• U value guide.
• Insulation suggestions and advice.
• Airtight advice.
• Ventilation advice.
• Site visits and inspections.
• Insulation and associated building material product training available on site or at our premises.

Insulating the ROOF RAFTERS sloping ceilings

Pitch Roof Type 1: Ventilated roof.

High performance glasswool insulation roll or batt applied Partially Filling the roof rafters Plus Insulated plasterboards fixed below the roof rafters.

Pitch Roof Type 2: Un-Ventilated roof.

High performance glasswool insulation roll or batt applied Filling the roof rafters Plus Insulated plasterboards fixed below the roof rafters. Timber counter battens applied above the breathable roofing underlay.

Pitch Roof Type 3: Ventilated roof.

High performance glasswool insulation roll or batt applied Partially Filling the roof rafters Plus High performance glasswool insulation roll or batt applied below the roof rafters between timber counter battens.

The Roof Build-up for Pitch Roof Type 1.

7: Roof tile or slate.

6: Roof tile battens.

5: Rothoblaas Traspir 150 R breathable roofing underlay draped over the roof rafters.

4: Crossflow ventilated airspace.

3: High performance glasswool insulation roll or batt applied partially filling the roof rafters.

2: Rothoblaas Vaporvlies 120 airtight membrane taped and sealed below the roof rafters.

1: PIR Insulated plasterboards fixed below the roof rafters.

Educate to Insulate:

NOTE: The crossflow ventilated airspace (4) above the insulation layer (3) and below the breathable roofing underlay (5) is key to a healthy roof.

Ventilation of the roof is important to ensure that moisture can dissipate freely from the roof structure. Over time condensed trapped moisture will cause damage to timber roof rafters if drying or removal of moisture is obstructed.

NOTE: For the purpose of calculating the U value for roof type 1: we apply a crossflow ventilated airspace.(4)

NOTE: U value calculation results identifying the airspace between the insulation layer (3) and breathable roofing underlay (5) as partially ventilated or un ventilated are commonly applied to U value calculations to improve the U value result.

NOTE: An un ventilated airspace can only be achieved between the insulation layer (3) and the underside of the breathable roofing underlay (5) where the breathable roofing underlay is totally sealed at all overlaps, joints, penetrations and abutments.

Sealing the breathable roofing underlay is not common practice on Irish or UK building sites.

In most cases the airspace (4) will be crossflow ventilated. As for partially ventilated air spaces the question has to be; is it a ventilated air space or a true unventilated air space?  Is the window open or is the window closed; you decide.

The Roof Build-up for Pitch Roof Type 2.                   (insulation filling the roof rafters)

7: Roof tile or slate.

6: Roof tile battens.

5: Timber counter battens.

4: Rothoblaas Traspir 150 R breathable roofing underlay applied over the roof rafters.

3: High performance glasswool insulation roll or batt applied filling the roof rafters.

2: Rothoblaas Clima Control 80 airtight membrane taped and sealed below the roof rafters.

1: PIR Insulated plasterboards fixed below the roof rafters.

Educate to Insulate:

NOTE: When fully filling the roof rafters with high performance glasswool insulation; timber counter battens are highly recommended applied above the breathable roofing underlay. This is especially important where fibre cement slates are applied as the finished roof covering.

Timber counter battens will ensure that there is adequate ventilation between the topside of the breathable roofing underlay and the underside of the fibre cement slates.

Wind driven rain and snow must run freely of the roof.

If we fully fill the roof rafters with high performance glasswool insulation we can unintentionally create an opportunity for rain water or wind driven snow to become trapped between the roof tile battens and the breathable roofing underlay. It is not uncommon in Ireland and the UK to experience high levels of wind driven rain and, in many cases, horizontal wind driven rain.

