Lead is a chemical element with the symbol Pb and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cut, lead is silvery with a hint of blue; it tarnishes to a dull grey color when exposed to air. (Source: Wikipedia)
Lead in the Building Trade
Lead is the most durable material and resists the impact of the weather.
In the UK lead flashing and fittings are still readily available, despite the environmental concerns associated with bulk use of this heavy metal. The Lead Sheet Association supports its recyclability and extreme durability, 500 years, compared to modern materials that can fail within 20 years. As with all metals the price fluctuates and lead remains an expensive building material but one that will last a lifetime and more. BS 6915 specifies the correct design and construction of lead sheet roofs and wall coverings.
Lead colour codes
Lead and Other Materials – A Brief History
Before the availability of sheet products for flashing carpenters used creative methods to minimize water penetration such as angling roof shingles away from a joint, placing chimneys at the ridge, and building steps into the sides of chimneys to throw off water. Birch bark was occasionally used as a flashing material.
The introduction of manufactured flashing decreased water penetration at obstacles such as chimneys, vent pipes, walls which abut roofs, window and door openings; therefore making buildings more durable and reducing indoor mould problems.
Flashing may be exposed or concealed. Exposed flashing is usually of a sheet metal such as lead, aluminium, or copper, galvanized steel, stainless steel, zinc alloy, tern, lead-coated copper, or other architectural metals. Metal flashing should be provided with expansion joints on long runs to prevent deformation of the metal sheets due to expansion and contraction and should not stain, or be stained by, adjacent materials or react chemically with them.
Flexible, adhesive backed, flashing materials can be used around wall penetrations such as window and door openings. Types of flexible flashing products are rubberized asphalt, butyl rubber and acrylic. The different types have different application temperature ranges, material adhesion compatibility, chemical compatibility, levels of volatile organic compounds, durability to ultra-violate light exposure. No flexible flashing material is designed to remain exposed like metal flashing materials. The adhesive backing is helpful during installation but should not be relied on for full protection against water penetration.
Copper is an excellent material for flashing because of its malleability, strength, soldering ability, workability, high resistance to the caustic effects of mortars and hostile environments, and long service life. This enables a roof to be built without weak points. Since flashing is expensive to replace if it fails, copper’s long life is a major cost advantage. Cold rolled 1/8”-hard temper copper is recommended for most flashing applications. This material offers more resistance than soft copper to the stresses of expansion and contraction. Soft copper can be specified where extreme forming is required, such as in complicated roof shapes. Thermal movement in flashings is prevented, or is permitted only at predetermined locations. The discolouration of copper also adds to design effect.
Soft zinc is another flashing alternative gaining popularity. Soft zinc is an exceptionally malleable material, making it extremely useful for complex roofing connections. This material provides normal soft soldering capabilities and delivers easy folding. Soft zinc is a sustainable solution for replacing lead flashing. This environmentally friendly material is completely recyclable and provides 100% clean run off.
Lead Flashing is used in different areas:
Roof flashing is placed around discontinuities or objects which protrude from the roof of a building (such as pipes and chimneys or the edges of other roofs) to deflect water away from seams or joints and into valleys where the runoff is concentrated.
Wall flashing may be embedded in a wall to direct water that has penetrated the wall back outside, or it may be applied in a manner intended to prevent the entry of water into the wall. Wall flashing is typically found at interruptions in the wall, such as windows and points of structural support.
Sill flashing is a concealed flashing placed under windows or door thresholds to prevent water from entering a wall at those points.
Roof penetration flashings are used to waterproof pipes, supports, cables, and all roof protrusions. Stainless steel penetration flashings have proven to be the longest lasting and most reliable roof flashing type.
A structure incorporating flashing has to be carefully engineered and constructed so that water is directed away from the structure and not inside. Flashing improperly installed can direct water into a building.