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 4. Masonry

WTSV4.jpgDetails for junctions and openings in masonry walls

Introduction
Additional requirements
Companion documents
Masonry units
Interpretation and definitions

View/buy individual details:
4.1 Masonry veneer
4.2 Concrete masonry

Introduction

This collection contains a comprehensive selection of details for masonry veneer (with timber framing) and single skin masonry construction. Construction details are given for aluminium and timber doors and windows and specific building features such as building corners, the tops of walls, the base of walls, parapets and balcony walls. Junctions between the masonry construction and a range of commonly used claddings, such as stucco and weatherboards, are also covered.

For veneer construction, the details follow the principles of E2/AS1 External moisture. However, they give an added level of safety by increasing the flashing cover dimensions and by including jamb and sill back flashings to all window and door details.

Single skin masonry, however, must be consented on a case-by-case basis as an Alternative Solution. Details are aligned to NZS 4229 Concrete masonry buildings not requiring specific engineering design.

Flashing systems are an essential element of any cladding system to prevent rainwater entry. For masonry veneer, they are particularly important at window and door openings, roof/wall junctions and where the veneer abuts another cladding type. For single skin masonry, flashings are required at roof/wall junctions and where the veneer abuts another cladding type.

The information given in this and other BRANZ weathertight solutions collections combines current BRANZ and industry knowledge to provide designers and contractors 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 this, these collections will be updated so the best information can be made available.

The details may also serve as a guide for designers and Building Consent Authorities designing and assessing details that are adapted or differ from those illustrated in this collection for NZBC compliance.

Additional requirements

In addition to E2 External moisture, the design and installation of masonry veneer (with timber framing) and single skin masonry construction and its fixings, flashings and other components must meet the minimum requirements of NZBC clause B2 Durability (NZS 3604 Timber-framed buildings Section 4 is called up as an Acceptable Solution for masonry veneer construction).

Masonry construction must also meet the requirements of NZBC clauses:

  • B1 Structure (NZS 3604 is called up as an Acceptable Solution for masonry veneer construction and NZS 4229 for single skin masonry)
  • E2 External moisture
  • H1 Energy efficiency.

The specifications for materials, underlays, fasteners and workmanship are available from BRANZ Good practice guide - masonry veneer and BRANZ Good practice guide - concrete masonry.

Companion documents

BRANZ Good practice guide - masonry veneer and BRANZ Good practice guide - concrete masonry detail the NZBC and design requirements for masonry veneer (with timber framing) and single skin masonry construction and their application. These requirements include material specification, framing, wall underlays, separation layers, cavity construction and flashings.

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

Masonry units

Drawings show:

  • for veneer - standard 230 long x 70 mm wide brick units
  • for solid masonry - 200 series blockwork.

For solid masonry, designs to NZS 4229 walls may be constructed from 150 series concrete masonry units. Details may be used as the basis when using 150 series. However, integrating the 150 mm width into the design (compared to using the 200 series where the width, height and length are in 200 mm nominal increments) is more difficult.

Interpretation and definitions

E2/AS1 risk matrix
Designers should always use the risk matrix in E2/AS1 Third Edition to assess the level of risk (i.e. identify at-risk features of the design) of the building faces and design to meet that level of risk. The majority of details are considered suitable for any wind zone and all exposure situations and an E2/AS1 risk score of up to 21. On less exposed parts of a building or lower site wind zones, the details will be conservative.

Wind zones
The wind zones used in the E2/AS1 risk matrix are those as defined in NZS 3604 Section 5. 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 General structural design and design loadings for buildings 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

Eaves width
Buildings that have design features that reduce the level of exposure of a building face to the weather, i.e. they protect or shelter the face of the building from rain wetting, are known to reduce the risk of water entry. Assessing the width of eaves or overhang under the E2/AS1 risk matrix takes account of the amount (or lack) of protection provided.

  • Protected: a wall protected by an eave, verandah, permanent awning or other device that projects from the wall surface a horizontal distance greater than the vertical distance (D) from its underside to the sill of the joinery item. It also extends the full width of the joinery item, plus a distance D/2 beyond the outside edge of the joinery item.
  • Sheltered: a wall protected by an eave, verandah, permanent awning or other structure that projects from the wall surface a horizontal distance greater than the vertical distance (D) from its underside to the head of the joinery item. It must also extend the full width of the joinery item, plus a distance D/2 beyond the outside edge of the joinery item.
  • Exposed: a wall with no protection from eave, verandah, awning or other projection.

Flashing materials
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.

Wall underlays for masonry veneer
All masonry veneer details show a wall underlay fixed directly to the timber wall framing. Designers must specify the exact wall underlay they require. Window details generally show an additional layer of wall underlay installed after the head flashing is installed and lapped over the flashing upstand. As in E2/AS1, a second option is to seal the top edge of the upstand to the cladding underlay with flexible flashing tape.

For horizontal flashings between dissimilar claddings, the details note the use of flexible flashing tape to maintain a drainage path from the face of the cladding underlay over the flashing upstand. Two other options that could be specified are to install:

  • an additional layer of wall underlay after the flashing is installed and lapped over the flashing upstand - it is envisaged that this option would be used where the distance to the next lap in the wall underlay is short
  • the wall wrap to the lower portion of the wall with the top edge above the top edge of the flashing, and then install the flashing and complete the upper layer of wall underlay, lapping it over the flashing upstand.

Air barriers in veneer construction
An essential part of any cladding design is ensuring there are no airflow paths from outside the building to the inside - the reason being that airflow can carry water with it. Veneer details in this collection rely on the provision of an air barrier. These are either the internal sheet linings, typically plasterboard, or the use of a cladding underlay meeting the requirements for an air barrier in Table 23 of E2/AS1.

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.

Weatherproofing single skin masonry construction
Concrete masonry units are inherently porous and will readily absorb moisture. A single skin concrete masonry wall must be coated (under NZS 4229) with a weatherproof coating to prevent this moisture absorption. Single skin masonry buildings should also have the door and window openings coated with an applied waterproofing membrane before the window or door joinery is installed.

Weathergrooves in timber
Where shown, weathergrooves in timber trims shall be as detailed (see also BRANZ Bulletin 361 Weathergrooves).

Timber sizes and profiles
Timber joinery sections are drawn in accordance with NZS 3610 Specification for profiles of mouldings and joinery.