tehnologia-posi

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CONTENTS

Posi -Joist Flooring

An Introduc on to Posi -Joists Ground Floor Applica ons

Intermediate Floor Applica ons

Separa ng Floor Applica ons

Standard Details

Span Informa on

Site Handling and Storage

Roof Applica ons

Posi -Ra er Standard Details

The X-Ra er Posi -A c trusses

Wall Applica ons

The Posi -Stud

Sample construc on details

The World of PosiTechnology

THE POSI-STRUT TECHNICAL HANDBOO

Issue 2


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Introducing Posi -Joist

You simply cant a ord to ignore theadvantages of the Posi -Joist system.

To start with, because Posi -Joistcombines the lightness of timber with

the strength of the Posi -Strut steelweb, you can span far greater

distances than would be possible withalternative timber products.

This gives you unequalled designfreedom across a wide range of

applications for both oor and roof indomestic, industrial and commercialapplications. The Posi -Joist allows

a variety of internal room layoutswithin an external shell due to its clear

spanning capabilities.

THE ALTERNATIVE

JOIST SYSTEM

Available in Six Standard Depths

PS8 202mm PS9N 225mm PS14N 373mm PS10N 253mm PS16N 421mm PS12N 304mm

Posi - Joist is a tested product with a European Technical Approval

ETA-07/0161. Fire tests of 30, 60 and 90 minutes have been successfully passed. Acous c tests for impact and airborne sound transfer

have also been successfully passed. See Page 10 for more details.


3/35Page 3

The Posi-Joist ability to span greater distances than its timber competitors

and the fact that they are fully

competitive with steel and concretebeams makes it immediately obvious

that they o er considerable savings inraw materials. The open web design

gives the contractor another importantadvantage: it makes installation ofservice and utilities far simpler and

quicker, reducing both labour costsand build -up time on site.

Whats more, since they eliminate

the need for load -bearing intermediatewalls they dramatically cut overallbuilding costs.

Quite simply, theres no more e cientor economical way to construct

oors and roofs.

ECONOMY

FLEXIBILITY IN US Design exibility is inherent in the

concept of the Posi -Joist. The depthlength and speci cation can be adjusted

to produce an enormous number of di erent speci cations, each with

clearly de ned performance criteria. In addition, end details of the beam can

be altered to give a variety ofsupport conditions.

You will never come up short with thePosi-Joist Trimmable End. Each end can

incorporate a solid timber block whichcan be engineered with up to 130mm

allowance for trimming on site .

EFFICIENCY

Exceptional oor performancefrom a minimum 72mm widexing surface makes ooring

easy, controls shrinkage andwith precision engineering it allreduces those tiresome returnvisits and remedial work.

More bene ts such as theunique open web design pro-vide an area in which Plumbersand Electricians will nd it easy

and convenient to work. Thejobs done far more quickly andthe contractor makes worth-while savings.

There when you need it Posi-Joists Trimmable Endprovides eld cuttingexibility!

Even on long spans, no herring bonestrutting is necessary with the Posi -

Joist system. If thespan exceeds 4m astrong -back is installed atmid-span.

The Posi-Joist can adequately spanfor at and pitched roofs.

Its span capability and timber ang-es make it the more desirable alter-native to all steel systems.


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Tested by TRADA and accepted by theNHBC , staggered Posi-Strut webbingeduces the material content of the joist

providing economic and environmentalsavings.

TRIM-IT VARIATION

MATERIAL SAVINGS Posi-Joists can be designed to include single sid-

ed Posi-Strut webbing where appropriate toprovide considerable material savings.

The use of staggered webs can give as much as a12% reduction in the amount of steel used in aPosi-Joist compared to its competitors.

This webbing technique is subject to a patent andis typical of the ongoing development

of Posi-Joist.

The Trim-It end detail provides a exible

end detail perfect for applications withvarying and uncertain spans. Trimmedon site prior to installationup to600mm can be removed per Posi -Joist.

Maximum 600mm can be trimmed from a stock length


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The World of Posi Technology

Ground Floor Applications


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1Since there is no ceiling attached to the underside of the Posi -Joists, the bottom ange will nothave any lateral restraint. Therefore, multiple spans should either be avoided, or restraint nogginsshould be inserted at bottom ange level on each side of internal supports where the lower ange islikely to be in compression.

