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Frequently Asked Questions
Why does this joint need a connector?
Because the alternative is a toe-nail into the end of a sloping member.
That is close to the weakest connection possible in timber.
The stringer arrives at an angle, so fasteners cannot be driven square.
The cut end exposes end grain, which holds fasteners poorly.
Notching for treads removes material where the connection needs it.
All three problems compound at the same point.
How much load does a stair connection carry?
More than people assume, and more than the floors it connects.
Stairs carry concentrated live loads.
They also carry dynamic loading as people move.
Codes generally specify higher design loads for stairs than for floors.
A connection sized by eye is usually under-specified.
The published tables give the figure rather than the appearance of the timber.
Why is failure here particularly serious?
Because it happens under a person, at height, with nothing to catch them.
Most timber connections fail into something else.
A stair connection failing drops someone down a flight.
That makes the joint worth attention out of proportion to its size.
It is also a joint that is used constantly rather than occasionally.
Deterioration therefore shows up in service rather than sitting unnoticed.
What does notching do to the stringer?
It removes material exactly where the connection needs it.
Cut stringers are notched to receive the treads.
The remaining section is much smaller than the original timber.
Connectors designed for that geometry support the remaining section.
Others rely on material that is no longer there.
Matching the connector to whether the stringer is cut or housed matters.
Does the connector suit any stair angle?
Only within the range it is made for.
Stair pitch varies between installations.
Some connectors accommodate a range of angles.
Others are specified for a particular pitch.
Forcing a flat connector into a pitched joint leaves it bearing on an edge.
Measuring the actual pitch rather than assuming the drawing is more reliable.
What about the bottom of the stringer?
It needs its own connection, and it is a different problem.
The bottom bears on a floor or a slab.
It has to resist the stringer sliding outward.
That thrust is what pushes a flight apart under load.
Where the base sits on concrete, moisture is a further consideration.
A standoff base keeps the end grain out of any water that collects.
Are stair requirements consistent between markets?
No - stair construction and loading are covered in detail and differ.
Design loads for stairs vary between codes.
Dimensional requirements for rise and going differ too.
Connector approvals are market-specific as always.
Public and workplace stairs generally carry stricter requirements.
The local code governs alongside the manufacturer's tables for that market.