There’s been plenty on the news regionally and nationally about tenants in low-rental properties, as well as homeowners, suffering from horrible outbreaks of an evil-looking black mould. The first assumption is that this is caused by rising damp and can be ameliorated with an injected dampproof course, which of course is possible. But many living at first floor levels and above have experienced this nasty phenomenon which can’t be due to rising damp.
This photograph showa the problem in a two-storey apartment at first and second floor levels with potentially health-threatening mould appearing on the inside of exterior walls. The building dates from the first decade or two of the 20th Century and was built very cheaply with single-skinned brick walls finished outside with thin concrete render and pebbledash.
Home might be a castle, but first of all it’s a shell
Think of a building as a Beef Wellington. The inside fillet is gently cooked within a secure, sealed cladding of pastry. That’s a basic principle of physics when it comes to a building; the exterior walls shroud the interior, but the ambience of the internals is directly affected by the effectiveness of the external “cladding”.
This applies especially to older buildings with single-skinned walls but extends to those with cavity walls where the insulation between the inner and outer “shells” is either non-existent or past its useful effectiveness. The solution – clad the outside. Before anyone gets too excited about the flammability of external cladding (we all remember the tragedy of Grenfell), any cladding should not be ACM – Aluminium Composite, which in Grenfell was highly combustible polyethylene hung in “cassettes” between thin sheets of aluminium.
A safe alternative which has been in very widespread use for several decades across northern Europe uses graphite mineralised sheets – 50 mm thick as in this project (photographs below), finished with a very low maintenance, self-coloured fire-resistant render, which resembles a lightly grained concrete finish (see Ceresit.com for example). The insulation sheets include some polystyrene which is not especially carbon-friendly but the sheets are far less toxic in the consequences of their production than the materials such as expanded foam used in the injection of insulation into cavity walls or indeed loft-insulation.
All building materials, be they clay-based (such as bricks) or concrete-based (such as Thermalite blocks) generate vast carbon emissions but this external solution is relatively carbon-friendly. However “green” we want to be, the end result will be costly in terms of carbon output but is essential initially to mitigate the use of carbon-generating fuels to warm our homes. We can endlessly argue about the impact that new buildings or the construction of more electric cars will have on the environment, but the reality is that all these solutions are not carbon-friendly or neutral. Batteries for electric cars require the destruction of vast areas of rainforests to extract lithium and other minerals to create batteries that require charging by an electricity grid that is mostly dependent on burning gas or coal to feed an increasing electrical demand.
Insulation against mould is more important in creating a more economically viable home, initially to help mitigate emissions from central heating, and it is a great defence against unpleasant and potentially fatal breathing problems caused by dark mould. Ideally, all materials should be “green” but that’s not practical as an ambition in the short to medium term.
Aesthetics
Those who prefer a traditional external finish rather than render could add “slips” which are thin “bricks” about 7 or 8mm thick (rather like tiles) and available in all types, red, yellow stocks etc or fix shiplap timber to the insulating cladding.
Protect your shell and it will protect you
The basic principle is that external insulation envelopes the exterior shell (rather like the pastry on the Wellington) and stabilises both the wall temperature and the absorption of damp from the air. Internal insulation does not achieve the efficiencies of anything applied externally, is very disruptive to living in the space and takes away useful inside rooms by adding to the walls which will also require total replastering and decoration.
This external solution in turn reduces the moisture coming through the walls to the interior; combined with moderate internal heating and trickle ventilation in or around the window frames, external insulation helps to create a moderated internal ambience and reduces the moisture inevitably generated by “living” – use of hot water for personal hygiene and cooking, washing machines, tumble dryers, dishwashers etc. The use of moderate heat, effective insulation and mild ventilation will eventually eradicate mould and damp. And, actually, opening windows a little helps increase fresh air ventilation in bathrooms and bedrooms.
Saving money comes at a price
Of course, there’s a price attached to this work. This building consisting of these two average-sized semi-detached homes has taken about three weeks to complete on all four sides of the outer building’s “shell”. The total cost is £26,000 including VAT and repairs or maintenance of the rainwater gutters and downpipes, shared between the two properties. However, it is a permanent and highly effective way of stabilising the ambient internal temperatures, significantly reducing the possibility of health-threatening mould and damp and improving the overall energy efficiency of these homes.