2The absence of a ceiling will result in a ground oor feeling less sti when compared with other oors of the same joist depth and span. Additionally the kitchen/utility areas containing large kitch-en appliances that produce dynamic movement are likely to be located on the ground oor. It maybe appropriate to consider specifying more stringent de ection limits than those normally applied.This should be discussed with the building designer early in the project cycle to control vibration per-formance.

3When planning the arrangement of Posi -Joists for suspended ground oors considerationshould be given where practical to making the joists discontinuous between kitchen/utility areassupporting large kitchen appliances and living/dining areas, so as to minimise the occurrence of ap-pliance induced vibration in living areas.

4The environment within a suspended ground oor is classi ed as Service Class 2 and hence thede ection characteristics of the Posi -Joists may be di erent than for intermediate oors. Provided

the void beneath the oor is well ventilated and drained and the ground cover layer inert the oor will perform as expected.

5Joists in suspended ground oor applications need particular attention to construction detailingwith regard to ground preparation, ventilation, insulation and disabled access.

DPC

DPC

150mm min

150mm min

When designing Posi -Joists for use in suspended ground oors the following ground oor speci cpoints should be considered :

Notes to Diagram

The ground cover layer should be inert and resist the passage of moisture. One of the following con-structions may be used, although other options may also be suitable:

i) 50mm of inert sand, gravel or concrete on 300 micron (1200g) polythene (1000g if PIFA branded) lapped andturned at the edges, on 25mm sand blinding; ii) 100mm concrete on well consolidated hardcore; iii) 50mm concrete on polythene membrane on 50mm sand blinding.


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Notes to Diagram (Continued)

On sites where external ground levels are higher than internal, the internal ground cover should fallto a suitable drainage outlet.

Under oor ventilation should be in accordance with The Building Regulations and ventilator manu-facturer speci cations. Special care should be taken to ensure that adequate cross -ventilation isachieved. A minimum clear height of 150mm should be provided between the underside of the joistsand the internal ground cover.

Where protection is required against Radon gas or other ground gases, specialist advice should besought.

Insulation requirements will vary depending on the oor size and should be calculated by the BuildingDesigner for each oor construction. Insulation can be installed in ground oor constructions by sup-porting the insulation between the Posi -Joists on either a rigid mesh, a breather membrane or bre-board xed between the joists.


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Intermediate Floor Applications


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Typical Construction Details

Posi-Joists can be built into the inner leaf of an external cavi-ty wall as illustrated. This method of construction meets thethermal and air leakage requirements of Building RegulationsApproved Document L1 &L2 (2006) provided that the perime-ter of the Posi -Joist is sealed with silicone sealant as shownand the wall is insulated to the Building Designers speci ca-tion. Alternative proprietary built -in constructions may beused, such as joist end caps, provided that they have beenshown by third party tests to meet or exceed the air leakage

performance of the construction illustrated. The constructionillustrated provides lateral restraint to the wall. Note: Certainend caps may not provide lateral restraint to the wall, and re-straint straps may therefore be required.

Posi-Joists can be supported in masonry hangers at an

external masonry wall. This method of construction meetshe thermal and air leakage requirements of Building Reg-

ulations Approved Document L1 & L2(2006). This detaildoes not provide lateral restraint to the wall unless a re-straint type hanger is used, if standard masonry hangersare used restraint straps will be required.

This detail illustrates a popular construction detail for support-ing Posi-Joists at an external timber frame wall. This con-struction meets the thermal and air leakage requirements ofBuilding Regulations Approved Document L1 & L2 (2006) pro-vided that the oor edge is insulated by a material with a mini-mum R-value of 0.75m K/W and that a bead of sealant isplaced between the skirting board and the oor deck and thatan e ective air barrier is maintained within the oor zone bymeans of solid noggins or header joists. The construction pro-vides lateral restraint to the wall provided that the connectionis designed and detailed by the Building Designer.

Silicone Sealant

Block work to con nue between Posi - Joists to providerestraint. Note: This is not allowed on solid external walls

Top Chord restraint xed between Posi - Joists. (Choose correct hanger for load, bearing width and coursework level of hanger bearing ange.)


