Powerroof system
1. Traditional method
2. 'Sarking'-system
1. The Powerroof-board
2. Installation
1. Drain connections
2. Roof ridge joints
3. Chimney joints
4. Skylight joints
5. Roof edge
6. Wall joints
7. Fixation of solar panels
- In the traditional method (see fig. 1) insulation is generally positioned between the load bearing structure.
- The insulation material, usually mineral wool, is installed between the trusses or beams of the roof where they always form a potential cold bridge. On the one hand, because of the low insulating capacity of wood (see the table) and on the other hand because correct positioning of the insulation between trusses or beams with irregular spaces between them is sometimes more difficult than it would appear at first sight.
- This results in the insulation barrier not being continuous, which can lead to cold bridges that in the course of time even have an effect on the interior finish of the roof.
- Moreover, under the insulation an additional air and vapour barrier must be installed, otherwise there is a chance that condensation will occur in the structure and that the heat losses increase due to air leaks.
- Insulation below the roof is done after sealing the roof. Because of this, the work is generally carried out in a badly ventilated, closed attic space as a result of which the body is exposed to rather commonly irritating fibres.
- In any case, an insulation must be chosen that does not sag due to the daily vibration of the building
Fig. 1: traditional method
1. Roof tile
2. Batten
3. Batten strip
4. Lower roof
5. Truss
6. Roofinsulation
7. Air and vapour barrier
Table: thickness required (mm) for RC-value of 2,5 m2K/W
| λ-value | Thickness required | |
| POWERROOF | 0,024 W/mK | 60 mm |
| POLYURETHANE* | 0,028 W/mK | 70 mm |
| EPS* | 0,040 W/mK | 100 mm |
| MINERAL WOOL* | 0,040 W/mK | 100 mm |
| WOOD* | 0,120 W/mK | 300 mm |
* value NBN B65-002
- The POWERROOF insulation boards are attached on top of the load bearing structure.
- A major advantage of this method is that the well-known problems of a traditional method can be avoided.
- Even with irregular spaces between trusses and beams, this method of working ensures the continuity of the insulation barrier, which excludes cold bridges.
Fig. 2: 'SARKING' system
1. Batten
2. Batten strip
3. RECTIVENT roof underlay foil
4. POWERROOF roof insulation
5. Truss
6. Foil (for making airtight)
- Of course proper installation remains essential.
- Moreover, the SARKING system means an extra thermal protection for the load bearing elements of the roof. These are insulated in the same way as the rest of the house.
- With this method, the insulation material must satisfy a few requirements:
• Stability: avoid unacceptable bending of the insulation material
• Compressive strength: prevent unacceptable compression as a result of the roof loads (tiles, snow, wind)
• Heat resistance: sufficiently high heat resistance (R) or low lambda value (λ).
A material that satisfies these requirements without any problems is POWERROOF, especially because of its:
- resistance to humidity and dimensional stability
- high compressive strength (on average 1.5 kg/cm2 with 10% distortion)
- low lambda value (0.024 W/mK)
- tongue and groove joints
- waterproof top layer with RECTIVENT type overlap
- improved air tightness - > tongue and groove joints all round
(if necessary the joints can also be taped or sealed with a kit)
1. The POWERROOF – board (see fig. 3)
- POWERROOF has been specially developed for the insulation of pitched roofs with the Sarking system.
- POWERROOF is a board with a core of Recticel Taufoam, a new and improved PIR foam (polyisocyanurate foam), held on both sides with lightly pleated aluminium foil (thickness 50 µ).
- The Recticel Taufoam has an improved fire response; A1 according to RD 19/12/1997.
- On top of the Powerroof board, a waterproof but vapour permeable RECTIVENT roof underlay foil is installed. This foil serves as a roof underlay on top of the insulation. This quickly creates a waterproof protection for the structure. The POWERROOF board therefore serves as insulation and a roof underlay at the same time.
- The board also has tongue and groove joints, which ensure the continuity of the insulation barrier and avoids any resulting condensation problems.
- The board comes in standard 60, 80 or 100 mm thicknesses. Dimensions: 1200 mm x 2500 mm.
Fig. 3
- Thanks to the excellent insulation value of POWERROOF, a maximum of insulation and comfort can be realised with a minimum thickness.
- To achieve the higher insulation requirements, more important thicknesses are available on order.
| RD-VALUE | |
| POWERROOF 60mm | 2,50 m2 K/W |
| POWERROOF 80mm | 3,30 m2 K/W |
| POWERROOF 100mm | 4,15 m2 K/W |
POWERROOF insulation boards are extremely light: 6 to 7 kg per board, depending on the insulation thickness.
2.1. Method of fixation
- The fixation of the batten strips through the insulation boards to the underlying roof structure is done with a combination of screws placed perpendicular and at an angle of 67° with respect to the roof surface. This fixation pattern stops the elements being lifted by the wind and sliding.
- The choice of the type of screw and the fixation pattern are determined by the parameters specified here.. For pre-drilling the batten strips at an angle of 67° and 90°, you can order a drill gauge from Recticel Insulation.
