Our house is still cold after installing external insulation. What can we do?

External insulation was added to our cold 1960s four-bed semidetached house. The rear wall was taken down in the refurb and replaced with blocks positioned flat (as opposed to the norm where they are placed on their edge or side). It didn’t bring the level of insulation I’d hoped for. We have triple-glazed windows and doors facing north, with double-glazed ones facing south, and the attic is insulated. We also installed a heat-pump system. The engineer and builders were registered. Despite all this, the rear bedrooms are still cold and the new wardrobe next to the wall smells musty.
There is a ground-floor rear extension, so the upper rear wall insulation stops a little above the flat roof and is indented, which seems a common feature in external insulation.
The bathroom needs an extractor vent as there’s a lot of black damp developing on the walls and ceiling. How do I fix this and know that the remedy is a long-lasting investment and not just cosmetic until the damp comes back? Which trade is best equipped to address these issues?
The real problem that you are experiencing here is one of condensation. Condensation arises due to a number of factors, including poor insulation standards, poor levels of heating, high levels of moisture vapour and poor levels of ventilation.
I note that you have installed a new heating system, and provided that this has been correctly installed and is being used, then I would expect that the levels of heating being provided here are reasonable. I also note that you have upgraded the thermal insulation standards to include installing new double glazed/triple glazed windows and installing an external insulation and again you should now have achieved a good insulation standard.
You refer to an “indent” in the insulation just above the flat roof and no doubt this was required to avoid interfering with the flashing at the roof/wall junction. Unfortunately, this creates a “cold bridge”. The principle of external insulation is to have a house “wrapped”, with no gaps, but it is inevitable when retrofitting a property that there will be certain obstacles and difficulties associated with achieving a perfect solution. It sounds like the installers had little option but to compromise on the insulation by indenting same here and this is a shortcoming that you will just have to accept.
The two biggest contributing factors to condensation are the levels of moisture (relative humidity) in the environment and the ventilation standards. It is inevitable that one creates moisture due to everyday activities including cooking, showering and drying clothes etc, and whilst one needs to take steps to minimise the amount of moisture created within a house, it is inevitable that some moisture will be created.
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Accordingly, the single biggest factor affecting the level of condensation is the degree of ventilation provided. This matter could be largely controlled by simply opening windows. However, given the busy lives that we all lead, this can be difficult to do in an efficient way and thus one is very dependent on backup ventilation systems.
In addition to regularly opening windows, it is typical to have permanent vents for the habitable rooms (livingrooms and bedrooms) and mechanical extractor fans to the kitchen and bathrooms. In fact, there are whole air systems available which are incorporated in new properties. However, it is relatively difficult to install these systems retrospectively. But if you have a good combination of background ventilation and mechanical extractor fans, it should be possible to keep condensation under control.
The black staining you describe is very typical of condensation and you will find it is most noticeable between late October and early March. You will generally find it occurring in the bathrooms and the colder rooms in a house and/or the areas where there is limited air movement, such as within wardrobes or behind headboards or pictures. But if the levels of moisture are reduced where possible and the levels of ventilation are improved, you should be able to reduce or eliminate the problem that you are experiencing here.
As regards the best trade for addressing this, I would suggest that it simply needs to be a qualified or skilled tradesperson that understands what the problem is and what they are trying to achieve. Alternatively hire someone that can be guided by a qualified professional who has the required knowledge, such as a chartered building surveyor.
Val O’Brien is a chartered building surveyor and member of the Society of Chartered Surveyors Ireland
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