How do I tell if a lintel has failed?

Every opening in a masonry wall needs something spanning it, and on a domestic house that is a steel lintel, a concrete lintel, a brick arch, or — on older or altered work — sometimes a timber that has since rotted. The failure is progressive and quiet, and the point of knowing the signs is to catch it while it is a repair rather than a collapse. The drawing shows the four ways an opening is spanned and the six signs that the support is going.

Safety

Step by step

1. Work out what is spanning the opening.A painted metal edge above the window in a modern cavity wall is a steel lintel. A grey band with a visible soffit is often precast concrete. Bricks turned on end are a soldier course, which usually is not the structure — there is normally a hidden steel or concrete lintel behind it. Bricks curving over the opening are an arch, which carries load into the piers each side.
2. Sight along the wall rather than at it.Stand at one end of the elevation and look along the face. A sag of a few millimetres over an opening is nearly invisible from in front and obvious from the side. Do the same along the head of the opening from inside.
3. Look at the ends, not the middle.A lintel that is failing usually cracks the masonry at its bearings, where it sits on the wall each side, rather than at the centre. Vertical or diagonal cracking at both ends of an opening is a strong signal.
4. Check for a diagonal crack from a top corner.Openings concentrate stress at their corners and a fine diagonal crack there is often benign. But the same crack is what a failing lintel produces, so this is the location where the two possibilities have to be separated rather than assumed.
5. Look for dropped bricks or a slipped soldier course.Bricks that have dropped out of line above an opening, a soldier course sagging in the middle, or an arch whose voussoirs have slipped, all mean the support has moved.
6. Look for rust staining or a swollen line.A steel lintel or an old steel angle corroding inside the wall expands and pushes the masonry apart, producing a horizontal crack, a bulge, or rusty staining bleeding out at the joint above the opening. This is a well-recognised failure on mid-century steel.
7. Check the window and door.A frame that has begun to bind, a sash that has stopped running, a door catching at the top, or glass that has cracked without impact all suggest the frame is taking load it was not designed for — which happens when whatever is above it stops carrying the load.
8. Check inside and outside.In a cavity wall the two leaves may be spanned separately, and one can fail while the other looks fine. Look above the opening on both faces.
9. Stop and get a structural engineer.This is the boundary. A suspected failed lintel is a structural assessment, and a replacement is a propped operation requiring a designed lintel with correct bearings, and building regulations approval. It is not a DIY job at any level and it is not a job for a general handyman.
10. Do not disturb anything in the meantime.No drilling, chasing or fixing near the opening. Do not remove the window or the door. Do not take out an internal wall below or beside it. And do not fill the crack, because it is the evidence.
11. Deal with the water if corrosion is the cause.Steel corrodes because it gets wet, so any repair goes alongside sorting out the cavity tray, the weep holes, the pointing and the sill detail above and around the opening.

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