After a summer spent building driveways, digging lakes and fencing paddocks we finally turned our attention back to the barn project and specifically the interior. The first task was to set up the floor for underfloor heating that was to be driven by an air source heat pump (whose electricity supply is in part from the solar array we installed) in an effort to be more environmentally friendly in our energy choice and, of course, more efficient. The existing floor in the barn is a concrete slab that is not insulated, but as it was in reasonable condition we decided to leave it in-situ and work over the top of it. Ideally we would have liked to put 100mm of insulation down on it as a minimum, but we were struggling with the available overall floor height and therefore realised we were restricted to 50mm of insulation with flow screed over the top which was less than ideal. However, on doing some research I found what might be a better method as follows:
to lay a damp proof membrane on the floor.
install a 100 x 47 timber grid at 400 centres in one direction with noggins at 600mm centres in the other.
infill these with 75mm of PIR insulation.
install the underfloor heating pipes on top of the insulation (notched through the timbers where necessary.
cover the pipes with a 6:1 sand/cement dry mix and screed off to the same height as the timbers.
fix 21mm moisture resistant chipboard flooring to the timbers.
This had the added bonus in that we could do it all ourselves and while not quite as efficient as a flow screed option in ideal conditions the additional insulation over the 50mm we were restricted to here would be a better thermal solution. Additionally, we decided to put the underfloor pipes at 133mm centres to give the thermal mass a better chance of conducting the heat.
With this the chosen approach we set to work initially laying damp membrane, setting out the timbers and at the same time installing the internal hot/cold water pipes, the incoming water main, the flow and return for the air source heat pump and the meter tails for the consumer unit. Once this was done the noggins for the timbers were cut and the whole grid screwed together. The internal studwork walls were then marked out and some were built up in order to help us with visualising the pipework routing.
The damp proof membrane and floor ‘grid’ being installed (with timber work inspection cat surveying from the A frame).
We then cut and installed Celotex GA4075 PIR insulation slabs into each grid ‘aperture’ and built up more of the internal walls before laying the underfloor heating pipes. These can have a run of no more than 100m per ‘loop’, the runs ideally must be continuous with no joints and they all have to start and end at the same heating manifold ideally without crossing each other. In our case I had designed the system to have the following zones:
Bedroom 1 – 1 loop approximately 100m
Bedroom 2 – 1 loop approximately 100m
Bedroom 3 – 1 loop approximately 100m
Bathrooms – 1 loop approximately 65m
Living area/kitchen – 3 loops approximately 100m per loop
The underfloor heating manifold was to be in the plant cupboard near the front door so careful laying out was undertaken to ensure all the pipes would fit and not cross each other or foul any other service. Notching of the floor timbers was carried out in order to have the pipes cross them where necessary and the pipes were all fixed down with the specially provided pipe clips that simply push into the insulation. A slight problem was that the pipes were a tiny bit too close to the top of the timbers so 12mm plywood strips were then cut and screwed to all the long timbers effectively increasing the eventual thickness of the dry screed.
Insulation fitted and pipes being laid.
The manifold was set up on a temporary mount and all the pipes were connected before a pressurisation test was carried out whereby the entire system was filled, bled and pressurised to 6 bar via a specialist underfloor heating pressure test pump. The test went well and the system was able to maintain 6 bar with no drop off over 24 hours so the dry screed and flooring could now be laid. One minor problem with this whole design was that the flooring was to be screwed to the timbers and yet in places the pipes were notched through the very same timbers. To avoid accidentally piercing the pipework with a screw we marked in red (on the plywood strips that went over the pipes) the positions where the pipes crossed and we also made maps of each room detailing the points on each timber where we couldn’t put a screw. Then we started filling the voids with the dry 6:1 sand/cement mix and screwing the floor down in each room as we went. All went well until we were finishing the living area and I misread joist 12 as joist 13 and put a screw straight through the pipework as indicated by a wet floor and 6 bar becoming 0 bar in about a second…. arghhh!!! Anyway a patch kit was obtained and we dug the pipe out of the screed, fixed it, retested it and work could then continue... the best laid plans and all that.
The dry screed going in, floor going down and the manifold in place.
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