Details for junctions and openings in stucco clad walls

Introduction
Aims and scope
Companion documents
Interpretation and definitions

View/buy individual details:
2.1 Stucco

Introduction

This collection of details is based on the traditional New Zealand stucco wall cladding of solid plaster over timber framing using either a rigid backing or non-rigid backing over a drained and vented cavity. These claddings rely on traditional skills and careful detailing for their successful application. Flashing systems are an essential element of any cladding system. The stucco details combine these with a cavity to provide a secondary back-up that is able to drain moisture away.

Rainwater getting into buildings can cause deterioration of framing (timber or steel) and fixings, and failure or degradation of insulation materials, linings, flooring and other elements. These failures increase the risk of ill health for occupants and compromise the safety and performance of buildings.

The information provided in this and other collections of details combines current BRANZ and industry knowledge to provide designers, contractors and approvers with details designed to minimise the entry of rainwater. BRANZ recognises that further research into weathertightness and the forces that contribute to the entry of rainwater into buildings is required. As the results of ongoing research become available, these collections will be updated to provide the best information available.

This collection provides an extensive range of details covering the junctions and openings in stucco claddings that are likely to be encountered on buildings in New Zealand. The majority of the details provided are not given in E2/AS1.

The details may also serve as a guide for checking details which are adapted, or differ, from those illustrated in this collection, such as those with metal or other supporting framing, to assess them for the levels of weathertightness achieved.

Aims and scope

This collection provides construction details for junctions and openings in stucco on timber framing to provide a means of supporting compliance with NZBC clause E2.3.2.

It covers:

• junctions and openings in solid plaster (stucco) claddings with details for timber, aluminium and uPVC joinery - details for timber windows and doors, aluminium sliding doors and uPVC are not given in E2/AS1
• junctions between the stucco cladding and a range of other cladding types - details that are not contained in E2/AS1
• penetrations through the stucco.

The details are limited to buildings that fall within the parameters of E2/AS1, that is buildings that are:

• timber-framed
• no more than 3 storeys in height (10 m maximum)
• a maximum of very high wind zone
• a maximum cladding height of one storey unless a movement control joint is located at each floor level.

Additional requirements:

• Fixings, flashings and other components must meet the minimum requirements of NZBC clause B2 Durability (NZS 3604 Timber-framed buildings Section 4 provides an Acceptable Solution).
• The specifications for painting, reinforcement, mix design, fasteners, backing materials and workmanship are available in the BRANZ Good practice guide - stucco and NZS 4251 Code of practice for solid plastering.

Companion documents

BRANZ Good practice guide - stucco details the design of stucco systems and their application, including framing, building underlay, cavity construction, backing, reinforcing, stucco materials and application and waterproof coatings.

A range of details is also provided in the other collections of BRANZ weathertight solutions details:
1. Horizontal weatherboards
3. Profiled metal
4. Masonry
5. Roofing
6. Membrane roofing

Interpretation and definitions

• Drained and vented cavity
• Wind zones
• Exposure to rain
• E2/AS1 risk matrix
• Flashing materials and details
• Wall underlays
• Air seals to penetrations
• Stucco backing
• Air seals to joinery items
• Weathergrooves
• Timber sizes and profiles
• Compatibility
• Exterior finish
• Aluminium windows

Drained and vented cavity
Stucco will always include a drainage cavity. This recommendation is in line with the requirements of E2/AS1 and is considered best practice to provide assurance that weathertightness is achieved. The drainage cavity detailed will substantially reduce the risk of rainwater penetration into the framing behind. All cavity details in this collection show cavity battens at 400 mm maximum centres with blocking as shown in E2/AS1 along all edges of the stucco.

Wind zones
The wind zones are as defined and determined for a particular site in NZS 3604 Section 5. The wind zones are established from wind regions, based on data supplied by the New Zealand Meteorological Service and included in NZS 4203 General structural design and design loadings for buildings. The regions are based on wind speeds that have a 5% probability of being exceeded in 50 years. The wind zones are calculated for a particular site by considering the modified wind speed as outlined in NZS 4203 for a building with an eaves height of 8 m above the ground.

Wind zones are identified as:

• Low wind zone (L) = wind speed of 32 m/s
• Medium wind zone (M) = wind speed of 37 m/s
• High wind zone (H) = wind speed of 44 m/s
• Very high wind zone (VH) = wind speed of 50 m/s

Details are considered suitable for use in up to VH wind zones.

Exposure to rain
Details are considered suitable for use for direct exposure to rain wetting except as noted in the drawing title. Exclusions are window head details 2.1.2.1, 2.1.3.1 and 2.1.5.1, the vent detail 2.1.17.3, and Section 2.1.17 on penetrations. (These details should only be used in situations protected from direct rain wetting.)

E2/AS1 risk matrix
Carrying out an assessment of weathertightness risk using the matrix in E2/AS1 is recommended for all building faces even when the design is not following E2/AS1. Stucco details within this collection are considered suitable for all risk scores up to 20. However, there may be limits placed on the cladding materials used in conjunction with the stucco. Limitations (as noted on the individual drawing) have been placed on the stucco junctions with:

• vertical shiplap weatherboards
• direct-fixed horizontal rusticated weatherboards
• direct-fixed fibre-cement sheets.

Flashing materials and details
Flashings must be sufficiently rigid to maintain the shape specified, when fixed and in continuous use. Materials must be compatible with other contacting elements, particularly contact with cement. Back flashings in this collection differ from those shown in E2/AS1 details in that they provide 65 mm rather than 50 mm cladding cover, thus giving an increased margin of safety.

Wall underlays
A wall underlay (rigid or flexible) is required to be installed over the framing before the cavity battens are installed. Flexible wall underlay should be continuous around corners.

Air seals to penetrations
The gaps between all types of joinery elements, plus meter boxes and other penetrations and the structural framing, must have an airtight seal. Continuous compressible foam rods (to prevent the trim cavity being filled with the seal) installed behind a low expansion rate foam or sealant are suitable to achieve this airtight seal.

Stucco backing
All solid plaster must be applied over a rigid or non-rigid backing as defined in the BRANZ Good practice guide - stucco. For a rigid backing, a breather-type building paper or synthetic wrap must be provided as a slip layer behind the stucco.

Air seals to joinery items
All window details incorporate an air seal between the framing and the window reveal or frame. Air seals are formed by inserting a compressible polyethylene foam (PEF) backing rod and filling the gap with a low expansion foam or sealant to give an airtight seal.

Weathergrooves
Where shown, weathergrooves shall be as detailed (refer also to BRANZ Bulletin 361 Weathergrooves).

Timber sizes and profiles
Framing and other timber dimensions shown are the actual dimensions as given in NZS 3601 Metric dimensions for timber.

Compatibility
The details in this collection use a number of materials in contact or close proximity. Users must therefore ensure that framing, battens, flashings, claddings and fixings are compatible with each other to meet NZBC clause B2 Durability requirements and be suitable for the environment in which the completed building will be located. An example is isolating timber containing copper-based treatments from metal (zinc) components.