Profiled Metal Buildings

Profiled metal clad buildings insulated with glasswool are the most common form of construction for industrial and warehouse buildings throughout the world.

Overview

The walls and roofs of profiled metal buildings typically consist of a profile metal inner liner sheet, separated from an outer, higher profile, metal weather sheet. The cavity is filled with a layer of insulation to provide maximum thermal performance. This insulation is normally a glasswool roll or batt, to offer a high performance, A1 fire resistance and material handling advantages (e.g. lightweight, higher compression etc).Built-up roofing and cladding systems are assembled on site. The design and components used are often part of a proprietary system.

Advantages

• Fast method of construction
• Lightweight construction, reducing structural steel and foundation costs
• High levels of fire resistance with potentially lower insurance premiums compared to foam composite panels
• Secure
• Cost effective
• Easy to install

The Advantages of Glasswool

The inherent properties of glasswool mean that it can offer superior thermal performance at lower density compared to rock wool. This lower density enables higher packaged compression resulting giving an increased quantity of insulation in roll or pack and therefore more insulation in a delivery. This then results in a reduced amount of storage space on site and less lifting time to move product to the roof the building. Of course, glasswool has unbeatable A1 Euroclass fire classification.In summary:

• Transport and storage efficiency – more m2 per of glasswool versus rock wool per truck
• Superior roll length or quantity of batts for glasswool resulting in faster installation
• Weatherproof packaging – glasswool has palletised, weatherproof packaging enabling outside storage
• Less unloading and lifting time of glasswool for faster transfer of product onto the roof
• Lighter weight of glasswool can result in a reduced requirement structural steel
• The lower density of glass enables better resistance to on-site weather exposure during installation.
• Unbeatable A1 Euroclass fire classification. Building owners can usually obtain lower insuarance premiums from using glasswool compared to foam composite panels

Knauf Insulation Products

Knauf Insulation FactoryClad Roll is a range of flexible, lightweight, non-combustible, resilient glasswool quilts. It is available in three thermal conductivities:

• 0.040 W/mK – good
• 0.037 W/mK – excellent
• 0.035 W/mK – super performance

Knauf Insulation Rocksilk Slab is a high density rock wool slab with a high degree of acoustic absorbency.

Detailed Design Considerations

Thermal Insulation

Built-up profiled metal wall and roof cladding typically consists of a profile inner liner sheet, separated from an outer, higher profile, weather sheet by a spacer system. The spacer system is used to create a cavity for the layer of insulation. Built-up cladding systems are assembled on site. There are three main positions for the insulation:

• Insulation outside sheeting rails or purlin
• Insulation in liner trays
• Insulation inside sheeting rails or purlin

Thermal Bridging at the Spacer System

In built-up profiled metal cladding systems, the spacer system used to create a cavity between the inner and outer cladding sheets forms repeating thermal bridges. Spacer systems are designed to incorporate a thermal break to reduce the effect of heat flow through the rail and bracket components. The spacer system usually takes the form of zed bars, rail and bracket systems or insulated spacer systems. Rail and bracket spacer systems should have their brackets spaced at least 1m apart, and include a thermal break.

Minimising Thermal Bridging

Thermal bridging is minimised if the full thickness of insulation is maintained across the whole roof and wall area and fixings through the insulation are kept to a minimum. Details at corners, gutters, junctions and openings should be designed to maintain the continuity of insulation wherever possible. On site, check that there are no gaps in the insulation layer.

Continuity of Insulation and Thermal Bridging at Junctions and Openings

In order to maximize thermal insulation performance, the building envelope should be constructed so that it does not contain significant thermal bridges or gaps in the insulation layer(s).Typical areas requiring careful consideration are joints between construction elements and linear details such as window jambs, heads and sills.

U-value Calculations

Alternatively, contact the Knauf Insulation Technical Advisory Centre to calculate the thickness of insulation needed to achieve specific U-values, including the effect of thermal bridging by rail and bracket and Zed spacer systems only.

