Question 1

Which type of flat roof is best?

Accepted Answer

For a plain rectangular extension or garage, EPDM rubber is usually the simplest and best value — one sheet, no joints, no flame, and it goes down in a day. For complicated shapes, upstands and roofs that are on show, GRP fibreglass is generally better because it cures as one seamless laminate including the edges. There is no universally best flat roof; there is a best one for the roof in question. The variables that decide it are the shape, whether it is on view, whether anyone walks on it, and what the weather is doing when it has to be laid. EPDM rubber is the workhorse. It comes in wide sheets, so most domestic roofs are covered in one piece with no joints at all in the field — and since joints are where flat roofs fail, that removes most of the failure modes. It stays flexible in cold weather, tolerates deck movement, involves no flame, and goes down quickly. On a plain rectangle it is hard to beat on value. GRP fibreglass is laid wet and cures into a single rigid laminate that includes the upstands, corners and bonded edge trims — so there is no joint anywhere, not even at the perimeter. That makes it the better answer where the geometry is complicated: dormer tops, roofs with several penetrations, anything with kerbs and lanterns. It also finishes in a pigmented topcoat with optional anti-slip aggregate, which matters on a roof overlooked from a bedroom window. The trade-offs are real. GRP needs a dry, correctly specified deck and reasonable temperatures to cure, so it is not a November job — pushing it through in the wet is the commonest reason one fails early. And because it is rigid, a deck that moves underneath it can crack the laminate at a board joint. EPDM is more forgiving on both counts. Modern high-performance felt is still a legitimate choice, particularly on larger roofs, and is nothing like the 1970s product. The consideration there is hot work: torching an open flame against a timber-decked roof attached to a house carries a genuine fire risk, which is one of the reasons the domestic market has moved so far towards EPDM and GRP. Whichever is chosen, the same three things decide the outcome: a sound dry deck, a real fall, and properly detailed upstands and outlets. A cheap material laid well outlasts an expensive one laid badly, every time.

Question 2

EPDM or fibreglass?

Accepted Answer

For a plain rectangular extension or garage, EPDM rubber is usually the simplest and best value — one sheet, no joints, no flame, and it goes down in a day. For complicated shapes, upstands and roofs that are on show, GRP fibreglass is generally better because it cures as one seamless laminate including the edges. There is no universally best flat roof; there is a best one for the roof in question. The variables that decide it are the shape, whether it is on view, whether anyone walks on it, and what the weather is doing when it has to be laid. EPDM rubber is the workhorse. It comes in wide sheets, so most domestic roofs are covered in one piece with no joints at all in the field — and since joints are where flat roofs fail, that removes most of the failure modes. It stays flexible in cold weather, tolerates deck movement, involves no flame, and goes down quickly. On a plain rectangle it is hard to beat on value. GRP fibreglass is laid wet and cures into a single rigid laminate that includes the upstands, corners and bonded edge trims — so there is no joint anywhere, not even at the perimeter. That makes it the better answer where the geometry is complicated: dormer tops, roofs with several penetrations, anything with kerbs and lanterns. It also finishes in a pigmented topcoat with optional anti-slip aggregate, which matters on a roof overlooked from a bedroom window. The trade-offs are real. GRP needs a dry, correctly specified deck and reasonable temperatures to cure, so it is not a November job — pushing it through in the wet is the commonest reason one fails early. And because it is rigid, a deck that moves underneath it can crack the laminate at a board joint. EPDM is more forgiving on both counts. Modern high-performance felt is still a legitimate choice, particularly on larger roofs, and is nothing like the 1970s product. The consideration there is hot work: torching an open flame against a timber-decked roof attached to a house carries a genuine fire risk, which is one of the reasons the domestic market has moved so far towards EPDM and GRP. Whichever is chosen, the same three things decide the outcome: a sound dry deck, a real fall, and properly detailed upstands and outlets. A cheap material laid well outlasts an expensive one laid badly, every time.

