Is It Cheaper to Repair or Replace an Old Roof?

This is the question we are asked most, and the honest answer is that repair is right more often than a roofer with a full diary might admit. The point is knowing which situation you are in.

The comparison people make, and the one that matters

A roof with one damaged area and forty sound years left is a repair, comfortably. A roof that has needed something doing every eighteen months for six years is a roof telling you the answer, and continuing to repair it is a way of spending replacement money slowly without ever getting a new roof.

Repair is the right answer when

• The problem is in one identifiable place.
• The rest of the covering is sound and has life left.
• Damage was caused by an event — a storm, a fallen branch, a slipped aerial — rather than by age.
• The roof is relatively young for its material.
• The battens and underlay underneath are in reasonable condition.
• You have not had to call anyone out about it before.

Replacement starts winning when

• Problems are appearing in different places rather than the same one.
• You have had three or more repairs in a handful of years.
• The covering is at or beyond its expected life.
• The underlay has perished, or there never was any.
• Nail fatigue is general rather than local — slates slipping at random.
• Repairs are becoming harder because matching material is no longer available.
• Something structural is showing: a dipped ridge, a sagging slope, spread rafters.

The scaffolding arithmetic that changes the answer

Here is a real cost that gets left out of the comparison. Most meaningful roof repairs need access, and access on a two-storey house means scaffolding or a tower. That cost is incurred every single time.

So a repair is rarely just the price of the work — it is the work plus getting up there. Four repairs over six years means paying for access four times, and that is money that would have contributed to a re-roof where the access is paid for once.

The questions worth asking a roofer

Any roofer can tell you a roof needs replacing. The useful ones will tell you when it does not, and these questions get you there.

• Is this problem isolated or is it a pattern? The single most important question.
• What condition are the battens and underlay in? If they have gone, repairs are cosmetic.
• Is the covering itself sound, or is it the fixings? Slate outlasts its nails; that changes the answer.
• How long would a repair realistically buy me? A specific answer is a good sign.
• Is there anything structural going on? Ridge lines and slope planes tell you a lot.
• If it were your house, what would you do? The answer, and how readily it comes, is informative.

What you can check yourself, from the ground

• Stand back and look along the ridge line. It should be straight.
• Look along each slope from the end. It should be flat, not dished.
• Look for slipped or missing units — and note whether they are grouped or scattered.
• Look at the mortar on the ridge and verges for cracking or missing sections.
• In the loft, look for daylight, for staining on the timbers, and for whether there is any underlay at all.
• Check whether the loft insulation is damp — that points at the roof rather than at condensation alone.

Scattered rather than grouped is the telling one. Damage in one place has a cause; damage all over is a covering wearing out.

The case for replacing before you have to

There is one argument for replacement that is not about cost, and it is worth stating plainly: a roof replaced on your timetable is cheaper and less stressful than a roof replaced on the weather's.

A planned re-roof is booked when the diary suits, quoted properly, and done with the option of shopping around. A roof replaced after water has come through a bedroom ceiling costs the same to do plus everything inside the house it damaged first.

And one thing replacement gives you that repair does not

A complete re-roof renews a thermal element, so under regulation 23 of the Building Regulations 2010 it brings an insulation upgrade with it — a U-value of 0.16 W/(m²K) for an existing dwelling. Repairs carry no such requirement and deliver no such benefit.

It also produces a certificate, which repairs do not. That matters years later when a buyer's solicitor asks what was done to the roof and when.

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