Your GIB® Helpline Questions Answered: Intertenancy Walls and Stairs

News Articles Your GIB® Helpline Questions Answered: Intertenancy Walls and Stairs

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Your GIB® Helpline Questions Answered: Intertenancy Walls and Stairs

Monday, 8 December 2025
By Gordan White

We have details, answers, and solutions for most GIB® Helpline enquiries. Some straightforward, some elegant, and some are more involved, particularly when modifications are required during construction.

One common question relates to stairs adjacent to inter-tenancy (IT) walls.

Whether using GIB Barrierline® or a conventional double-frame specification, stairs need to be carefully detailed.

Where possible, it is always best to run stair stringers from floor to floor independently of the IT wall framing and lining(s). This avoids interfering with the wall linings and their intended function.

Fixing stringers to IT wall frames, whether direct or through linings, can lead to issues with the fire-resistance rating (FRR) and sound transmission class (STC) of the inter-tenancy wall specification. Although not controlled by the New Zealand Building Code, it can also lead to undesirable footfall noise being transmitted by stair users.

Stringers fixed through linings

When stair stringers are fixed through the inter-tenancy linings to the wall framing behind, the solution is straightforward. As the stringer offers joint protection, there is no need for plaster stopping behind it. However, and although the wall specification’s FRR and STC will be maintained, footfall noise might still annoy your neighbours.

Stringers fixed direct to framing

When stair stringers are fixed direct to the inter-tenancy wall framing, nogging above and below the stringer will be required to support the wall linings, and the final solution depends on the wall specification. Case by case assessment may be required.

For a GIB Barrierline® system, a simple solution is often possible because the apartment wall linings play a limited role in achieving the published FRR and the weight of the stringer and stairs will likely compensate for any loss in STC performance. Structural connections could still cause stair footfall noise transmission.

The solution for a conventional double stud system, with double linings and no central barrier, is often more complicated when linings have been compromised. Evaluation by acoustic and fire experts and sign-off by your local Council may be required. The impact of footfall noise can be significant.

Mid-level stair landing

In some applications the unit design calls for a mid-level stair landing. It is acceptable for a landing to connect to the frame of an IT wall however certain measures must be taken to maintain the fire and noise performance of the wall. Essentially the landing should be treated like a mid-floor. Solid blocking must be installed to support the edges of any wall linings that are interrupted by the landing and the underside of the landing must be lined with plasterboard. It is also essential that sound control infill (insulation) is installed in the framed cavity of the IT wall behind the stair landing.

Conclusion

To avoid complications design stringers and stairs to span between floors and away from IT wall framing and linings!