- Screws:
Insulation thickness 60 mm = screw 6 x 160 mm
Insulation thickness 80 mm = screw 6 x 180 mm
Insulation thickness 100 mm = screw 6 x 200 mm
Type: ABC - spax Torx
1. Batten strip
2. POWERROOF insulation
3. Foot beam
4. Truss
5. Foil (for making airtight)
2.2. Fixation pattern
The parameters described below are considered for the determination of the number and length of the screws and the space between them.
Calculation parameters for the load transfer to the underlying roof structure:
- Base force area I and II
- Snow load: 750 N/m2 (75 kg/m2)
- Roof covering weight: 550 N/m2 (55 kg/m2 = tiles and battens)
- Batten strip dimensions: 32x36 mm
- Pitched roof between 25° and 60°
- Distance between trusses: 50 cm
- Pre-drilled battens (prevents splitting and give the correct position with respect to the trusses, this is done with the gauge supplied).
1. Definitive edge zone:
To simplify the work and avoid complicated calculations at the building site, the decision has been taken to work with a general edge and corner zone of 2 m. This includes a wide safety margin.
2. Perpendicular screws (intermediate position) of which the first screw is 40 cm from the foot beam.
| Area I | Area II | |
| Middle zone | 0,9 m | 1 m |
| Edge zone | 0,6 m | 0,7 m |
3. Screws at an angle 67° (intermediate position), the first screw of which is in the foot beam.
| Pitch | Area I | Area II |
| 25° - 40° | 1,75 m | 1,75 m |
| 45° - 50° | 1,50 m | 1,50 m |
| 55° - 60° | 1,25 m | 1,25 m |
1. Batten strip
2. POWERROOF insulation
3. Foot beam
4. Truss
5. Foil (for making airtight)
2.3. Practical implementation
- A foil is placed on the trusses to ensure air tightness.
- Underneath the roof structure a beam (foot beam) is screwed to the trusses parallel to the roof ridge. The thickness of this beam corresponds to the thickness of the POWERROOF board used. The first board is positioned against this. In most cases this beam will also act as a fixation zone for the roof drainage systems.
- If the roof has a large, uninsulated overhang, this part can be equipped with beams that are nailed to the trusses so that the same thickness of the insulation layer is obtained.
- Before starting the work, the contractor must first determine his exact starting point to avoid unnecessary cutting of the boards afterwards at the roof ridge and avoid roof overhangs.
- The POWERROOF boards are attached to the load bearing structure horizontally, working from the foot beam towards the roof ridge. The POWERROOF boards are therefore laid from left to right. The length of the first board is chosen according to the total width of the roof to be insulated, so that small pieces at the end are avoided. The vertical joints between the boards do not require support.
- The POWERROOF boards can easily be cut with an ordinary saw. The bottom lip of the lay of the first row of Powerroof boards is cut off with a knife so that they are completely flush with the starting beam. Moreover the overlap of the roof underlay foil ensures that the sealing of this joint is watertight.
- The first two rows of POWERROOF boards are preferably laid first and then the RECTIVENT roof underlay foil. The RECTIVENT is rolled out over the Powerroof boards.
- The complete assembly is attached by means of the batten strips.
- The roof underlay foil ensures that both the horizontal and vertical joints are covered, so that the roof is waterproof after installing the insulation system.
- The tongue and groove system ensures that the POWERROOF boards are more airtight.
- At roof interruptions, chimneys, skylights, edge channels etc., the interruptions must be finished in the roof underlay foil so that they are waterproof and airtight, see the implementation details for this.
- Pre-drilling of the batten strips is done with a drill gauge, this has been designed so that when using 30 mm x 50 mm batten strips the holes drilled perpendicularly and at an angle of 67° are positioned in the centre of the batten strip. If the dimensions of the batten strips differ, it is advisable to adjust the gauge to ensure that the holes are also made in the centre of the batten strip. Centring the holes in the batten strip ensures that the screws will also be in the centre of the trusses and beams as much as possible afterwards.
2.4. Wood details
2.4.1. Tile battens
The thickness of the tile battens depends on the distance between the beams and trusses, on the type of tile or slate and on the pitch of the roof. Use of POWERROOF boards does not require a more important thickness of tile batten than a traditional construction. Nailing the batten strips to the tile battens is also done in the same way.
2.4.2. Batten strips
The selection of the batten strips is made on the basis of the following criteria:
- sufficient thickness since the tile battens are attached to the batten strips.
- sufficient width so that they do not split when nailed.
These criteria produce the following acceptable dimension, namely: 30 mm x 50 mm
Exemple Pre-drilling with a drill gauge.
Screwing the system.
C. Implementation details
1.1. Hanging drain without an overhang
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1. Roof covering |
1.2. Hanging drain in a low energy house
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1. Roof covering |
1.3. Hanging drain in a low energy hous (bigger insulation thickness)
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1. Roof covering |
1.4. Hanging drain with insulated overhang
1.5. Gutter with uninsulated overhang
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1. Roof covering |
1.6. Gutter
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1. Roof covering |
1.7. Edge channels
The POWERROOF panels are bevelled off at the edge channel. The space created is filled with PUR foam. Parallel with the edge channel, two tile battens (5) are nailed to the underlying truss. The zinc covering (4) is laid between these battens. A kit or self-adhesive tape (6) is applied to the battens. Between the POWERROOF board roof underlay foils (7), a strip of foil (8) is applied that passes under the channel and connects with the opposite POWERROOF boards..
