Why not just fill the cavity, then?

When I've explained our plans to wrap a bungalow in strawbales (even when I just say "externally insulate it") a number of people have asked why we don't just fill the cavity to insulate it.  It's becoming quite irritating, but that's my problem not anyone elses.  It does deserve a proper answer, which sort of serves as an example of what's wrong with general standard construction too.

The rented bungalow we currently live in does have insulated wall-cavities, and around 35cm depth of glass-fibre-blanket loft insulation (albeit poorly fitted with lots of gaps between rolls and an area in the centre with no extra blanket at all, apparently to leave the existing boarded area free for storage).  The windows are all double glazed (more on them later).  So it should be nice and warm and efficient to heat, then?

Nope.

In winter it gets cold very quickly once the heating goes off (ie: the heat escapes quickly through the walls, window, roof and the cold uninsulated floors).  In summer it gets very hot when the sun is on the building.  According to our latest gas bill (we have no gas cooker so our gas use is only for heating and hot water) our average daily usage for the last 3 months is 38kwh.  According to Which that's about average for non-condensing boilers, equalling a yearly bill of £760 in our case.  That will increase as it gets colder though.  It's been unusually warm lately; we used much more gas this time last year when it was so much colder.



Even if 38kwh per day was our average use during the whole year, that would equal an annual carbon dioxide release of 2.56 tonnes (based on figures from www.carbonindependent.org who quote DEFRA figures of 0.185kg of CO₂ per kwh of natural gas burned).  And we're fairly sparing with our heating, preferring to put on more jumpers than have the heating blazing to the point where we can wonder around in T-shirts.

So by super-insulating the bungalow (the walls with strawbales, the ceiling with Warmcell recycled newspaper insulation, and the floors with wood-pulp  boardinsulation) to the point where virtually no heating is needed we'll be putting at least 2 tonnes less CO₂ into the atmosphere.  The added advantage of the materials we'll use is that they are also storing carbon in their structure.

I'll complain about the double glazing next time, with pictures.