I am considering buying a solid block bungalow and, whilst bulldozing it and starting again seems attractive, that is a lot of embodied energy and expense. So I was wondering about the feasibility of renovating to passivhaus standard. Sitewise it is perfect - south facing to the garden with minimal overshading, and it is of compact rectangular form. The roof and the windows need replacing anyway so external insulation, installing MHRV and re-sizing of windows is not problematic . Any thoughts?

VAT is not applicable where I live so not an issue. With the floor I was consideringthe possibility of simply raising it and adding another round of blocks before replacing the roof, as all windows and doors would have to be changed anyway.

Historically because they would be subject to too much weathering, especially at the head. Not sure there is an effective way to eliminate the risk of water ingress

I suspect that achieving the high levels of airtightness required will also be quite a challenge.

if you are putting in a new slab/insulation, raising the wall height, replacing the roof, doors and windows, it sounds like a full passivhaus treatment will remain a compromise to what is left of the existing fabric, (which doesn't sound like much!)

i think a full audit on the merits of retaining what is left is worthwhile. The extent to which you have to rebuild will be determined by how close you want to get to these standards

Posted By: rogerwhitHistorically, Mike?

I just meant that good design [in my eyes] has always meant windows being positioned well in from the external face. The Victorians for example placed them up against the inner face of external brickwork. Newer buildings often place them only 50mm in from the external face, though I prefer a deeper reveal.

Thermal bridges will be the greatest challenge, quickly followed by airtightness. If replacing the roof bridging can be addressed at eaves junctions, then it's the wall/floor junction (to achieve the standard thicker insulation will be required). Here the umbrella type detail works well (2m insulation running, say 450mm, below ground perpendicular to the wall.) Windows, move and mount on the external face of the building with cramps and then have the 250-300mm Neopor insulation overlap the frame to minimise themal bridge. This depth of insulation means that you are left with a 150-200mm deep reveal that protects the windows/wall junction from the weather (fairly standard detail in German PH refurb).

Airtightness, good continuous plaster with no gaps with membranes to all junctions and interfaces with other materials.
Careful planning is critical.

Hope this helps.

Mark

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Have I missed something in the last 3 posts?

I am fairly new to this and don't quite understand you description of what I should do with the floor - it is currently an uninsulated concrete slab. Are you suggesting that the main body of it is left uninsulated - I realise that the ground temperature below the floor will be higher than the outside temperature on cold days, but there will still surely be a thermal gradient of about 10C ??

large eaves will help to protect windows and doors (particularly in a bungalow) and also give summer shading

Thin cork will not do very much insulating but it will do something. Couldn't you dome perimeter insulation in the cavity?