Abutment flashings — roof to wall junctions
In short
Wherever a roof runs into a wall — an extension against the house, a lean-to, a dormer cheek — the junction needs proper lead soakers and a cover flashing chased into the brickwork. Mortar fillets and bituminous paint are what you normally find there, and both crack.
Also called: Roof to wall flashing · Wall abutment · Cover flashing · Soakers
Signs you need this
- Damp on the wall or ceiling where an extension meets the house
- A mortar fillet at a roof-to-wall junction, cracked or falling away
- Black bituminous paint along an abutment
- Lead flashing lifted out of the wall joint
- One long unbroken run of lead along a junction
- Render taken down over the top of a flashing
An abutment is any place a roof slope meets a vertical wall, and it is one of the small number of details responsible for most roof leaks. Extensions abutting the main house, lean-tos, dormer cheeks, porches against a gable — all of them are the same problem and all of them want the same solution.
The correct detail has two parts. Soakers are individual pieces of lead that interleave with each course of slate or tile and turn up the wall — so water on the covering is lifted and taken up rather than running into the joint. Over the top of them, a cover flashing is chased into a mortar course in the wall, wedged with lead wedges, pointed in, and dressed down over the soakers. Water on the wall lands on the flashing and is thrown clear.
What you find instead, on a large proportion of houses, is a mortar fillet: a triangular wedge of mortar filling the angle between the roof and the wall. It works when it is new and it cracks, because brick, mortar and roofing material all move differently and the fillet is restrained on both sides. Once it has cracked it is worse than nothing, because it holds water in the joint instead of shedding it.
The other thing you find is bituminous paint — a black stripe over the whole junction, sold as a repair and functioning as a concealment. It bridges the crack for a season or two, and behind it the water carries on getting in and the timber carries on rotting where nobody can see. Removing it is part of the job rather than painting over it again.
The lead rules apply here as everywhere: pieces kept short and lapped rather than run as one length, correct code for the position, no sharp arrises under the sheet, and compatible fixings. A cover flashing run twenty feet along an extension abutment in one piece will split, and it will split in the middle.
Where the wall is rendered rather than brick, the detail changes — the flashing has to be taken behind the render or into a purpose-formed chase, and rendering over the top of a flashing is a guaranteed future leak because the render cracks at the joint and water runs behind it. That is a coordination point worth raising before a renderer arrives, not after.
What the job covers
- Old fillets and bituminous coatings removed rather than covered
- Individual soakers interleaved with each course of covering
- Cover flashing chased, wedged and pointed into the wall
- Lead sized and lapped correctly for thermal movement
- Correct code lead for the position and exposure
- Timber behind the junction checked for rot while it is open
What it costs
We don't publish a price for this yet, because a number pulled out of the air is worse than no number at all — your roofer has to honour it. On roofing it would also be close to meaningless: access is often the biggest single factor, and it varies enormously house to house. You'll get a firm price for your actual job when they ring you back, before any work starts. The quote itself is free and there's no obligation either way.
Common questions
Is a mortar fillet ever acceptable?
Not as a permanent detail at a roof-to-wall junction. Brick, mortar and roof covering all move at different rates, so a restrained fillet cracks — it is a question of when. Once cracked it holds water in the joint rather than shedding it, which is worse than having nothing there. The correct detail is soakers and a chased cover flashing.
What are soakers and do I need them?
Individual lead pieces that interleave with each course of slate or tile and turn up the wall, lifting water away from the joint. On a slated or plain-tiled abutment, yes, you need them — a cover flashing on its own leaves the water free to run into the joint between courses. A flashing job with no slates disturbed has usually skipped this.
Can the flashing go over the render?
It should go behind it, or into a proper chase. Render taken down over the top of a flashing cracks at the joint and lets water run behind the flashing, which is a guaranteed future leak and an awkward one to diagnose. If rendering is planned, the flashing detail needs agreeing first.
Why does my extension leak where it meets the house?
It is the single commonest place for an extension to leak, and it is nearly always the abutment detail — a mortar fillet, a flashing not chased in properly, or missing soakers. It is also entirely fixable, and once done correctly it should not need touching again for decades.
Need this doing in Macclesfield?
Tell us the job and it goes straight to our local roofer — one call back, usually the same day. Free quote, no obligation.