Specification Clauses

The advisory service is based at the LSA’s Technical Office in Kent, and is there to provide technical guidance and assistance to help others obtain the best performance from BSEN 12588 rolled lead sheet. Technical officers are there to be consulted and offer independent advice and guidance, based on many years of experience, which has been developed through on-site investigations and research, into the performance of an outstanding long enduring roofing and weathering material. The following clauses will be of particular value to Architects and Surveyors.

MA – Materials and Accessories

  • M1 Type and thickness of Lead Sheet
    Lead sheet shall comply with the requirements of BS EN 12588 for lead and lead alloys-Rolled lead sheet for building purposes.
  • MA 1 Clips
    The free edge of the lead flashing must always be ‘adequately clipped’ to prevent lifting and distortion in high wind conditions, Adequate clipping will depend on the location, orientation and exposure of the building and these, in turn will determine the material used for the clips, their spacing and, most important, the method of fixing. Clips should be spaced at between 300 and 500mm centres depending on exposure. For sheltered exposures clips fixed at the top (as in Fig.1) with a clip at each lap joint and at about 500mm centres will be adequate. However in more exposed situations, this method will not prevent wind lift in storm conditions and additional restraint will be needed. The important principle: ‘the lower the fixing the stronger the clips’ is illustrated in Fig.3. A typical example of extra fixings to clips is shown in Fig.2. Therefore, although the spacing and the material used are important, the method of fixing is an essential factor to be considered if the clips are to provide effective resistance to wind lift in storm conditions.
    Clips should be of copper, tinned copper, stainless steel or lead.

    • MA. 1.1 Copper clips
      Copper or tinned copper clips should be not less than 50mm wide and cut from copper sheet of not less than 0.60mm thickness, conforming to BS EN 1172. Soft temper in welts, seams and rolls and of ¼ H temper elsewhere.
    • MA.1.2 Stainless steel clips
      Stainless steel clips should be cut from 50mm wide fully annealed stainless steel strip of not less than 0.375-mm thickness. The strip should conform to BS EN 10088. It may be terne coated if exposed to view. For high exposure situations a thicker sheet (0.46 stainless steel) should be used.
    • MA. 1.3 Lead clips
      Lead is only suitable for clips in sheltered locations. The thickness of the sheet used should not be less than the thickness of the flashing.
      Lead clips should be not less than 50mm wide and not less than the thickness of lead sheet used for roofing and cladding work
  • MA 2 Nails
    • MA 2.1 Nails and sizes
      Generally nails should be of copper or stainless steel and should be clout nails conforming to BS 1202-1 and -2. The shanks should be annular ring, helical ring or serrated. Nails should also be not less than 20mm long. For heavy-duty fixings they should be not less than 3.35mm diameter and for light duty they should be not less than 2.65mm diameter, the nail head being approximately three times the shank diameter.
    • MA 2.2 Stainless steel nails
      Stainless steel nails should be of austenitic stainless steel, excluding free machining grades.
  • MA 3 Screws
    Screws should be brass or stainless steel conforming to BS 1210 and not less than 20mm long.
  • MA 4 Underlays
    The type of underlay selected for use with lead sheet should:

    • Allow for thermal movement by reducing the amount of drag between the substrate and the lead sheet;
    • Help protect the lead sheet by providing a barrier against corrosive attack from stone, concrete or discharge from timber and roof condensation;
    • Provide an even surface and level out any imperfections such as nail heads, board edges and knots which could damage the lead;
    • Fully support the lead sheet so that it cannot sag or be punctured;
    • Provide a sound reducing layer in periods of heavy rain;
    • Reduce the risk of moisture being trapped between the lead and the substrate;
    • Be free of any substances, which could be deleterious to the lead sheet.
    • Typical underlays that could be considered are:
    • Class A building paper conforming to the requirements of BS1521.
    • Non-woven needle punched polyester geotextile that has a weight of not less than 210/mm2 (+ or -5%)
  • MA 5 Solder
    Solder should conform to BS EN 29453.
    (Generally solder is only used for soldered dots or where lead welding or bossing is impracticable.)
  • MA 6 Patination of external leadwork.
    In rainy or damp conditions new lead sheet flashings will produce an initial, uneven white carbonate on the surface. This can be aesthetically unacceptable in some situations but, more importantly, the white carbonate can be washed off by rain to cause unsightly staining on materials below flashings. To reduce staining and also provide a pleasing appearance, lead sheet should be treated as soon as practical after fixing and preferably the oil should be applied no later than the end of the day’s work. It is important to apply a coating under the lower edge of leadwork and between the laps. Clips along the edges of flashings should be turned over after application of the treatment.
    There are two types of treatment, solvent based and water based. Whatever type is used, to obtain the best results it is important to follow the manufacturers’ instructions.

