Roofing: A Lead Valley Installation Guide
Roof valleys are a frequent source of leaks in older homes. Installation procedures differ depending on the type of roof and the materials used. We will look at the basic installation of an open lead-lined roof valley here.
A roof valley is basically a gutter placed between two sloped roofs that meet. Depending on the area of the roof it serves, the valley is the exit point for a large volume of water, so great care must be taken with installation. If the roof has been leaking for a while or there are signs of rot, you’ll need to start by replacing the valley boards. Lead sheet is not self-supporting and must be placed on treated roof boards of sufficient strength to support a large person. (Most roofing contractors are big!) Lay boards wide enough to accommodate the lead plus 100mm on each side. This will give you something to nail the roof sticks to.
The top of the valley boards should be level with the top of the roof joists. If you lay the boards directly on the joists, the shingles may lift and restrict water runoff. You will need to cut the valley boards to fit between the joists. Support valley boards with studs or spikes. The valley should end in an even plane at the eaves. It should not rise higher than the lower beams. If so, you will need to cut the fascia board or adjust the gutter to fit. It is a good idea to place a tilting fillet on each side of the valley. This angled strip of wood runs the length of the valley and should be a minimum of 150mm from the center of the valley. It should sit no higher than the roofing battens with the thinner end closer to the center of the valley.
It is common practice to lay a single sheet of roofing material the entire length of the valley. The adjacent roof deck will remain on top of this sheet. I recommend that you use one of the new advanced synthetic base materials. Older bituminous felts are fine for normal roofing situations, but are not suitable for valleys. Over time, the bitumen will bond the lead to the boards and restrict thermal movement. You must ensure that you purchase lead of a sufficient grade/code for valley applications. This should be between 1.80mm and 2.24mm thick. If you are not sure, ask your roofing dealer for the correct grade. The cable should be cut into sections no more than 1.5 meters long to allow for sufficient thermal movement. Bend a 25mm cable trim on each side. This acts as a last line of defense for water penetration. It also has the added benefit of hardening the lead, making it much easier to transport across the roof.
Starting at the bottom of the valley, smooth the lead neatly over the valley boards and over the sloping fillets. The bottom of the cable must allow proper drainage into the gutter. Drive two rows of nails into the top of the flashing. Use copper or stainless steel nails. Never use galvanized or aluminum nails as they will react with lead and corrode. I recommend that you use the minimum amount of fastener possible to keep the cable in place. If you repair the lead sheet too much, it will eventually split due to thermal movement. So don’t nail the sides. When you have successfully covered the first sheet, you can go up to the roof by placing the next sheets. Overlap each sheet a minimum of 150mm. On valleys with lower ceilings, you will need to increase the lap. Where the valley ends at the ridge, you will need to coat the lead so it can sit perfectly under the ridge shingles. You are now ready to begin attaching the batons and laying the shingles. The key points to remember are to keep blade lengths to 1.5 meters and not to set them too tight. If you follow the procedure described and are careful with the bandage, you will produce a durable valley without maintenance.