NOTE: When fully filling the roof rafters with high performance glasswool insulation it is also important that we select and apply the most suitable airtight/vapour control membrane. Rothoblaas Clima Control 80 airtight membrane is a variable sd membrane. (Variable sd airtight membranes are often referred to as intelligent airtight membranes)

A condensation risk analysis is advised when considering fully filling the roof rafters with insulation. (all insulation types)

NOTE: For the purpose of calculating the condensation risk analysis the foil facing on the reverse side of insulated plasterboards or standard plasterboards should not be considered a vapour control layer as the board joints, penetrations and abutments cannot be adequately sealed to form a seamless vapour control layer.

Roof Build-up for Pitch Roof Type 3.

9:  Roof tile or slate.

8:  Roof tile battens.

7:  Rothoblaas Traspir 150 R breathable roofing underlay.

6:  Crossflow ventilated airspace.

5:  High performance glasswool insulation roll or batt applied partially filling the roof rafters.

4:  Rothoblaas Vaporvlies 120 airtight membrane.

3:  50mm High performance glasswool insulation roll or batt applied between timber counter battens.

2:  Timber Counter battens.

1:  Plasterboard.

Educate to Insulate:

Glasswool Insulation - Thermal Conductivity

For the purpose of calculating the U values in this insulation guide the high performance glasswool insulation rolls or batts that are applied between the roof rafters have a thermal conductivity of 0.034 W/mK and the high performance glasswool insulation rolls or batts that are applied between timber battens below the roof rafters have a thermal conductivity of 0.035 W/mK

PIR Insulated Plasterboards - Thermal Resistance Guide

PIR = Polyisocyanurate foam insulation.

The thermal resistance is calculated to include the insulation and the 12.5mm plasterboard

Insulated Plasterboard Thickness             Overall Thermal Restance

37.5mm                                                                   1.205 m²K/W

42.5mm                                                                   1.430 m²K/W

50.5mm                                                                   1.793 m²K/W

52.5mm                                                                   1.884 m²K/W

62.5mm                                                                   2.339 m²K/W

72.5mm                                                                   2.793 m²K/W

82.5mm                                                                   3.248 m²K/W

92.5mm                                                                   3.702 m²K/W

Educate to Insulate:

• Not all breathable roofing underlays are the same.
• Not all airtight membranes are the same.
• Trapped condensation can destroy timber building materials.
• Ventilation and quality installations is the key to a healthy home.

Understand the Product Not the Brand…..

Natural Building Materials

Timber roof rafters are natural building materials and will continue to expand and contract over the entire life time of the building.

Choosing flexible high performance glasswool insulation materials can make it easier to ensure a snug sustainable fit between the insulation layers and the sides of the roof rafters.

A snug fit reduces the risk of cold air moving from the ventilated airspace above the insulation layer into the warm side (inside) of the roof.

A snug fit is easily achieved by cutting the high performance glasswool insulation slightly oversize and compression fitting between the roof rafters.

High performance glasswool insulation will not slump between the roof rafters when applied compression fitted.

High performance glasswool insulation is vapour permeable and fire safe. Fire classification A1 Non-Combustible and will also provide a level of sound reduction from external noise intrusion.

Airtight membranes when applied correctly will reduce heat loss by restricting the movement of air and also provide protection against moisture damage.

Breathable roofing underlays when applied correctly will provide protection against moisture damage and water ingress.

Eaves trays are recommended applied to the roof rafter feet. Eaves trays will provide additional protection to the roof rafter feet from water damage and can also protect the visible ends of the breathable roofing underlay from damage through ultra-violate light.

Insulation that is installed correctly provides protection from the cold in winter, protection from the heat in summer and contributes to reducing fuel bills.

Key words: Protection and applied correctly………

Technical Support

U Value calculations to include the insulation layers, breathable roofing underlay and airtight membrane options are available upon request; the following information is required.

Q. What type of roof tile or slate are you applying?

Is it a concrete tile, a clay tile, a natural slate or fibre cement slate?

The answer to this question will determine the most suitable insulation type and identify any additional ventilation that may be required.  

Q. What type of roofing underlay are you applying over the roof rafters?

Is it a high performance LR (low resistance) breathable underlay?