FR – Joints in the leadwork.

  • FR1. Wood cored rolls are suitable for flat roofing, pitched roofing and vertical cladding and are positioned in the direction of the fall except at ridges, hip intersections and high points in gutter linings. Wood rolls are acceptable for use where there is likely to be foot traffic. Typical specification clauses may be written as follows:
    • FR1.1. Joints running with the fall to be wood cored rolls and the overcloak detailed with a 40mm splash lap. Rolls to be positioned inline and spaced at…….mm.centres for code…….OR
    • FR 1.2. Joints running with the fall to be wood cored rolls and the overcloak detailed with a 40mm splash lap. Rolls to be staggered and spaced at…….mm.centres for code…….OR
    • FR 1.3. Joints running with the fall to be wood cored rolls and the overcloak detailed with a 25mm return welt and clipped within the welted edge with 50mm wide copper clips at 450mm centres. Rolls to be staggered and spaced at…….mm. centres for code…….OR
    • FR 1.4. Joints running with the fall to be wood cored rolls and the overcloak detailed without a splash lap. With the free edge terminated between 3-5mm above the roofline Rolls to be staggered and spaced at……..mm centres for code……. (Codes 7 & 8 only)
  • FR 2. Drips are used across the fall for roofs at minimal fall of 1 in 80 and up to 10 degrees. They are also used in lead lined box, parapet and centre valley gutters. The minimum height for drips is 50mm, 55mm for drips in conjunction with rolls using codes 4, 5 and 6; and 60mm for codes 7 and 8.
    A typical clause would be:

    • FR 2.1. Joints across the fall to be drips……….mm in height with the underlap dressed into a 25mm minimum wide rebate and secured with a single row of nails at 50mm centres. Form overlap to provide a 40mm splash lap.
    • FR 2.2. Flat Roofs with a gradient of between 30 and 100 will require extra fixings on the flat area immediately in front of the drip. A typical clause would be:
      • Joints across the fall to be drips……….mm in height with the underlap dressed to the full height of the drip upstand. The head of the bay abutting the drip to be secured with two rows of nails. The rows to be 25mm and 50mm from the face of the upstand with the nails spaced at 75mm centres in a staggered pattern. The heads of the nails to be sealed by soldering or lead welding to ensure the fixings will be watertight. The overlap from the upper bay to be formed with a 75 mm splash lap, and secured with……no. lead clips lead welded to the under lying sheet, (Insert number of clips See paragraph MA1)

PR1. Pitched Roofs at between 11 and 80 degrees.

  • For chart showing spacing of joints see page 2/6Typical clauses as follows:
    PR 1.1. Joints running with the fall to be wood cored rolls and the overcloak detailed with a 40mm splash lap and rolls spaced at…….mm.centres for code…….

    OR
  • PR1. 2. Joints running with the fall to be wood cored rolls and the overcloak detailed with a 25mm return welt and clipped within the welted edge with 50mm wide copper clips at 450mm centres and rolls spaced at…….mm. centres for code…OR
  • PR1.3. Joints running with the fall to be hollow rolls and detailed with 50mm wide copper clips within the rolls at 450mm centres with the rolls spaced at…….mm. centres for code…….
  • PR1. 4. Joints across the fall to be overlaps…………mm in length with the free edge clipped with …….No. 50mm wide lead clips lead welded to the under lying sheet, (Insert number of clips See spec on clips**)OR
  • PR1. 5. Joints across the fall to be overlaps…………mm in length with the free edge clipped with …number. 50mm wide ………………. clips secured with ………nail fixings, (Insert number of clips and whether copper or stainless steel is to be used. See paragraph MA1)

G1. Gutters linings.