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Fire and Sound Resistance

Plasterboard Ceiling Fire resistancefrom below

Sound resistancefrom above

The requirement for re resistance is normally 30 minutes for 1st and 2nd oors and this is provided almost entirely by theceiling plasterboard. The responsibility for the plasterboardspeci cation and xing rests with the Building Designer.

Posi-Joist oors with a variety of oor build ups have beenindependently tested and certi ed for 30, 60 and 90 minutesre resistance.

The following table provides details of Posi -Joistre certi cation.

Time Period Floor Build-up

30 Minutes 12.5mm Bri sh Gypsum Gyproc Wallboard with 5mm Plaster Skim and a 22mm Chipboardwalking surface

30 Minutes 15mm Bri sh Gypsum Gyproc Wallboard with a 22mm Chipboard walking surface

30 Minutes with Down lighters 15mm Bri sh Gypsum Wallboard with a 22mm Chipboard walking surface

60 Minutes Robust Detail E -FT-3 See Page 12 for details

90 Minutes 2 No. layers of 15mm Lafarge Firecheck plasterboard suspended on galvanised resilient barsxed to the underside of the Posi -Joists. 18mm Oriented Strand Board (OSB) subdeck.

The requirement for sound resistance of oors in England and Wales is that they should achieve a soundreduction of 40dB for airborne sound based on laboratory tests. The following table provides details ofPosi-Joist acoustic laboratory test results.

Floor Build-up Weighted AirborneSound Reduction

253mm Posi -Joist, 22mm Chipboard walking surface, 100mm Insula on 44

253mm Posi -Joist, 22mm Chipboard walking surface. No insula on. 43

253mm Posi -Joist, 18mm Ply walking surface, 100mm Insula on 41

223mm Posi -Joist, 22mm Chipboard walking surface, 100mm Insula on 44

223mm Posi -Joist, 22mm Chipboard walking surface. No insula on. 42

Note: 15mm Gypsum Wallboard ceiling used throughout, xes to the Posi - Joists at 300mm centres using 38mm Gyproc drywalltimber screws.


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Separating Floor Applications


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Separating oors need to meet enhanced requirements for re resistance and sound resistance when com-

pared to intermediate oors. Consequently the additional materials used to meet these requirements meanthat the dead weight of a separating oor will be signi cantly greater than the notional dead weight of an in-termediate or ground oor.

The period of re resistance required is at least 60 minutes and this is provided almost entirely by the ceilingplasterboard. The responsibility for the plasterboard speci cation and xing rests with the Building Designer.

Posi- Joist oors with a ceiling construction comprising of 2 No. layers of 12.5mm Gyproc Fireline plasterboardhave successfully passed 60 minute re testing.

Sound Resistance in Separating Floors

RSD E-FT3

Separating oors need to achieve sound reductions of greater than 45dB for airborne sound and less than 62dB for impactsound and this should be demonstrated by pre -completiontesting on site, or by adherence to Robust Details.

Robust Detail E-FT

-3 is the tested, proven detail for the use ofPosi-Joists in separating oors in timber frame construction.

The detail comprises of ceiling treatment CT 2 made up of two layers of 15 mm (nominal 12.5 kg/m) reline plasterboardxed with 25 mm and 42 mm screws to resilient bars at 400 mmcentres. On top of an 18 mm T&G Subdeck, a resilient compo-site deep batten system with a minimum depth of 70 mm isplaced with 25 mm (10 -33 kg/m) insulation placed between thebattens. On these battens a 19mm Gypsum based board

(nominal 13.5 kg/m) is placed with a nal deck of 18 mm (min)T&G ooring board on top.

Working in conjunction with our partners Prestoplan, MiTek ensured that Posi -Joistwas the rst metal web joist system in the UK to obtain a Robust Detail for the

resistance to the passage of sound.


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When an acceptable Posi - Joist design has been achieved with respect to structural, re and sound requirements

it should be noted that the performance of any separating oor can be compromised by poor detailing and work-manship. In particular care should be taken to isolate oor nishes from wall nishes since friction between ceiling lining, coving and dry -lining can result in impact sound transfer from the upper dwelling to the lower dwelling.


An alternative separating oor detail for Posi -Joist is theScreed o dB system.

