Passivhaus Consultant and Designer, Bristol.  Very Low Energy Buildings.  Domestic and non-domestic.  New build and refurbishment. 

07502 425158

Bristol, UK

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External Wall Insulation

Work started on insulation of the back wall of our house a few weeks ago.  The existing render has cracked and leaked and the wall has become increasigly damp over recent years.  The wall was 'waterproofed' internnally about 15 years ago with cement render and the moisture has begun to appear at the edges of this area. Trapped on both sides the moistiure has built up in the brick wall.

We are insulating the back wall externally with Diffutherm wood fibre board from Natural Building Technologies.  The work involves:

  • hacking off existing cement render
  • extending the eaves
  • cutting back window reveals
  • levelling coat of lime
  • replacing door and window
  • mechaniclly fixing about 30m2 of wood fibre board including reveal board
  • base coat of lime with fibreglass mesh on boards
  • final coat of lime render
  • air tightness taping of junctions between wall and windows, doors and services.

The idea is to remove the cracked cement render and complete the wall with a breathable construction so that penetrating moisture as well as moisture generated internally can make its way through the wall.  The wood fibre board absorbs and releases the moisture and prevents build up of moisture in the wall.

The U value of the wall will be reduced from approximately 2.1W/m2K to 0.33W/m2K, resulting in a heat loss reduction by a factor of more than 6.  It's difficult to achieve that by changing your windows. 

The work is being done by Kevin Milsom and his assistant Phil.

Reader Comments (3)

Piers, Thanks for this as it is very interesting that you have managed to use lime render (i have always wanted to do this and never have!). And btw, what is diffutherm made of?
October 1, 2012 | Unregistered CommenterCharlie
Charlie, Diffutherm is a wood fibre board. I have edited the text now to explain.
October 2, 2012 | Unregistered CommenterPiers Sadler
thanks piers - interesting to see the process.

October 2, 2012 | Unregistered Commenterlouise

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