1940s-60s case studies

These case studies show how to choose and apply a compliance path for a 1940s-60s house renovation.

They give examples of the compliance path options that may be used demonstrate performance with relevant clauses of the Building Code.

They follow the six steps set out in the page on selecting compliance paths.

The case studies cover:

  • Case study 1: As part of a proposed renovation, the BCA is requiring that underlay is installed behind existing weatherboards.
  • Case study 2: A new extension is proposed for a stucco-clad house. It is proposed to install new stucco cladding without a drainage cavity so it aligns with existing cladding.
  • Case study 3: The proposed renovation of a 1940s-60s house is to include a new extension and to insert a new double-glazed aluminium window (R-value = 0.26) into a wall where there is currently no window.
  • Case study 4: The proposed renovation of an art deco house is to include a first floor addition.
  • Case study 5: The owners of a 1950s modern style house with a reinforced concrete floor want to add an extension maintaining a consistent floor level throughout, but the existing floor is too close to the ground to provide the clearance required under E2/AS1.

1940s-60s houses – compliance case study 1

Preliminary investigation of an ex-state house built in 1947 has revealed that wall underlay was not installed behind the bevel-back weatherboard cladding when the house was built. As part of the proposed renovations, the roof and underfloor spaces are to be insulated but as the existing claddings and internal linings are in good condition the owner does not want to insulate the walls. However, the BCA is requiring that underlay is installed in the walls of the existing house as part of the proposed renovations.

Step 1. Identify the aspects of the proposed design that fall outside the scope of Acceptable Solutions Without building underlay, the proposed renovation is outside the scope of the Acceptable Solutions.
Step 2. Identify the Building Code clauses for which performance must be demonstrated by the design and supporting documentation.

The Building Code clauses to be addressed by this Alternative Solution are:

• B2 Durability

• E2 External moisture

Step 3. Identify the performance criteria that apply.

The performance criteria that apply include:

• B2.3.1 Building elements must have a not less than 15 year durability

• E2.3.2 Roofs must prevent penetration of water

• E2.3.5 Concealed spaces and cavities must prohibit the transfer of moisture that could cause condensation and deterioration of building elements.

Step 4. Select the most relevant compliance path(s).

The most relevant compliance path options could be:

• Compliance path 3 – comparison with in-service history

• Compliance path 4 – expert opinion

Step 5. Determine what type of information is required to demonstrate compliance. Information to demonstrate compliance should include evidence that the current construction performance has been satisfactory for the past 63 years in terms of durability and preventing water ingress.
Step 6. Provide the evidence.

Photographs demonstrating that there has been no deterioration of the existing wall framing despite the lack of building underlay can be used to provide evidence of an in-service history and satisfactory performance for both clauses B2 and E2. This will require the removal of a small section of cladding or internal lining to take photographs. 

To provide additional support for clause E2, an inspection report provided by a reputable building surveyor would provide evidence that the performance of the existing wall cladding has been satisfactory for the life of the house (63 years) and that there has been no deterioration to the building framing due to water ingress. 

 

Back to top

1940s-60s houses – compliance case study 2 

A stucco-clad house that was built in 1951 is to have an extension added with a stucco cladding to match the existing. However, the existing stucco is on a rigid backing but does not have a drained cavity whereas the new work will require one, which means the alignment of the cladding will be lost at the junction of the old and new. It is  therefore proposed that the stucco is installed without the drained cavity.

Step 1. Identify the aspects of the proposed design that fall outside the scope of Acceptable Solutions The proposed cladding material is outside the scope of the Acceptable Solution E2/AS1.
Step 2. Identify the Building Code clauses for which performance must be demonstrated by the design and supporting documentation.

The Building Code clauses to be addressed by this Alternative Solution are:

• B2 Durability

• E2 External moisture

Step 3. Identify the performance criteria that apply.

The performance criteria that apply include:

• B2.3.1 Building elements must have a not less than 15 year durability

• E2.3.2 Roofs must prevent penetration of water

Step 4. Select the most relevant compliance path(s).

The most relevant compliance path options could be:

• Compliance path 3 – comparison with in-service history

Step 5. Determine what type of information is required to demonstrate compliance. The type of information to demonstrate compliance should include evidence of the performance of the existing cladding in terms of durability and preventing water ingress.
Step 6. Provide the evidence.

The condition of the existing stucco without a cavity would provide evidence of the in-service history and satisfactory performance. Removal of a small part of the wall to demonstrate the lack of damage to the wall behind the cladding would reinforce the evidence of the satisfactory performance. 

A report by a building surveyor on the state of the framing behind the cladding would provide the expert opinion that the performance of the existing wall cladding has been satisfactory for the life of the house.

