NZCMA MM - 6.2 - Garden Walls

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February 2012 Page 1 Section 6.2New Zealand

Concrete Masonry

Association Inc.

New Zealand Concrete Masonr Manual

6.2 Garden Walls

Introduction

Concrete masonry garden walls can provide manyuseful functions privacy, separation, protection,ornamentation, shade and shelter from wind.

With a wide variety of concrete masonry shapessizes and finishes available the design possibilitiesfor walls are virtually unlimited.

Use of this Document

This publication provides design charts andconstruction details for two main types of concretemasonry garden walls:

cantilevered walls; and

reinforced masonry pilasters supporting infillpanels.

Walls of up to 2.0 m height are considered. Walls ofup to 2.5 m height may not require building consentunder a pending amendment of the Building Act2004, however it is considered that specificengineering advice should be sought for masonrywalls above 2.0 m height.

Structural Design

These concrete masonry walls have beenstructurally designed in accordance with theappropriate New Zealand Standards and recognisedcodes of practice. To allow designers and TerritorialAuthorities to choose and confirm the structuraladequacy of designs, options are provided aligningwind and earthquake actions with the TimberFramed Buildings Standard NZS 3604. Windactions in the new Extra High wind category areexcluded.

Foundation conditions are also aligned to therequirements of NZS 3604.

The strength of masonry is very sensitive to thequality of workmanship. Therefore, every effort mustbe made to ensure the workmanship is of thehighest standard. It is recommended thatconstruction be carried out by a Licenced BuildingPractitioner, Bricklaying and Blocklaying.

Building Consents

The circumstance when a building consent isrequired is set out in Schedule 1 of the Building Act

2004. That clause explains that a consent is notrequired for a fence or garden wall provided:

1. It is not a retaining wall.

2. The height does not exceed 2.0 m.

3. It is not a fence as defined in section 2 of theFencing of Swimming Pools Act 1987.

The height is to be measured from the lowest pointof the adjoining ground to the highest level of thefence. If a capping is to be incorporated in thedesign, then it too should be within the total height of2.0 m.

An amendment to the Act extending the exemptionto cover fences and walls up to 2.5 m in height isproposed. It is recommended that engineeringadvice be sought for masonry walls higher than2.0 m.

If there should be any doubt regarding theinterpretation of these requirements in relation to aparticular proposal, the matter should be discussedwith the territorial authority.

Design Charts

Selection of Environmental Design Actions

The principal actions governing the design of gardenwalls arises from wind or earthquake effects. Thewall must be designed to withstand the forcesarising from these phenomena.

Both wind and earthquake actions vary throughoutthe country. Design tables have been produced toenable designers to assess these actions by the

methods used in the Timber Framed BuildingsStandard, NZS 3604. Some territorial authoritieshave web maps available with NZS 3604classification Wind speed categories identified forspecific areas or on a property by property basis.This will enable rapid identification of the appropriatefactor. Extra High and Specific Design categorieshave been excluded from the design tables and it isrecommended professional engineering designadvice should be sought in these cases.

Figure 1 (pages 5-6) provides a map of the seismiczones given in NZS 3604. While this is the current

seismic zone map from NZS 3604 2011, there havebeen further changes by the Department of Buildingand Housing to the Canterbury region which extends


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the Zone 2 status to Waimakariri and Selwyndistricts including Banks Peninsular. This require-ment is part of their compliance document B1 AS1.Users of the designs in these areas are advised tocontact the appropriate Territorial Authority for finalconfirmation of the seismic zone for their project.

Users should seek professional engineering adviceshould they wish to design in the highest earthquakerisk Zone 4.

Design for the garden walls has included for theappropriate Importance Level from the StructuralDesign Actions Standard, AS/NZS 1170, this being alesser risk than that of a habitable structure. Thewall designs provided herein should not be usedwhere the wall is intended to form part of a buildingstructure.

Choice of Wall Type

Having identified the Environmental Design Actions,the tables will provide details for either of the walltypes, i.e. cantilevered walls, or reinforced pilasterswith infill panels. Designers must choose the worstcase of either Wind or Earthquake actions for theparticular site, within each table.

Cantilevered Walls

These are free-standing walls on a symmetricalconcrete strip footing. They must be reinforced and

be of all cells filled construction.

