Types of Insulation
One of the types of insulation used in building construction and retrofitting is reflective insulation. Other types of insulation like fiberglass wool, rock mineral wool and polystyrene are also available. Some polystyrene insulation is backed with reflective foil to combine the advantages of both. Each has its own advantages and disadvantages, and this article focuses on reflective insulation.
Reflective insulation (also known as foil insulation) is usually made from aluminum foil or aluminized polyester. Reflective insulation is commonly used in two main areas. The first is in unventilated cavity walls; the second is as insulation in pitched or angled roofs.
Reflective insulation reflects radiant heat and works best with a still air layer of at least 25mm/1 inch. It is most effective when kept clean and dust free. The layer of still air itself gives it a degree of extra insulation—provided it is still, otherwise it will be taking heat away through convection.
How Houses Lose Heat
To understand about how insulation works, some knowledge of how heat is transferred is required. Heat is transferred in three ways: radiation, convection, and conduction.
- Radiation is where the heat is transmitted directly from a hot surface in a straight line to a cooler surface; sunlight is a good example of radiant heat.
- Convection is where the heat is transferred via liquid or gas movement, such as hot central heating radiators. It is also the reason things like water are hotter at the top than at the bottom.
- Conduction is where heat is transmitted along a material or two materials touching each other. A good example of this is metal pans. Different materials transmit heat better than others. (Metal is a better conductor than wood, for example.)
Advantages of Reflective Insulation
- It is very effective in warm climates where it is useful in keeping buildings cool.
- Unlike other insulation, it does not degrade over time due to compacting, disintegration, or from absorbing moisture.
- It is thin and fairly lightweight and much less bulky than other forms, making it easy to work with and fit.
- It can also be used as a vapor barrier, as it is relatively waterproof and unaffected by moisture.
- Unlike other forms of insulation, it is also non-toxic and non-carcinogenic, making it safer and easy to install with the use of less safety equipment.
Disadvantages of Reflective Insulation
- It is generally more expensive due to being a metal-based product.
- Though effective in warmer climates, it will require being combined with other forms of insulation in colder climates. This is in order to prevent heat loss in cold weather from convection.
- There is the potential of reflective insulation becoming an electrical hazard should a wiring fault occur. After all, it is a metal and conducts electricity.
- It also relies on being clean and free of dust and debris, both when fitted and when in use. This means in some areas, such as roofs, it may require being cleaned of dust from time to time to ensure maximum efficiency.
Questions & Answers
Question: Would you recommend reflective insulation?
Answer: Yes, I would.
Question: When using reflective foil, which side should face the inside and outside?
Answer: It depends on which way you want the heat to go. Put it on the side where you want the heat to radiate away from. If you want to keep a room warm, put it on the inside. If you want to cool a room, then put it on the outside.