Q. What is the total depth of the roof rafters?

Are they 125mm, 150mm, 175mm, 225mm or other?

The answer to this question will determine the insulation space available between the roof rafters.

NOTE: Existing roof rafters: Roof rafters can be extended using internal timber counter battens to increase the insulation space.

Q. What is the spacing/centers between the roof rafters?

Are they 400mm centres, 600mm centres or other? The answer to this question will determine the thermal bridging factor.

Q. Are you applying an airtight membrane below the roof rafters?

Yes, is the best option, airtightness helps to reduce heat loss. An airtight membrane is also considered a vapour check or vapour control layer.

Q. Are you applying insulated plasterboards below the roof rafters?

Yes, is the best option, the insulated plasterboards will help reduce thermal bridging and improve the overall U value result.

Note: Existing roof rafters.

When insulating older existing roof rafters, the roofing underlay will generally be of a non-breathable type? A 50mm crossflow ventilated air space must be maintained between a non-breathable roofing underlay and the insulation applied between the roof rafters.

Alternatively, the existing roofing underlay may be removed and replaced with a high-performance breathable roofing underlay.

Where the pitch roof is insulated at rafter level building regulations clearly identifies a 50mm crossflow ventilated air space below the breathable and non-breathable roofing underlays.

Building professionals, architects and assigned certifiers will generally accept a reduced depth for the crossflow ventilated airspace where 1; a high-performance breathable roofing underlay is applied over the roof rafters and 2; a condensation risk analysis is provided identifying ZERO condensation risk.

Educate to Insulate

The U value Results - Pitch Roof Type 1

In this section there are four insulation thickness options available for the insulation materials applied between the roof rafters.

1. 100mm
2. 150mm
3. 180mm
4. 220mm

Included in the U value Guide; is breathable roofing underlay and airtight membrane suggestions and PIR insulated plasterboards; thicknesses ranging from 37.5mm to 92.5mm

Pitch Roof Type 1; Option 1

• The insulation thickness applied between the roof rafters is 100mm

Roof Build-up;

7:  Roof tile or slate.

6:  Roof tile battens.

5:  Rothoblaas Traspir 150 R breathable roofing underlay.

4:  Crossflow ventilated airspace.

3:  100mm Knauf Earthwool OmniFit Stud Roll 34 applied partially filling the roof rafters.

2:  Rothoblaas Vaporvlies 120 airtight membrane taped and sealed below the roof rafters.

1:  37.5mm PIR Insulated plasterboards fixed below the roof rafters.

U-value (rounded) 0.26 W/m²K

To improve the U value result for the roof type and build up identified above increase the insulated plasterboard thickness applied below the roof rafters to;

Insulated plasterboard thickness                 Thermal resistance                        U-value (rounded)

                  42.5mm                                          1.430 m²K/W                                   0.25 W/m²K

                  50.5mm                                          1.793 m²K/W                                   0.23 W/m²K

                  52.5mm                                          1.884 m²K/W                                   0.22 W/m²K

                  62.5mm                                          2.339 m²K/W                                   0.20 W/m²K

                  72.5mm                                          2.793 m²K/W                                   0.19 W/m²K

                  82.5mm                                          3.248 m²K/W                                   0.17 W/m²K

                  92.5mm                                          3.702 m²K/W                                   0.16 W/m²K

• Minimum roof rafter depth. 125mm
• Minimum crossflow ventilated airspace. 25mm
• Roof rafter centres. 400mm
• Insulation type and thermal conductivity in layer 3, High performance glasswool insulation roll with a thermal conductivity of not less than. 0.034 W/mK
• PIR Insulated plasterboard thermal resistance guide. (see below)
• Roof rafter centres set at 600mm will show a marginal improvement on the U value result.

Rothoblaas Vaporvlies 120 (layer 2) is a fixed sd airtight membrane and is suitable for ventilated roof spaces.

