How to Repair A Roof Valley Leak

Roof Care & Maintenance
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How to Repair A Roof Valley Leak

Valleys are some of the areas most prone to roof leaks, due to the continuous wear and tear from rainwater and debris gathering and flowing through them before draining into your gutters. It can be quite common for valleys in an older roof to leak when it snows, as the excess weight and freezing temperatures can compromise worn flashing. Roof valley leaks can happen for many reasons, but thankfully, these can often be fixed quickly and inexpensively.

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Safety First

Whilst no specialist tools will be required to fix a leaking roof valley, if you’re going to tackle this job, we’d recommend investing in a sturdy pair of roofing boots. These, along with other safety equipment will ensure you minimise your risk when working at height. And of course, if you don’t feel comfortable getting onto your roof, or carrying out the job, you should always hire a professional. While this option is more expensive, you’ll be given the peace of mind that the job is being done safely, and to the highest standard. Find out how to find a good roofer.

Why Do Roof Valleys Leak?

Does your roof valley leak in heavy rain? There are many reasons why this could be happening, but these leaks are most often down to age or general wear-and-tear. Roof leaks have many causes, and we will go through some of the most common culprits for a leaky roof valley below.

Aging Roofing Materials

Father Time is undefeated, and there’s no exception when it comes to your roof. Over time, the materials that make up your roof such as the roof tiles, lead flashing, and even underlay will wear away and suffer damage. Once this damage is done, such as a cracked roof tile, this can allow water to seep in and work its way into your roof space, eventually causing a leak. Due to how often roof valleys are exposed to water and debris, the area around them is often where roof leaks begin.

Broken Flashing

There’s no question that the lead flashing used to seal and protect your roof valleys and other areas against water ingress is one of your roof’s strongest lines of defence. However, as with all materials, lead flashing can become worn and damaged over time, eventually exposing your roof space to unwanted moisture. When inspecting roof flashing, you should look out for areas where it has been lifted, perhaps by high winds, and ensure that all fixings are still securely in place.

Strong Winds

Fierce winds can often lift, damage, or even displace roof tiles entirely. This is especially true for older roofs which may have already experienced some wear, or where tiles haven’t been fixed properly. As roof valleys take a beating from their constant exposure to wind, rain, and snow, they are often the first place tiles are compromised. After storms or high winds, inspect your roof valleys to ensure no tiles are damaged or missing, or you could be dealing with a roof leak before long.

Damaged Roofing Membrane

Often when your roof valley is leaking, the true cause is the membrane or underlay beneath your roofing materials. As these membranes are often not expected to last as long as the tiles above, they can become damaged far sooner and lead to roof leaks and other issues. This is why whenever you come to do a job such as replacing a roof tile, you should always check the condition of the membrane. Often it may be rotting away, signalling you to get a new membrane installed.

Thermal Expansion

Another major issue which can cause roof valley leaks is thermal expansion. Prolonged hot weather can eventually cause roofing materials such as tiles and underlay to shrink and expand as the temperature changes, making them more vulnerable. This means that when storms or high winds come about, your roof is more likely to suffer damage and spring a leak. The best way to prevent this is to ensure that your roof has been installed correctly, with enough give to absorb movement.

How to Fix a Leaking Roof Valley

As long as you choose the right materials, follow the manufacturer’s guidelines during installation, and regularly inspect your roof, most issues can be prevented long before they become severe. However, if your roof valley is leaking, there’s plenty you can do, and thankfully, these fixes should prove simple for any confident DIYer.

Temporary Roof Valley Leak Repair

If you’d just like to perform a temporary fix, the best thing to do is locate the source of your leaking roof valley and apply an appropriate sealant to stop any more leaks for now. This should give you enough time to save up for a full repair or replacement, get quotes in from contractors, or just figure out the best course of action. Eventually however, you will need to perform a full repair by removing the surrounding roof tiles, and replacing whatever is causing the roof leak, such as the lead flashing or roofing underlay.

How to Repair a Leaking Roof Valley Permanently

If a valley in your roof is leaking, more often than not a partial or full replacement will be in order. This could mean replacing your roof tiles, the flashing used, your roofing membrane, or all three.

  1. Perform a full inspection of your roof to determine what exactly is causing your leaking roof valley, and what needs replacing.
  2. Lift up as many tiles as necessary around the damaged area, so that the damaged flashing can be removed and replaced.
  3. The new layer of flashing can now be installed, using either wet-fixing or dry-fixing, depending on your needs and chosen product.
  4. If your valley flashing is made from lead, this should only be removed and replaced by a qualified professional. This is due to the toxicity of lead, and the experience needed to install lead flashing correctly.
  5. Once your new flashing is in place and any wet fixings have been given time to dry, carefully fit the tiles you removed previously back into place, replacing any damaged or broken tiles.

How Much Does It Cost to Repair a Leaking Roof Valley?

Of course, the cost of repairing a roof valley leak depends entirely on how much work is needed. However, on average, including the price of labour should you hire a professional, replacing a single roof valley should cost around £450. Fixing or replacing a roof valley should take between 6 and 8 hours, as long as there are no issues with access and your roof valley is of a standard size (around 3 metres).


We hope this guide has been helpful, especially if you're dealing with a leaky roof valley right now! If you've still got questions, be sure to ask our award-winning customer service team. They'll be able to answer any query you may have. Call them on 01295 565 565, email [email protected], or use our handy livechat below.

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