Chimneys and guttering

Chimneys

If we had to name the most misdiagnosed damp in a house it would be the chimney, and it is not close. A stack is exposed on all four sides, has no roof of its own, and is held together by mortar that is often a century old. Water gets in at the top through cracked flaunching or open joints, runs down inside the flue, and shows up on a wall a floor or two below - which is why people spend money on entirely the wrong wall.

The other thing we find constantly is a cement fillet where the lead flashing should be. A lot of stacks had theirs replaced with a triangle of sand and cement at some point in the eighties, because it is quicker. Cement is rigid, the stack and the roof move independently, and it always cracks in the end. Lead flexes and lasts forty to sixty years.

Worth knowing: not all chimney damp is a leak. It can be condensation in a cold unventilated flue, or salts drawn out of an old lining. Three different problems, three different fixes, so we look inside as well as up before recommending anything.

Flashings in lead are £450 to £950. Repointing above the roof line is £600 to £1,500 - and on older soft brickwork it wants a lime mix, because hard modern cement traps moisture and pushes the decay into the bricks. New flaunching with the pots rebedded is £350 to £700, much less if it is done while the access is already up. Taking a redundant stack down to below the roof line and making good is £900 to £2,000.

Guttering, fascias and soffits

Clearing a gutter is the cheapest job on this website and it prevents the most expensive one. A gutter that overflows at one corner soaks the fascia behind it, the fascia rots, the rafter ends follow, and a fifty pound bracket job becomes several thousand pounds of timber work. Bromley is one of the greenest boroughs in London, which is lovely to live in and hard on gutters every October.

When a fascia does need replacing we take the old board off rather than capping over it. Capping means fixing new plastic over the existing timber - quicker, cheaper, and it seals a rotten board and whatever is happening to the rafter ends behind a nice new cover. You cannot tell the difference once it is finished, which is exactly why it is worth asking about.

Clearing gutters and downpipes on a standard semi is £90 to £180. New guttering is £25 to £45 a metre. A full roofline - gutters, fascias and soffits together - runs £1,400 to £3,200 depending on the length and the access.

A few questions we get

My chimney breast is damp but the roof looks fine.

That is the classic. It usually means water is getting in at the top of the stack rather than through the roof at all. Worth having looked at before winter.

Can you take a chimney down?

Yes, normally to below the roof line with the covering made good over the top. Removing the breast inside the house too is a bigger and structural job. We will be honest about whether you will regret losing the fireplace.

How often should gutters be cleared?

Once a year, late autumn, after the leaves are down. Twice if you have mature trees directly overhead, which on a lot of streets round here you do.

There are birds nesting in my soffit.

Then it has to wait. Nesting birds are legally protected while the nest is in use. We will make a temporary repair to keep the weather out and come back properly from late summer.