1. Dr. Ruth Collins TrinityHaus ruth.collins@tcd.ie
OFF SITE CONSTRUCTION
Dr. Ruth Collins
TrinityHaus

2. TYPES OF MODULAR CONSTRUCTION
OFF SITE CONSTRUCTION
RE-CAP
TYPES OF MODULAR CONSTRUCTION
Modular/POD Method
Panelised System
Infill Panels
Hybrid Construction
Re-Cap of the different types of offsite construction…ask them to describe

3. OFF SITE CONSTRUCTION RE-CAP WHY CHOOSE EACH METHOD Modular/POD Method
Need for fast construction
Regular shapes
Need for internal finishes to be done off site
Re-Cap of the different types of offsite construction…ask them to describe

4. OFF SITE CONSTRUCTION RE-CAP WHY CHOOSE EACH METHOD Panelised System
Need for Fast Construction
Large Open Space
Irregular Shapes
Re-Cap of the different types of offsite construction…ask them to describe

5. OFF SITE CONSTRUCTION RE-CAP WHY CHOOSE EACH METHOD Infill Panels
Multi-Storey Design
Hybrid Construction
Shear core required for services
More economical to use more than 1 method
Architectural Considerations etc.
Re-Cap of the different types of offsite construction…ask them to describe

6. OFF SITE CONSTRUCTION LIGHT GAUGE STEEL COMPONENTS Load Bearing Walls
Non-Load Bearing Walls or Partitions
Floors
Roof Trusses
Light gauge steel can be used for lots of types of components such as

7. OFF SITE CONSTRUCTION LIGHT GAUGE STEEL ADVANTAGES
Dry Building Material
Not susceptible to moisture or movement
High Tolerances
High Precision Production of Profiles
Lengths cut within 2mm tolerance
Strength to Weight Ratio very high
Environmental Benefits
100% recyclable
Flexibility in Size and Design
Re-Cap of the different types of offsite construction…ask them to describe

8. OFF SITE CONSTRUCTION LIGHT GAUGE STEEL COMPONENTS
Hot Dipped Galvanised
Cold Rolled Steel
Load Bearing Wall Depth, 70mm to 200mm
Non-Load Bearing Wall Depth, 70mm to 100mm
Floor depth, 200mm to 350mm
Roof Trusses, 90mm U-Chord Section
Re-Cap of the different types of offsite construction…ask them to describe

9. OFF SITE CONSTRUCTION LIGHT GAUGE STEEL COMPONENTS Stud and Track
Re-Cap of the different types of offsite construction…ask them to describe

10. OFF SITE CONSTRUCTION LIGHT GAUGE STEEL COMPONENTS Stud and Track
Re-Cap of the different types of offsite construction…ask them to describe

11. OFF SITE CONSTRUCTION LIGHT GAUGE STEEL COMPONENTS Back to Back Stud
Re-Cap of the different types of offsite construction…ask them to describe

12. OFF SITE CONSTRUCTION LIGHT GAUGE STEEL COMPONENTS Boxed Stud
Re-Cap of the different types of offsite construction…ask them to describe

13. DESIGN CONSIDERATIONS
OFF SITE CONSTRUCTION
DESIGN CONSIDERATIONS
Structural Requirements
Resist Gravity and Lateral Loads
Other Physical Requirements
Depth of Required Insulation
Interface Details i.e. type of cladding, amount of glazing etc
Architectural Requirements
Depth of the window reveal
Floor spans
Handling and Erection Conditions
Draw examples on board

14. OFF SITE CONSTRUCTION STRUCTURAL DESIGN Gravity Loads Lateral Loads
Wall studs must be aligned with the floor joists
Lateral Loads
Cross Bracing
K-Bracing
Sheathing Board
Openings
Avoid lines of high vertical load
Ensure lintel is strong enough to transfer load
Provide strength either side of the opening to transfer load
Structural Requirements – Must be able

15. STRUCTURAL DESIGN (cont...)
OFF SITE CONSTRUCTION
STRUCTURAL DESIGN (cont...)
Floor to Floor Dimensions i.e. height
Floor Zones and Spans
Section size depends on floor span
For large spans a lattice floor may be required
Building Height
For practical purposes, limit to 4-6 storeys
Progressive Collapse
Inter-connectivity between walls and floors
Structural Requirements – Must be able

16. OTHER DESIGN CONSIDERATIONS
OFF SITE CONSTRUCTION
OTHER DESIGN CONSIDERATIONS
Acoustics
Fire Resistance
Thermal Insulation
Durability
Environmental Performance
Structural Requirements – Must be able

17. OFF SITE CONSTRUCTION EFFECTIVE WIDTH
Effective width is a function of:
Boundary conditions
Stress conditions
Material
Width to thickness ratio etc
Stress distribution vs cross section property
Iterative process
Only certain portions of the plate width are considered to be effective in carrying loads after exceeding the local buckling stress. Therefore the actual cross section is replaced with by an effective cross section and the properties of the effective cross section are what is used in the design of the member.
The effective width of a cross section element is a function of a number of parameters such as boundary condition, stress condition, material and width to thickness ratio, etc. The stress distribution cannot be computed until the cross section property is calculated. Therefore, it is necessary to assume a certain stress distribution and compute the associated effective property.