Lead-lined gutters are used where a lead-covered flat roof, or a tiled or slated roof, is designed with a parapet wall. They are also used where a flat or pitched roof abuts a vertical wall, where two pitched roofs are joined by a horizontal valley gutter, and between adjacent areas of lead roofing. To allow for thermal movement, lead gutter linings must always be divided into separate pieces (bays).

The size of a piece of gutter lining will depend on the thickness of lead sheet used. Table 7 shows the maximum length and girth for the five codes of lead sheet normally used for lining both box and tapered gutters.
Although Code 4 is the minimum thickness for gutter linings, its use is recommended only for very short gutters, because the maximum drip spacing of 1 .5m is usually uneconomical when compared to using Code 5 with drips at 2m centres.
To accommodate thermal movement, drips are used across the fall for both box and tapered gutter linings
For chart showing spacing of joints see page 2/6

A typical clause for gutter linings would be:

  • G1.1. Lead lined parapet gutters.
    Typical clauses may be:
  • G1.2. The width of the box gutter shall be not less than 225mm. The gutter lining shall be formed in
    Code …….. lead sheet divided into bays in lengths not exceeding ……….mm with drips not less than …….mm deep. (Refer to the chart in section 2/6 for codes, thicknesses and maximum sizes.) Where the girth of the gutter exceeds the maximum recommended, one or more wood cored rolls will be required to divide the gutter.

F1 Abutment Flashings

Typical clauses for flashings could be:

  • F 1. Apron flashings at lean-to abutments in code………in lengths not exceeding …….mm with end to end lap joints of not less than 100mm. Upstand to the abutment not less than 75mm and with a lap of……….mm over the pitched roof covering. The 25mm turn in to the masonry joint to be lead wedged at laps and at 450mm centres, prior to pointing. The free edge of the flashing to be clipped with……..clips spaced at…… ..Centres (Insert spacing of clips and whether copper or stainless steel is to be used. See paragraph MA1)
  • F 2. Step flashings in code…… in lengths not exceeding 1500mm with end-to-end lap joints of not less than 100mm. The 25mm turn in to each step to be lead wedged prior to pointing.
  • F3. Soakers
    Soakers shall be formed from code…….. lead sheet with a minimum upstand at the abutment of 75mm and a lap of not less than 100mm over the tiles or slates. The length of the soaker to be equal to the gauge plus lap plus 25mm.
  • F4. Single step flashings. Individual step flashings to be cut from code…. …with a minimum-passing lap of 50mm between each single step, covering over the upstand of soakers or cover flashing by not less than 65mm. Each step to be turned into the brick joints by 25mm and secured with lead wedges on every course. The width and length of the steps to be calculated on site to suit the pitch of the roof and type of brick or stonework encountered.
  • F5. Step and cover flashings in code… in lengths not exceeding 1500mm with a passing lap of not less than 150mm between each section. Each step to be turned into the brick joints by 25mm and secured with lead wedges on every course. The free edge of the flashing to be clipped with…clips spaced at… Centres (Insert spacing of clips and whether copper or stainless steel is to be used See paragraph MA1)
  • F6. Secret gutters in code… in lengths not exceeding 1500mm with a passing lap of not less than 150mm between each section. The top end of each piece should be secured with two rows of clout nails.
  • F7. Cover flashing to upstands on flat and pitched roofing membranes in code…….in lengths not exceeding 1500 mm with end-to-end lap joints of not less than 100mm. With a cover over the upstand of the roofing material of not less than 75mm. The 25mm turn in to the masonry joint to be lead wedged at laps and at 450mm centres, prior to pointing. The free edge of the flashing to be clipped with…clips spaced at… Centres (Insert spacing of clips and whether copper or stainless steel is to be used. See paragraph MA1)
  • F8. Pitched valley gutters shall be in code…….. installed in lengths not exceeding 1500mm with the head of each piece secured with two rows of ……… clout nails. (Insert thickness of lead and whether copper or stainless steel is to be used See spec on clips) The overlap between each lining piece shall be not less than ……..mm. (See lap diagram to determine lap length to suit the pitch of the valley)