With a build up of only 74mm from sub -deck to nished surface, a Screed-o dB oor can be considerably shallower than some common construc-tion details. This often allows the removal of a course of brickwork at eachlevel.

Ideal for under oor heating systems, services may be run in ductingthrough the screed, or through the open web zone of the Posi -Joist. Un-like other joist systems there is no requirement to add a service void belowthe standard ceilingonce more conserving the height of the building.

The Screed o dB system should only be installed once the roof and win-dows are in place and the building is weather tight. Ideally, any serviceswhich penetrate the oor zone should also be installed to allow them to beisolated acoustically. The screed takes 24 hours to cure su ciently to bewalked on. During this period, windows should be kept shut to prevent toorapid drying. After 24 hours, some windows should be opened to provideventilation. The screed will then dry at a rate of nearly 2mm per day, a typi-cal oor will fully dry over a 3 week period. Floor nishes, including tiles,can then be applied.

Posi-Joists have undergone long term testing withScreed o and have obtained a TRADA Q Mark. The

process of obtaining a Robust Detail for this method ofconstruction is under way.

High quality compressionresistant foam

FSC cer ed moistureresistant bre board

500 gauge polythene slipmembrane

40mm Screed o anhydritescreed


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Posi-Joist Standard Details

Masonry Bearing Details

Con nuous 47x72mm top chord restraint xedover ribbon block

Figure 3: Masonry Hanger Detail. With con nuous ledger. Minimumbearing determined by design (choose correct hanger for load, bearingwidth and coursework level of hanger bearing ange).

Figure 4: Top Chord Built into Masonry

Note: This is not allowed on single skin external walls

Con nuous 38x38mm Ledger xed to wall tosupport ceiling

Gap

Silicone Sealant

Figure 1: Bo om Chord Built Into Masonry Block work to con nue between Posi - Joists to providerestraint. Note: This is not allowed on single skin external walls

Figure 2: Masonry Hanger Detail. Top Chord restraint xed betweenPosi - Joists. (Choose correct hanger for load, bearing width and coursework level of hanger bearing ange.)

Soil Pipe Corner Details

Figure 5: Fixing Around Soil Vent Pipe Using Bearers 38x38 bearers xed directly to the wall to pick up both oor and ceiling.

Masonry Hanger Masonry Hanger

Solid mber or LVL trimmer (depth to suit)

Simpson IUBhangers

Figure 6: Fixing Around Soil Vent Pipe Using Trimmer See Robust Detail E -FT -3 (11) for treatment of service void

penetra ng the separa ng oor.


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Figure 7: Non -load bearing par ons parallel to Posi -Joists

Timber Frame Details

47x89mm packing piece

Gap

38x38mm con nuousplasterboard

47x89mmcon nuous pack

Ringbeams in solidmber or LVL

Servicevoid

Posi -Joists bearing on wall

First Posi -Joist setback approx 200mm

from wall Plasterboard noggin

47x89mm packsbetween Posi -Joists

Figure 8: Timber Frame Party Wall (with service void) Floor comprising: 22mm T&G chipboard on 19mm plasterboard and plank on47x75mm resilient oor batten at 400mm centres on 18mm T&G chipboard. AllT&G edges glued. Ceiling (not shown) comprising: 2 layers 15mm Gyproc Fireline board on 25mmresilient bars at 400mm centres. First layer xed with 25mm Gyproc screws at230mm centres. Second layer xed with 42mm gyproc screws at 230mm cen-

tres. Staggered with rst layer. Lay Fireline board in echelon pattern with stag-gered joints. Ceiling boards and xings must not penetrate or touch joists

Bead of sealant applied to oor deck prior to xing 19mm plasterboard plank.

