Roof Valley REPAIR and RePLACEMENT Prices

Written by Daniel Woodley. Fact checked by Paul Farley. Published to Prices. Updated: 8th March 2023.

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A roof valley is located where two sloped roofs meet, it’s designed to guide rainwater down the roof where it then typically discharges into the guttering.

Roof valleys are subjected to more rainwater than any other part of the roof. During a downpour, the valley can experience a torrent of water, and it’s not uncommon for older valleys to leak.

A common issue is leaks caused by blockages.

If the valley is full of leaves, twigs and other organic materials such as pine needles or roof moss, rainwater may back up and enter the loft via the overlapping tiles.

Blockages are fairly easy for a roofer to resolve and the work shouldn’t take long.

If however, the leak is due to failure of the valley components, then a complete replacement or substantial repair may be required.

The purpose of this page is to explain the most common causes of valley leaks and how much they cost to repair or replace.

6 Reasons Why Roof Valleys Leak – Based on My Experience

I’ve seen roof valleys leak for a number of reasons.

Here are the six most common reasons roof valleys leak and what you can do about it:

1) Concrete Roof Valleys

Concrete valley tiles are heavy, prone to movement and cracking, difficult to repair and almost impossible to replace. They are considered by most in the roofing industry (inc me) to be an outdated and obsolete material. 

Does your roof valley contain concrete tiles like this?

These types of valleys are notorious for leaking, and I’ve seen dozens of homeowners experience problems with them. The tiles are so heavy that they cause the roof timbers to sag, gaps then appear, or the tiles slip, the end result is always the same; they leak.

I’ve found that concrete valley tiles often crack, and they can be difficult, if not impossible, to replace without damaging more tiles (due to the way they overlap and are cemented together).

I have repaired concrete valleys before, and I found the best approach is to cover a broken tile with lead but in my opinion, they should ideally be replaced with a more reliable and modern product such as fibreglass:

2) Blocked Roof Valleys

This is another common issue I’ve seen first-hand many times.

If the roof valley is blocked with organic material such as leaves and twigs, etc., then rainwater may back up and enter the loft.

Leaves aren’t the only thing that can block a valley. I’ve seen bits of broken tile, concrete, old aerial cables and brackets etc., or other parts of the roof that’s damaged or broken off became lodged in the valley where it blocked the flow of water.

If your valley is leaking, any blockages should be removed, and the valley itself should be inspected for any signs of damage or wear and tear.

3) Fatigue Splits

Some roof valleys are made with lead as the main material and for good reason; it’s long-lasting, waterproof and flexible enough to use almost anywhere on a roof.

Does your leaking valley roof look like this?

I’ve found that lead is prone to splitting, which can result in water ingress. From what I’ve seen, the most common reasons are:

• The lead is too thin.
• The original roofer cut the lengths far too long.

Lead has a high thermal expansion rate, meaning it expands a lot when it gets hot. It then shrinks a lot when it’s cold. This thermal expansion and contraction can result in splits.

If the lead has split, one should consider either a repair with a sleeve or replacing the whole valley.

In my opinion, if the lead is too thin, it should be fully replaced with thicker lead or fibreglass.

4) Fibreglass Failure: Splits, Holes and Cracks

Fibreglass is a popular material to use in a roof valley, it’s lightweight, cheap, resists UV rays and watertight.

Unfortunately, I’ve found that older fibreglass products aren’t as sturdy as their modern counterparts. I’ve seen some that were installed 30 years ago are now cracking, splitting or leaking through small holes.

Does your roof valley look like this?

While it can be repaired, the feasibility will depend on why the fibreglass has cracked.

From my experience, one-off damage, perhaps from a fallen tree branch etc., can often be repaired, while damage due to age, wear and tear etc., may require a full valley replacement.

5) Plain Tiles

Plain tiles are small tiles and many roofs constructed with these tiles will have a valley that looks like this:

These valleys fail and leak for two reasons:

• A broken tile in the centre of the valley.
• The general age of the roof, wear and tear, failed or rotten timbers etc

I often found that repairing these types of valleys was fairly easy and straightforward and 99% of the time it was just a tile or two that needed replacing.