18. EFFECTIVE SECTION PROPERTY
OFF SITE CONSTRUCTION
EFFECTIVE SECTION PROPERTY
Cee Section
Structural Requirements – Must be able

19. EFFECTIVE SECTION PROPERTY
OFF SITE CONSTRUCTION
EFFECTIVE SECTION PROPERTY
Lipped Section
Structural Requirements – Must be able

20. EFFECTIVE SECTION PROPERTY
OFF SITE CONSTRUCTION
EFFECTIVE SECTION PROPERTY
Back to Back Section
Structural Requirements – Must be able

21. EFFECTIVE SECTION PROPERTY
OFF SITE CONSTRUCTION
EFFECTIVE SECTION PROPERTY
Boxed Section
Structural Requirements – Must be able

22. DESIGN EXAMPLE OF LIPPED SECTION
OFF SITE CONSTRUCTION
DESIGN EXAMPLE OF LIPPED SECTION
Structural Requirements – Must be able

23. OFF SITE CONSTRUCTION FIRE Requirements vary according to height
Protected by layers of plasterboard
Staggered layers and importance of detailing
Allowed temperature of the steel
Cavity Barriers and Connections
Testing
Fire resistance varies according to height, for houses and apartments up to 2-3 storeys, 30 minutes is typically required for structural elements, 60 minutes would be needed for separating walls or buildings and taller buildings may require 90 or even 120minute fire resistance, so it really depends on the design.
The fire protection is generally provided by the layers of plasterboard, 1 layer would typically achieve 30 minutes and 2 layers 60 minutes.
When exposed to the fire, the plasterboard shrinks and cracks, allowing hot gases into the cavity and heating the structural members. To avoid this, when you use two layers, you must stagger the joints, or fire boards with fibre reinforced material could be used to stop the plasterboard from shrinking quickly. It is also very important that the correct number and spacing of fixings are used as these also provide a weak point where the gasses can get into the cavity
In addition to this, as the wall heats up, so does the steel, there’s difference guidance on how hot the steel is allowed to get but it is recommended that it does not exceed 350 degrees Celsius
Also, the detailing must incorporate cavity barriers to prevent the spread of fire between compartments (such as two apartments or a semi-d house), the services must have adequate fire protection and connections between load bearing columns and beams must be protected to the same standard as other connected elements
Some plasterboard manufactures have tests done to steel frame but not very many and therefore most companies have to get tests carried out anyway, they’re also talking about brining in a European legislation that says you not only have to test a single panel for fire but that you have to test a two storey, 3D model incorporating windows, doors and services to prove the fire resistance. These tests are a good idea to ensure that construction will resist the relevant fire codes but will be extremely expensive to carry out

24. OFF SITE CONSTRUCTION ACOUSTICS Mass Absorption
Distance Between Layers
Stiffness
Resilience
Detailing for acoustic breaks and flanking transmission
Mass resists the passage of airborne sound, this is generally taken care of by the number of layers of plasterboard which can also be used for fire resistance. Also mineral wool is a very good absorber of sound and therefore will resist airborne sound through the wall.
The further the distance between the layers, the longer the sound has to travel and the more likely it will be absorbed by the materials around it, this is also a good way of limiting the vibrations through the wall….modern equipment etc…
The stiffness of the wall also affects the vibrations that carry the sound, care must be taken to avoid any resonance
An then of course the resilience, if the wall is badly constructed and someone bangs a door, the sound can carry which also comes into the detailing, care must be taken that between houses or apartments there are thermal breaks to ensure no flanking transmission and especially in light gauge steel that there are no steel connections over party walls which would carry the sound, for example take the following wall

25. OFF SITE CONSTRUCTION ACOUSTICS
1 is the wall lining, 2 is the absorbent material such as mineral wool and 3 is the wall width which is a recommended minimum of 200mm between the inner linings of the wall.
This would be an example for a typical part wall construction, you can see that the steel studs form the two structural load bearing walls and then they are breaked by the mineral wool, these two walls are independent to each other, in other words there is no strucutral dependence on each other and therefore there is no connections between the two, therefore no sound can be transferred through the steel across the junction. In addition to this, it is not allowed to place any services through this wall and if sockets are required they have to be either flush fixed with the wall or the wall has to be battened out to create a cavity for the sockets or any other services that are required. Basically this wall is treated as the external envelope similar to a stand alone structure.
60 t0 65dB can be achieved with this type of wall construction

