Context 164 - May 2020

C O N T E X T 1 6 4 : M A Y 2 0 2 0 15 The war on damp ROBYN PENDER Rethinking retrofit Ill-advised retrofits not only waste carbon, but they can severely damage buildings – through dampness, among much else – that have hitherto worked well for perhaps hundreds of years. The UK parliament’s aspiration that the country be ‘net-zero’ by 2050 is focusing minds on that substantial portion of carbon attributable to the built environment. While cutting carbon is to be welcomed, there are risks inherent in hasty action, not least maladaptation (where ‘improve- ments’ end up costing more carbon than they actually save). Ill-advised retrofits not only waste carbon, but can severely damage buildings that have worked well for perhaps hundreds of years. The potential of ‘deep retrofit’ to cause damage is well proven, and the energy benefits of adding insulation to many solid walls is much debated. And these are not benign systems that one might add ‘just in case’. Many systems of insulation (together with the vapour barriers crucial to them) lead to damp. Current research appears to indicate that moisture can build up over time due to condensation: and as water builds up in pores and capillaries, it will attract more water. Deep retrofits usually include draught-sealing, limiting the opportunity to decrease indoor humidity. Of even greater concern is systems trapping water from elsewhere, such as gutter and plumbing leaks. External wall insulation often compro- mises those very elements designed to keep rain from entering the walls, such as eave overhangs, cornices, hood mouldings and sills. Once a wall becomes wet, it will transfer heat, negating any supposed benefits for carbon and energy. The risk of sealing buildings extends beyond impacts on the fabric: there is a signifi- cant reduction in indoor air quality, and not just in older buildings. Meanwhile, the whole-life carbon costs of retrofit measures are discussed surprisingly little. How much carbon do they cost to make, install and operate? How long will they last? We know triple glazing embodies a great deal of carbon but has such short a life span that that it can not deliver a true carbon benefit; but almost nothing is published about insulation systems. When will replacement be needed, and what would it entail: will it be necessary to strip the roof or walls?We need this information to reduce untimely failure, and to judge whether ben- efits outweigh risks. Since we are dealing with buildings with extremely long lifespans, carbon costing of retrofit measures must be factored out across many years, and take into account lifespan and replacement. If an intervention Heating the air, especially periodic heating or heating in spaces with tall ceilings, induces air movement and brings in draughts. Draughts are also an unpleasant side-effect of air conditioning, since to be conditioned the air must be passed through a system of ducts and vented back into the space (Image of Peterborough Cathedral: Tobit Curteis Associates)