6) It’s Not The Valley That’s Leaking

On most roofs, the tiles are laid over a felt underlay that offers a second layer of protection.

If a roof tile breaks on a roof, the water should hit the underlay and flow downward until it reaches either the edge of the roof or a roof valley.

If a broken tile is located at the 1st red circle in this image, water may not penetrate the roof until much further down the roof, see red circle 2:

If there’s no obvious fault in the valley, look out for:

• Broken, chipped, missing or slipped tiles anywhere above the valley.
• Missing, slipped, cracked or poorly installed leadwork above the valley.
• Chimney leaks above the valley.

I often found that valley leaks were caused by issues further up the roof, and based on my experience, these are often cheaper to repair.

How Much Does it Cost to Repair a Roof Valley?

Repairs aren’t always viable and are almost impossible on heavy concrete tiles (see example 1).

However, see the price table below where a minor repair is possible.

A minor repair is any one of the following:

• Replacing a small number of broken tiles.
• Refixing slipped tiles or slates.
• Repairing a lead split by cutting in a sleeve.
• Repairing a fibreglass hole or crack with an extra few layers of fibreglass.

This price guide assumes that an access tower is erected up to gutter height for edge protection. The figures below do not include scaffolding:

Cost to Replace a Roof Valley

The entire valley can be removed and replaced if a repair isn’t possible.

In most cases, the new valley will be either fibreglass or lead.

Here’s a project schedule and example price for this type of work:

• Erect access equipment to the edge of the roof.
• Remove and set aside the existing tiles.
• Remove the cement, underlay and existing valley, lower to ground.
• Lay a new felt underlay.
• Lay new fibreglass valley trough.
• Bed tiles onto new mortar and point in to leave a neat finish.
• Remove the access tower and remove all waste.

The prices below do not include scaffolding, but this type of work can often be carried out via an access tower.

Cost to “Repoint” a Roof Valley

On most roofs, valley tiles are held in place with mortar – a mix of sand and cement.

It’s not uncommon for the mortar to fail and come loose.

Below is a price guide for a roofer to pull out the loose mortar to a 4-metre roof valley. This work doesn’t involve the removal of any roof tiles, the loose mortar is simply pulled out, and the gap is repointed with new mortar.

In my opinion and based on my experience, this type of work shouldn’t take more than a few hours on a typical property with good access.

The price includes the cost to erect an access platform, as this isn’t the type of work that should be done from ladders.

Other Costs to Consider

Access – the price guide on this page assumes that the roof can be accessed via tower platforms. If roof access is troublesome, perhaps it’s three or four storeys high or is next to a busy road or public footpath or just difficult to reach, the cost for scaffolding can easily double or even triple the prices we’ve suggested.

Leadwork – I’ve provided a price guide for a replacement fibreglass valley as this material is the cheapest and lasts for decades. If you choose a lead valley, the cost will be higher as the lead is more expensive.

Extra timbers – The prices assume that the roof timbers, the rafters and joists, etc., are in good condition and not rotten. Replacing timbers will add time, materials and cost to the project.

Roof steepness – Simply put, it’s easier to work on a shallow roof than a very steep one. Steep roofs will add to the valley replacement cost but not by much.

Get Your Custom Roof Valley Price Today

I hope you found this guide to roof valley replacement and repair prices insightful.

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Roof Valley FAQs

My Experience

I know there’s a lot of nonsense published online, usually by those that have never worked in the industry.

I have over 18 years of experience in the construction industry, including 10 years as a roofing contractor. I am also a qualified roofline installer, and more recently, I have gained experience in project management on larger developments.

The prices shown on this page are meant as a guide and reflect the time and materials required to complete a typical 4-metre valley – they do not include the cost of scaffolding and are my estimate.

I also asked Paul Farley to fact-check the important statements I’ve made in this guide.

Fibreglass Flat Roof

Fibreglass is a tough, long-lasting material that’s often found on flat roofs, ship hulls and in building materials. See how much a fibreglass flat roof costs here.