The brand of the high performance glasswool insulation roll 34 (layer 3) is not important. If the insulation is the same thickness and has a thermal conductivity of 0.034 W/mK or better you will achieve at least the same result. The brand of the PIR insulated plasterboard is not important (layer 1). If the overall thermal resistance for the PIR insulated plasterboard is the same or better you will achieve at least the same result.

Rothoblaas Traspir 150 R is a high-performance breathable roofing underlay.

Pitch Roof Type 1; Option 2

The insulation thickness applied between the roof rafters is 150mm

Roof Build-up;

7:  Roof tile or slate.

6:  Roof tile battens.

5:  Rothoblaas Traspir 150 R breathable roofing underlay.

4:  Crossflow ventilated airspace.

3:  150mm Knauf Earthwool OmniFit Stud Roll 34 applied partially filling the roof rafters.

2:  Rothoblaas Vaporvlies 120 airtight membrane taped and sealed below the roof rafters.

1:  37.5mm PIR Insulated plasterboards fixed below the roof rafters.

U-value (rounded) 0.20 W/m²K

To improve the U value result for the roof type and build up identified above increase the insulated plasterboard thickness applied below the roof rafters to;

Insulated plasterboard thickness                 Thermal resistance                        U-value (rounded)         

                  42.5mm                                          1.430 m²K/W                                   0.19 W/m²K

                  50.5mm                                          1.793 m²K/W                                   0.18 W/m²K

                  52.5mm                                          1.884 m²K/W                                   0.18 W/m²K

                  62.5mm                                          2.339 m²K/W                                   0.16 W/m²K

                  72.5mm                                          2.793 m²K/W                                   0.15 W/m²K

                  82.5mm                                          3.248 m²K/W                                   0.14 W/m²K

                  92.5mm                                          3.702 m²K/W                                   0.13 W/m²K

• Minimum roof rafter depth. 175mm
• Minimum crossflow ventilated airspace. 25mm
• Roof rafter centres. 400mm
• Insulation type and thermal conductivity in layer 3, High performance glasswool insulation roll with a thermal conductivity of not less than. 0.034 W/mK
• PIR Insulated plasterboard thermal resistance guide. (see opposite page)
• Roof rafter centres set at 600mm will show a marginal improvement on the U value result.

Rothoblaas Vaporvlies 120 (layer 2) is a fixed sd airtight membrane and is suitable for ventilated roof spaces.

The brand of the high performance glasswool insulation roll 34 (layer 3) is not important. If the insulation is the same thickness and has a thermal conductivity of 0.034 W/mK or better you will achieve at least the same result. The brand of the PIR insulated plasterboard is not important (layer 1). If the overall thermal resistance for the PIR insulated plasterboard is the same or better you will achieve at least the same result.

Rothoblaas Traspir 150 R is a high-performance breathable roofing underlay.

Pitch Roof Type 1; Option 3

The insulation thickness applied between the roof rafters is 180mm

Roof Build-up;

7:  Roof tile or slate.

6:  Roof tile battens.

5:  Rothoblaas Traspir 150 R breathable roofing underlay.

4:  Crossflow ventilated airspace.

3:  180mm Knauf Earthwool OmniFit Stud Roll 34 applied partially filling the roof rafters.

2:  Rothoblaas Vaporvlies 120 airtight membrane taped and sealed below the roof rafters.

1:  37.5mm PIR Insulated plasterboards fixed below the roof rafters.

U-value (rounded) 0.18 W/m²K

To improve the U value result for the roof type and build up identified above increase the insulated plasterboard thickness applied below the roof rafters to;

Insulated plasterboard thickness                 Thermal resistance                        U-value (rounded)         

                  42.5mm                                          1.430 m²K/W                                   0.17 W/m²K

                  50.5mm                                          1.793 m²K/W                                   0.16 W/m²K

                  52.5mm                                          1.884 m²K/W                                   0.16 W/m²K

                  62.5mm                                          2.339 m²K/W                                   0.15 W/m²K

                  72.5mm                                          2.793 m²K/W                                   0.14 W/m²K