Reinforced Walls are made of plain masonry blocks,uniformly reinforced vertically and horizontally. Inthis respect they are similar to a bearing wall orretaining wall.

Refer to Figures 2 and 3 (pages 7-8) for constructiondetails.

Reinforced Masonry Pilasters Supporting InfillPanels

These walls consist of reinforced pilasterssupporting masonry infill panels, refer to Figures 4, 5and 6 (pages 9-10) for layout details. The pilastersmay also be used to support other types oflightweight panel such as timber, profiled sheetsteel, insulated sandwich panel etc, the design ofwhich is not covered in this manual.

Three pilaster types, which are shown in Figures 7,8 and 9 (pages 11-13), have been groupedaccording to their strength characteristics. Type C,being the strongest, can be used in any situation.Types B and A are of lesser capacity and are

restricted to less demanding applications shown inthe tables.

The infill panels may be constructed from a widerange of masonry types, or other materials suchtimber or fibre cement board.

Masonry panels require a minimum reinforcing asindicated and should be all cells filled construction.

Construction Details

Reference should be made to the tables anddiagrams appropriate to the particular zone and typeof wall.

General

These tables and diagrams provide recommend-ations for fences and garden walls up to 2.0 m in

height. They do not apply to structural bearingwalls, nor to retaining walls.

Footings

The base for all footings must be not less than 250mm below the surrounding ground. The soil must beequivalent to Good Ground having an ultimaterupture capacity of no less than 300 kPa as definedin the Timber Framed Buildings Standard NZS 3604.Ground should not slope away from the front of thefooting more than 10 from the horizontal for a

distance equal to two times the height of the wall.

Cantilevered walls, refer Figure 2 (page 7), areconstructed on continuous strip footings of minimumdepth 200 mm and reinforced with three D12 bars.The footings must be symmetrical about the centreof the wall and the width not less than indicated inthe tables. Figure 3 (page 8), provides details forincorporating screen blocks into the top section ofpanels.

For pilaster and infill panel type walls (Figure 4 onpage 9 and Table 1 on page 3), the footing should

be sufficient to support the infill panel selected andto act as a tie between pilasters. It should be notless than 150 mm deep and reinforced with two D12bars which extend into the pilaster footings. Thewidth of the strip footing should be at least 60 mmwider than the blockwork it supports.

Footings for pilasters may be either "post hole" typeor "pad" type. Dimensions and reinforcing detailsmust be in accordance with Figures 5 and 6 (page10).

It should be noted that with a "post" type footing, the

vertical reinforcing is continuous throughout the fullheight of the footing and the pilaster itself.


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All concrete used in footings shall be 25 MPastrength and 80 mm slump. It must be thoroughlycompacted and the finish on the upper surfacesuitable for the blockwork.

Masonry

Concrete Masonry units shall comply with NZS3102. Masonry construction shall comply with NZS4210, and in particular:

(a) Mortar shall consist of one part Portlandcement thoroughly mixed with 3-4 parts ofbuilding sand.

(b) Grout infill to all cells shall have a spread of340-530 mm and a strength of 20 MPa.

(c) All joints shall be adequately filled with mortar

which shall be compacted by joint tooling afterthe initial set.

(d) Masonry walls should follow a running bondpattern.

Pilasters and Infill Panels

Pilaster types A, B or C should be selected for thestrength requirements indicated in Table 1 below.

Within each type alternative construction details are

given. These are minimum requirements, but one ofthe stronger types can be selected if desired. Thuswhere a type A pilaster is recommended any of thedetails of types A, B or C can be selected.

For a reference type B, the choice is either type B orC, but only type C can be used where this isspecified in the Tables. The infill panel betweenpilasters must have reinforcing as shown in thetables and shall be of all cells filled construction.

Dimensions given for infill panels refer to the lengthof the panel itself between pilasters.

It should be noted that masonry units aremanufactured to a 400 mm module (half block 200mm) and screen blocks may well be some otherdimension.

