The short answer
In a semi or terrace there is rarely a single rule. Each owner is usually responsible for the roof over their own home, but parts that serve both houses, such as a shared ridge, valley or chimney stack, are often split. Your deeds can say who is responsible, and a written agreement with your neighbour before work starts avoids arguments about the bill later.
How the cost of a shared ridge, valley or chimney is usually handled between neighbours in semis and terraces, and how to raise it.
What is shared and what is yours
Start with the roof itself. In a pair of semis or a row of terraced houses, the covering over your rooms belongs to you and the one over theirs belongs to them. Trouble starts at the places where one roof runs into another, because a fault there does not respect the boundary.
The ridge is the line of tiles along the top where two slopes meet, and in a terrace it often runs the whole length of the row. The hip is the sloping line at the end of a roof where two slopes meet at an outer corner. A valley is the internal channel where two slopes meet, and where a roof turns a corner or two roofs join, it is lined with lead or other metal. A chimney stack on the party wall serves both houses and sits half on each side.
Where a repair affects only your side, it is normally yours to pay. Where the fault sits on the shared line, such as a cracked ridge tile above the party wall or a failed flashing around a stack that both homes use, the cost is often split. Your title documents and deeds may state who must repair what, so check them before assuming anything.
A solicitor can read the documents if the wording is unclear.
Raising it with next door
Raise it early and keep it friendly. A leak that appears in your bedroom may start on their side, and the reverse is true too, so an early conversation helps both of you. Explain what you can see, and offer to show them. Photos taken from the garden, or from the upstairs window, often help more than a long description.
Follow up with a short message or letter, so what was said and when is on paper. Suggest that a roofer looks at both sides, and offer to let your neighbour be present. If they would prefer their own opinion, that is reasonable, and a second survey costs little against a disputed repair.
Try to agree three things before any work begins: what is wrong, who will do the work and how the bill will be divided. Write down the answers and each sign or reply to confirm. Without that, a neighbour who was keen at the start can feel differently when the invoice arrives.
If your neighbour is a tenant, the landlord may be the right person to approach. Our answer on landlord responsibility for roof repairs explains the usual position.
Splitting the work and the bill
There is no automatic formula, but there are fair ways to divide a job. Where the benefit is even, such as a ridge that runs along the whole row or a valley that drains both homes, equal shares are the simplest. Where one house gains much more, as with a stack that mostly serves one chimney, the shares can reflect that. What matters is that both owners agree beforehand.
One written total price, from a survey of both sides, makes the split easier because everybody is looking at the same figure. Ask the roofer to say what the price covers on each house and whether scaffolding and VAT are included. Scaffold can be a sizeable part of a small roof job, and one frame across both fronts can serve both owners instead of two separate hires.
Doing the repair together also saves money on access and avoids a roof fixed on one side while the faulty part next door keeps leaking back into it.
If the work involves the wall between the homes, our answer on the Party Wall Act and roof work explains when notice to a neighbour is needed.
When the neighbour will not pay
Sometimes a neighbour will not agree. Do not simply stop at that point. If water is entering your home from a fault on the shared line, you may need to make it safe quickly and sort out the cost afterwards. Keep the photos, the survey and every receipt, because they show what was done and why.
Next, check your deeds again and think about asking for advice. A solicitor can explain what the documents say about repair duties, and mediation can help when relations are strained. Citizens Advice also gives free guidance on disputes between neighbours.
For a shared chimney in particular, see our answer on who repairs a shared chimney stack, and if you own a flat the position is different, as our answer on leaseholder roof repairs shows.
We can survey your side, send you photos and give a written total price. Where a fault clearly continues next door, we tell you plainly, so you have something to show your neighbour. The homepage lists the roof work we cover.
More on this in Roofers in Crawley: the full guide
Two more shared roof questions
Can my neighbour make me pay for work on their half?
Not simply by asking. Unless your deeds or an agreement you signed say otherwise, you are not automatically liable for their side. A fault on a part that serves both homes is different, and sharing the cost is the usual fair outcome. Ask for the survey and the written price, look at both together, and then decide how the cost is divided.
Should we use the same roofer for both houses?
It often helps. One roofer can see how the two roofs meet, price the shared parts once and share a single scaffold. Each owner should still receive a clear written price for their own side, and either of you remains free to get a second opinion before agreeing to the plan.