Service Void

Posi -Strut web

Mineral wool cavity barrier

100mm mineral wool insula on quilt weight 1036 kg/m

Figure 10: Bo om Chord Fixing to Timber Frame(with con nuous restraint)

Con nuous 47x72mm topchord restraint xed overribbon block

Head binder

Figure 11: Bo om Chord Fixing to Timber Frame(with restraint noggins)

Head binder

47x72mm top chordrestraint noggins

Figure 9: Top Chord Fixing to Timber Frame


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Figure 13: Edge Closure Detail

Posi - Joist requires a minimum 50mm bearing

35mm Prefabricated edge closurePre -faced with sheathing andinsulated as required

Internal Bearing Details

Figure 14: Top Chord Fixing to Steel Downstand Beam

47x97mm between chords

Timber pack xed to beam (size to suit)

Gap

Timber plate xed to top of beam

Figure 15: Steel Beam Within Floor Zone Posi - Joist bo om chord to be notched over steel bearer plate

without interfering with connector plate

Steel Bearer PlateFully welded to underside of steel

45mm Rim Board (Depth to Suit)

Packing totop of steelsizes tosuit

Solid mber block (grain parallel to span)

Note: This is not allowed on external walls or re walls.

Timber Frame Details (Continued)

Figure 12: Edge Closure Detail Using MiTek F -Frame Where there are larger openings in the upper storey wall which causea concentrated load a suitable mber ver cal should be inserted un-der the point load to transfer it down to the wall below.

Posi -Strutbraces atmaximum2400mm centres

Plasterboard noggins

Insula on Ba s

Figure 16: Con nuous Posi -Joist ThroughMasonry

Figure 17: Shared Internal Bearing Figure 18: Internal Bearing


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Strongback Bracing DetailsFix at Maximum 4.0 Metre Centres

Strongback

Posi on strongback ght to the under

side of the topchord. As close as

possible to centre of joist for maximum

e ect .

Insert strongbackthrough

Posi -Joists beforexing joists. It may

not be possiblea er the joists have

been xed.

Figure 19: Strongback DetailPosi -Joists with Strongback blocks 38x75mm (min) blocks twice nailed to top and bo om members and twice nailed to brace using 3.1x75mm long galvanised wire nails.

Twice nailed tobrace using3.1x75mm longgalvanised wirenails.

Figure 21: Horizontal Restraint Straps Fixed Directly to Strongback Strap xed with a minimum of four xings of which at least one is tobe over the third joist.

Figure 20: Strongback DetailPosi -Joists with built in ver cals Posi - Joists can be designed with built in mber ver cals for strongback xing. The strongback is twice nailed as above.

Figure 22: Strongback Splice

1200mm long splice xed with 10 no 3.1x100mm long galva-nised wire nails each side of splice, nailed through and clenched over on far side.


Web Size Min. Strongback Sec on

PS8 & PS9 35 x 97 mm

PS10(N) 35 x 120 mm

PS12(N) 35 x 145 mm

PS14(N) & PS16(N) Min 35 x 145 mm *

Strongback Size Chart

* The deeper the strongback, the sti er the oor Figure 23: Strongback Detail for Change of Span

38x75mm (min) blocks twice nailed to top and bo ommembers and twice nailed to brace using 3.1x75mm longgalvanised wire nails.


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Stairwell Details

Simpson IUBhangers

Simpson SDSScrews

Figure 24: Staircase Opening Trimmer to be notched over the bo om ange of the hanger

Solid mber orLVL trimmer

(depth to suit)

Simpson LBVhanger

Single or doubleply Posi -JoistBeam

Figure 25: Posi -Joist to Posi -Joist Connec on Plywood nailed to both faces of trimmer beam. Ply/nailing asspeci ed by design

Figure 26: Posi -Joist to Posi -Joist Connec on Bo om member of Posi - Joist to be notched over the angeof the hanger

Simpson IUBhanger

Figure 28: Narrow Opening Detail

Beam (depth tosuit slo ed

through trimmers)

Packing piece topick up ceiling

Figure 27: Narrow Opening Detail

Trimmer to benotched over

the bo omange of the

hanger

Simpson IUBhangers

W CircleDia

Square

Rectangle Depth Posi -Strut Size

50 75 100 125 150 175 200

Rectangle Width

PS8 108 105 95 270 180 90 - - - -

PS9N 134 130 115 310 240 180 100 - - -

PS10N 159 150 135 320 270 210 160 80 - -

PS12N 210 190 155 350 310 260 210 160 110 70

Maximum Duct Sizes

W


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Internal Load Bearing Walls

Figure 29: Posi -Joists Parallel to Internal Load Bearing WallUsing MiTek F -Frame Where there are larger openings in the upper storey wall whichcause a concentrated load a suitable mber ver cal should beinserted under the point load to transfer it down to the wall below. Plasterboard noggins a ached as shown.

