Laying a Metal Roof Valley

A valley that is badly holed by corrosion, or wrinkled and pitted too much for flashing strip to bed down smoothly, will have to be replaced.
The metal should be laid over two boards that run down the valley, meeting at the angle. Near the sides, the metal rises over triangular wooden fillets fixed to the boards. The tiles or slates should be sealed to the metal with mortar so that the valley becomes a water-proof channel about 4in (100mm) wide.
When you are fitting the new metal, do not work with strips longer than 5ft (1.5m). A longer piece will expand too much in hot weather.
Nail the strips only at the top. Too many fixing nails will cause the metal to buckle and distort when it expands.
Laying a Metal Roof Valley
Things you will need
tools Ladder with a stand-off bracket, roof ladder, bolster chisel and club hammer, wooden wedges and a large builder's trowel, or a slate ripper, and perhaps all three, chalk, a bucket on a long rope, claw hammer, tinsnips, soft-faced mallet, pointing trowel.
materials Lead or zinc, No. 11 aluminium alloy nails l&1/2in (40mm) long, mortar mixed as for replacing ridge or hip tiles.

1. Use the bolster chisel and club hammer to chip away the mortar sealing the tiles or slates to the metal valley.

2. You will need to remove the cut tiles or slates that edge the valley at each side, and probably also the ones next to these to allow you to fold back the edge of the felt and reach the triangular fillets. You may have to take off pieces of batten to do this.
To remove tiles, push wooden wedges under the top most tile to prop it up. Slide the trowel under the next tile down and lift it until its nibs are clear of the batten. Then draw the tile out towards you.
ALTERNATIVELY, if it is a single-lap interlocked tile, draw it towards you to clear the tile above, then wiggle it slightly from side to side to free it from its neighbour. You will be able to remove the lower tiles without using wedges. Some of the tiles will be nailed to the battens, push the slate ripper under them and strike its handle down with a hammer to cut through the nails.
Take the tiles to the ground a few at a time or lower them in a bucket to a helper.
To remove slates, slide the slate ripper under each one to cut through the nails. As soon as the nails of a slate are cut, lift off the slate and take it to the ground or lower it in a bucket on a rope.

3. Use the claw hammer to lever out the nails holding the lead or zinc to the fillets on the valley boards.
Again start at the top and remove each piece of metal as you work down.

4. At the very top of the valley the metal is usually fixed under a lead saddle, a piece of lead covering the area where the ridge and the valley meet and shaped to fit snugly over the timbers. Raise the saddle very carefully to free the top of the metal valley.

5. Check the condition of the valley boards and the wooden fillets on them. Treat or repair them as necessary.

6. Use tinsnips to cut new strips of lead or zinc to the same width as the strips used for the old valley and to lengths of not more than 5ft (1.5 metres).

7. Work up from the bottom to fit the new valley. Use the soft-faced mallet to tap the metal gently into the angle of the valley, shaping it to lie closely against the timber. Allow the first piece of metal to overlap into the gutter. At the fillets, tap the metal in place so that it follows the shape of the wood.

Laying a Metal Roof Valley
8. Nail the metal to the fillets on the slope farthest from the centre of the valley. Use one nail at each side, placing it about 1in (38mm) from the top of the metal.

9. Continue working up the valley, letting each strip overlap by about 3in (75mm) onto the strip below it.

10. Cut the top strip to length, allowing it to overlap onto the strip below and also to extend under the saddle by at least 2in (50mm).

11. When the top strip is fixed, tap the saddle to fit closely over it.

12. At the bottom of the valley, trim the metal with the tinsnips to cover the bottom edge of the valley boards completely. Tap the metal closely against the boards.

13. Put the felt back in position.

14. Replace the tiles or slates, working from the bottom up and replacing them in the right order. Plain tiles simply have their nibs lodged over the battens. Where a nib has been cut off to make the tile the right shape, nail it securely in place. In any case, nail the tile in every third or fourth course as you work up the valley.
Interlocked tiles must be pressed into the matching grooves firmly. Nail alternate courses to the batten. Slates have to be nailed in every course to the batten.

15. Seal the tiles to the metal with mortar all the way up the sides of the valley. Use mortar also to seal any gaps at the eaves if the tiles you have replaced have curved profiles.