Table 1: Pilaster and Infill Panel Wall

Wind / E/Q Zone Wind / E/Q Zone Wind / E/Q Zone Wind / E/Q ZoneInfillType

Blockthickness

(mm)

Horizontal Reinforcing

Max. PanelWidth

PilasterType

Max. PanelWidth

PilasterType

Max. PanelWidth

PilasterType

Max. PanelWidth

PilasterType

Screen 90 L / Zone 1 M / Zone 2 H / Zone 3 VH

2/R4 Galv. - 400 3.6 m A 3.1 m A 2.7 m A 2.5 m B

90 Block 90 L / Zone 1 M / Zone 2 H / Zone 3 VH

D10 600 3.6 m A 3.1 m A 2.7 m A 2.5 m B

140 Block 140 L / Zone 1 M / Zone 2 H / Zone 3 VH

D10 - 600 4.0 m A 3.4 m B 3.0 m B 2.7 m C

190 Block 190 M / Zone 1 H / Zone 2 VH / Zone 3

D12 600 4.8 m C 4.1 m C 3.6 m C

D12 600 240 H / Zone 1 VH / Zone 2 Zone 3

D12 600 4.7 m C 4.3 m C 3.6 m C

Notes: For any infill type choose the lower panel width for either of the wind or earthquake zone applicable for the chosen site.Refer to Figures 3 to 8 (pages 6-10) for definitions, construction details, and pilaster types.Refer to NZS 3604 for derivations of wind levels and earthquake zones.2/R4 refers to double R4 rod lattice as per Eagle Wire Products Bricklock STR 1000/2000Lattice, or equivalent.

Reinforcing

All reinforcing shall be deformed bars of thediameters indicated, except for bars designated R,which are to be plain round.

In cantilevered walls, the vertical reinforcing shouldbe full height in a single length, being located underthe horizontal bars of the strip footing and extending

into the top bond beam. A D12 horizontal bar shallbe located in the top course, with the remaining barsbeing uniformly distributed through the height of thewall.

Reinforcement for screen blocks shall be hot dip

galvanised 2/R4 lattice, e.g. Eagle Wire ProductsLimited Bricklock STR 1000/2000, laid in the freshmortar in the centre of horizontal joints where


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indicated in the diagrams or Table 1. Rods shall becontinuous through pilasters and lapped as indicatedon Figure 4.

Control Joints

Vertical control joints should be provided in thefollowing positions:

(a) in reinforced cantilevered walls the spacingshould not exceed 6.0 m.

(b) in pilaster and infill panel walls, a verticalcontrol joint should be provided at the junctionof panel and pilaster, at no more than 6.0 mcentres.

Control joints should be formed to the provisions ofNZS 4210.

Copyright and Disclaimer

2010 New Zealand Concrete Masonry Association Inc.

Except where the Copyright Act and the Limited-LicenseAgreement allows otherwise, no part of this publication may bereproduced, stored in a retrieval system in any form ortransmitted by any means without prior permission in writing ofthe New Zealand Concrete Masonry Association. Theinformation provided in this publication is intended for generalguidance only and in no way replaces the services ofprofessional consultants on particular projects. No liability cantherefore be accepted, by the New Zealand Concrete Masonry

Association, for its use. For full terms and conditions seehttp://www.nzcma.org.nz/manual.html.


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Copyright Standards New Zealand.Content from NZS 3604:2011 has been reproduced by New Zealand Concrete Masonry Association Inc with permission from Standards New Zealand under Copyright Licence 000923.Please see Standard for full details, available from www.standards.co.nz.

Figure 1: Earthquake Zones


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Copyright Standards New Zealand.Content from NZS 3604:2011 has been reproduced by New Zealand Concrete Masonry Association Inc with permission from Standards New Zealand under Copyright Licence 000923.Please see Standard for full details, available from www.standards.co.nz.

Figure 1: Earthquake Zones (continued)


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Figure 2: Cantilever Wall


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Figure 3: Cantilever Wall, Screen Block Infill Option


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Figure 4: Infill Panel Wall


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Figure 5: Post Hole Type Footing

Figure 6: Pad Type Footing Suitable for Good Ground Soils


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Figure 7: Pilaster Type A Details


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Figure 8: Pilaster Type B Details


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F b 2012 P 13 S i 6 2New Zealand


Figure 9: Pilaster Type C Details

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NZCMA MM - 6.2 - Garden Walls