Movement joints: Provision ofBrickwork Expansion Joints

Supported by

May 2014

Background:

Clay brickwork has to have provisions forthermal expansion. Bricks expand irreversiblyfor up to 20 years after they are removedfrom the kiln. Most of the irreversibleexpansion occurs within the first six monthsafter production. The supporting structureoften reinforced concrete or blockwork willactually contract or creep and soaccommodation has to be made, fordifferential movement by flexible wall ties ormovement joints. This advice is onlyconcerned with clay brickwork, other brickssuch as calcium silicate products do notbehave in the manner described below, theadvice is only relevant for current climaticconditions in the UK.

Movement joints are not solely for expansion,but also for contraction. In common with otherbuilding materials, bricks will contract duringdryer colder weather. Brickwork must beconstructed to enable movement in bothdirections to occur. Thirdly, joints can berequired to cater for differential movement andframe settlement. Correct design is achievedby following the advice within PD 6697 andother sources such as this document. Thissection will identify how to avoid stresses inbrickwork design and relieve potential issuesby correct position of movement joints.

It should be within the province of mostarchitects and certainly all structural engineersto interpret the provisions of PD 6697. Inparticular, they should select suitable positionsfor movement joints. It is one of the benefitsof brickwork that there is no area that thedesigner cannot understand and therefore thedesigner does not require the advice of anoutside expert, although a checking procedurewith a second opinion is part of good practise.

Buildings prior to the 1890s were built in limemortar; lime mortar allows the provision ofmovement within brickwork allowingexpansion to take place. Brick buildings fromearlier periods have a greater degree of detailand overhanging features as part of the detaildesign of the building. The South elevation ismore onerous than other elevations. Modernbuildings tend to have cleaner lines, have less

This is of course not to say that there are notmovement joints failures; only the bestbuildings survive. Prior to the provision ofcavity walls brickwork walls were generally atleast one brick thick 215mm, 327 or 440 wide.The bricks were also under load, taking thedead load from floors and roofs and internallive loading the bricks being undercompression. If a brick is under compressionand fully loaded, its potential movement willbe restricted and therefore the provision ofmovement joints may not be as essential.

This advice is concerned only with movementprovision for brickwork expansion. Additionalcreep in reinforced concrete, compression orshrinkage in other materials is in addition tothis advice. For example, brickwork supportedby a long span steel beam may have ahorizontal brickwork expansion joint of 10mmfor brickwork expansion. The beam has apotential deflection of 15mm from thedesigned loading. The total movement jointwill be 25mm. This may well cause visualproblems which have to be considered by thedesigner. A potential solution for this horizontaljoint may be to corbel out a brick to place thehorizontal joint into shadow.

No provision of movement joints necessary withheavy lime mortar structures slowly built.

overhanging and therefore, less shadowing sothere can be higher temperatures withconsequentially higher expansion in thebrickwork. It may well be that we are living ina time of potential climate change, and highertemperatures have been recently experiencedwithin the UK than it have been traditional.

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Lambeth Palace

needs to be staggered to avoid stressing thewall ties. If a brickwork column or chimney isbuilt with an adjoining panel wall, they must beseparated by a compression joint allowingmovement tied appropriately. Differentthickness of wall may move differently andrequire a joint between the elements.

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1

2

225 225

1

Brickwork expands

Blockwork contracts

Flexibility and Wall Ties:

Movement and flexibility is required in allbuilding elements. Foundations settle andrespond to clay heave, steelwork expands andcontracts. Typically a timber frame willcontract by up to 6mm over a 2.5mm storeyheight. Movement joints should be consideredin the light of other materials.

A brick panel should never be set into a rigidframe, and movement should always beconsidered and designed. Flexibility shouldalways be permitted with expansion andmovement possible. This includes the provisionof wall ties which while allowing connection toan inner skin providing stability do allow flexand movement between dissimilar materialsand internal and external temperatures. It is notadvisable that wall ties are too stiff restrictingmovement. Wall ties should be installed to therequirements of PD 6697. The minimumrequirement for a sheltered site is for ties to beinstalled at 450mm centres vertically and900mm vertically arranged in a diamond withties either side of the Movement joint within225 of the joint and minimum 300mmvertically.

