Residential Insulation Strategies

The UK has embarked on an ambitious journey to achieve net zero greenhouse gas emissions by 2050. One key facet of this initiative is the insulation of homes to reduce energy consumption and consequent emissions. Here, we delve into two primary insulation methods, their potential drawbacks, and strategies to maximize their efficacy.

External Wall Insulation (EWI)

EWI involves applying non-porous material to external walls, subsequently covered by render. This method, however, isn’t without its challenges:

Shallow Fit Installations:

Shallow fit refers to sub-optimal insulation application to cut costs, notably around windows, doors, or behind gutters and downpipes. This shortfall can be addressed by:

  • Internally insulating behind less-insulated areas.
  • Ensuring effective ventilation and/or dehumidification to mitigate associated issues.

Water Ingress:

The impermeability of EWI inhibits a wall’s ability to evaporate rainwater. Defects like cracks can cause water ingress, resulting in wet walls that:

  • Are poor insulators.
  • May incur wall damage.
  • Can cause internal dampness and mould.

Internal Insulation:

Internal insulation requires careful consideration of vapour permeability, especially if the wall’s internal surfaces are permeable.

Vapour Permeability:

The choice between vapour-permeable and impermeable insulation is critical. Impermeable insulations like Celotex or Kingspan can alter a wall’s thermal profile, potentially leading to interstitial condensation within the wall. This internal moisture can drip down, posing a rot risk to structural timber.

Tailored Insulation Strategies:

In case of externally rendered walls in good condition with removed sub-floor timber, the risk is lower. Precautions include:

  • Monitoring and filling any cracks in the external render.
  • Maintaining internal humidity at around 65%RH through ventilation or dehumidification.
  • Considering vapour-permeable insulations like wood fibre or SpaceTherm for certain areas.

Focusing on High Heat Loss, Low-Cost Areas:

Targeting areas of significant heat loss can yield energy savings of approximately 5% – 10% p.a. for the initial £2,000 spent, through measures such as:

  • Insulating around heat sources like radiators and boilers.
  • Employing thermal imaging to identify and address areas of significant heat loss.
  • Opting for cost-effective solutions like thermal-lined curtains, shutters, and draught-proofing (balanced by targeted ventilation).


Targeted insulation, although complex, emerges as a viable strategy towards achieving the UK’s net zero ambitions. The complexity arises from potential thermal imbalances and the risk of interstitial condensation within walls. A well-thought-out insulation strategy, complemented by targeted ventilation and possibly dehumidification, especially in a zoned insulation or heating system, can significantly contribute towards energy efficiency and emission reductions. This nuanced approach, however, requires a thorough assessment to align with one’s financial and practical needs, serving as a pivotal discussion starter en route to a greener future.

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