Service cavity batten installation
June 29, 2015
Today the service cavity batten installation began throughout.
The service cavity zone is to be insulated with more wood fibre insulation, and contributes to the overall U-Value of the walls. If it were not necessary to insulate it to achieve the desired / required U-Value this would then simply be a zone for service pipes (up to a certain diameter) and cables to run on the inside of the airtightness layer. It is an important feature of many passivhaus (or otherwise very airtight) buildings as it allows for the future amendment of many services without damaging the airtightness layer, although obviously localised repair would be needed to the plasterboard finish internally once this zone has been accessed.
We are using 45x45mm regularised treated timber battens to form the service cavity, as this allows plenty of space for the deepest electrical back-box of 40mm as this is often necessary when there is 2 or 3 way switching for lights (or other specialist electrical installations) taking place.
We have currently omitted the bottom batten to facilitate the laying of the floor finishes on the upper storey – this will be added immediately prior to sheeting the walls.
The battens are fixed at min. 600mm centres to coordinate with either vertical or horizontal sheet orientation for the plasterboard, and there is a continuous batten around each window / door opening to support the sheet edges here (we used a plywood ‘spacer’ to ensure the battens are in the correct position each time). The aim is to minimise the amount of battening in order to maximise the amount of insulation in this space.
Each batten is fixed back to the structural stud behind to ensure adequate support for the plasterboard sheets (it would not be sufficient to simply screw them into the airtightness board as it is only 12mm thick).
Our insulation is to be 40mm deep which leaves a 5mm space for the electrical cables to run to ensure they are not completely encased in insulation – if they were fully encased they may have needed to be increased to the next available size in order to eliminate the risk of overheating, which would add a considerable cost.
Once the first fix wiring is completed the next task is to insulate this whole zone. We have begun doing the window & door reveals using the off-cuts from our Steico Flex insulation – time consuming but cost effective and waste reducing!
As we are lining our window & door reveals with timber boards we need short horizontal battens as well to support the edge of the board nearest the window – this is a more efficient use of timber than running another vertical batten and allows for maximum insulation to be placed in the reveal. Again, this insulation is important as it contributes to the overall PSI value of the window installation, and therefore to the heat loss calculations performed in the PHPP. (Incidentally, up to this point I have been using THERM to evaluate all of the relevant PSI values in the building, however I have recently invested in PSI Therm for ease of interface so I am looking forward to exploring that software in more detail soon.)
Although it is a little piece-meal in appearance it gets the job done without having to buy more material or dispose of perfectly good 'waste' material.