Following on from planning permission, Hesketh Hayden developed the detailed design and specification of the EcoBungalow ready for costing by the builder, Alex Burn of 4Site Engineering & Construction. With spiralling inflation, the costs came back significantly over budget. We got together for a strategy meeting: how could we get this project back on track? I said at the meeting: ‘This is not Grand Designs. I’m not going over budget. And I’m NOT having a baby’ (For the uninitiated, the TV programme ALWAYS features a couple blowing the budget, frequently along with an unexpected pregnancy halfway through the build).
Examining the costs, it was clear that the majority of the overspend was in the external wall insulation and the changes to the roof. We needed a different approach, as fiddling with things like floor finishes and downgrading bathroom fittings was not going to save us enough. Alex was instrumental in developing a radical change of strategy from insulating on the outside of the building to insulating on the inside. This reduced costs significantly, particularly as no changes needed to be made to the roof, but it still maintains significant improvements in insulation over the existing fabric as shown in the table.
Strategy | Heating demand kwh/m2 |
As existing | 200 |
Previous external wall insulation | 36 |
Internal wall insualtion | 42 |
The system we’re using for the internal insulation is Retro EcoWall by Ecological Building Systems. Originally developed for older buildings, this system will work just as well for the EcoBungalow. The biggest risk with internal insulation is condensation forming between the insulation and the original external wall, leading to damp problems. Making sure the wall is breathable as well as airtight (no, the two are not mutually incompatible) is a key component of avoiding this problem. Link here:
There is a small loss of floorspace (90mm around the external walls). However, as the approach is to strip out all of the internal walls, we can work with this and this small reduction won’t be apparent in the final layout.
The strategy means that the attic is no longer a ‘warm’ space – that is, the insulation remains in its current location above ceiling level rather than the previous strategy of following the roofline. This has implications for the mechanical ventilation system, which needs to be insulated and ideally located within a warm space to prevent condensation. Hesketh Hayden developed a strategy of a shallow ceiling void for services, within which the MVHR ducting system could be located.
So, this project is hopefully NOT replicating the typical Grand Designs scenario and is back on track.
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