Layered flat roofs with membrane

Standing Seam COMBI ROOF with Membrane

The combined insulation for lightweight roof envelopes in prefabricated halls is a combination of EPS insulation (expanded polystyrene) and MW (mineral wool) with fire resistance REI 15 DP1 up to REI 30 DP1, with a top layer of EPS 100 with a compressive strength of 100 kPa. For fire partition strips, mineral wool boards are used in full thickness to prevent the spread of fire.

Advantages of the system for prefabricated halls:

• Use for fire requirements on the roof RE 15 DP1 – RE 30 DP1
• Lower load on the supporting structure compared to a full mineral wool composition
• More economical option than a composition made only of mineral wool boards
• Suitable also for assembly areas (shopping centers, etc.)
• Alternative solutions to meet various fire resistance requirements
• Suitable for snow zones I - V with snow loads of 70-250 kg/m2
• High-quality and effective thermal insulation SG CombiRoof

COMBI ROOF Composition

• 6- Waterproofing
• 5- Separation membrane
• 4- Thermal insulation EPS (expanded polystyrene)
• 3- Thermal insulation MW (mineral wool boards)
• 2- Vapour barrier
• 1- Load-bearing trapezoidal sheet

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Soft PVC Waterproofing

In the system used by our company, we apply membrane systems based on soft PVC, e.g. SIKAPLAN, DEKPLAN, ALKORPLAN, etc. The lifespan of these systems depends on the location and is from 15 to 25 years or more. The membrane is mechanically fastened through the composition to the trapezoidal sheet, and the seams are welded using automatic welders or hand guns for details such as drains or parapets. If a DP1 construction part classification is required, we use a membrane suitable for fire hazardous areas with classification B ROOF (t3). The color of the membrane is usually grey, but other colors are available for an extra charge. The most common membrane thickness we use is 1.5 mm; for exposed areas with foot traffic, a thicker walkable membrane can be welded. For a 1.5 mm thick membrane, the surface weight is 1.85 kg/m². Application is done down to 5°C and up to a certain humidity as specified by the manufacturer.

Separation Membrane Flies

As a separation membrane, we use glass Flies 120 g. The separation layer serves to separate the soft PVC membrane from the polystyrene thermal insulation (EPS) to prevent migration of plasticizers and material damage.

EPS Slope Wedges

Slope wedges are used on flat roofs with a minimal slope to direct rainwater to skylights or drains, which can also be heated. In the COMBI ROOF system, we use polystyrene slope wedges. The most common are single-sided slope wedges with a slope of 0.5%, i.e. 1%, 1.5%, 2%, etc. If needed, wedges can be made up to 15%. For sloping valleys or transitions at parapets, single-sided slope wedges are used for EPS, and double-sided slope wedges are used if mineral wool boards (MW) are required.

Thermal Insulation EPS (Expanded Polystyrene)

EPS thermal insulation is the main component that provides the thermal value of the roof composition. It is produced in dimensions 2500 x 1000 mm in various thicknesses and strengths. Expanded polystyrene (EPS) is made by foaming solid beads, which increase their volume 20x to 50x. EPS is produced in various strengths: EPS 70, 100, 150, and 200.

Use according to EPS strength:

• EPS 70 (70 kPa) – can be used as a base layer only in the non-load-bearing bottom layer of the roof composition, the system is marked as 15M-i or 30M-i (15 or 30 is the fire resistance, -i means the use of EPS 70 and EPS 100). Bulk density is given as 13 – 18 kg/m³.
• EPS 100 (100 kPa) – used for standard stabilized roofs, i.e. suitable for regular roofs. The system is usually marked 15M or 30M. Bulk density is given as 18 – 23 kg/m³.
• EPS 150 (150 kPa) and 200 (200 kPa) – used for highly loaded roofs with high compressive stress, i.e. roof terraces, green roofs, etc. For EPS 150, bulk density is 23 – 28 kg/m³, for EPS 200 it is 28 – 35 kg/m³.

The thickness of the EPS determines the final thermal transmittance (U-value) of the hall roof. The composition is always made in 2 layers, so that the upper and lower joints do not align in both directions, with a minimum offset of 200 mm.