Concrete blockwork will contract as theproduct dries. Brickwork expands and so themovement joints to blockwork and brickwork

225 225

2

1. Ties to within 225 of MJ at 300mm min. vertically

2. MJ normally compressible strip (to 50% thickness)

with mortar matching finish to face

Blockwork contracts

Blockwork expands

MJ’s to brickwork and blockwork should alternate to avoid stressing wall ties

MOVEMENT JOINT

Mortar:

This advice assumes an M4 mortar similar toa 1:1:6 Cement, lime, sand mix the normalmortar designation for external walls. If astronger mortar is used for a parapet or freestanding wall designation M6 1:1/2:4 to 4.5 themovement joints should be at closer thanrecommended centres. If traditionalconstruction is used with a full brick wall;215mm wide in conjunction with lime mortarmovement joints could be increased but onlywith the advice of an expert in mortar whoalso understands the structure of the building.

Mortar should never be stronger thannecessary, a weaker mortar will tolerate moremovement than a stronger mortar. An overstrong mortar, considered elsewhere, does alsohave an adverse effect in the provision ofmovement joints, which may have to be atcloser centres than advised.

While an experienced practitioner may afterconsidering the geometry of the facadeslightly stretch the distances for Northelevations which will have less thermal gain,the advice should be strictly observed forSouth and West Elevations. If movement jointsare placed at closer centres or at greaterfrequency no harm will occur.

There are three ways to design the provisionof movement joints, which if badly positionedcan be scars on the face of the building. Firstly,you can either hide the joints behind otherelements or hide the joints in corners.Secondly, the joints can be disguised byconsidering the bonding; for example,designing a straight joint as part of the bondpattern. Thirdly, the joints may be emphasisedand be part of the rhythm of a building withrepeated elements.

Movement Joints:

Most of the movement which occurs inbrickwork is due to thermal expansion. Whilemoisture does have an impact as its smaller,difficult to predict and, is generallydisregarded. There are two kinds of thermalexpansion. Reversible thermal expansionwhich is accommodated by the movementjoint expanding and contracting. There is alsoirreversible thermal expansion, which ispermanent.

The UK climate assumes a 60 deg C range: thefollowing advice is correct for the UK climate.The designer should allow 1.3mm per linear runof brickwork for the provision of movementjoints. This means for a joint at 7m centres thejoint should be 10mm wide. For a joint at 12mcentres the dimension should be 16mm wide.

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If a particularly demanding movement jointoccurs such as a joint being placed close to abuilding corner a stronger de-bonded tie canbe used crossing the joint, but also providingadditional security.

1

225 225

DE-BONDED TIE

Reused bricks will need the provision of themovement joints because not only do theyrequire provision against expansion whichmay occur. There is also some elements ofmovement joints that may be required to act

against the differential movement of otherbuilding materials. Reused bricks may havealso been under compression carryingsubstantial loads. Release of weight mayallow expansion to take place.

Successful joint design

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West Hampstead Railway Station Sugar Mills, Edinburgh University of London, Bloomsbury

University of London, Bloomsbury

Movement Joint Positioning:

The general principles outlined apply both toboth horizontal and vertical joints, and ingeneral terms they can be considered to bebroadly similar. The rules for horizontal jointsfor vertical compression are slightly moreonerous as many supporting frame materialscompress or shrink over time.

The general principle is to break the elevationinto rectilinear areas. Irregular or L shapedbrickwork is to be avoided.

Movement joints cannot pass throughstructural members such as beans and lintelsalthough they may be routed around the end

of a lintel both in the horizontal and verticalplane. Movement joints must be continuousunless terminating in a slip planes such as theDPC. It is quite possible for movement joint topass through a shelf angle and for the shelfangle to be stopped and started say 20mmapart to allow the movement joint to passbetween the supporting steelwork.

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H e s

b

c

While MJ’s cannot pass through structural members if shelf angles are used they can be stopped to allow MJ. The window jamb can then be used

7m 7m

Standard construction.

Horizontal MJ required

every 9m. (Compression of

structure may require more

frequent MJ).

Above 9m to 12m MJ can

be accommodated by wall

ties in sliding connectors

Sliding ties not

recommended above 12m

generally unless

calculated

Vertical dimensions

for horizontal MJ

3m

3m

9m

Break elevations into rectilinear areas

MJ’s do not need to be

continuous if the geometry allows

While MJ’s cannot pass through

structural members if shelf

angles are used they can be

stopped to allow MJ.

The window jamb can

then be used

London School of Economics

Modern brickwork is generally used in a singleskin facade. Single skin are supported on shelfangles not of great height. More failures occurat the top of the wall than lower down wherebrick is under load. Parapets which have smallloads upon it are particularly prone to havefailures due to inadequate movement jointprovision.

