A Look at Roof Valley Leaks

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 material 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 full replacement or substantial repair may be required.

Reason 1 – Concrete Valley Tiles

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and cracking, difficult to repair, almost impossible to replace and considered by most in the roofing industry to be an outdated material.

Does your roof valley contain concrete tiles like this?

These types of valleys are notorious for leaking, the tiles are so heavy that they often cause the roof timbers to sag, gaps then appear, or the tiles slip, the end result is always the same; they leak.

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).

While temporary repairs are possible, perhaps by patching over cracks with a glue or other material, concrete valley tiles should ideally be replaced with a more reliable and modern product such as fibreglass:

A fibreglass valley is lightweight, cheap and comes in very long lengths so few overlaps are needed.

Reason 2 – Blocked Valley

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. Bits of broken tile, concrete, old aerial cables or brackets etc., or any other part of the roof that’s damaged or broken off can become lodged in the valley where it blocks the flow of water.

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

Reason 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?

Lead is prone to splitting, which can result in water ingress. The most common reasons are:

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

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

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

If the lead is too thin, it should be fully replaced, either with thicker lead or with fibreglass.

Reason 4 – Fibreglass Failure (cracks, splits, holes etc)

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

Unfortunately, older fibreglass products weren’t as sturdy as their modern counterparts. Some that were installed 30 years ago are 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.

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.

Reason 5 – Plain Tiled Valley (broken tiles, age)

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.

Repairs are often straight-forward, replace a broken tile for a new one while a full replacement takes longer, requires more materials and costs much more.

Reason 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.

In short; valley leaks can be caused by issues further up the roof and these are often cheaper to repair.

How Much Does it Cost to Repair a Roof Valley?

Repairs aren’t always viable, and almost impossible on heavy concrete tiles (see example 1), but to carry out a minor repair, see our cost guide in the table below.

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.

How Much Does it Cost to Replace a Roof Valley?

If a repair isn’t possible, the entire valley can be removed and replaced.

In most but not all 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.

What is the 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 repointed with new mortar.

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:

Our roof valley prices are based on a few assumptions:

Access – We assume that the roof can be accessed via tower platforms. If the 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 – We’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 to buy.

Extra timbers – Our 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 – To put it simply, it’s easier to work on a shallow roof than a very steep one. Steep roofs will add to the valley replacement cost.

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We hope you found our guide to roof valley replacement and repair prices insightful.

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