Table of thermal transmittance (U = W/m²K) incl. weight of each composition per m²

Note:

*The composition is considered for 30M and 30Mi: membrane – 1.5 mm 1.85 kg/m², glass Flies 120 g/m², EPS and MW as per composition (EPS 100 – 23 kg/m³, EPS 70 18 kg/m³ and MW 2x 30 mm 10.5 kg/m² at 175 kg/m³), vapour barrier 100 g/m² and load-bearing trapezoidal sheet CB 160/250/0.75 11.78 kg/m².
**The composition is considered for 15M and 15Mi: membrane – 1.5 mm 1.85 kg/m², glass Flies 120 g/m², EPS and MW as per composition (EPS 100 – 23 kg/m³, EPS 70 18 kg/m³ and MW 2x 20mm 7.0 kg/m² at 175 kg/m³), vapour barrier 100 g/m² and load-bearing trapezoidal sheet CB 160/250/0.75 11.78 kg/m².

Thermal Insulation MW (Mineral Wool Boards)

Thermal insulation from MW determines the final fire resistance of the roof composition, i.e. 15 to 30 minutes. The strength of mineral wool boards is 70 kPa and for Isover is marked ISOVER S or S-i. Insulation boards are always laid in 2 layers with offset joints in both directions by at least 200 mm. This is important for good distribution of point loads. Bulk density is given as 147 – 175 kg/m³.

Mineral wool boards are used:

• 2x 20 mm for fire resistance RE 15 DP1 (rarely used due to installation issues)
• 2x 30 mm for fire resistance RE 30 DP1

Vapour Barrier

The vapour barrier prevents moisture from penetrating the roof envelope composition and prevents degradation of the thermal and physical properties of the composition. The vapour barrier is placed on the trapezoidal sheet and does not affect the final fire resistance.

Types of vapour barriers:

• PE vapour barrier
• Self-adhesive vapour barrier

PE vapour barrier, most commonly 0.2 mm thick, is laid loose on the trapezoidal sheet and is most commonly used for non-demanding buildings where no additional moisture is generated inside, such as warehouses or other dry production halls. To meet DP1 classification, the vapour barrier must not exceed 2 mm thickness, and the joints must be taped with original tape suitable for PE membrane joints on flat roofs.
Self-adhesive vapour barrier, e.g. Vedagard, is then cold-applied directly onto the trapezoidal sheet. The advantage is high vapour tightness, it additionally insulates the roof before the final completion of the standing seam roof composition, is resistant to foot traffic and airtight thanks to taped joints (8 cm). For coated sheets, no prior priming is needed, for galvanized sheets, priming is required. At temperatures below 5°C, the self-adhesive layer must be heated with a flame.

Trapezoidal Sheet

The trapezoidal sheet is the final component of this composition, forming the load-bearing element of the standing seam roof system. The minimum thickness of the sheets must be 0.75 mm.

The following types of sheets are used:

• Self-supporting trapezoidal sheets with high ribs 135 to 160 mm
• Non-self-supporting trapezoidal sheets with ribs 45 to 60 mm

Self-supporting trapezoidal sheets are most commonly used because no auxiliary structures (so-called purlins) are needed. The sheet is mounted on a steel or concrete structure on individual frames/purlins, usually with a module of 5 – 7 m. According to the span, snow load, and technology, the supplier of trapezoidal sheets will size the type and thickness of the sheet. They are designed as single-span or double-span (i.e. over 2 modules). The length of the sheet is limited only by transport possibilities, so they are designed up to a length of 13.5 m.
The sheets are designed in the following thicknesses: 0.75 mm, 0.88 mm, 1.0 mm, 1.13 mm, 1.25 mm, and in extreme cases 1.5 mm.

Types of self-supporting sheets we use:

• CB 135/310 developed width 930 mm
• CB 150/280 developed width 840 mm – most commonly used
• CB 150/290 developed width 870 mm
• CB 160/250 developed width 750 mm – most commonly used

Non-self-supporting trapezoidal sheets must be supplemented with a secondary structure, most often METSEC purlins. They are used for more complex roofs where it is economically worthwhile to add a secondary structure.
The sheets are designed in the following thicknesses: 0.75 mm, 0.88 mm, and a maximum of 1.0 mm.

Types of non-self-supporting sheets we use:

• CB 45/333 developed width 1000 mm
• CB 50/260 developed width 1040 mm
• CB 55/250 developed width 1000 mm – most commonly used
• CB 60/235 developed width 940 mm

Table of weights of trapezoidal sheets per m²

* trapezoidal sheets with thickness 0.5 and 0.63 mm do not meet the requirements for COMBI ROOF 15 DP1 and 30 DP1, the minimum sheet thickness is 0.75 mm or higher

CB Profile Trapezoidal Sheets