Question 3

Rubber roof vs GRP

Accepted Answer

For a plain rectangular extension or garage, EPDM rubber is usually the simplest and best value — one sheet, no joints, no flame, and it goes down in a day. For complicated shapes, upstands and roofs that are on show, GRP fibreglass is generally better because it cures as one seamless laminate including the edges. There is no universally best flat roof; there is a best one for the roof in question. The variables that decide it are the shape, whether it is on view, whether anyone walks on it, and what the weather is doing when it has to be laid. EPDM rubber is the workhorse. It comes in wide sheets, so most domestic roofs are covered in one piece with no joints at all in the field — and since joints are where flat roofs fail, that removes most of the failure modes. It stays flexible in cold weather, tolerates deck movement, involves no flame, and goes down quickly. On a plain rectangle it is hard to beat on value. GRP fibreglass is laid wet and cures into a single rigid laminate that includes the upstands, corners and bonded edge trims — so there is no joint anywhere, not even at the perimeter. That makes it the better answer where the geometry is complicated: dormer tops, roofs with several penetrations, anything with kerbs and lanterns. It also finishes in a pigmented topcoat with optional anti-slip aggregate, which matters on a roof overlooked from a bedroom window. The trade-offs are real. GRP needs a dry, correctly specified deck and reasonable temperatures to cure, so it is not a November job — pushing it through in the wet is the commonest reason one fails early. And because it is rigid, a deck that moves underneath it can crack the laminate at a board joint. EPDM is more forgiving on both counts. Modern high-performance felt is still a legitimate choice, particularly on larger roofs, and is nothing like the 1970s product. The consideration there is hot work: torching an open flame against a timber-decked roof attached to a house carries a genuine fire risk, which is one of the reasons the domestic market has moved so far towards EPDM and GRP. Whichever is chosen, the same three things decide the outcome: a sound dry deck, a real fall, and properly detailed upstands and outlets. A cheap material laid well outlasts an expensive one laid badly, every time.

Question 4

Best flat roof material

Accepted Answer

For a plain rectangular extension or garage, EPDM rubber is usually the simplest and best value — one sheet, no joints, no flame, and it goes down in a day. For complicated shapes, upstands and roofs that are on show, GRP fibreglass is generally better because it cures as one seamless laminate including the edges. There is no universally best flat roof; there is a best one for the roof in question. The variables that decide it are the shape, whether it is on view, whether anyone walks on it, and what the weather is doing when it has to be laid. EPDM rubber is the workhorse. It comes in wide sheets, so most domestic roofs are covered in one piece with no joints at all in the field — and since joints are where flat roofs fail, that removes most of the failure modes. It stays flexible in cold weather, tolerates deck movement, involves no flame, and goes down quickly. On a plain rectangle it is hard to beat on value. GRP fibreglass is laid wet and cures into a single rigid laminate that includes the upstands, corners and bonded edge trims — so there is no joint anywhere, not even at the perimeter. That makes it the better answer where the geometry is complicated: dormer tops, roofs with several penetrations, anything with kerbs and lanterns. It also finishes in a pigmented topcoat with optional anti-slip aggregate, which matters on a roof overlooked from a bedroom window. The trade-offs are real. GRP needs a dry, correctly specified deck and reasonable temperatures to cure, so it is not a November job — pushing it through in the wet is the commonest reason one fails early. And because it is rigid, a deck that moves underneath it can crack the laminate at a board joint. EPDM is more forgiving on both counts. Modern high-performance felt is still a legitimate choice, particularly on larger roofs, and is nothing like the 1970s product. The consideration there is hot work: torching an open flame against a timber-decked roof attached to a house carries a genuine fire risk, which is one of the reasons the domestic market has moved so far towards EPDM and GRP. Whichever is chosen, the same three things decide the outcome: a sound dry deck, a real fall, and properly detailed upstands and outlets. A cheap material laid well outlasts an expensive one laid badly, every time.

Which type of flat roof is best?

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