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Retro Wall Thermal Insulation
Retro wall insulation - Good or Bad?
There are several retro wall insulations on the market. Are they any good though? Will they reduce your energy bill, or cost you a fortune to rectify?
There are several different types of wall construction: Solid brick or stone, cavity brick / block, stone and brick, timber frame with a masonry veneer are perhaps the most common. The last one probably doesn't need any additional thermal insulation, so that only leaves solid walls and masonry cavity walls.
Thermal insulation - What exactly is it? [There is another Blog explaining the science behind heat]. But for now we will look at the pros and cons of retro thermal insulation of walls.
Cavity wall construction has been around for hundreds of years. As early as 1750 where a house for a Church Rector was built using two leaves of masonry tied together with clay wall ties. Not for thermal reasons, but to stop damp penetration through the walls.
Centuries later Building Bye Laws started to insist on walls that would prevent rain water passing through them. Manchester has more than its fair share of rain. The idea of putting a damp proof course allegedly originated from the Bye-Laws instigated in Manchester.
Generally though, across much of England and Wales cavity wall construction didn't really become popular until the late 1920's. Even so they were not that popular until the 1960s.
Why cavity walls?
Not for thermal reasons. They were purely to overcome damp penetration through the walls. On the wet side of England and Wales wind driven rain could force its way through thick masonry walls. On a test rig using water jets producing water pressure equal to a very windy day and heavy rain, water actually went through most of the wall making it very damp on the living side.
Building a wall in two leaves allowed the water to go through the outer leaf of masonry and gravity pulled the water down the cavity and out of the weep holes at the foot of the wall or above lintels etc. That is the reason for cavity walling.
Now in the 21st century as fuel costs increase dramatically and 'officials' tell us that burning fossil fuel is creating 'Climate Change' (Another blog explains why that is not true), it is logical to think about ways of reducing the amount of energy being used.
There are several factors that should be considered when deciding upon retro thermal insulation. Firstly actually considering the real science involved.
There are websites and 'official' websites that claim that putting extra thermal insulation onto the outside of a wall will reduce your energy bill.
Now a quick bit of science - (a full explanation is in the other blog)
Heat is a product of molecules colliding - nothing else. Heat cannot exist if there are no atoms or molecules to collide. Atoms are specific. They are only one form. A molecule is more than one atom. For example a molecule of H2O is an atom of Hydrogen bonded to 2 atoms of Oxygen.
When the temperature is considered the molecules can be close together as water, further apart as ice, or really far apart as gas - vapour. It is still H2O though. The only difference is the temperature - the amount of energy being used for mobility.
If the H2O is as a gas / water vapour, it has plenty of energy and can move about freely. It requires lots of energy to remain in a gaseous state. Lose some of the energy and the molecule slow down. They become water (liquid state). If there is a lot of water vapour in a property (gaseous state) it will not be visible. You can't see gas. However, it is still there, it is termed 'humidity'.
Dry air is non-existent other than in a laboratory. Even in the hottest and driest deserts there is still humidity - albeit not much.
Air molecules and atoms are mainly Nitrogen, Oxygen plus a few trace gases. Into the air H2O in gaseous form can exist. We call it the humidity factor. We breath out humidity, we sweat (okay - girls glow). Our pets are doing the same. It is part of respiration. Plants, flowers in a vase, fish in an aquarium are all contributing to the moisture in the air. Have a shower or bath. All that steam is going somewhere. Cooking and baking. Boiling water in a pan and the steam is going somewhere. Bake a cake. Where does all the liquid go? Into the air. If you use a towel to dry yourself - where does all that water go?
Some people suggest opening a window to 'air the room'. A German neighbour used to open her windows and put the duvets hanging out each day to air them. Yes, there are many sources of moisture going into the air in our homes. The latest Building Regulations require new builds to be vapour locked. A seal around each dwelling to reduce 'heat loss'.
Now we shall look at the technical side based on proven science.
Heat is purely a product of molecular movement (can also be atomic). No atoms means no molecules - means no heat. Simple and straightforward. A material with lots of molecules is classed as being dense. Scientifically density is the product of mass divided by volume. No, we are getting too technical now.
