Water is coming in around the chimney

What has probably happened

• The flashing where the chimney meets the roof has failed, lifted or was never done properly.
• The crown — the concrete slab on top — has cracked, so water runs straight into the masonry.
• There is no cap, so rain goes directly down the flue.
• The brick and mortar have gone porous, and the whole stack is soaking up water.
• Freeze and thaw has spalled the brick faces off.
• Condensation inside the flue, which looks exactly like a leak and is not one.

What the technician does

• The entry point is traced rather than sealed over — water travels before it drips.
• Flashing replaced and properly counter-flashed into the mortar joint.
• Crown repaired or recast so it sheds water away from the brick.
• A cap fitted, which also keeps out animals and cuts down draft problems.
• Repointing where the mortar joints have gone, and spalled brick replaced.
• Water-repellent treatment on the masonry where it is appropriate — the breathable kind, not a sealer that traps moisture in.

Questions people ask

The stain only appears when it rains hard from one direction.

That points at flashing or a crown crack on that side. Wind-driven rain finds gaps that ordinary rain runs past, which is why these leaks are so intermittent and so often misdiagnosed.

Can it be fixed without a whole rebuild?

Usually. Flashing, crowns and caps are the common repairs. A rebuild is for a stack that has lost its structure, and your technician should be able to show you why if they say so.

There is white powder on the brick.

That is efflorescence — salts left behind as water moves out through the masonry. It is cosmetic in itself, but it is proof the chimney is taking on water.