                  82.5mm                                          3.248 m²K/W                                   0.13 W/m²K

                  92.5mm                                          3.702 m²K/W                                   0.12 W/m²K

• Minimum roof rafter depth. 205mm
• Minimum crossflow ventilated airspace. 25mm
• Roof rafter centres. 400mm
• Insulation type and thermal conductivity in layer 3, High performance glasswool insulation roll with a thermal conductivity of not less than. 0.034 W/mK
• PIR Insulated plasterboard thermal resistance guide. (see opposite page)
• Roof rafter centres set at 600mm will show a marginal improvement on the U value result.

Rothoblaas Vaporvlies 120 (layer 2) is a fixed sd airtight membrane and is suitable for ventilated roof spaces.

The brand of the high performance glasswool insulation roll 34 (layer 3) is not important. If the insulation is the same thickness and has a thermal conductivity of 0.034 W/mK or better you will achieve at least the same result. The brand of the PIR insulated plasterboard is not important (layer 1). If the overall thermal resistance for the PIR insulated plasterboard is the same or better you will achieve at least the same result.

Rothoblaas Traspir 150 R is a high-performance breathable roofing underlay.

Pitch Roof Type 1; Option 4

The insulation thickness applied between the roof rafters is 220mm

Roof Build-up;

7:  Roof tile or slate.

6:  Roof tile battens.

5:  Rothoblaas Traspir 150 R breathable roofing underlay.

4:  Crossflow ventilated airspace.

3:  220mm Knauf Earthwool OmniFit Stud Roll 34 applied partially filling the roof rafters.

2:  Rothoblaas Vaporvlies 120 airtight membrane taped and sealed below the roof rafters.

1:  37.5mm PIR Insulated plasterboards fixed below the roof rafters.

U-value (rounded) 0.15 W/m²K

To improve the U value result for the roof type and build up identified above increase the insulated plasterboard thickness applied below the roof rafters to;

Insulated plasterboard thickness                 Thermal resistance                        U-value (rounded)         

                  42.5mm                                          1.430 m²K/W                                   0.15 W/m²K

                  50.5mm                                          1.793 m²K/W                                   0.14 W/m²K

                  52.5mm                                          1.884 m²K/W                                   0.14 W/m²K

                  62.5mm                                          2.339 m²K/W                                   0.13 W/m²K

                  72.5mm                                          2.793 m²K/W                                   0.12 W/m²K

                  82.5mm                                          3.248 m²K/W                                   0.12 W/m²K

                  92.5mm                                          3.702 m²K/W                                   0.11 W/m²K

• Minimum roof rafter depth. 245mm
• Minimum crossflow ventilated airspace. 25mm
• Roof rafter centres. 400mm
• Insulation type and thermal conductivity in layer 3, High performance glasswool insulation roll with a thermal conductivity of not less than. 0.034 W/mK
• PIR Insulated plasterboard thermal resistance guide. (see opposite page)
• Roof rafter centres set at 600mm will show a marginal improvement on the U value result.

Rothoblaas Vaporvlies 120 (layer 2) is a fixed sd airtight membrane and is suitable for ventilated roof spaces.

The brand of the high performance glasswool insulation roll 34 (layer 3) is not important. If the insulation is the same thickness and has a thermal conductivity of 0.034 W/mK or better you will achieve at least the same result. The brand of the PIR insulated plasterboard is not important (layer 1). If the overall thermal resistance for the PIR insulated plasterboard is the same or better you will achieve at least the same result.

Rothoblaas Traspir 150 R is a high-performance breathable roofing underlay.

Educate to Insulate - People fail products; products do not fail people.....

• A U value calculation is a paper exercise, If you wan't the best results choose the correct insulation type and associated building materials to suit the construction project.
• To insulate is to protect.
• Radon barriers protect.
• Fire barriers protect.
• Vapour control/airtight membranes protect.
• Breathable roofing membranes protect.
• Ventilation protects.