 

Back to top

1940s-60s houses – compliance case study 3

The proposed renovation of an ex-state house is to include a new extension and to insert a new double-glazed aluminium window (R-value = 0.26) into a wall where there is currently no window. The wall where the new window is to be installed is timber-framed with bevel-back weatherboard external cladding, plasterboard internal lining and is uninsulated, giving an R-value of approximately 0.5.
Step 1. Identify the aspects of the proposed design that fall outside the scope of Acceptable Solutions The extension is able to meet the performance requirements of the relevant NZBC clauses but the installation of the new window will reduce the thermal resistance of the existing wall.
Step 2. Identify the Building Code clauses for which performance must be demonstrated by the design and supporting documentation.

The Building Code clauses to be addressed by this Alternative Solution are:

• H1 Energy efficiency.

Step 3. Identify the performance criteria that apply.

The performance criteria that apply include:

• H1.3.1 The building envelope must provide adequate thermal resistance and limit uncontrollable air flow.

Step 4. Select the most relevant compliance path(s).

The most relevant compliance path options could be:

• Compliance path 9 – use of an Acceptable Solution.

Step 5. Determine what type of information is required to demonstrate compliance.
The type of information to demonstrate compliance should include evidence of adequate thermal resistance (schedule method from NZS 4218) and how the air flow is controlled (window manufacturer’s information). 

In this situation, some upgrading of the existing wall is required to bring the performance up to at least that of the pre-alteration performance. This could be achieved by adding insulation to the existing wall at the same time as the new window is installed. Alternatively, it may be possible to increase the R-value in the new addition sufficiently to compensate for the reduced R-value of the existing wall.

Step 6. Provide the evidence.

The compliance path option is an Acceptable Solution, so it must be accepted by the BCA. Where the existing wall has insulation added to it, the resulting R-value of the wall is likely to be better than the performance of the wall prior to the alteration work.

 

Back to top

1940s-60s houses – compliance case study 4

A proposed villa renovation is to include a first floor addition.

Step 1. Identify the aspects of the proposed design that fall outside the scope of Acceptable Solutions The proposed work requires an assessment of the existing bracing to ensure that the lower level structure is sufficiently rigid to support the upper level addition.
Step 2. Identify the Building Code clauses for which performance must be demonstrated by the design and supporting documentation.

The Building Code clauses to be addressed by this Alternative Solution are:

• B1 Structure

Step 3. Identify the performance criteria that apply.

The performance criteria that apply include:

• B1.3.1 Buildings and building elements must remain stable and not collapse

Step 4. Select the most relevant compliance path(s).

The most relevant compliance path options could be compliance path 2 – comparison to other documents.

Step 5. Determine what type of information is required to demonstrate compliance. The bracing levels for the existing structure must be demonstrated to be adequate to support a new upper structure.
Step 6. Provide the evidence.

There are no detailed drawings that provide information about the bracing of the existing floor. However, the building had been lined with plasterboard fixed directly to wall framing. 

In this case, the building could be assessed in accordance with NZS 3604:1984, which can give generic bracing ratings for the plasterboard sheet lining. A generic bracing rating can be calculated to establish that the existing structure is adequately braced to be able to support an upper level. 

 

Back to top

1940s-60s houses – compliance case study 5

The owners of a 1950s modern style house with bevel-back weatherboard cladding and a reinforced concrete floor slab wish to add an extension and maintain a consistent floor level throughout. Unfortunately the height of the floor slab above finished ground level is only 95 mm. Although there is a small fall away from the building in the direction of the proposed extension, it is not enough to provide the clearance required under E2/AS1 (150 mm to paved surface).

Step 1. Identify the aspects of the proposed design that fall outside the scope of Acceptable Solutions The height of the floor level of the proposed extension is less than permitted under E2/AS1 and is therefore outside the scope of the Acceptable Solutions.
Step 2. Identify the Building Code clauses for which performance must be demonstrated by the design and supporting documentation.

The Building Code clauses to be addressed by this Alternative Solution are:

• E2 External moisture

Step 3. Identify the performance criteria that apply.

The performance criteria that apply include:

• E2.3.3 Floors and structural elements in contact with the ground must not absorb or transmit moisture that could cause dampness or damage.

Step 4. Select the most relevant compliance path(s).

The most relevant compliance path option could be:

• Compliance path 3 – comparison with in-service history.

• Compliance path 7 – MBIE determination.

Step 5. Determine what type of information is required to demonstrate compliance. The information to demonstrate compliance must show that the construction will not cause damp or moisture ingress.
Step 6. Provide the evidence.

Demonstrating that there has been no deterioration of the existing construction despite the lack of adequate ground clearance can be used to provide evidence of an in-service history and satisfactory performance for clause E2.

Otherwise a MBIE determination could be used to establish whether the proposed alternative method will be Building Code compliant.