A house built to nZEB standards has a highly insulated solid concrete ground floor with a hardwood finish, as shown - Leaving Cert Construction Studies - Question 5 - 2020

To calculate the cost of heat loss, we use the formula:

$Q = U imes A imes \Delta T$

where:

• Q = heat loss (in Watts)
• U = U-value of the floor (0.100 W/m²°C)
• A = area of the floor (6.5 m × 9.0 m = 58.5 m²)
• \Delta T = temperature difference (20°C - 6°C = 14°C)

Calculating heat loss:

$Q = 0.100 imes 58.5 imes 14 = 819.3 \, Watts$

Next, calculate the annual energy usage:

$ext{Energy per day} = Q imes ext{hours per day} = 819.3 imes 24 = 19663.2 \, Watts/day$

Thus, per year:

$ext{Annual Energy} = 19663.2 imes 365 = 7,177,045.2 \, Watts$

Now, converting Watts to KiloWatts:

$ext{Annual KiloWatts} = \frac{7,177,045.2}{1000} = 7177.045 \text{ kWh}$

Using the cost of energy, calculate:

$ext{Total Cost} = KiloWatts imes ext{Cost of oil per litre} = 7177.045 imes 0.96 = €6,895.086 \ ext{per annum}$

Thus, the total annual cost is approximately €18.62.

To prevent thermal bridging at the junction of the concrete floor and external wall, the following best practices should be implemented:

1. Continuous Insulation: Ensure that insulation is continuous across the junction area to minimize any thermal weaknesses where the floor meets the wall.

2. Thermal Break Materials: Use thermal break materials (materials with low thermal conductivity) between the concrete and the external wall to limit heat transfer.

3. De-coupling Layers: Consider incorporating de-coupling layers that separate the concrete slab from the wall, which can help reduce direct conductive paths.

4. Proper Flashing and Sealants: Install proper flashing to direct water away and use high-quality sealants to prevent air leaks that can lead to thermal losses.

5. Detailed Layout in Sketch: The detailing should be illustrated in a freehand sketch to highlight the materials and methods, ensuring that there are no gaps that might lead to thermal bridges in the junction.