Flat Roof Problems On 1960s Extensions: Repair Or Replace?

By Chris, owner of Everlast Roofing North West (20+ years on Merseyside roofs) · About Everlast Roofing · Last updated 2026-08-16

There are thousands of them across Crosby, Maghull, Formby and the rest of north Liverpool. A kitchen or a dining room stuck on the back of a semi somewhere between about 1960 and 1980, with a flat roof over it. They were built quickly, they were built cheaply, and the flat roof was almost always three-layer bitumen felt on a chipboard or timber deck.

Sixty years on, most of them are on their second or third covering, and the owners are stuck in the same loop: a leak appears, someone patches it, it stops for a winter, then it comes back somewhere else. If that is where you are, the question is not really how to stop this leak. It is whether the roof has anything left in it at all. Here is how I work that out on Merseyside extensions, and what each answer costs.

Common Flat Roof Problems On 1960s And 1970s Extensions

Almost every flat roof problem I see on a Merseyside extension falls into one of five categories. Knowing which one you have tells you most of what you need to know about the bill.

• Ponding water. Water still sitting on the roof more than 48 hours after rain. It means the falls are wrong or an outlet is blocked, and standing water will find any weakness eventually.
• Blisters and bubbles in the felt. Moisture trapped between layers expanding in the sun. A blister that has not split is not urgent. One that has split is an open hole.
• Cracked or perished felt. Bitumen goes brittle with UV exposure. On a roof over about fifteen years old you will see a crazed, alligator-skin surface, and that is the covering telling you it is done.
• Failed upstands and flashings. Where the flat roof meets the house wall. This is the single most common leak point on an extension, and it is almost always a repair rather than a replacement.
• A soft or sagging deck. Walk on it and it gives underfoot. The chipboard or timber below has been wet long enough to fail structurally. This one changes everything.

The first four are repairs. The fifth is not. That distinction is the whole point of this article, and I will come back to it properly further down.

One thing worth saying early: a flat roof leak almost never appears directly under the hole. Water runs along the underside of the deck and drops at the lowest point or at a joist, which can be two metres away from where it got in. If water is coming in right now, get a temporary cover on it first. Our emergency roof repair service exists precisely for that gap between the leak starting and the proper fix being scheduled.

Why Flat Roof Leak Problems Start At The Upstands

If I had to bet on where a 1960s extension is leaking without seeing it, I would say the upstand, and I would be right most of the time.

An upstand is the bit where the flat roof turns up the house wall. On a properly built roof the covering runs up that wall at least 150mm and is tucked into a chase cut in the brickwork, then covered with a lead or aluminium flashing. On a lot of Merseyside extensions it was never done that way. The felt was simply turned up the wall and the top edge sealed with mastic, which lasts perhaps five years before it shrinks and cracks.

The second favourite is the outlet. Sixty-year-old extensions often have a single small outlet at one corner and no overflow. Leaves, moss and grit off the main roof wash down, the outlet blocks, and the whole roof becomes a shallow pond. Then the water finds the weakest joint and comes in.

Third is the junction between the extension roof and the main roof above it, where the flashing has lifted or the mortar chase has weathered out. This is where flat roof problems and pitched roof problems meet, and where a lot of roofers guess. It is worth having someone actually get up there and photograph it rather than diagnose it from a ladder.

The reason all of this matters financially is simple: upstand, outlet and flashing failures are repairs. They typically sit between two hundred and six hundred pounds. Nobody needs a new roof because a flashing has lifted, and if someone quotes you a full replacement without showing you a soft deck, get a second opinion. A roof inspection with photographs will settle it either way.

Flat Roof Lifespan: How Long Should A Flat Roof Last?

The honest answer depends entirely on what is up there, and on a 1960s extension it has usually been recovered at least once already. Here is what each system realistically gives you in the North West.

Covering	Realistic lifespan	How you spot it
Original 1960s bitumen felt	10 to 15 years	Crazed surface, grey mineral chippings, brittle edges
Modern three-layer torch-on felt	15 to 20 years	Smooth, welded seams, usually charcoal or green
GRP fibreglass	20 to 30 years	Seamless, slightly glossy, no joints across the field
EPDM rubber	25 to 35 years	Matt black, one large sheet, soft underfoot
The timber deck underneath	Indefinite if kept dry	Give underfoot means it is not

That last row is the one that matters. The covering is a consumable. The deck is the asset. A flat roof that has been recovered promptly every fifteen years can have its original 1965 deck in perfectly serviceable condition. A flat roof that was left leaking for three winters will have a deck that needs replacing whatever you put on top.

So when someone asks me how long their flat roof has left, the first thing I do is walk on it. Not the covering. The deck.

Flat Roof Repair Or Flat Roof Replacement: How To Decide

Here is the test, and it takes about ten minutes on the roof.

