Myth, mystery and how a ubiquitous industry standard confuses us all

Internal wall insulation is often the most practical method of retrofitting insulation to a house, but often choosing a solution can be difficult and confusing especially in older buildings with solid walls, listed buildings or those of ’breathable’ construction. Firstly, what are the technical implications? should you use a vapour barrier or stick with a breathable system? And will your building control officer or mortgage provider insist on installing plastic membranes “to keep the wall dry”?

Breathable or vapour control?

Conventional thinking insists that without a vapour membrane, a solid brick or stone wall will inevitably become damp or soaking wet as the warm air from inside the room migrates into the masonry, cools and condenses.

The theory is based on the Glaser method from 1950’s, incorporated in to building regulations as BS 13788. However, the introduction of this clearly states it is a simplistic method, which ignores many important physical processes, such as liquid water transfer, or the moisture content of building materials! Crucially, BS13788 acknowledged these weaknesses, and suggests that if a proposed design fails, further, more sophisticated modelling can be carried out – but in many cases the easy option of switching to a design with plastic insulation or membranes that satisfies the theory is taken, irrespective of whether it will work in the real world.

IWI GraphicOur supplier of lime plasters Lime Green is  convinced of the merits of breathable lime plasters and insulation in many situations – not just from practical experience and common sense, but from the extensive research being carried out on their materials installed in-situ in real houses, such as Solo and Steico woodfibre insulation. This pioneering research carried out by the Society for the Protection of Ancient Buildings (SPAB)  is some of the first in the world to measure what really happens in historic solid masonry walled buildings when they are insulated, instead of guessing using computer models. Work is also underway at the Building Research Establishment (BRE) on a similar but larger basis. You can find further information on the research by following the  links below.

Ecomerchant Internal Wall Insulation system is the result of this extensive testing, not only has it been monitored in situ for several years but Lime Green are the only supplier to have carried our fire testing, vapour permeability and impact testing.

Building Regulations and retro-fitting insulation

There is still a lot of misunderstanding over Part L1B: Conservation of Fuel and Power (Existing Buildings). Many still believe it requires damp proofing or vapour membranes to be installed, and insulation to meet new build standards. In fact completely the opposite is the case! A brief summary of the key clauses is outlined below – it is worth reading in conjunction with Part L1B, which is free to download (see link at bottom)

1)        Buildings which are listed, scheduled ancient monuments or in a conservation area

are exempt if the work would change their appearance or character. See Part L1B, Section  3.6

2)       Buildings of traditional construction with permeable fabric

or in other words, traditional solid wall buildings (including stone, brick, cob and oak frames), are due “Special Consideration”. See Part L1b, Section 3.8c

3)       Energy efficiency for the types of buildings in 1 & 2

should be improved “as far as reasonably practicable. The work should not... increase the risk of long term deterioration of the building” See Part L1B, Section 3.9

4)       Breathability is specifically required in some cases!

“Particular issues in historic buildings...include... making provisions enabling the fabric of the historic buildings to breathe”. See Part L1B, Section 3.12c

5)       The U value required is not always U=0.30

Rather, it should take into account English Heritage’s guidance, and the views of the Conservation officer should be sought. See Part L1B, Section 3.10 and Section 3.13

At Ecomerchant we believe it is possible to successfully insulate solid stone and brick walls, using the right materials. We have a range of lime plasters, paints and natural breathable insulation, and we’re always happy to give you advice specific to your project.

Content and research thanks to James & Simon Ayers
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