Question 1

Why is my roof sagging?

Accepted Answer

Many old roofs have carried a gentle dip for a century with no consequence at all — settlement in a Victorian roof is normal. What matters is whether it is moving. A dip that has appeared or deepened in the last few years is a structural question and needs looking at properly. A sagging roof line worries people more than it usually should, and the useful distinction is between a shape and a movement. Plenty of old roofs settle. Victorian carpenters worked with the timber they had, purlins deflect slowly over decades, and a slate roof beds down. A gentle, even dip that looks the same in today's photograph as it does in one from twenty years ago is a characteristic of the building rather than a fault, and it needs nothing doing to it. What is not benign is change. A dip that has appeared, deepened or gone from even to localised in a few years means something is still moving, and that needs identifying before any money goes on the covering. The classic serious cause is spreading. A pitched roof pushes outwards at the eaves, and something has to resist that — traditionally ceiling joists acting as ties, or a proper collar arrangement. If those have been cut, usually to make a loft conversion and sometimes decades ago by somebody who did not think it mattered, the roof spreads, the walls bow outwards and the ridge drops. The tells are a dropped ridge, walls bulging at first-floor level, and cracked plaster following the line of a wall head. Rot is the other cause, and it is usually local. A leak that has run for years soaks a rafter or a purlin end and the timber softens where it bears. Rafter feet at the eaves are the classic location, because that is the wettest, coldest, least ventilated part of the roof and it sits directly behind the gutter. The honest position on when to call a structural engineer: for localised rot in a rafter foot, no — that is a carpentry repair. For a roof that is spreading, a purlin that has deflected, or anything where the walls are moving, yes. A roofer who tells you plainly that this one is beyond them is doing you a favour, because the alternative is a new covering laid over a problem that is still moving.

Question 2

Dip in my roof line

Accepted Answer

Many old roofs have carried a gentle dip for a century with no consequence at all — settlement in a Victorian roof is normal. What matters is whether it is moving. A dip that has appeared or deepened in the last few years is a structural question and needs looking at properly. A sagging roof line worries people more than it usually should, and the useful distinction is between a shape and a movement. Plenty of old roofs settle. Victorian carpenters worked with the timber they had, purlins deflect slowly over decades, and a slate roof beds down. A gentle, even dip that looks the same in today's photograph as it does in one from twenty years ago is a characteristic of the building rather than a fault, and it needs nothing doing to it. What is not benign is change. A dip that has appeared, deepened or gone from even to localised in a few years means something is still moving, and that needs identifying before any money goes on the covering. The classic serious cause is spreading. A pitched roof pushes outwards at the eaves, and something has to resist that — traditionally ceiling joists acting as ties, or a proper collar arrangement. If those have been cut, usually to make a loft conversion and sometimes decades ago by somebody who did not think it mattered, the roof spreads, the walls bow outwards and the ridge drops. The tells are a dropped ridge, walls bulging at first-floor level, and cracked plaster following the line of a wall head. Rot is the other cause, and it is usually local. A leak that has run for years soaks a rafter or a purlin end and the timber softens where it bears. Rafter feet at the eaves are the classic location, because that is the wettest, coldest, least ventilated part of the roof and it sits directly behind the gutter. The honest position on when to call a structural engineer: for localised rot in a rafter foot, no — that is a carpentry repair. For a roof that is spreading, a purlin that has deflected, or anything where the walls are moving, yes. A roofer who tells you plainly that this one is beyond them is doing you a favour, because the alternative is a new covering laid over a problem that is still moving.

Question 3

Is a sagging roof dangerous?

Accepted Answer

Many old roofs have carried a gentle dip for a century with no consequence at all — settlement in a Victorian roof is normal. What matters is whether it is moving. A dip that has appeared or deepened in the last few years is a structural question and needs looking at properly. A sagging roof line worries people more than it usually should, and the useful distinction is between a shape and a movement. Plenty of old roofs settle. Victorian carpenters worked with the timber they had, purlins deflect slowly over decades, and a slate roof beds down. A gentle, even dip that looks the same in today's photograph as it does in one from twenty years ago is a characteristic of the building rather than a fault, and it needs nothing doing to it. What is not benign is change. A dip that has appeared, deepened or gone from even to localised in a few years means something is still moving, and that needs identifying before any money goes on the covering. The classic serious cause is spreading. A pitched roof pushes outwards at the eaves, and something has to resist that — traditionally ceiling joists acting as ties, or a proper collar arrangement. If those have been cut, usually to make a loft conversion and sometimes decades ago by somebody who did not think it mattered, the roof spreads, the walls bow outwards and the ridge drops. The tells are a dropped ridge, walls bulging at first-floor level, and cracked plaster following the line of a wall head. Rot is the other cause, and it is usually local. A leak that has run for years soaks a rafter or a purlin end and the timber softens where it bears. Rafter feet at the eaves are the classic location, because that is the wettest, coldest, least ventilated part of the roof and it sits directly behind the gutter. The honest position on when to call a structural engineer: for localised rot in a rafter foot, no — that is a carpentry repair. For a roof that is spreading, a purlin that has deflected, or anything where the walls are moving, yes. A roofer who tells you plainly that this one is beyond them is doing you a favour, because the alternative is a new covering laid over a problem that is still moving.

Question 4

Wavy roof

Accepted Answer

Many old roofs have carried a gentle dip for a century with no consequence at all — settlement in a Victorian roof is normal. What matters is whether it is moving. A dip that has appeared or deepened in the last few years is a structural question and needs looking at properly. A sagging roof line worries people more than it usually should, and the useful distinction is between a shape and a movement. Plenty of old roofs settle. Victorian carpenters worked with the timber they had, purlins deflect slowly over decades, and a slate roof beds down. A gentle, even dip that looks the same in today's photograph as it does in one from twenty years ago is a characteristic of the building rather than a fault, and it needs nothing doing to it. What is not benign is change. A dip that has appeared, deepened or gone from even to localised in a few years means something is still moving, and that needs identifying before any money goes on the covering. The classic serious cause is spreading. A pitched roof pushes outwards at the eaves, and something has to resist that — traditionally ceiling joists acting as ties, or a proper collar arrangement. If those have been cut, usually to make a loft conversion and sometimes decades ago by somebody who did not think it mattered, the roof spreads, the walls bow outwards and the ridge drops. The tells are a dropped ridge, walls bulging at first-floor level, and cracked plaster following the line of a wall head. Rot is the other cause, and it is usually local. A leak that has run for years soaks a rafter or a purlin end and the timber softens where it bears. Rafter feet at the eaves are the classic location, because that is the wettest, coldest, least ventilated part of the roof and it sits directly behind the gutter. The honest position on when to call a structural engineer: for localised rot in a rafter foot, no — that is a carpentry repair. For a roof that is spreading, a purlin that has deflected, or anything where the walls are moving, yes. A roofer who tells you plainly that this one is beyond them is doing you a favour, because the alternative is a new covering laid over a problem that is still moving.

Why is my roof sagging?

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