26. OFF SITE CONSTRUCTION ACOUSTICS
The following is the typical build up of a floor that resists both airborne and impact sound. The control of the impact of sound is usually more problematical with floors as you can imagine, kids running, women in high heels, loud sounds that can’t be transmitted. You can see underneath the chipboard that there is a resilient layer, here it is shown to be a layer of rigid insulation but it has been proven that an acoustic mat such as a rubber or cork mat, minimum of 5mm is also very effective and the result of using this instead of insulation is that if the client does want screed on top of the chipboard (like I mentioned last week), then there is much less movement involved and less likely hood of cracking and you can get away with thinner screeds. You also have the option of resilient bars underneath, these bars look like…show…and therefore the sound is absorbed as it transfers through. So depending on the level of sound resistance you require depends on how many of these factors you add in.

27. OFF SITE CONSTRUCTION THERMAL PERFORMANCE
Thermal performance depends on
Thermal performance of the building envelope
Ventilation rate and form of construction
Air leakages
External climate
Internal gains

28. OFF SITE CONSTRUCTION THERMAL PERFORMANCE
Thermal performance of building envelope
Depends on position of steel studs
Insulation Type
Insulation Thickness
Insulation Placement
Wall Penetrations
Thermal Bridging

29. OFF SITE CONSTRUCTION THERMAL PERFORMANCE The ‘Warm Frame’ Approach
The following two walls show the build up of a typical light gauge steel wall, 1 with brick and the other with render. You can see that there is insulation within the stud and insulation outside the stud. What this does…draw on board…is it prevents any cold air being transferred through the steel stud into the wall which prevents any mould growth on the wall which you would expect because of the difference in temperatures. Same for the render. A cold frame would look like this and is not recommended for light gauge steel framing, the more insulation outside the stud, the better.
Similar, you need to make sure that there is no cold bridges around junctions such as under window sills, door jambs, corner details. And this can normally be achieved by a cavity closer which is also used as a fire break and an acoustic break, so more than 1 issue can be solved with 1 product which ultimately minimises the cost at the end of the day.
The U-Values are easy enough to calculate but thermal bridges are a lot more complicated because of the fixings and connections that are used and 3D modelling software using finite analysis is normally used for this.

30. OFF SITE CONSTRUCTION THERMAL PERFORMANCE Air Tightness
No point in placing lots of insulation if there are lots of air leaks letting all the hot air escape
Comes back to detailing
Comes back to detailing, whatever method of air tightness that you choose, whether it be a membrane or a board, you must ensure that the joints are properly lapped and taped and there is continuity of the selected material

31. OFF SITE CONSTRUCTION THERMAL PERFORMANCE General Guidance
Maximise the stud spacing
Minimise the stud steel thickness
Use ‘warm frame’ construction
Minimise cold bridging at openings and joints
Provide air tight seal around the building envelope
In addition to these, as light gauge steel gives very tight connections and there is no movement involved that would occur with the expanding and contracting of timber studs, this provides much more assurance to achieving air tight values compared to other methods.

32. OFF SITE CONSTRUCTION DURABILITY
Light Gauge Steel protected by Galvanised Coating
Must look at all components regarding durability
Insulation materials
Claddings
Fixings etc…

33. ENVIRONMENTAL PERFORMANCE
OFF SITE CONSTRUCTION
ENVIRONMENTAL PERFORMANCE
Steel is 100% recyclable
Light gauge steel companies use recycled steel
Risk of moisture problems reduced
Efficiency of Production – Little Waste
High Quality – Little Waste
Light weight – Transport more at one time
Components can be re-used
Moisture problems lead to mould growth and health problems and also deterioration of the buildings materials

34. USING OFF SITE CONSTRUCTION FOR CONSTRUCTION INNOVATION?
Mass resists the passage of airborne sound, this is generally taken care of by the number of layers of plasterboard which can also be used for fire resistance. Also mineral wool is a very good absorber of sound and therefore will resist airborne sound through the wall.
The further the distance between the layers, the longer the sound has to travel and the more likely it will be absorbed by the materials around it, this is also a good way of limiting the vibrations through the wall….modern equipment etc…
The stiffness of the wall also affects the vibrations that carry the sound, care must be taken to avoid any resonance
An then of course the resilience, if the wall is badly constructed and someone bangs a door, the sound can carry which also comes into the detailing, care must be taken that between houses or apartments there are thermal breaks to ensure no flanking transmission and especially in light gauge steel that there are no steel connections over party walls which would carry the sound, for example take the following wall