If you don’t apply and inspect the installation of all products or systems mentioned above; don’t expect the best results.

Thermal insulation, acoustic insulation, firestopping insulation, ventilation, breathability and airtight systems are inextricability linked.

A good building specification provides protection and will assist the builder in achieving the best results and a healthy home.

Educate to Insulate

The U value Results - Pitch Roof Type 2

In this section there are three insulation thickness options available for the insulation materials applied between the roof rafters.

1. 150mm
2. 180mm
3. 220mm

Included in the U value Guide; is breathable roofing underlay and airtight membrane suggestions and PIR insulated plasterboards; thicknesses ranging from 37.5mm to 92.5mm

Pitch Roof Type 2; Option 1

The insulation thickness applied between the roof rafters is 150mm

Roof Build-up;

7:  Roof tile or slate.

6:  Roof tile battens.

5:  Timber counter battens applied above the breathable roofing underlay.

4:  Rothoblaas Traspir 150 R breathable roofing underlay.

3:  150mm Knauf Earthwool OmniFit Stud Roll 34 applied filling the roof rafters.

2:  Rothoblaas Clima Control 80 airtight membrane taped and sealed below the roof rafters.

1:  37.5mm PIR Insulated plasterboards fixed below the roof rafters.

 U-value (rounded) 0.20 W/m²K

To improve the U value result for the roof type and build up identified above increase the insulated plasterboard thickness applied below the roof rafters to;

Insulated plasterboard thickness                 Thermal resistance                        U-value (rounded)         

                  42.5mm                                          1.430 m²K/W                                   0.19 W/m²K

                  50.5mm                                          1.793 m²K/W                                   0.18 W/m²K

                  52.5mm                                          1.884 m²K/W                                   0.18 W/m²K

                  62.5mm                                          2.339 m²K/W                                   0.16 W/m²K

                  72.5mm                                          2.793 m²K/W                                   0.15 W/m²K

                  82.5mm                                          3.248 m²K/W                                   0.14 W/m²K

                  92.5mm                                          3.702 m²K/W                                   0.13 W/m²K

• Roof rafter depth. 150mm
• Minimum timber counter batten depth. 25mm
• Roof rafter centres. 400mm
• Insulation type and thermal conductivity in layer 3, High performance glasswool insulation roll with a thermal conductivity of not less than. 0.034 W/mK
• PIR Insulated plasterboard thermal resistance guide. (see opposite page)
• Roof rafter centres set at 600mm will show a marginal improvement on the U value result.

Rothoblaas Clima Control 80 (layer 2) is a variable sd airtight membrane and is suitable for ventilated and un-ventilated roof spaces. (variable sd membranes are often referred to as intelligent membranes)

The brand of the high performance glasswool insulation roll 34 (layer 3) is not important. If the insulation is the same thickness and has a thermal conductivity of 0.034 W/mK or better you will achieve at least the same result. The brand of the PIR insulated plasterboard is not important (layer 1). If the overall thermal resistance for the PIR insulated plasterboard is the same or better you will achieve at least the same result.

Rothoblaas Traspir 150 R (layer 4) is a high-performance breathable roofing underlay.

Pitch Roof Type 2; Option 2

• The insulation thickness applied between the roof rafters is 180mm

Roof Build-up;

7:  Roof tile or slate.

6:  Roof tile battens.

5:  Timber counter battens applied above the breathable roofing underlay.

4:  Rothoblaas Traspir 150 R breathable roofing underlay.

3:  180mm Knauf Earthwool OmniFit Stud Roll 34 applied filling the roof rafters.

2:  Rothoblaas Clima Control 80 airtight membrane taped and sealed below the roof rafters.

1:  37.5mm PIR Insulated plasterboards fixed below the roof rafters.