Minimising the Condensation Risk

There are two main ways to minimise the risk of condensation in this type of construction:

1. Providing adequate ventilation to replace humid air with drier air as close as possible to the water vapour source, using fan assisted air extraction if necessary.
2. Stopping relatively warm, humid air reaching colder surfaces, by including a vapour control layer on the warm side of the insulation and providing some ventilation to disperse any water vapour which does get through.

Vapour Control Layer

A vapour control layer is required in the roofs of all grades of building. This is to restrict the amount of water vapour, from inside the building, which enters the construction by diffusion and air leakage. The vapour control layer can be formed by ensuring that the laps in the metal liner are well sealed. Alternatively a separate membrane can be used. In both cases, the vapour control layer should be continuous. The vapour control layer should be integrated with and be sealed to other building elements such as, roof to wall connections, adjoining masonry, upstands and roof penetrations such as rooflights. Joints in the vapour control layer should be minimised and suitably sealed. Penetrations should be avoided wherever possible, but where these are necessary, they should be suitably framed with upstands or curbs to permit the installation of vapour seals.

Breather Membranes

Even where an effective vapour control layer is provided, condensation can still form on the inner face of the outer sheet. Under clear night skies, 'supercooling' of the roof sheets below ambient temperatures can cause water vapour in the roof voids to form as condensation on the outer sheet. The provision of a vapour permeable underlay allows water vapour to pass through it. However, any condensate on the outer sheet will either fall onto the vapour permeable underlay and drain to the gutter or, if conditions allow, will re-evaporate and be carried away by ventilation. The vapour permeable underlay also prevents air from moving through, under and over the insulation to generate cold spots and reduce energy efficiency. Where a vapour permeable underlay intersects with a penetration or upstand, it should be detailed to provide a waterproof escape for leakage and or condensation. Ensure adequate movement of air through rib voids above the underlay from eaves to ridge. Ventilated openings should be resistant to ingress of rain, birds and large insects and not prone to blockage by dust or debris.

Air Tightness

Buildings should be reasonably airtight to avoid unnecessary space heating and cooling demand, and to enable the effective performance of ventilation systems. Several measures can be adopted to achieve satisfactory airtightness including the provision of a continuous air barrier in contact with the insulation, sealing gaps around penetrations and draughtproofing external doors and windows.

Specification Details

1&2) Wall Rail and Bracket

FactoryClad Roll 40*/37*/35* ......mm thick, to be positioned over the inner lining sheet and under*/ between* the spacer system prior to positioning of outer cladding sheet. Insulation to be installed according to system manufacturer’s instructions. (* delete as required)

3) Wall Liner Trays

Liner trays fixed horizontally to the vertical steel members. Crown FactoryClad 40*/37*/35* ......mm thick, placed in liner trays. Insulation should be cut to accommodate the tray dimensions and positioned in tray prior to fixing the outer weather cladding. Crown FactoryClad to be installed according to system manufacturer’s instructions. (* delete as required)

4) Underpurlin

Vapour check plasterboard or fibre cement lining board to be supported in an industrial metal tee bar system. FactoryClad 40*/37*/35* ......mm thick, to be laid over lining boards prior to positioning of outer cladding. Insulation to be installed according to system manufacturer’s instructions. (* delete as required)

5) Thermal Overpurlin

Liner panels to be positioned over purlins and a metal spacer system secured to the liner and purlin to ensure the full thickness of insulation is maintained between the liner and cladding sheets. FactoryClad 40*/37*/35* ......mm thick, to be laid over the lining sheets and installed according to system manufacturer’s instructions, with all joints closely butted. Cladding sheets to be securely fixed in position. (* delete as required)

6) Acoustic Overpurlin

Perforated metal lining sheets to be positioned over purlins and support brackets fixed to the purlins. Rocksilk Universal Slab RS100, ......mm thick, to be laid over the lining sheets and overlaid with a vapour control layer. Secure a metal spacer system through the vapour control layer to the support bracket to ensure the full thickness of thermal insulation is maintained between the vapour control layer and cladding sheets. FactoryClad 40*/37*/35* ......mm thick, to be laid over the vapour control layer and tucked under the metal spacer as each tier is completed with all joints closely butted. Cladding sheets to be securely fixed in position. (* delete as required) Insulation to be installed according to system manufacturer’s instructions.