1. Roof covering
2. Batten strip
3. Batten
4. Gutter
5. Retainer batten
6. Sealing strip or kit
7. RECTIVENT roof underlay foil
8. Foil
9. POWERROOF roof insulation
7. + 9. POWERROOF-system
10. PUR foam filler
11. Edge channel beam
12. Truss beam
13. Foil (for making airtight)
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1. Edge channel |
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2.1. Roof ridge in mortar
At the roof ridge, the POWERROOF boards are bevelled off according to the angle of the pitch of the roof. Any seams or openings at the runner are filled with PUR foam.
After smoothing off the PUR foam and before attaching the batten strips, a strip of underlay foil is placed over the join.
1. Roof ridge tile
2. Mortar
3. Roof tile
4. Batten
5. Batten strip
6. RECTIVENT strip
7. Foam filler
8. RECTIVENT roof underlay foil
9. POWERROOF roof insulation
8. + 9. POWERROOF-system
10. Truss
11. Roof ridge beam
12. Foil (for making airtight)
2.2. Dry installation
1. Roof ridge tile
2. Runner
3. Roof ridge profile
4. Roof tile
5. Batten
6. Batten strip
7. RECTIVENT strip
8. Foam filler
9. RECTIVENT roof underlay foil
10. POWERROOF roof insulation
9. + 10. POWERROOF-system
11. Truss
12. Roof ridge beam
13. Foil (for making airtight)
When flue elements are used in a chimney, polyurethane foam aerosols can be used for the POWERROOF board - chimney join. If this is not the case then a strip of mineral wool must be used here.
A lead flashing and collar is used for the join between the chimney and the tiles (slates).
Above the chimney the water from the roof above is drained via a diagonal batten strip past the chimney opening. The upper part of the facing batten is sealed with a kit or a sealing strip is applied. Under this batten and parallel with the chimney, the secondary battens ensure that water is led past the opening.
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1. Facing brick 4. Open butt joint |
1. Batten strips 2. POWERROOF-system 3. Auxiliary tile 4. Water barrier 5. Chimney opening |
4. Skylight joints
When flat skylights are used, the extra thickness of the insulation material must be taken into account. The roof window must therefore be raised by means of support beams. The top surface of these beams must be roughly level with the upper surface of the POWERROOF boards.
Above the flat skylight the water from the roof above is drained past the window by a sloping batten strip.
The upper part of the facing batten is sealed with a kit or a sealing strip is applied. Under this batten and parallel with the window, the secondary battens ensure that the water is led past the opening.
| 1. Batten strips 2. POWERROOF-system 3. Auxiliary tile 4. Water barrier 5. Skylight opening |
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1. Window frame
2. Roof tile
3. Protective strip
4. Foam seal + tile support
5. Batten
6. Batten strip
7. Lead flashing
8. Insulating block
9. Water barrier
10. RECTIVENT roof underlay foil
11. POWERROOF roof insulation
10. + 11. POWERROOF-system
12. Plank roof structure
13. Truss
14. Interior finishing
15. PUR foam filler
16. Foil (for making airtight)
5.1. Long cross-section roof edge with overlap
1. Lead flashing
2. Roof tile
3. Batten
4. Batten strip
5. RECTIVENT roof underlay foil
6. POWERROOF roof insulation
5. + 6. POWERROOF-system
7. Construction battens
8. Storm plank
9. Truss
10. Finishing planks
11. Truss reinforcement
12. Facing brick
13. Partial cavity insulation with EUROWALL
14. Load bearing wall
15. PUR foam filler
16. Kit
17. Plaster
18. Foil (for making airtight)
5.2. Long cross-section roof edge with edging tile
1. Roof tile
2. Fascia board
3. Mortar
4. Batten
5. Batten strip
6. Waterproof membrane
7. RECTIVENT roof underlay foil
8. POWERROOF roof insulation
7. + 8. POWERROOF system
9. Truss
10. Load bearing wall
11. Partial cavity insulation with EUROWALL
12. Facing brick
13. PUR foam filler
14. Kit
15. Plaster
16. Foil (for making airtight)
6. Wall joints
6.1. Wall joints with or without covered gutter
1. Load bearing wall
2. Partial cavity insulation with EUROWALL
3. Facing brick
4. Window opening
5. Covered gutter
6. Flashing
7. Roof tile
8. Batten
9. Batten strip
10. RECTIVENT roof underlay foil
11. POWERROOF roof insulation
10. + 11. POWERROOF-system
12. Truss
13. Insulating block
14. Plaster
15. Kit
16. Foil (for making airtight)
17. PUR foam filler
For the installation instructions for solar panels, refer to the manufacturers of the solar panels.
Some solar panels are incorporated into the roof, as a result of which tiles are replaced with a series of solar panels. There must be sufficient ventilation under the solar panels.
The installation instructions for the Powerroof system do not change.
