Welcome! Heating a home is expensive – and a lot of that energy escapes straight outside. In this lesson you’ll learn how energy is lost from buildings, then advise a family on how to cut their energy bills on a budget. It takes about one hour. Work through the steps in order.
Before you start
- You need: your exercise book or paper, a pen and a calculator.
- Write the title and date: Insulating a home – Cut the Bills.
- The golden rule: write your answer first, then tap Show answer. Correct mistakes in a different colour.
- Look out for the blue 📝 boxes. Copy each one into your book neatly – these are your revision notes.
📝 Copy into your book
By the end of this lesson I will be able to:
1. explain what affects how quickly a building loses energy
2. describe ways to reduce unwanted energy transfers
3. use payback time to choose the best-value insulation.
Step 1: Starter (5 minutes)
Picture a house on a cold winter’s day with the heating on. List every place you think heat escapes from. Try for at least five.
Show answer
Through the roof, the walls, the windows, the floor, and through gaps around doors and windows (draughts). In a typical uninsulated house, the walls and roof lose the most.
📝 Copy into your book
Energy always moves from hot to cold. A house loses energy through the roof, walls, windows, floor and draughts.
Step 2: Read and write (8 minutes)
First, copy these three questions into your book. Then read the text below carefully and answer them in full sentences.
- What does a high thermal conductivity mean?
- Name two ways of reducing unwanted energy transfers.
- How does the thickness of a wall affect how quickly a house cools?
📖 Read: Keeping the heat in
Energy is always transferred from a hotter place to a colder one. In a home, energy that escapes outside is wasted, so we try to reduce these unwanted energy transfers.
Every material has a thermal conductivity. A material with a high thermal conductivity, such as a metal, lets energy pass through it by conduction quickly. A material with a low thermal conductivity, such as air, wool or foam, transfers energy slowly – so it is a good insulator. The thicker the walls of a house, and the lower their thermal conductivity, the more slowly the house cools down.
There are two main ways of reducing unwanted energy transfers. Thermal insulation, such as loft insulation and cavity wall insulation, slows down energy transfer out of buildings. Lubrication, such as oiling the moving parts of machines, reduces friction so less energy is wasted by heating.
Show answers
(a) The material transfers energy by conduction quickly – it’s a poor insulator.
(b) Thermal insulation (e.g. loft or cavity wall insulation) and lubrication (to reduce friction in machines).
(c) Thicker walls cool more slowly – the rate of energy transfer is lower.
📝 Copy and complete
A material with a __________ thermal conductivity transfers energy quickly. Good insulators have a __________ thermal conductivity. Two ways to reduce unwanted energy transfers are thermal __________ and __________.
Check your gaps
high · low · insulation · lubrication
Step 3: Key facts (7 minutes)
These three factors come up in the exam every year. Copy them carefully:
📝 Copy into your book
A building loses energy faster when:
1. its walls have a HIGH thermal conductivity
2. its walls are THIN
3. there is a LARGE temperature difference between inside and outside.
Now read how insulation works, then copy the box.
Examples of insulation: loft insulation (fibre wool), cavity wall insulation (foam between the two layers of wall), double glazing (a gap between two panes of glass), draught excluders, and hot water tank jackets.
📝 Copy into your book
Many insulators work by TRAPPING AIR. Air has a very low thermal conductivity, so energy is transferred through it slowly.
Quick check: which would lose energy faster – a thin brick wall or a thick brick wall? Why?
Show answer
The thin wall – energy is conducted through a thinner wall at a higher rate.
Step 4: Payback time (7 minutes)
Insulation costs money, but it saves money every year. Copy the equation:
📝 Copy into your book
payback time = cost ÷ saving per year
The SHORTER the payback time, the BETTER value it is.
Copy this table and work out the payback time for each:
| Option | Cost | Saving per year | Payback time |
|---|---|---|---|
| Loft insulation | £400 | £250 | ? |
| Cavity wall insulation | £800 | £300 | ? |
| Double glazing | £6000 | £150 | ? |
| Draught excluders | £50 | £40 | ? |
| Hot water tank jacket | £20 | £30 | ? |
Show answers
Loft insulation: 400 ÷ 250 = 1.6 years
Cavity wall: 800 ÷ 300 = 2.7 years
Double glazing: 6000 ÷ 150 = 40 years
Draught excluders: 50 ÷ 40 = 1.25 years
Tank jacket: 20 ÷ 30 = 0.67 years (about 8 months)
✅ Score out of 5. Which option is the best value? Which is the worst?
Step 5: Main task – Cut the Bills (12 minutes)
You’re an energy adviser. The Patel family live in an old house with no insulation at all. They have £1500 to spend and want to cut their bills as much as possible.
Your task: using your payback table, write them a short report with these headings:
- What to buy (total cost must be £1500 or less).
- How much they’ll save each year, and the payback time for the whole package.
- How it works: explain the physics of one option, using the words thermal conductivity and air.
- What not to buy yet, and why.
Stuck? Start with the options that have the shortest payback time.
Show a model report
1. What to buy: loft insulation (£400), cavity wall insulation (£800), draught excluders (£50) and a tank jacket (£20). Total: £1270.
2. Savings: £250 + £300 + £40 + £30 = £620 per year. Payback time = 1270 ÷ 620 ≈ 2 years. After that, it’s all savings.
3. How it works: loft insulation is made of fibres that trap air. Air has a very low thermal conductivity, so energy is transferred through the roof much more slowly and the house stays warm for longer.
4. Not yet: double glazing. It costs £6000 – far over budget – and takes 40 years to pay back.
Step 6: Exam practice (13 minutes)
Look at the marks – they tell you how many points to make. Answer in full sentences, then mark yourself.
Q1 (2 marks) Explain how loft insulation reduces the energy lost from a house.
Show model answer
It traps air, which has a low thermal conductivity (1), so the rate of energy transfer through the roof is reduced (1).
Q2 (3 marks) Loft insulation costs £450 to fit and saves £180 per year. Calculate the payback time.
Show model answer
payback time = cost ÷ saving per year (1)
= 450 ÷ 180 (1)
= 2.5 years (1)
Q3 (4 marks) Two houses are identical except that House A has thin walls made of a material with a high thermal conductivity, and House B has thick walls made of a material with a low thermal conductivity. Explain which house cools down faster on a cold night.
Hint: use your three factors from Step 3 – explain both differences, then give your conclusion.
Show model answer
House A cools down faster (1). A higher thermal conductivity means energy is conducted through the walls at a higher rate (1). Thinner walls also increase the rate of energy transfer (1). So House A loses energy to the outside more quickly, and its temperature falls faster (1).
✅ Add up your marks out of 9 and write the score in your book.
Step 7: Exit ticket (8 minutes)
Think about your own home. Which one change would save your family the most money? Then finish:
- The best insulation to buy first is… because…
- Materials that trap air are good insulators because…
- One thing I’m still not sure about is…
🎉 Well done – lesson complete! Your 📝 boxes are your revision notes for this topic. Want more? Try the Energy key definitions and the Thermal insulation practical (Separate).
🖨️ Want this lesson on paper? Download the whole lesson as a printable worksheet – answers are on the last page.
