Art deco case studies

These case studies show how to choose and apply a compliance path for a art deco 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: An art deco house with a very low roof pitch requires re-roofing.
  • Case study 2: The proposed renovation of an art deco 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 3: The proposed renovation of an art deco house is to include a first floor addition.

Art deco – compliance case study 1

The existing roof of an art deco house with continuous parapet walls, a very low-pitched roof (3°) and a 200 mm wide by 50 mm deep internal gutter draining to an original galvanised steel rainwater head, requires re-roofing. The existing roof is a bitumen-impregnated membrane roofing which replaced a similar roofing material approximately 30 years ago. There is no insulation or building paper in the roof.

Step 1. Identify the aspects of the proposed design that fall outside the scope of Acceptable Solutions
This will depend on exactly how the job is specified.

The existing roofing must be removed. A new ply substrate will be required and a new membrane roofing system could be installed.

However, as there is no insulation or building paper, a recommendation would be to replace the substrate and install insulation and a building wrap in the roof. This would also require new framing to be added to provide the minimum 25 mm air gap required between the insulation and the roof substrate, so the roof pitch could be increased at the same time. The new framing would also enable a new internal gutter to be built to meet the current Acceptable Solution requirements.
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

• H1 Energy efficiency

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

• E2.3.1 Roofs must shed precipitated water

• E2.3.2 Roofs must prevent penetration of water

• H1.3.1 The building envelope must provide adequate thermal resistance.

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

If the roof framing is replaced, the internal gutter increased in size and insulation added, the most relevant compliance path option would be:

• Compliance path 9 – acceptable solutions as the new roof construction would be built to meet the acceptable solutions of Clauses B2, E2 and H1.

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 roofing in terms of durability, shedding water, preventing water ingress and thermal efficiency.
Step 6. Provide the evidence.

If compliance path 9 is used, this is an Acceptable Solution so must be accepted by the  BCA. The drawings and specification submitted to the BCA should also include fixing and flashing details.

 

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Art deco – compliance case study 2

The proposed renovation of an art deco 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 before the alteration work.

 

 

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Art deco – compliance case study 3

A proposed bungalow 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. To demonstrate compliance, it is necessary to show that the bracing levels for the existing structure are 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.