Insulation, insulation, insulation!

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In cold weather, most people will wear a coat. It is the same for buildings, except the majority of the UK‘s buildings only wear t-shirts at best…

A building wrapped in a scarf and a hat

Insulating buildings is the single most effective way of saving energy long-term and we always look at doing this before any more advanced measures such as heat pumps or photovoltaics are added.


As heat rises, it makes sense to start by insulating the roof – 25% of heat losses occur here. For most people that is the easiest and most cost-effective thing to do first. Before doing so, it might be worth thinking about extending the building upwards into the loft at the same time.

Note: While extruded PIR insulation still is commonly used and offers great thermal performance at minimal thicknesses, consider heavier natural insulation materials such as wood fibre. This will be thicker but has many advantages:

  • the weight helps against noise from airplanes etc
  • the weight helps to keep the roof space cooler in summer, especially when combined with good ventilation behind roof tiles
  • Natural fibre insulation materials are fully recyclable and use less energy in production
  • Natural fibre material is breathable (vapour-open)



When refurbishing a floor, consider taking up the floor boards and fitting insulation between the joists.

While this lowers your carbon emissions the immediate benefit of this is a comfortable, draught-free floor. This will also enable fitting a wet underfloor heating system which is particularly suited in combination with renewable low-temperature heating solutions such as heat pumps (ground source or air source).




Wall insulation can be retrofitted externally or, in heritage buildings, internally. Internal insulation is a little more complicated to fit and also takes up space but often this is the only available solution if the building has historic brick facades for example. However, the rooms will be significantly more comfortable and as a result more usable.

When choosing an insulation system the main consideration next to its thermal resistance is how moisture from the building is managed. Breathable solutions tend to work well with historic buildings where the external building skin is made from breathable materials (including lime mortar brick walls for example). In this scenario it is important to specify breathable internal finishes such as lime-based plasters and vapour-open natural paints. Different systems are available for cement-based existing walls and cavity walls.

A nice upshot of fitting internal insulation is that the internal reveals often become quite deep – perfect for integrating blinds, perching on or displaying objects.


A bedroom with a curved wall panelled in fluted timber battens with a timber joist ceiling


Upgrading windows to double- or triple-glazed systems helps make a space warmer as well as more comfortable. We are often asked if it is worth going for triple: It is. Apart from further energy savings the difference is that the inner surface temperature of a triple-glazed window is high enough that there is no cold down-draught along the glass, meaning it does not feel cold sitting next to the window, even if it is large.

In historic buildings it is often necessary to use sliding sash windows which tend to have limits

A few things to look out when selecting and installing new windows:

  • Ensure the U-value stated is for the assembled window, including the frame.
  • Use as little frame as possible – this is usually the weak point of the window.
  • Choose a thermally broken system that reduces internal condensation on the frames
  • Chose a system with at least two lines of weather seal
  • Check the air tightness class of the window 9ideally class 4 upwards.
  • If possible, use casement windows, hinged or lift/ slide doors as these use compressible rubber seals. Avoid brush seals if possible.
  • Don’t forget to insulate the wall around the windows, including the reveals
  • Check gaps around windows are fully sealed airtight and against weather on all sides. In cavity construction, check a cavity closer has been installed around the opening.
  • Steel/ aluminium systems cost more carbon to produce than timber windows yet sometimes are unavoidable when framing large panes of glass.
  • Consider heat gain through south/ west facing windows – sun shading systems such as awnings, roller blinds or Venetian blinds will make a big difference as long as these are installed on the outside. Otherwise consider solar coatings on the glass.


Roof lights/ skylights:

The same glazing specification will lose more energy in a roof light than in a window as heat rises. Therefore triple-glazed roof lights are becoming the norm now for low energy developments. Note these are limited in size, yet often it is possible to use a slightly smaller roof light and still achieve good levels of daylight. For context: The best roof lights still lose 4-5 times more heat than a well-built flat or pitched roof.

Note: there are roof lights on the market with integrated blind systems. However, fitting blinds externally is significantly more efficient in keeping the heat out.



Doors are often forgotten in this equation. Unless an exact hardwood copy is required for conservation purposes consider a timber door with an insulated core and consider placing the letter box outside of the building rather than cutting a large slot into the door leaf.

Read more on what to do about climate change here

See a selection of our low energy projects here

A building wrapped in a scarf and a hat