 U-value (rounded) 0.18 W/m²K

To improve the U value result for the roof type and build up identified above increase the insulated plasterboard thickness applied below the roof rafters to;

Insulated plasterboard thickness                 Thermal resistance                        U-value (rounded)  

                  42.5mm                                          1.430 m²K/W                                   0.17 W/m²K

                  50.5mm                                          1.793 m²K/W                                   0.16 W/m²K

                  52.5mm                                          1.884 m²K/W                                   0.16 W/m²K

                  62.5mm                                          2.339 m²K/W                                   0.15 W/m²K

                  72.5mm                                          2.793 m²K/W                                   0.14 W/m²K

                  82.5mm                                          3.248 m²K/W                                   0.13 W/m²K

                  92.5mm                                          3.702 m²K/W                                   0.12 W/m²K

• Roof rafter depth. 180mm
• Minimum timber counter batten depth. 25mm
• Roof rafter centres. 400mm
• Insulation type and thermal conductivity in layer 3, High performance glasswool insulation roll with a thermal conductivity of not less than. 0.034 W/mK
• PIR Insulated plasterboard thermal resistance guide. (see opposite page)
• Roof rafter centres set at 600mm will show a marginal improvement on the U value result.

Rothoblaas Clima Control 80 (layer 2) is a variable sd airtight membrane and is suitable for ventilated and un-ventilated roof spaces. (variable sd membranes are often referred to as intelligent membranes)

The brand of the high performance glasswool insulation roll 34 (layer 3) is not important. If the insulation is the same thickness and has a thermal conductivity of 0.034 W/mK or better you will achieve at least the same result. The brand of the PIR insulated plasterboard is not important (layer 1). If the overall thermal resistance for the PIR insulated plasterboard is the same or better you will achieve at least the same result.

Rothoblaas Traspir 150 R (layer 4) is a high-performance breathable roofing underlay.

Pitch Roof Type 2; Option 3

• The insulation thickness applied between the roof rafters is 220mm

Roof Build-up;

7:  Roof tile or slate.

6:  Roof tile battens.

5:  Timber counter battens applied above the breathable roofing underlay.

4:  Rothoblaas Traspir 150 R breathable roofing underlay.

3:  220mm Knauf Earthwool OmniFit Stud Roll 34 applied filling the roof rafters.

2:  Rothoblaas Clima Control 80 airtight membrane taped and sealed below the roof rafters.

1:  37.5mm PIR Insulated plasterboards fixed below the roof rafters.

 U-value (rounded) 0.15 W/m²K

To improve the U value result for the roof type and build up identified above increase the insulated plasterboard thickness applied below the roof rafters to;

Insulated plasterboard thickness                 Thermal resistance                        U-value (rounded)        

                  42.5mm                                          1.430 m²K/W                                   0.15 W/m²K

                  50.5mm                                          1.793 m²K/W                                   0.14 W/m²K

                  52.5mm                                          1.884 m²K/W                                   0.14 W/m²K

                  62.5mm                                          2.339 m²K/W                                   0.13 W/m²K

                  72.5mm                                          2.793 m²K/W                                   0.12 W/m²K

                  82.5mm                                          3.248 m²K/W                                   0.12 W/m²K

                  92.5mm                                          3.702 m²K/W                                   0.11 W/m²K

• Roof rafter depth. 220mm
• Minimum timber counter batten depth. 25mm
• Roof rafter centres. 400mm
• Insulation type and thermal conductivity in layer 3, High performance glasswool insulation roll with a thermal conductivity of not less than. 0.034 W/mK
• PIR Insulated plasterboard thermal resistance guide. (see opposite page)
• Roof rafter centres set at 600mm will show a marginal improvement on the U value result.

Rothoblaas Clima Control 80 (layer 2) is a variable sd airtight membrane and is suitable for ventilated and un-ventilated roof spaces. (variable sd membranes are often referred to as intelligent membranes)

The brand of the high performance glasswool insulation roll 34 (layer 3) is not important. If the insulation is the same thickness and has a thermal conductivity of 0.034 W/mK or better you will achieve at least the same result. The brand of the PIR insulated plasterboard is not important (layer 1). If the overall thermal resistance for the PIR insulated plasterboard is the same or better you will achieve at least the same result.