What we find	What it means	Verdict
Deck firm, covering sound, leak at the upstand	Detailing has failed, the roof has not	Repair
Deck firm, one or two split blisters	Localised covering failure	Repair
Deck firm, covering crazed all over	Covering is at end of life, deck is fine	Re-cover, keep the deck
Deck soft or springy anywhere	Water has been getting in long enough to rot timber	Strip and rebuild
Ponding plus a soft deck	Falls are wrong and the damage is done	Strip, re-fall, rebuild

The middle option is the one people do not know exists, and it is the one that saves the most money. If the deck is sound but the felt is finished, you do not need a rebuild. You need a re-cover: strip the old felt, check and fix the deck, add insulation if there is height for it, and lay a new EPDM or GRP membrane. That is typically half the cost of a full strip-and-rebuild and gives you thirty years.

Which membrane depends on the roof. EPDM rubber suits big simple rectangles because it goes down as one sheet with no seams to fail. GRP fibreglass suits roofs with lots of edges, upstands and penetrations because it cures seamless around awkward shapes. Both comfortably outlast felt.

One caveat worth knowing before you get quotes: if you are thinking of turning the extension roof into a balcony or a terrace, that is a structural question and a different job. We cover that separately in our guide to flat roof conversions in Liverpool.

Flat Roof Replacement Cost In Crosby, Maghull And Liverpool

These are the figures I quote across north Liverpool and Sefton on a typical extension roof of around 15 to 20 square metres. Access is usually straightforward on a single-storey extension, which keeps scaffold costs down or removes them entirely.

• Repair a failed upstand or flashing: £200 to £600.
• Patch split blisters and reseal: £180 to £400.
• Clear and re-set a blocked outlet, correct a local fall: £250 to £600.
• Re-cover in EPDM or GRP, keeping a sound deck: £1,800 to £3,200.
• Full strip and rebuild with new deck, insulation and membrane: £3,000 to £5,500.

Those ranges assume a standard rear extension. A wraparound, a roof with several penetrations, or anything needing scaffold will sit higher. For a fuller breakdown of repair pricing specifically, including what drives each number, see our detailed guide to flat roof repair costs in Liverpool.

The comparison that catches people out is repair against re-cover. If your covering is crazed all over and you are paying three hundred pounds a year to keep patching it, you will spend the cost of a full EPDM re-cover in about eight years and still have a sixty-year-old felt roof at the end of it. Re-covering resets the clock for thirty years.

Whatever you are quoted, get it itemised: strip and dispose, deck repairs, insulation, membrane, edge trims, outlet, and labour as separate lines. If a quote is one number with no breakdown, you cannot tell whether the deck and the insulation are included, and those are the two things most commonly left out. Call Chris on 07933 828 045 if you would rather talk it through than read a quote.

How To Fix Ponding On A Flat Roof

Ponding is water still sitting on the roof two days after it stopped raining, and it is worth treating as a problem in its own right rather than waiting for it to cause a leak.

A flat roof is not actually flat. It should have a fall of at least 1:80 built in, so water runs to the outlet. On a 1960s extension the fall was often 1:120 or nothing at all, and sixty years of slight deck deflection has made it worse. Standing water then does three things: it accelerates UV and frost damage to the covering, it adds weight, and it finds any pinhole given long enough.

• If the outlet is blocked, clearing it is a twenty minute job and may solve the whole thing.
• If the fall is slightly out, tapered insulation boards laid under a new membrane will correct it without touching the structure.
• If the deck has deflected between joists, the deck needs attention before any covering goes on, because a new membrane over a dished deck will pond exactly the same way.
• If there is no outlet at all, which happens more than you would think, one needs cutting in and connecting properly.

What does not fix ponding is another layer of felt over the top. It adds weight to a deck that is already deflecting, and the water sits in the same place it did before.

We see this most on extensions in the flatter parts of Crosby, Maghull and Bootle where the original build quality varied a lot street to street. If you are local, we cover Crosby, Maghull, Bootle and the rest of Liverpool, and the survey and written quote work the same way wherever you are.

• Water still on the roof 48 hours after rain is ponding, and it needs the fall or the outlet fixing.
• A leak rarely appears under the hole; water runs along the deck and drops at the lowest joist.
• Upstand, flashing and outlet failures are repairs, typically two to six hundred pounds.
• Walk the roof: if the deck gives underfoot, no patch or new covering will fix it on its own.
• A sound deck with dead felt means a re-cover, not a rebuild, and that halves the bill.
• Original 1960s felt gives 10 to 15 years; EPDM gives 25 to 35.
• Another layer of felt over a ponding roof adds weight and changes nothing.
• Get the quote itemised: strip, deck, insulation, membrane, trims, outlet, labour.

Frequently Asked Questions

For more local roofing advice, browse the Everlast Roofing blog or call Chris on 07933 828 045.