How is heat lost from a building, and how do we make a building energy efficient?
Energy efficiency in buildings: how heat is lost, the use of insulation and U-values to reduce heat loss, and energy ratings.
A CCEA GCSE Construction answer on energy efficiency in buildings: how heat is lost through the fabric, how insulation and low U-values reduce heat loss, and how energy ratings measure a building's efficiency.
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What this dot point is asking
CCEA wants you to explain how heat is lost from a building, how insulation and low U-values reduce that loss, and how energy ratings measure how efficient a building is. Energy efficiency is one of the most important ways to make a building sustainable, because it cuts both running costs and carbon.
The answer
Why energy efficiency matters
A large share of the energy a building uses over its life goes on heating (and cooling). The less heat a building loses, the less energy is needed to keep it warm, which lowers fuel bills and carbon emissions. Making a building energy efficient is therefore good for the occupier (cheaper bills), the economy and the environment, hitting all three pillars of sustainability.
How heat is lost
Heat flows from the warm inside of a building to the colder outside through every part of its fabric.
Because heat rises, the roof is one of the biggest routes of loss in an uninsulated house, followed by the walls and windows.
Insulation
Common measures include loft and roof insulation, cavity wall insulation (filling the gap in a cavity wall), insulated floors, double or triple glazing (two or three panes with a gap that traps air), and draught-proofing to stop air leaking through gaps.
U-values
The performance of a part of the building is measured by its U-value.
So a wall with a U-value of loses heat more slowly, and is better insulated, than a wall of .
Energy ratings
Buildings are given an energy rating that shows how efficient they are, usually on a scale from A (most efficient) to G (least efficient), shown on an Energy Performance Certificate. A higher rating means lower running costs and lower carbon, and helps buyers and tenants compare buildings.
Worked example: choosing the most efficient wall
Examples in context
- Example 1. Insulating the loft
- A cold house with no loft insulation loses a great deal of heat through the roof. Rolling out loft insulation traps air and cuts this loss, lowering bills quickly for a low cost, so it is one of the first measures recommended.
- Example 2. Upgrading windows
- Replacing single glazing with double glazing adds a sealed air gap between two panes, which has a much lower U-value, so less heat escapes through the windows and the rooms feel warmer and less draughty.
- Example 3. Reading an energy certificate
- A buyer comparing two houses sees one rated B and one rated F. The B-rated house will cost much less to heat and produce less carbon, so it is the more sustainable choice even if it costs a little more.
Energy efficiency is the single biggest opportunity to cut a building's lifetime environmental impact, because it reduces the operational energy used for decades. It works hand in hand with the next topic, renewable energy, which provides the remaining energy a well-insulated building still needs, but from clean sources.
Try this
Q1. Name two parts of a house through which heat is lost. [2 marks]
- Cue. For example the walls, roof, floor, windows or through draughts.
Q2. Is a high or a low U-value better for an energy-efficient wall? [1 mark]
- Cue. A low U-value, because less heat passes through.
Q3. What does an energy rating of A mean compared with G? [1 mark]
- Cue. A is the most efficient (lowest running cost and carbon); G is the least efficient.
Exam-style practice questions
Practice questions written in the style of CCEA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
CCEA style4 marksDescribe two ways heat is lost from a house and state how each loss can be reduced.Show worked answer →
Any two routes of heat loss with a matching method:
- Heat lost through the walls: reduce it by insulating the cavity and adding insulation to the walls.
- Heat lost through the roof: reduce it by laying insulation in the loft or roof.
Other acceptable pairs include heat lost through the floor (insulate the floor), through windows (use double or triple glazing), and through gaps (draught-proofing to cut air leakage).
Markers reward one mark for each correct route of heat loss and one mark for a correct way to reduce it.
CCEA style4 marksExplain what a U-value is and state whether a high or a low U-value is better for an energy-efficient wall.Show worked answer →
A U-value measures how easily heat passes through a part of the building, such as a wall or window: it is the rate of heat loss per square metre for each degree of temperature difference. A lower U-value means less heat passes through, so it is the better-insulated, more energy-efficient option.
Markers reward a correct description of the U-value as a measure of heat loss or heat transfer (two marks), and the statement that a low U-value is better with a reason (two marks).
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