Most building materials such as timber,reinforced concrete, and steel will both expandand contract in response to thermal changes intemperature. While all materials will move inresponse alterations in temperature changesbrick is amongst the very few materials whichactually have permanent and irreversibleexpansion. The advice contained below will setout deemed to satisfy provisions.

l When placing movement joints in a building, there are a few simple rules that must be understood which are not common sense

l One does not have to look at corners as providing the end of the wall the plan form of the building must be opened out as if the corners didn’t exist

l One starts placing movement joints from one area on the wall normally in plan with reference to the elevation and follows the building round until one arrives back at the original point

l Do not take any account of the corners orchanges of direction of the building into account when working at the provision of movement joints

Alternatively, bricks may be calculated on theirirreversible thermal characteristics which mayenable movement joints to be put in at greaterdistances than the advice contained below.This calculation is normally carried out by thestructural engineer conscious of the rest of thebuildings requirements.

There are some exceptions to the generalrequirement of always having to providemovement joints. Internal walls do notgenerally require the provision of movementjoints. Buildings of a square or nearly squarenature of less than 10 M in either direction orplan form do not generally require theprovision of movement joints as the forces areopposite and equal.

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g p to 10M sq does not require any MJ’s

than 1m

changes of angle

W

10m

m

MJ to wall/building junction

MJ hidden in corner

Can twin sym

ELEVATIONPotential MJ positions

6m 6m

2m 8m

Maximum MJ to cornerExample (A)

Example (B)

A small building up to

10m sq does not require

any MJ’s

10m

10m

MJ to wall/building

junction

MJ’s to less than 1mMJ’s can be to

changes of angle

Can be

twinned for

symmetry

MJ hidden

in corner

ELEVATION

Potential MJ positions

Maximum MJ

to corner

Example (A)

Example (B)

6m6m

2m8m

Movement advice is contained within PD6697clause 6.2.6 entitled Movement in Masonry. Thereare two ways to design for movement in Masonry.

The provision of movement joints is not justabout the distance of linear runs of brickworkbut, also to do with the following factors listedbelow. For most bricks, the general industryadvice of 1.33mm per linear metre run ofbrickwork should be followed. This advice isdeemed to satisfy and a designer can rely on thisas being a sale failsafe option. For a maximumdistance between movement joints in straightrun of brickwork 12m this means one would havemovement joint of 16mm wide. For this reasonmany designers choose to put movement jointsin at between 7 and 8m allowing for a 10 metermovement joint.

At the parapet level movement joints are installedat 6m centres, this is also true of freestandingwalls. Within a single wall movement joints maybe at 12m for the general run of the wall and 6mfor the parapet. The separating DPC requiredunder cavity tray for typical parapet will act as aslip plane allowing the wall to accommodate twoseparate areas of movement.

Damp proof membranes are often incorrectlyplaced. The DPC is placed on a full bed of mortarminimum of 6mm thick. The DPC should be ofthe type that has good adhesion with mortar.The next layer of mortar above is also a full bed

of mortar the DPC is sandwiched between twobeds of mortar. It is not possible to put a bedjoint unless the mortar joint is a minimum of13mm wide. The DPC thereby acts as a slip playallowing the wall to move differently in differentpositions. The DPC should protrude slightly fromthe finished a joint, so that the visible effects ofthe DPC are seen. If the DPC does not protrudethe evidence of it cannot be seen water will drainpast the DPC into the masonry below.

In the event of a soldier course of bricks orcoping or capping of typical brickwork which isnot recommended because of poor weatheringcharacteristics the movement joints should beplaced at 3m centres. The provision of a separateseries of movement joints to copings andcappings is accomplished by using a DPC as slipplane.

Movement joints should be positioned in thereturn angle of a short return. According to PD6697 movement joints should be placed in anyreturn which is less than 675mm. The Industryadvice is that movement joints must be placed inshort returns of less than 1m. It is in these areaswhere the movement differing movement offoundations and cracking to masonry is likely.The provision of movement joints in short returnsis a very good place to hide movement joints. Forreturns greater than 1m the wall has enoughflexibility to allow flexing in the connecting wallto take place.

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1m MJ MJ

Returns greater than 1m can fl ex

M Joint can be in either planeReturns less than 1m require MJ

1m MJ MJ

2 MJ’s if a corner joint is not possible

2m 2m

2 MJ’s if a corner joint

is not possible

Returns greater

than 1m can flex

2m 2m

SHORT RETURNS

Movement joints can also be hidden behindother features for example behind Rainwaterdownpipes, or at the junction with othermaterials such as timber or other materials. Atypical way of disguising the provision of

movement joints in larger commercialbuildings is to place them in the jam of thewindow. The movement joint can then carriedon down to the spandrels panel in brickworkand therefore minimised.

movement joints also have to be placed, totake stress off the facade of the building.Narrow vertical columns joining a junction ofhorizontal brickwork can impart considerablestress to the junction. Cracking may occur inthe corners unless there is a provision forexpansion provided. Similarly, if one has a large

opening with a smaller opening above thestresses imposed on the facade could lead tocracking. The general principle to be adoptedis of the facade to be broken up by theprovision of openings and movement jointsinto rectilinear not L-shaped areas of masonrywhich can lead to problems.

