Building envelope components – such as walls, roofs, and fenestration – play a crucial role in creating comfortable indoor environmental conditions. Additionally, they present an opportunity for significant energy savings if designed with energy efficiency in mind. This article aims to highlight the importance of thermal insulation in walls and roofs, with a particular focus on AAC (Autoclaved Aerated Concrete) blocks, a popular choice for energy-efficient building envelopes.

The Role of Insulation

Energy-efficient walls and roofs are designed with thermal insulation to minimize heat ingress. The insulated thermal mass reduces energy usage for heating and cooling, providing occupants with a thermally comfortable environment. Insulation materials come in a variety of forms, including cellulose, glass wool, rock wool, polystyrene, urethane foam, and many others. The choice of insulating materials can be determined based on the building type, its usage, and specifications defined by ECBC 2017. By employing an energy-efficient building envelope, energy efficiency can be improved by 8-10%.

AAC Blocks: The Advantages

AAC blocks offer several advantages that make them an attractive option for wall and roof construction:

1. Reduced Dead Load: AAC blocks significantly reduce the dead load, resulting in less use of steel and concrete in construction.
2. High Compressive Strength: Despite their lightweight nature, AAC blocks offer higher compressive strength.
3. Low Heat Transmittance: AAC blocks offer low heat transmittance (U-value: 0.95 W/m2-K), further enhancing their energy efficiency.

Several studies have demonstrated that the use of AAC blocks in buildings can reduce energy usage by 1.5-2% of total energy consumption.

Suppliers of AAC Blocks

Several companies offer AAC blocks, including NCL Buildtek, UltraTech Cement Ltd, Fusion Building Materials Private Limited, and Godrej Constructions. These companies have leveraged AAC’s energy efficiency and light weight to create environmentally-friendly construction materials.

NCL Buildtek manufactures AAC blocks, dry-mix cement mortars, and a wide range of tile adhesives. They also produce putties, textures, and a wide range of emulsion paints.

UltraTech Cement Ltd has established the UltraTech building products division, which manufactures and markets technologically re-engineered products for construction and infrastructure industries, including light-weight AAC Blocks.

Fusion Building Materials Private Limited is a certified manufacturer of AAC blocks, which they provide as eco-friendly bricks.

Godrej Construction offers a wide range of construction materials, including specially engineered ready-mix concrete products, AAC blocks, recycled concrete blocks, and pavers for different types of applications.

The U-value (also known as thermal transmittance) is a measure of how well a building element, such as a wall or window, conducts heat. The lower the U-value, the better the insulation properties of the material or assembly, as less heat is transmitted.

For the comparison of U-value between a brick wall with both side plaster and an AAC wall with both side plaster, both having sizes as 200+50+50 mm, consider the following table:

	Brick Wall with Plaster	AAC Wall with Plaster
Wall Material	Brick	AAC
Wall Thickness (mm)	200	200
Plaster Thickness (mm – both sides combined)	100	100
U-Value (W/m²K)	~1.5 – 2.0	~0.4 – 0.8

The U-values mentioned above are approximate and can vary significantly based on the specific type and quality of the materials used, as well as the precise assembly of the wall. The lower U-value for AAC wall indicates it is more thermally efficient than the brick wall with plaster, meaning less heat is conducted through the AAC wall, making it a better insulator.

Note: The actual U-value will depend on various factors, including the specific type and quality of the materials used, the presence of any additional insulating materials, and the precise construction of the wall. Therefore, this table should be used as a general guide rather than a definitive source of information. For accurate calculations, it is recommended to use dedicated software or consult with a building physics professional.

To calculate the U-value of a wall, we need to consider the thermal resistance (R-value) of each layer of the wall. The R-value of a layer is given by the thickness of the layer (in meters) divided by the thermal conductivity of the material (in W/mK). The U-value of the wall is then the reciprocal of the total R-value (U = 1/R).

The thermal conductivities for common construction materials are approximately as follows:

• AAC: 0.11 – 0.16 W/mK
• Brick: 0.6 – 1.0 W/mK
• Plaster: 0.2 W/mK

Let’s use these values to calculate the approximate U-values for the two wall types.

Brick Wall with Plaster

1. Brick (200mm): R = 200mm/1000 / 0.8 W/mK = 0.25 m²K/W
2. Plaster (50mm): R = 50mm/1000 / 0.2 W/mK = 0.25 m²K/W
3. Plaster (50mm): R = 50mm/1000 / 0.2 W/mK = 0.25 m²K/W
4. Total R = 0.25 m²K/W + 0.25 m²K/W + 0.25 m²K/W = 0.75 m²K/W
5. U = 1 / R = 1 / 0.75 m²K/W = 1.33 W/m²K

AAC Wall with Plaster

1. AAC (200mm): R = 200mm/1000 / 0.14 W/mK = 1.43 m²K/W
2. Plaster (50mm): R = 50mm/1000 / 0.2 W/mK = 0.25 m²K/W
3. Plaster (50mm): R = 50mm/1000 / 0.2 W/mK = 0.25 m²K/W
4. Total R = 1.43 m²K/W + 0.25 m²K/W + 0.25 m²K/W = 1.93 m²K/W
5. U = 1 / R = 1 / 1.93 m²K/W = 0.52 W/m²K

Please note that these are rough estimates and the actual U-values may vary depending on the exact specifications and quality of the materials used. Furthermore, these calculations assume a steady state (no changes over time) and ignore other factors such as thermal bridging, moisture content, and surface resistances. For more accurate calculations, it is recommended to use a dedicated software tool or consult with a professional.

Building envelope heat gain is determined by the U-value of the building’s envelope components, the area of each component, and the temperature difference between the inside and outside of the building. For simplicity’s sake, we’ll consider only heat gain through walls, ignoring windows, doors, roofs, and floors.

Let’s say the building has an average wall height of 3m, and the exterior walls make up approximately 25% of the total floor area. This would give the building a total wall area of 25,000 sqm or 250,000 sqft.

The temperature difference between the inside and outside of the building (ΔT) is a crucial factor in calculating heat gain. The larger the temperature difference, the more heat is transferred. For our calculations, let’s assume a temperature difference of 10°C or 18°F (typical for a summer day with the building being cooled to 24°C (75°F) and the outdoor temperature being 34°C (93°F)).

Heat Gain with Normal Brick Wall

In a previous response, we calculated the U-value for a normal brick wall with plaster to be approximately 1.33 W/m²K.

Heat gain = U-value * Area * ΔT

= 1.33 W/m²K * 25,000 m² * 10 K

= 332,500 W or 332.5 kW

Heat Gain with AAC Wall

We calculated the U-value for an AAC wall with plaster to be approximately 0.52 W/m²K.

Heat gain = U-value * Area * ΔT

= 0.52 W/m²K * 25,000 m² * 10 K

= 130,000 W or 130 kW

This rough estimation indicates that the building with AAC walls would gain about 60% less heat through its walls compared to the building with normal brick walls, assuming the same conditions.

Again, these are simplified calculations that ignore many factors that could affect heat gain, such as solar radiation, thermal bridging, moisture content, and ventilation. For a comprehensive heat gain calculation, it is recommended to use a detailed building energy simulation tool or to work with a professional.

Conclusion

Insulation plays a critical role in energy-efficient building construction, significantly reducing the energy needed for heating and cooling. AAC blocks, in particular, offer a range of advantages that make them an ideal choice for constructing energy-efficient walls and roofs. As the construction industry continues to focus on sustainability and energy efficiency, the use of AAC blocks and other similar materials is likely to increase.