Beam widthto suit wall. Depth to SuitPosi -Joist. Plasterboardnoggins either side

Blocking widthto suit wall. Depthto Suit Posi -Joist.Plasterboard nog-gins either side

Con nuousPosi -Joists

Posi -Strut braces at maximum 2400mm centres

Figure 30: Posi -Joists Parallel to Internal Load Bearing Wall

Figure 31: Con nuous Posi -Joists Perpendicular to InternalLoad Bearing Wall

Blockingwidth to suitwall. Depth toSuitPosi -Joist.Plasterboardnoggins eitherside

Figure 32: Bu ng Posi -Joists Perpendicular to Internal LoadBearing WallWhere this detail is used in a Posi - Joist casse e construc onan addi onal blocking brace should be included to secure the

blocks.


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Posi-Joist Span Information

Indicative Span Information

If you are a member of the iStructE or RIBA you can download a free version of the 20/20 Posi -Joist designsoftware from the MiTek website to allow you to accurately specify Posi -Joist designs.

The following indicative table as to be used as a typical guide to the clear span-ning capabilities of Posi -Joists. Please consult a licensed Posi -Joist manufactur-er prior to specifying Posi -Joist sizes to discuss the loading conditions for theentire oor.

Clickhere to download the latest list of licensed Posi -Joist manufacturers.

600mm Centres

Overall Depth of Posi -Joist 72mm Joist Width 97mm Joist Width

202mm (PS8 Posi -Joist) 4300mm 4800mm

225mm (PS9(N) Posi -Joist) 4750mm 5100mm



These are indicative Posi - Joist clear spanning capabilities based upon domestic oor loads including a partition load. Posi - Joistscan span greater clear spans by reducing the joist centres, increasing the joist width ; and by increasing the size of the strongback

brace. Consult a licensed Posi- Joist manufacturer to establish the correct Posi

- Joist depth to specify for your oor.

Free Posi -Joistdesign So ware
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Storage on site should be for a limited period oftime prior to erection of the Posi -Joists.

Posi-Joists should either be stored vertically or on the at. If stored vertically there should be inter-mediate bearers at node points not within the bayof a joist, as shown below. If stored in a at posi-tion, su cient bearings should be provided to pre-vent excessive lateral bending.

It is recommend that completed Posi -Joists bestrapped together and wrapped in a waterproofprotective covering to protect them from shortterm exposure to inclement weather.

Special precautions should be taken when stackingtop chord supported oor cassettes to prevent thestack lozenging in storage. Additional bracing tothe ends of the stack should be xed to stop lateralmovement. Care should be taken when handlingthe Posi -Joists to avoid bending, twisting or drop-ping.

When loading/o oading with a crane, slings shouldalways be attached to the timber chords or the cas-sette lifting points, and not to the metal webs toavoid buckling. Slings should be attached at panelpoints closest to the quarter points of the Posi -Joists as shown below.

Site Handling & Storage

Set Out & Placement

Posi-Joists are generally placed perpendicular tothe load bearing supporting walls and should be lo-cated so that the distance between them does notexceed the design spacing always consult the Posi -Joist layout drawing and proceed with erection ofthe oors as follows: -

1- Plan the erection sequence and place the Posi -Joists close to where they are required, only dis-tribute a su cient number of joists around the build-ing which an be erected in a reasonable period oftime. Posi -Joists should be protected from inclem-ent weather and stored as noted above.

2- Before lifting the Posi -Joists to sca old level domake sure the correct end of the joist is at the ap-propriate support as the end details may be di er-ent. Also be aware of any internal supports whichare being used and that the special internal bearingdetail for the joist is in the correct position.

3- If the Posi -Joists are supported over more than 2supports make sure all the supports are the samelevel and when the joists are lifted into place theyrest on all of the supports.

4- If the Posi -Joists are supported on masonryhangers, make sure they are the ones speci ed andare rmly anchored in place and that the masonry iscured in line with hanger requirements. Joistsshould have a full bearing with no more than a 5mmgap between the end of the joist and the face of thehanger. Masonry hangers with a cavity return andintegral strap provide lateral restraint to wall heads.