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12m 6m 3m 3m

The Jambs of windows can be used for expansion. If no oversailing lintel is used

MJ

12m 6m 3m 3m

DPC acts as slip plane

DPC acts as slip plane

Brick coping

Parapet

Wall

Maximum distance between MJ

The Jambs of windows can be used for

expansion. If no oversailing lintel is used Large openings require MJ’s

to release pressure

Movement joints have to be placed under wallswhich are dissimilar in height as the walls willmove differently. If a movement joint is notpossible for design reasons 3 rows of bed jointreinforcement should be installed in the bedjoints below to give tensile strength to thebrick work carrying variable loads. Thisprinciple should be generally adopted to alsospread point loads.

Bed Joint Reinforcement is one solution tobrickwork which can break many of the ruleslisted above, and solve many problems. Bedjoint reinforcement is two of strips of stainlesssteel wire joined at intervals by cross wires ithas a similarity to a model railway track. Thewire is often oval in shape compressed downto around 3mm and 60mm wide. Joint

reinforcement is therefore hidden within thedepths of the bed joint and should be there forthe lifetime of the building. It should not beconfused with lightweight mesh which servesno purpose. BJR is not expensive but does adda cost to the wall for both labour and materials.BJR gives a simple masonry wall a tensilestrength adding to its compressivecharacteristics.

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MJ or BJR to junction

Ancon: Bed Joint Reinforcement

Bed joint reinforcement is used to build a stackbonded wall which would otherwise beunstable. Normally installed at 225 centres inthe bedjoint or every 3rd course in standardbrickwork it enables brickwork to achieveunusual designs effectively.

One of the most beneficial effects ofreinforcement is that if installed at 225mmcentres in the bedjoint, movement joints maybe increased to 17m from 12m. While this is notincluded in any standard this has been industryadvice for over 20 years with no apparentfailures. Additionally the Movement joints atthe termination of the run may then be 10mmas opposed to 22mm.

Apart from a slight increase in cost reinforcement hasno drawbacks in use in masonry and its use is generallyrecommended to avoid problems which mightotherwise occur.

Most designers will have noticed that manybuildings break the rules listed above. Ignoringthe rules may lead to failure and whilstbrickwork is forgiving the advice for MJprovision should generally be followed. Thedesigner is therefore advised to follow theadvice contained within PD 6697 or this set ofadvice which in most if not all circumstanceswill guarantee there will be no issue with theprovision of movement joints.

Glyndebourne and School of Slovonic and EastEuropean Studies shows heavyweight masonry andlime mortar. Both buildings achieved a masonryelevation with no movement joints, this requiredparticular structural engineering expertise.

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School of Slavonic and East European Studies

Glyndebourne

Telephone: 020 7323 7030

Fax: 020 7580 3795

Email: brick@brick.org.uk

www.brick.org.uk

twitter: @BricksUK

The Building Centre,

26 Store Street,

London,

WC1E 7BT

1. BS EN 771-1:2011 Specification for masonry units part 1: Clay Masonry Units

2. PD 6697:2010 Recommendations for the design of masonry structures to BS EN 1996-1-1 and BS EN 1996-2

3. BS 8221-1:2012 Code of practice for cleaning and surface repair of buildings

4. BS 7533-9:2010 Pavements constructed with Clay natural stone or concrete pavers

5. PAS 70:2003 HD clay bricks guide to appearance and site measured dimensions and tolerance

6. BS EN 15804:2012 Sustainability of construction works7. BS 8103-2:2012 Structural design of low rise buildings8. BS 8000-3:2008 Workmanship on building sites9. BS EN 1344:2003 Clay pavers – requirements and test methods

10. National Federation of Demolition Contractors: (NFDC). Demolition of refurbishment information data sheet 13. Nfdc-drids.com/sheet 13

11. BS EN 772-3:1998 Methods of test for masonry units determination of net volume

12. BS EN 772-1:2011 Methods of test determination of compressive strength

13. BS EN 1998-1.1:2005 and A1 2012: Design of masonry structures14. BS EN 998-2:2010 Specification for mortar and masonry15. BS EN 772-5:2001 Methods of test for masonry units’ determination

of the active soluble salts16. BS EN 772-7:1998 Methods of test of masonry units. Determination

of water absorption of clay masonry damp proof courses

Relevant British Standards