If you have a lot of dense materials they will require a lot of energy to make the molecules move. The most movement of a solid material is to vibrate. The molecules are packed in and only have enough space to vibrate when energised. To make them vibrate energy is required. There are different ways that energy can transfer. [It is all explained in the Science Blog]. That means a masonry wall made from densely packed molecules will require a lot of energy to make them vibrate. The vibration produce heat as they collide with adjacent atoms / molecules (kinetic energy).
For heat to exist the electrons have to collide with other electrons on adjacent atoms or molecules. It is a product of a molecular action. No molecular action means no heat is produced. Heat as such is not a 'thing'. It cannot exist without atoms therefore cannot move. It isn't like a fluid.
Evidence is required!
There are no atoms in a pure vacuum. Therefore there is nothing to produce heat. A vacuum flask made from two very thin layers of silvered glass with most of the atoms removed between the two layers prevent most of the heat transfer. Mr Themos (James Dewar and Reinhold Burger) back in the early 1900s came up with the idea to keep substances in a container to remain at the same temperature as they went in.
The energy being used remained relatively constant. However, even without any atoms radiation still remains. Radiation, more specifically electromagnetic radiation, can pass through a vacuum. If it doesn't collide with anything it can travel in theory for ever.
Therefore, some of the 'heat' being produced by the colliding molecules, both in the contained substance and outside will be giving off radiation. That means there will be less energy contained in the molecules and they will slow down. As they slow down they will not have the same impacts and so less heat is produced.
It is the theory that William Thomson (AKA: Lord Kelvin) was given his lordship for. If atoms stop moving no heat is produced and the point of reference is 'Absolute Zero'. That is minus 273.15°C = 0K
Back to thermal insulation rectro fitted.
There are advertisements and sales people making all types of claims. Are they correct though? Putting thermal insulation on the outside of a wall and rendering over it. Does it actually do what they are claiming - NO!
Sir Richard Head was known to his friends as 'Dick'. He had a thought: Why not put my steel armour on, then my chain mail and then my woollen comb's over the top. Those sales people and 'scientists' state it doesn't matter which order the materials go on, it is thermally the same result.
Yes - the current method for calculating thermal movement in buildings is using a 'U Value' calculation. It doesn't matter what order the materials or emissivity is used as the result is the same.
Now using logic:
Woollen comb's are thermally very efficient. Plenty of trapped air held in place by irregular natural fibres of wool. That next to your skin will retain your body heat as it will not transfer by conduction, minimal by radiation and virtually no convection = excellent thermal insulation.
Chain mail - small threads of metal, mainly steel or iron. Effective against some degree of impact. The diameter of the wire is relatively small so minimal conduction. Space between the wire is relatively trapped therefore minimal convection. Some radiation as it is metal.
Armour - thicker sheets of worked steel. The mass of the metal is very dense. A knight if knocked over or fallen from a horse would have found it difficult to stand up again due to the weight of the armour.
The diagram shows how layers of different materials minimise the heat being lost from the body. Woollen comb's are very efficient at reducing thermal energy passing through. The fibres of wool do not conduct much energy. They are randomly assembled trapping air between the fibres = very thermally efficient.
Chain mail, although metal is dense and readily conducts thermal energy, the wire diameter is relatively small with air spaces between each wire. The woollen comb's prevent any conduction from the body, creating a thermal barrier.
The dense and thick armour receives minimal thermal energy. The mass readily absorbs any energy.
If. as Sir Richard's idea, he puts the layers in a different order, logically thermal movement will be significantly changed.
In this order, the dense metal of the steel armour requires an enormous amount of thermal energy to raise the temperature. To the touch it will feel and remain to feel cold as the body cannot produce sufficient thermal energy to raise the temperature.
The chain mail is on the cold side of the armour therefore will receive no thermal energy.
The woollen comb's are on the outside and cannot provide any thermal resistance. There is virtually no energy to trap.
A comparison: Sit on a cold thick stone floor. Does your bottom heat the stone up?
Now compare putting thermal insulation on the outside of a masonry wall.
The room you are trying to keep at a suitable temperature is trying to heat up the dense masonry in a similar way to the body trying to heat up the armour. Putting thermal insulation on the outside is like the woollen comb's. It doesn't do what they claim.