If flashings or valley linings become defective, the first signs o’ trouble may be spoiled ceiling decoration or damp patches on chimney-breast walls due to rainwater penetration. Check these areas of the roof regularly, making any repairs as soon as possible. and you should be able to stop the trouble before it gets too bad. Many repairs are simple and ones you can do yourself.
Traditionally flashings are made from sheets of lead or zinc: but other corrosion-resistant materials. such as aluminium alloy, copper, bituminous felt and rigid bitumen-asbestos, are also used. A fairly recent development is the self-adhesive Hashing strip: this is available in various widths and is cheaper and easier to fit than most traditional materials. These flashing strips usually consist of heavy duly reflective aluminium foil, coated on one side with a thick layer of specially formulated pressure-sensitive bitumen adhesive. The adhesive surface is protected with a siliconized release paper which you peel off just before applying the Hashing. In some eases the aluminium foil is coated with a grey vinyl lacquer, so it looks like lead.
If flashings are torn or cracked, clean the damaged area thoroughly wilh a wire brush and go over it with emery paper. You can then cover the crack or tear with a patch of self-adhesive flashing strip: simply peel oil’ I he paper backing and smooth the strip firmly into place. Alternatively press thick bitumen mastic into each crack so there is about 1.5mm in of mastic over the crack and overlapping it by about 1.5mm all round. Lay a piece of aluminium foil or thin roofing felt over each repair and press the edges into the mastic. Apply another layer of mastic and brush liquid bitumen proofing over the entire flashings. Repointing Along its top edge, metal flashing is tucked into the mortar joints of the brickwork; if the joints are defective and the Hashing comes away from them, rainwater will trickle behind and eventually seep through the roof. To repoint the joints, first rake out the old mortar with a cold chisel and club hammer, then tuck the flashing back in place, wedging it at intervals with scraps of lead or small pieces of timber. Dampen the joint with water and fill it with a mix of four parts sand to one part cement.
Flashings which are badly corroded are best replaced with new material: the method of replacement varies with the type of flashing and the material used.
Stepped flashing With a single lap tiled roof the flashing at the side of the chimney is usually stepped and dressed over the tiles. Stepped flashing is inserted in the mortar joints all the way down the side of the chimney and il is difficult to replace in the same way. However, you can apply a self-adhesive flashing strip which does not need stepping or inserting in the mortar joints. Carefully lever out the old flashing and thoroughly clean the area with a wire brush; you can then apply a primer as recommended by the manufacturer – this is not essential, but it does ensure the strip adheres firmly to the brickwork. Cut the strip to length with a pair of scissors and carefully peel off the backing paper; press the strip into place and smooth it down with a cloth pad or A wood seam roller as used for wallpapering, making sure there are no gaps between the strip and the surface.
Soakers On a double lap tiled roof- and again on some slate roofs – the flashing at the side of the chimney and against parapet walls usually consists of separate pieces of metal, called soakers. interleaved with the tiles. The soakers are turned up against the wall or side of the chimney and a stepped flashing or mortar fillet covers their upturned edges. To replace faulty soakers, chip away the old mortar fillet, or lever out the flashing, and rake out the joints between the bricks to about 19mm. Remove adjacent tiles, numbering them as you work to enable you to replace them in the correct order, and remove the damaged soakers – again numbering them as you do so. Cut pieces of zinc to the shape of the soakers, using the old ones as templates. If you intend to use self-adhesive flashing dampen the raked out joints with water. repoint, and replace the soakers, interleaving them with the tiles in the same way as they were originally fitted. You can now apply the flashing over the soakers, as described above. If you intend to apply rendering over the soakers and to the wall above, leave the mortar joints open to provide a key for the rendering. Use a mix of four parts sand to one part cement and trowel on the mortar to a thickness of 13mm. Score the surface to ensure good adhesion, leave the render to dry and apply a second coat, again 13mm thick.
When replacing straight, horizontal flashings of traditional materials, such as lead or zinc, lever out the damaged flashing and rake out the mortar joints to about 25mm. Cut the lead or zinc sheet to the required length, lay it over a batten and bend over a 20mm strip at right-angles down one long edge. Use a sliding bevel to determine the angle between the roof and the wall; turn the sheet over and shape it to match the angle on the bevel, working from the centre of the sheet outwards. Dampen the mortar joints with water and insert the angled section of the new flashing in the joint, packing with small wedges of zinc or lead at both ends and overlapping joins in the flashing by about 150mm. Gently hammer the lower half of the flashing to match the slope of the roof then fill the joint with fresh mortar. Finally remove surplus mortar with the point of a trowel. Alternatively you can replace this type of flashing with a self-adhesive strip, as described for stepped flashing.
Occasionally the flashing round the base of a chimney or against a parapet wall is made from a triangular fillet of cement mortar; it is quite common for this type of flashing to crack where it joins the wall. If the damage is not severe, seal the gap with a non-hardening mastic; if the fillet is in bad condition, it is best to chip the fillet away and replace it with a self-adhesive flashing strip.
Lead, zinc and aluminium are all commonly used for valley linings. Small cracks and holes can be repaired in the same way as for metal Bashings; but after making such repairs, it is important to seal the entire valley with liquid bitumen proofing or liquid plastic coating.
REPLACING VALLEY LININGS
If the valley lining is severely corroded or wrinkled. it must be replaced; this involves lifting several tiles at each side of the valley, so have a tarpaulin or heavy duty polythene sheeting ready to cover the roof in case of rain. You can replace the lining with zinc or lead sheet or use roofing felt; but the simplest method is to apply a wide self-adhesive flashing strip.
ZINC OR LEAD LINING
Remove the tiles covering the valley edge at each side, numbering them so you can replace them in the correct order. Lever up the old lining and lower it carefully to the ground, then remove the fixing nails with pincers. Check the timber underlining is securely fixed and coat it with creosote for protection. Cut the replacement zinc or lead to length, allowing for a 50mm overlap at the eaves, and place it over the underlining; press the lining down firmly to fit the angle of the valley and hold it in place with galvanized nails. If you have to use more than one sheet of metal, make sure the sheets overlap by about 225mm. Where the lining meets the junction of the roof and wall, shape the end to match the junction, allowing a 75mm turning against the wall. Fix the sheet to the battens at both sides using galvanized nails. then relay the tiles; work from the eaves upwards and make sure you replace the tiles in the correct order. Finally apply self-adhesive flashing strip at the junction of the roof and wall to guard against rainwater penetration.
You can replace an old metal lining with three layers of roofing felt. Remove the tiles and old lining as before and cut the felt to length. Fix the first layer of felt to the valley underlining, using galvanized nails, and fix the second and third layers with felt adhesive. Then replace the tiles in their original positions.
The major concrete roof tile manufacturers now produce special valley tiles which can be used as a cheaper alternative to the traditional lining materials. However, the method of fixing these tiles involves modifying the tile battening on each side of the valley.