5- Make sure the Posi -Joists are erected the correctway around, the joists will normally be marked"TOP" and the rst metal web will normally start atthe top of the Posi -Joists.

Bearers as close as possible to web points

Bearers directly under web points

Use fabric sling. Do not use chains orwire rope which maydamage webs

60 or less


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6- The Posi-Joists are positioned to coincide withthe deck joints, the rst of which is normally1210mm away from the wall face in masonry con-struction or 1200mm from the cavity face in Timber Frame construction when the deck extends to thecavity face; when the joists are spaced at 400 or 600mm centres. There is normally a 10mm perime-ter gap between the face of the deck and the faceof the wall in masonry construction to allow for po-tential expansion of the deck. The board material isnormally 1200 x 2400mm, the long dimension span-ning at 90 to the joist span. The remaining joistsare normally spaced on a grid of 400, or 600mmcentres, on occasion at 480mm centres.

7- When the deck is set out from the face of thewall it is normal to have the rst joist edge 50mmfrom the face of the wall where in Timber Frameconstruction with the deck set out from the cavityface it is normal to not have a joist close to a wall,the deck and plasterboard being supported on atimber ledger nailed to the frame. Carefully followthe layout drawing and the wall/joist interface de-tails provided by the Building Designer, in particular in Timber Frame where the joist centres and thestud centres may have to line through.

8- The penultimate Posi -Joist in the run is set outon the standard module and the last joist is posi-tioned similar to the rst in the run.

9- Posi-Joist stair trimmer joists and trimmers willbe required around stair openings which may be onthe main joist grid or usually o the grid. Set thesejoists out strictly in accordance with the architectur-al and Posi-Joist layout drawing and x the trim-mer joist to the stair trimmer and the trimmed joiststo the trimmer joist with the metal hangers speci-ed making sure that any 2 ply joists are adequatelyconnected together as detailed.

10- To temporary brace and space the Posi -Joistswhich have been laid in position x a piece of 22 x

97 bracing to the top of the joists at their ends andmid span or around 2.4m centres on spans longer than 4.8m.

Site Handling & Storage

11- Install the strongback bracing as detailed, thestrongback is always installed on edge not on at andmust be xed to the integral strongback blocks or noggin pieces nailed to the face of the joist. Thestrongback must be xed tight to the underside ofthe top chord. Due to the width of the Posi -Joistchords and the additional sti ness installed in theoor due to the strongback bracing, it will not nor-mally be necessary to employ any temporary diagonalbracing.

12- When all the Posi -Joists have been positionedand xed in place, the partition noggins, perimeter noggins, rim boards, when required can be installed,and in the case of masonry construction the steel lat-eral restraint straps should be xed in place at nogreater than 2m centres and should extend over 3joists.

13- The oor carcass is now ready to receive the deck-ing material and acoustic material where required.

14- The maximum load of sheet materials temporarystored on the Posi -Joists is 250kg/m2 and should notbe greater than 300mm deep. This equates to 16sheets of 18mm chipboard, 13 sheets of 22mm chip-board or 20 sheets of 15mm plasterboard. Where thesheets are stacked by hand they should span length-ways across the joists, (Fig 1), when lifted mechanical-ly they should be seated on 5 bearers the width ofwhich are 600mm longer than the width of theboard. (Figs 2 & 3).


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DOs and DONTs

DONT

Drill holes in thetimber chords

DONT Cut notches inthe timber

DONT Cut through thetimber chords

DONT Cut or removethe metal webs

DO Store as shown in handlingand storage section

DO Lift the Posi-Joists in avertical position

DO Use the open web featurefor services

DO Protect Posi -Joists frominclement weather


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Roof Applications


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Posi-Rafter Standard Details

Recommended eaves and apex details for use withPosi-Rafters. All of these details are available for use by trained Posi -Rafter designers in the MiTek20/20 design software.


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The X-Rafter

This exciting new roo ng system provides a exible room in theroof solution capable of providing the thermal performance that

will increasingly be required by the planned revisions to Part L ofthe Building Regulations. The MiTek Posi -Strut technology en-sures that the roof panels are lightweight and easy to install. Thesystem arrives on site, felted and counter battened ensuring thatthe roof is watertight in a short period of time.

