It’s not everyday you get a phone call from an architect asking for help on a grade 2 listed mill building, but that is what happened to us back in April 2017 when Stephenson Studios contacted us with a problem they were having with floor to ceiling heights on their Brownsfield Mill project in Manchester.

Their design criteria was for the existing 75mm thick timber mill boards to be retained and each of the apartments in the building would have these as an exposed ceiling. The idea was to keep the building as rustic and to retain as much of the original look and feel of the listed mill building as possible. Because of this all of the acoustic (Part E.) and fire Building Regs. (Part B.) requirements would have to be installed above the existing floor.

The drawings we were sent through identified a floor build up, on top of the mill boards, at nearly 300mm thick. This started with a self levelling compound on top of the mill boards, to level them to, and then a timber on timber solution with a final layer of cement particle board prior to the oak flooring being installed.

This thick floor section was causing a problem due to the original oak beams that were in place meaning the floor to ceiling heights weren’t as high as they needed to be. This design was compounded flowing the removal of the bitumen floor covering. When the mill boards were exposed and then levels were taken across each of the floors it was clear that the original design was no longer suitable for the project.

With the age of the building some of the mill boards were beyond repair and each of the floors needed levelling up so the use of self levelling compound and a timber/ cement board solution also became a very expensive solution. We were asked if we could come up with a solution that was able to reduce costs and time and also to be able to achieve the required acoustic and fire requirements for this type of conversion project.

Our initial thoughts on the project was to use timber ferrings, 100mm wide at 600mm centres, to lay our Lewis Deck system onto. This was reducing the number of ferrings by 50% (these were originally at 400mm centres) and it also removed 4 layers of timber/ cement board as well as the self levelling compound from the project. Following a meeting on site however, and after being able to fully talk to the deisgn team and developer about what the Lewis Deck system can do we agreed that we would look at putting the ferring strips at 1400mm centres with the Lewis Deck being laid across at these centres. Rubber granulate acoustic strips would be installed on top of each of the timbers and mineral wool insulation would then be installed between. This would allow more material to be removed from the project but crutially still hit both the acoustic and fire requirements of the project.

A test floor was commissioned, by the acoustic engineer, and built in August 2018 which passed all tests. You can see from the photos below the Lewis Deck laid at 1400mm centres for the middle section of the test with the 15mm thick rubber granulate acoustic strip laid on top of the timber ferrings. These timbers, due to the nature of the mill boards below, had to be installed individually to differing heights.

Urban Splash Website – AVRO/ Brownsfield Mill

Continue reading to find out how the installation element of the grade 2 listed mill building project went.