Roger Bisby lays some Knauf Brio dry screed flooring.
Although it is perfectly possible to use warm water underfloor heating with timber and floating floors it is generally acknowledged that there is a loss of thermal transmission compared to pipe buried in sand and cement screeds. Knauf Brio dry screed board bring thermal transmission comparable with wet screed system in a convenient dry laid board made of fibres and gypsum. There is also a saving on floor height compared with wet screeds.
Unlike chipboard and other timber based boards Brio is said to be ‘thermally transparent’ which means it doesn’t resist heat to anything like the degree of timber. The warm up time of Brio is therefore a lot faster than other boards and because it is only 23mm thick it is even faster than pipe in screed. This allows you to easily achieve the designed watts per metre from underfloor heating without resorting to closer pipe spacings. I laid Brio on a NuHeat pipe in panel system. The last job I did with NuHeat panels was covered with chipboard and, though it works, it is slow to warm up and I only wish that this material had been around then.
If you have laid any kind of tongued and grooved boards there is nothing very different about Brio except that it uses a ‘Smart Tier Edge rather than a groove .
If you have laid any kind of tongued and grooved boards there is nothing very different about Brio except that it uses a ‘Smart Tier Edge rather than a groove . This is actually a lot easier the running glue into grooves and, because the glue isn’t trapped in the joints, they go together without resorting to a mallet. Stagger the joints and glue the host edge in the usual way.
Brio WF is an acoustic variation with a wood fibre underlay to protect against impact noises but in the case of my test installation the impact noise protection is provided by the NuHeat insulation. This gives it a winning combination of thermal transmission and sound proofing properties. Like any sound insulation it has to stop both air borne noise and impact noises. The impact resistance is achieved by density but airborne noises are largely blocked by closing up all the gaps.
The Rockwool perimeter batts provide thermal insulation, expansion and sound insulation. It is necessary to take the tongue off the first laid row in order to provide a solid edge right up to the Rockwool. If you leave the tongue on then it forms a void under the board through which sound can travel. My mistake was not being accurate with the rip to the wall on the second panel. I was thinking that the skirting would cover a couple of millimetres but for acoustic deadening you don’t really want any gaps. That said is can be filled with sand and cement. If ever acoustic flooring fails the sound test it is likely to be because of these small gaps and lack of attention to detail.
The only other potential problem with the Knauf Brio dry screed boards system is driving those screws into the boards with heating pipes underneath. If you adjust the torque setting on your drill accurately then Knauf says that you won’t over-drive the screws because the threads don’t pull the screws in on their own. Personally I don’t trust anyone (not even me) to set torques on drills and I don’t like critical processes on building sites. If a process is that critical then to my mind it needs to be redesigned. A building site is a war zone and you want things to be fail safe and idiot proof. I would not even be happy about driving any screw into a screed, wet or dry if there are heating pipes underneath. My solution is to mark the line of every pipe with an X so I can be sure that I am well away from the pipes when I put the screws in. It takes a few minutes but it means I can walk away with no nagging worries about a stray screw sitting in the edge of a pipe just waiting for a bit of expansion and contraction to make a hole. This is not paranoia I have seen it.
Note on acoustic flooring.
Knauf Brio dry screed boards also comes with a wood fibre underlay to form an acoustic floor. Putting it down is the same as laying any acoustic board. It must float with no fixings penetrating it or connecting to the structure.