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The Mixed Message

Mixedmesssage1The term ‘mixed use’ can cover buildings such as where flats are over retail units; but it can also be applied where flats come complete with an enclosed undercroft parking area.  In these situations, there will be a floor that separates the different uses.

The robustdetails® scheme is intended for dwelling-to-dwelling separation, so it would not normally be appropriate to apply the scheme to this floor.  Therefore, your building control body (BCB) will need to confirm their requirements regarding the acoustic performance.  In the case of commercial units, the BCB may request a higher-performing floor; or with undercroft parking, they may regard this as an external space, meaning that Approved Document E (Part E) would not apply to these areas.

Mixedmessage2Separating Walls

Buildings of this kind will often employ a podium slab, which can have implications on the first floor separating walls.

If the podium uses precast concrete (either plank, or beam & block), separating walls built off this cannot be Robust Details.  However, if the podium is reinforced concrete; or structural steel frame with a composite floor, provided the slab is insitu-poured with a min. 365kg/m2 mass and min. 150mm thickness, then robustdetails® walls can be constructed on top.

Light-framed separating walls can be erected directly on top of the slab following the raft foundation detail (above), but note that a floating floor treatment must be included (regardless of whether impact resistance is required), as this shields the junction at the base of the wall.

Cavity masonry walls could also be considered, provided they can incorporate the Icopal-monarfloor® bridgestop® system following the guidance in Appendix A2 to the Handbook.  However, not all cavity masonry walls have been approved for use with this system, so you should refer to Table 6a in the Introduction to the Handbook to check compatibility.


With all the above in place, 1st floor flats could be registered for the walls and the separating floor between the flats – as can flats on upper storeys – provided of course, they also meet all the relevant robustdetails® specifications.

If you have any techncial enquiries please do not hesitate to contact our technical team on 03300 882140 or email:

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