The floor’s finished, the ceiling’s done and the excellent Viking triple glazed windows are in. Now for the last remaining step in creating an airtight box: applying Diathonite plaster to the internal walls as the first layer of Ecological Building Systems’ ‘Retro EcoWall’ insulation.
Time to call in specialist sub-contractors. Border Lime Construction are more used to working on historic buildings, but their skills in spraying on Diathonite work equally well in 1970s bungalows. However – before they could get going - Alex Burn (from main contractor 4Site Engineering and Construction) had to put in some very thorough preparatory work to make sure we ended up with a perfectly flat, perfectly even layer of Diathonite. This is essential for successfully applying the next layer of insulation: Gutex Thermoroom woodfibre insulation board.
Alex set up a string 20mm from the internal face of the wall (40mm for the single skin southern gable end) and carefully fixed timber battens at regular intervals to accurately meet the string. With the string removed, the Border Lime team sprayed the Diathonite on and smoothed it to line up with the battens. The next day, the battens were removed and the gaps filled in with more Diathonite. We now have our flat internal wall finish and airtight line.
The Diathonite has the Christmas and New Year break to cure fully, after which the junctions between it and the floor and ceiling will be taped. At that point we’ll have our airtight box and be ready for the interim air tightness test, scheduled for 12th January. Diane Hubbard of Green Footsteps will follow up the initial test from October 2021. We’re expecting a very significant improvement on the original air change rate of 11.75m3/per hour/per sqm of building footprint. Will we be below the EnerPHit standard of 1.0? Watch this space!
And if you’re wondering how the building is ventilated if it’s airtight, then have a read of 'What is Passive House?' on this website. There will also be blog posts on ventilation early in the New Year.
Read more about the ‘Retro EcoWall’ insulation system here:
Specialists in lime-based render:
For energy assessments, airtightness testing and thermal imaging:
Very helpful UK suppliers of Viking windows:
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