Building a second storey is a significant financial investment. There are many practical ways to reduce the overall cost of adding a storey. Careful planning, a simple floor plan, standard window sizes and an efficient structural design will help keep costs within budget. Reusing structural elements from the existing house and avoiding unnecessary architectural complexity can also lead to savings. We will focus on one of the most important factors affecting the cost: the choice of materials for the extension’s external walls, frame and insulation. Wall systems vary in price, weight, assembly complexity, maintenance requirements and thermal insulation performance. These differences can affect both the construction budget and the long term running costs of a home in Melbourne. We will compare five common options, ranging from affordable lightweight systems to brickwork, and assess their relative cost and effectiveness. We hope this analysis will help homeowners determine which approach offers the best value for money when building second storey house extension.
1. EPS Foam Cladding
Cost rating: 1/5
Insulation rating: 5/5
Rendered EPS foam panels are among the most affordable external wall options for a second storey extension. The system consists of expanded polystyrene panels fixed to a timber or steel frame, followed by reinforcing mesh, base coats and a protective rendered finish.
Common EPS panel thicknesses include 50 mm, 75 mm and 100 mm. Some certified systems also offer 40 mm or 150 mm panels. Greater thickness generally provides better thermal resistance, although the correct panel must be selected as part of the complete wall design. The external EPS layer works together with insulation batts inside the frame, wall wrap, internal plasterboard and sealed window openings.
EPS panels are lightweight, which reduces the additional load placed on the existing house. This can simplify structural work and lower material, transport and installation costs. Large panels also allow external walls to be enclosed relatively quickly.
2. Fibre Cement Cladding
Cost rating: 2/5
Insulation rating: 2/5
Fibre cement siding and weatherboards provide a lightweight external wall option. Common products include horizontal weatherboards, vertical boards and large panels fixed to timber or steel framing.
Product dimensions vary between manufacturers. Typical fibre cement cladding thicknesses range from 6 mm to 16 mm. Common examples include 8.5 mm textured panels, 9 mm vertical cladding, 14 mm boards and 16 mm weatherboards. Panel widths are often around 1,200 mm, while lengths may range from 2,400 mm to 4,200 mm.
Fibre cement provides limited insulation by itself. Most thermal performance comes from insulation batts, wall wrap, the cavity and correct sealing around openings.
3. Sheet Substrate with Render Finish
Cost rating: 2/5
Insulation rating: 2/5
Rendered sheet cladding is a lightweight option for a second storey extension, creating the appearance of a solid rendered wall without the weight of brickwork. A builder typically fixes exterior grade fibre cement sheets, rather than ordinary plywood, to a timber or steel frame before applying reinforced joints, base coats and a textured finish. Common sheets are generally 7.5 to 9 mm thick and around 1,200 mm wide. The cladding itself provides little insulation, so wall batts, wrap and cavity detailing remain important. Correct joints, flashings, waterproofing and movement allowances are essential.
4. AAC Lightweight Concrete Panels
Cost rating: 4/5
Insulation rating: 4/5
AAC Lightweight Concrete Panels provide a lightweight alternative to traditional masonry for a second storey extension. The panels are fixed to timber or steel framing and usually finished with a compatible rendered coating. Their lower weight can reduce structural demands on the existing home, while their thermal and acoustic properties can improve comfort. Common residential panels are approximately 50 mm or 75 mm thick, depending on the certified wall system. AAC Panels generally costs more than EPS or fibre cement cladding, but its durability, fire resistance and solid appearance may add lasting value. Installation must follow NCC and manufacturer requirements.
Brick Veneer Cladding
Cost rating: 5/5
Insulation rating: 2/5
Brick veneer provides a traditional finish with a solid, luxury appearance. It offers excellent durability, weather resistance and low maintenance. Brickwork can also help the new level match an existing brick home or support an architectural design.
However, brick is the heaviest and most expensive option in this comparison. The foundations, walls and floor structure may require strengthening before construction begins. Additional labour, scaffolding, footings, structural steel and longer installation times can increase the total extension cost.
Brick itself provides limited insulation. Most thermal performance comes from the insulated framed wall, reflective wall wrap and designed cavity behind the veneer.
Conclusion
Each wall system offers a different balance of cost, insulation, appearance and structural weight. EPS is generally the most affordable and thermally efficient option, while brick provides a solid premium finish at the highest cost. The best choice depends on the existing house, extension design, budget and local building requirements.