Stairway to heaven or footsteps fall?
One of the most common design queries we get is how to design private staircases in flats so that both robustdetails® floors and walls can be used, thus avoiding the need for pre-completion testing (PCT). Basically there are two ways that work, and one way that doesn’t.
An example of the first way that works is the layout below. The stairwell is completely enclosed (i.e. with no under-stairs access), allowing the floor to be built into a cavity wall for its whole perimeter.
The resultant flanking junction around the stairwell can now be constructed in a very similar way to the external flanking junction for the concrete floors shown in the robustdetails® handbook, so it now meets the robustdetails® requirements.
The wall needs to resist noise transferring from the stairwell into the lower flat and so it needs to meet all the relevant robustdetails® specifications, including finishes to both sides.
The second way to design a private staircase that meets robustdetails® specifications is to put the staircase outside:
The most common way of getting it wrong is by mixing stairwell wall construction. A typical layout of this type would look something like this:
With this situation, the sound from the upper flat can more easily flank into the stairwell – so now it’s down to the cavity wall to stop the sound getting into the flat below.
But unfortunately, the isolation provided by the cavity has been totally compromised by the floor, resulting in a flanking path straight through from the stairwell.
Flats with this design will be outside the scope of robustdetails® and would have to go through PCT.
So to keep your flat designs compliant with robustdetails®, stick to the first two designs. After all, two out of three ain’t bad.
If you have any techncial enquiries please do not hesitate to contact our technical team on 03300 882140 or email: email@example.com
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