The answer is yes you can, but with great care. In an ideal world you would have made provision for the Klan spiral staircase baseplate at the installation stage of the underfloor heating. By that I mean that you would have left an area at the centre point of the stair approx 500mm x 500mm with no heating pipes or electrical cables in it. However it is not a perfect world so a different approach is needed if the floor is already complete..

There are two basic problems to overcome if you are trying to fit a spiral staircase over an existing solid floor with underfloor heating in it. First you must not at all costs drill a fixing hole into a water pipe or electricity cable. Secondly you have to make sure that the baseplate of the spiral staircase is not sitting on anything compressible which will cause the stair to move. Bear in mind that the 200mm diameter base plate of your 200 kgs. Klan spiral stair has to take not only its self load but also your 150kgs granny as she wanders drunkenly up the new spiral staircase. Modern construction requires an insulation layer somewhere in the floor construction, this normally will have something like a 75mm concrete screed over it; this being adequate to take all normal loads without compression. However a point load like a spiral stair may need considering.

Solutions to both of these problems is really a matter of common sense. First you need to know the details of the floor construction so that you are aware just how just how deep you can drill, and the amount of compression that is likely. If there is no floor finish on top of the screed I personally would consider carefully breaking up the screed around the area of the base plate and shoving any pipes or cables out of the way if possible or at least marking their position if not. I would also remove any under screed insulation for a small area directly under that baseplate. The floor would then be re-screeded including the area of removed insulation. Once this has cured you can mark the runs of pipes or cables on it, so that you know where you can drill. Assuming that this is not on, then alternately you will need to replace any supplied expansion bolts with shorter alternatives that you can be sure will not penetrate the screed. This will of course not help the compression of insulation problem, which may not be a problem anyway. Should you decide it is, then your options are limited to digging it out as above or spreading the load over a greater area by forming some form of plinth under the spiral stair. Bearing in mind that this will affect the overall height of the Klan spiral stair. A customer once suggested that rather than sit the stair on his wood block flooring he would sit the base plate down on the screed and carefully cut the wood block around it. This would prevent any lateral movement of the baseplate without any further fixing needed. I am not sure I could totally recommend this action but preventing lateral movement is for sure half the battle of fixing the baseplate.

In conclusion do not be put off, a Klan spiral staircase will look good and function well, and in my time I come across a great many spiral stairs that have been fitted on top of underfloor heating systems without any problems.

The Spiral Staircase Doctor