Insulating old properties
When insulating your old property it is imperative to pick a suitable, breathable method to avoid damp issues later down the line.
Insulated lime plasters/renders can outperform modern methods of insulation without any harm to your walls natural breathability.
Insulating the exterior is the best method however this can alter the look of your property.
Avoid;
Cement/Gypsum plaster
Vapour barriers
Closed cell insulation
Spray foam insulation
The science
Insulation needs to completely cover an area to be effective, any gaps in or around the insulation will dramatically reduce its performance. Most modern insulation is marketed focusing on the 'U-value', there are other things to consider when choosing an insulator.
Thermal mass - The ability of a material to absorb, store & release heat.
K-value - Thermal conductivity or ability to conduct heat.
U-value - Thermal transmittance is the rate of transfer of heat through matter.
Insulated Lime render/plaster
Render is the best method to insulate an older property as it forms a breathable & insulated envelope around the property.
​
Plaster keeps heat inside a & stores it so your home stays warm long after the heating is turned off.
​
Your solid wall being insulated will reduce the amount of condensation forming within the wall so it can escape more easily as water vapour.
Closed cell insulation
Used mostly in modern construction, often used on period properties despite its flaws.
​
This insulation isn't breathable & doesn't actually store heat, once the heating is turned off the heat will quickly pass through it & escape through any gaps, leaving you sat in the cold in no time.
​
In summer this magnifies the heat & is often unbearable to live with.
Spray foam insulation
This can be extremely damaging to your property as it traps moisture in your roof, there have been many cases of it causing the trusses to rot, leading to roof collapse if not dealt with.
​
It is difficult to remove and can often lead to your property being difficult/impossible to mortgage, sell or insure.​
Should be avoided like the plague...
Insulators
Closed cell insulation looks great when they show you the U-value; that's how they market their product: it has no place in old buildings as it isn't breathable.
Anyone who lives in a modern home insulated with these products also knows that the house soon gets cold once the heating is turned off. That's because it does not store heat; these properties also get uncomfortably hot in the summer. Thick, solid walls are best for keeping cool.
When choosing an insulator, it's important to look at all the factors involved, not just U-values. The table below shows a few of the variables worth considering.
​
Lambda: (k-value) thermal conductivity; the lower the value, the better.
​
Thermal mass is a material's ability to absorb, store, and release heat; the higher the mass, the better.
Acoustic absorption: (sound insulation) on a scale of 0 to 1, the higher the better.
​
Vapour permeability: (breathability) the ability for water vapour to pass through a material.
All figures are taken from several sources, we have not tested these products.
​
To reach desired U-values, you must take all aspects of the walls into account. You can simply increase the U-value by increasing the thickness of the insulation used. Insulation works best when air cannot pass through or around it; this simply proves that certain retrofit methods and cavity walls with air gaps are not always the best methods for insulating buildings.