and valley gutters
- Coverings to flat and pitched roofs
- Vertical cladding
- Cappings to parapet walls
- Cladding to dormer windows
- Many other specialist uses, such as radiation shielding and sound attenuation
Bossing, Welding, Jointing, Fixing, Corrosion
Bossing and Welding Methods
Lead sheet should
be carefully worked or welded so that the lead is not thinned by more than 25%
or weakened by creasing or stretching. Bossing and welding lead should be
carried out by experienced (preferably registered) operatives using the proper
tools and equipment.
It is important to check for compatibility when specifying
or using certain types of the following materials:-
Jointing Methods
Joints in leadwork are
weathertight but not watertight. Joints in leadwork are designed to keep water
out whilst allowing for thermal movement. It is therefore important that the
type of joint used is appropriate for the type of application or situation.
Support and Fixing Methods
Lead sheet
must be adequately supported on a smooth base sufficient to take the weight and
to allow for thermal movement to take place. It may be laid on timber, plywood,
concrete or masonry together with a suitable underlay. The lead sheet should be
held in position with fixings of a type, strength and position which:
- Support the weight of the lead sheet
- Are resistant to corrosion
- Allow for thermal movement to take place
- Resist wind uplift
Preventing Corrosion
Lead sheet is
resistant to most forms of corrosion likely to be encountered in a roofing
situation, but certain precautions need to be taken against the following:
Mortar: Unprotected lead damp proof courses and
cavity trays may corrode in the presence of moisture
Lichen Growth: The acid run-off from lichen or moss
on a roof may cause small holes to appear in the lead sheet under the drip-off
point from tiles or slates. A sacrificial flashing may be fitted to the lead
gutter or roof, or the growth may be treated with a chemical fungicide.
Condensation: In certain conditions the underside
of lead sheet may corrode and it is important to design the roof to reduce the
risk of condensation and provide adequate ventilation.
Properties of Lead Sheet
Physical and Mechanical Properties of Lead Sheet
Malleability - Lead is soft, malleable and
capable of being manipulated with hand tools and, by the technique of bossing,
can be worked into the most complicated of shapes or dressed to fit the many
types of profiled roofing tiles.
Fatigue and Creep Resistance - Attention to correct
sizing and fixing of individual pieces minimizes any risk of fatigue cracking or
creep. The chemical composition of rolled lead sheet is strictly governed by the
provisions of BSEN 12588:1999, which effectively control the grain structure to
make the lead sheet more resistant to thermal fatigue without affecting
malleability.
Durability and Thickness - When specified and
fitted correctly, rolled lead sheet can continue to provide a maintenance free
weather shield for 100 years. Rolled lead sheet is therefore extremely resistant
to atmospheric corrosion. The ideal thickness and size of each piece is
determined by the application.
Thicker sheets may be required:
- when dressing lead into deeply profiled tiles in areas of
frequent foot traffic
- on flat roofs and gutters where extra rigidity is required
to resist wind uplift
- Thermal Movement; Lead sheet has a high coefficient of
linear expansion and therefore due allowance for thermal movement must be made
in the design, layout, sizing of panels and fixing details to maximize
performance.
Fire Resistance - Lead is incombustible but melts
at 327.4°C.
Recyclability - Rolled lead sheet is totally
recyclable. Scrap material is recovered from end of life buildings in the UK by
a national network of reclamation merchants and channeled back to the
manufacturers where it is carefully refined back to new feedstock for the
rolling mills. The established recovery network, constant recycling of old
material and low melting point with resultant energy efficiencies in
manufacturing means the lead sheet industry has a solid reputation for
environmental awareness and as a conserver of natural and energy resources. |