The environmental bene ts include the low U -Values that the sys-tem can achieve of 0.17 W/mK; timbers impeccable sustainabilitycredentials; and the design of the loft as a cold area thus further reducing the energy consumption of the dwelling.

Based on a MiTek Posi - Joist floor, the working platform for the Posi X - Rafter roof is assured with theuse of laser levels.

Flat top spandrels are positioned incorporating location slots for the ceiling cassettes. The spandrel

panels are stubbed as required by the roof dimensions.

The structural ceiling cassette incorporating the roof support purlins are located. Timber frame dwarf wallsare positioned to provide a second Posi X - Rafter support.

Apex spandrel panels are positioned using the struc-tural ceiling as a safe working platform.

Posi X - Rafter cassettes are positioned and fastened tothe supports. Posi X - Rafters are insulated at the point of manufacture and are pre - felted and battened.

The underside of the Posi X - Rafter cassette is clad withOSB in the room area only.

Dormer windows are easily catered for by the system. Insulation material costs are lower than competitive systems as the loft area is a cold area, reducing theenergy consumption of the dwelling.

Call us for information on how to become a licensed MiTek Posi X - Rafter manufacturer.


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Ideal for use in narrow fronted gable to gable housing, the X -Rafter system starts with at top structuralgable panels, xed to o site manufactured Posi -Joist oor cassettes.

Spanning between the two structural gable panels, the next element of the X -Rafter system to be posi-tioned is a pre -fabricated structural ceiling cassette with up -stand beams to provide the support for theX-Rafter roof cassettes.


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Pre-Insulated, felted and counter battened o site, the X -Rafter cassettes are craned into position.

The Posi-Joist cassette oor and the structural ceiling cassettes form two safe working platforms provid-ing that the appropriate harnessing is worn by the installation team.


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The apex spandrels are lowered into position to complete the cold roof space above the pre -insulatedceiling panels.

Wind and water tight in hours not days, the X -Rafter combines health and safety bene ts with all thebene ts of o site timber engineering manufacture. Contact MiTek for further information.


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By rotating the timber anges through 90 so that the

timber is on edge rather than on at, the Posi-Joistbecomes much sti er and the span capabilities are

increased. The subsequent resulting instability of theon -edge joist can be removed by specifying that thePosi-Joists are pre -fabricated into cassettes for easeof installation.

Posi-Attic Trusses

Maximise Your Living Space with the MiTek Posi -Attic

Combining the solid feel of a MiTek Posi -Joist withthe bene ts of a conventional attic truss, theMiTek Posi-Attic enables you to span much larger spans than conventional systems. The strength ofthe Posi -Joist oor provides increased living spacewithin the attic, delivering maximum value to thehome owner.

The Posi- Joist oor is ideal for easy installation of Heat Recovery Ventilation Systems, soil pipes and the in-creasingly diverse range of services installed in modern homes

Picture reproduced with thanks to Pasquills

Posi-Joist Roof Cassettes

Picture reproduced with thanks to Donaldson McConnell (Midlands) Ltd


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Wall Applications


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The Posi-Stud

outer leaf of masonry

drained and vented 50mm cavity

High Performance Breather Membrane

OSB Sheathing

2 No. 150mm layers of 35 lambda Mineral Wool

OSB Sheathing

Posi -Stud lled with Mineral Wool

inner lining of plasterboard

vapour control layer

300mm Posi -Stud

Ba ened service zone

Calculated U -Value: 0.12 W/mK

Calculated U -Value: 0.17 W/mK

200mm Posi -Stud

outer leaf of masonry

drained and vented 50mm cavity

High Performance Breather Membrane

OSB Sheathing

2 No. 100mm layers of 35 lambda Mineral Wool

OSB Sheathing

Posi -Stud lled with Mineral wool

inner lining of plasterboard

vapour control layer

Ba ened service zone


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Sample Posi -Stud Details

Sample floor to wall connection detail

Sample exterior connection detail

Sample wall to roof connection detail

Sample sole plate connection detail


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Posi-Stud Photographs

Picture reproduced with thanks to OReilly Timber Frame


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MiTek Industries Ltd

Grazebrook Industrial Park Peartree Lane

Dudley DY2 0XW

t: 01384 451400 f: 01384 451411 www mitek co uk

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