What is a spiegeloplegging?
A spiegeloplegging is a way of supporting a hollow-core slab floor in which the insulation fitted to the underside of the slab is held back at the bearings. The concrete hollow-core slab rests at its ends directly on the foundation or load-bearing wall, while the area in between is insulated on the crawl space side. That insulated central area is called the mirror panel (spiegelveld). Spiegel (mirror) here means a panel set within a frame, in this case the uninsulated strips at the bearings.
How it works
- Factory-fitted insulation. Hollow-core slabs can be supplied by the manufacturer with insulation boards bonded to the underside. This saves work in the cramped crawl space.
- Concrete on concrete. Because there is no insulation at the bearings, the slab rests on the support with its full cross-section. The load is thus transferred directly.
- Alternative. With a nib bearing (nokkenoplegging), the insulation does run to the end of the slab and the floor rests on projecting nibs. Which variant suits depends on the foundation detail and the manufacturer’s system.
Application
- Agree the detail with the supplier. The length of the held-back strip and the minimum bearing length follow from the floor manufacturer’s system and the structural engineer’s calculation.
- Limit the thermal bridge. There is no insulation under the slab at the bearings. Make sure the foundation detail connects, for example with insulation against the ground beam or in the cavity down to below floor level, so that no major thermal bridge is created.
- Protect the insulation. Do not move or work in the crawl space in a way that damages the insulation boards; loose boards no longer work.
- Ventilate the crawl space. Even with an insulated floor, crawl space ventilation is still needed to remove moisture.
Common mistake: during installation, letting a slab still rest on the bearing with its insulated side, for example due to an incorrect slab length. The insulation is then compressed and the bearing does not match the calculation.
Related terms
- Hollow-core slab floor
- Bearing
- Crawl space
- Thermal bridge
- Structural topping
- Hinged bearing
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