The Fish House, 130 Bohemia Rd: proposed view by Ken Davis.

Exploring thermal upgrades to our homes

Local energy aware architect, Ken Davis, continues with his work on 130 Bohemia Road, aka The Fish House. This week he considers upgrading our building stock thermally and the problems that ideal presents.

I well remember – some 50 years ago now – helping my father install two inches (50mm) of fibreglass quilt in the loft of our 1930’s semi in Bromley and thinking at the time: “Surely this cannot do very much?” Well, of course, it didn’t – and we have moved on with successive government recommendations of about another 50mm every 10 years or so which, at 300mm, is now getting us to where we need to be if we use a quilt type material for insulation.

However, I made a few more discoveries in that loft when I was 15, which included that installing insulation is not as easy as you may think, and roofs – buildings generally in fact – are very dirty and indeterminate: things are not always as you expect them to be. Also, that government policy proceeds exceedingly slowly.

This is why a wry smile comes over my face when I hear of government initiatives such as the Green Deal (now recognised as not working), because it is obvious that whoever put it together knew very little about the practicalities of thermally upgrading old buildings.

Inside existing building with the original poor timber structure being gradually removed.

Many years on from my loft initiation – and now with plenty of professional and practical expertise under my belt – I decided to see if I could demonstrate a really good example of low (near zero) energy eco-refurbishment on the worst house I could find! The brief to myself was to find something small enough and cheap enough for me to practically stand a chance of completing the project, but with enough potential to really add both ecological and architectural value.

However, what appealed to me most about this particular building was its longish garden for such a location – some 11 metres – and that the garden is enclosed by quite high existing brick walls, meaning there would be few planning problems with a large extension into the garden. Even so, what I proposed design-wise required the two and a half floor building (one bedroom in the roofspace) to become a full three storeys – and so a fair amount of new structure was needed. What should this new structure be? After all, the existing structure already had a number of its own structural problems to sort out, such as rotten timbers embedded in brick walls, a party wall only half a brick thick and steel beams with precious little support.

One of the biggest debates in sustainable building design is about the choice between heavy construction (brick/block/concrete) or light construction using frames, usually of steel or timber: both have pros and cons. I opted for heavyweight on the basis of the extra mass being able to act as a heat store and because the old roof would need to be off for some time to build up the extra wall height, meaning that a timber frame would get very wet. Not good!

150mm of insulation and tanking membrane to existing wall.

Hardly a consideration at all was what type of insulation to use and where to put it: three sides of the building are right on the property boundary (neighbour on one side, party wall on another, pavement at the front), so it really is only possible to put the amount of insulation I needed on the inside of those walls. The small area of rear wall can be extended out, so here insulation is to be on the outside. Both new insulation and new structure internally means 550mm is taken off the old internal width, so the planned new space, rear extension and second floor is really needed. The chosen insulant is rigid polyisocyanurate board (Celotex or Kingspan), which gives best performance for minimal thickness.

My next update will discuss design/layout decisions and planning issues.

The project is open to enquiries/visitors, if anyone is really interested.                 Contact: kgdavis129@gmail.com.

See Ken’s previous piece: Energy…and our homes

Also in: Energy Wise