Rothoblaas Traspir 150 R (layer 4) is a high-performance breathable roofing underlay.

Educate to Insulate

The U value Results - Pitch Roof Type 3

In this section there are three insulation thickness options available for the insulation materials applied between the roof rafters.

1. 100mm
2. 150mm
3. 180mm
4. 220mm

Included in the U value Guide; is breathable roofing underlay and airtight membrane suggestions.

Pitch Roof Type 3; Option 1

• The insulation thickness applied between the roof rafters is 100mm
• The insulation thickness applied between the timber battens fixed below the roof rafters is 50mm

Roof Build-up;

9:  Roof tile or slate.

8:  Roof tile battens.

7:  Rothoblaas Traspir 150 R breathable roofing underlay.

6:  Crossflow ventilated airspace.

5:  100mm Knauf Earthwool OmniFit Stud Roll 34 applied partially filling the roof rafters.

4:  Rothoblaas Vaporvlies 120 airtight membrane.

3:  50mm Knauf Earthwool OmniFit Slab 35 applied between timber counter battens.

2:  50mm Timber counter battens.

1:  Plasterboard.

U-value (rounded) 0.26 W/m²K

• Minimum roof rafter depth. 125mm
• Minimum crossflow ventilated airspace. 25mm
• Roof rafter centres. 400mm
• Insulation type and thermal conductivity in layer 5, High performance glasswool insulation roll with a thermal conductivity of not less than. 0.034 W/mK
• Insulation type and thermal conductivity in layer 2, High performance glasswool insulation roll with a thermal conductivity of not less than. 0.034 W/mK
• Roof rafter centres set at 600mm will show a marginal improvement on the U value result.

Rothoblaas Vaporvlies 120 (layer 4) is a fixed sd airtight membrane and is suitable for ventilated roof spaces. Crossflow Ventilated Air Space (layer 6)

The brand of the high performance glasswool insulation roll 34 (layer 5) is not important. If the insulation is the same thickness and has a thermal conductivity of 0.034 W/mK or better you will achieve at least the same result.

The brand of the high performance glasswool insulation roll or batt 35 (layer 2) is not important. If the insulation is the same thickness and has a thermal conductivity of 0.034 W/mK or better you will achieve at least the same result.

Rothoblaas Traspir 150 R (layer 7) is a high-performance breathable roofing underlay.

Pitch Roof Type 3; Option 2

• The insulation thickness applied between the roof rafters is 150mm
• The insulation thickness applied between the timber battens fixed below the roof rafters is 50mm

Roof Build-up;

9:  Roof tile or slate.

8:  Roof tile battens.

7:  Rothoblaas Traspir 150 R breathable roofing underlay.

6:  Crossflow ventilated airspace.

5:  150mm Knauf Earthwool OmniFit Stud Roll 34 applied partially filling the roof rafters.

4:  Rothoblaas Vaporvlies 120 airtight membrane.

3:  50mm Knauf Earthwool OmniFit Slab 35 applied between timber counter battens. 

2:  50mm Timber counter battens.

1:  Plasterboard.

U-value (rounded) 0.20 W/m²K

• Minimum roof rafter depth. 175mm
• Minimum crossflow ventilated airspace. 25mm
• Roof rafter centres. 400mm
• Insulation type and thermal conductivity in layer 5, High performance glasswool insulation roll with a thermal conductivity of not less than. 0.034 W/mK
• Insulation type and thermal conductivity in layer 2, High performance glasswool insulation roll with a thermal conductivity of not less than. 0.034 W/mK
• Roof rafter centres set at 600mm will show a marginal improvement on the U value result.

Rothoblaas Vaporvlies 120 (layer 4) is a fixed sd airtight membrane and is suitable for ventilated roof spaces. Crossflow Ventilated Air Space (layer 6)

The brand of the high performance glasswool insulation roll 34 (layer 5) is not important. If the insulation is the same thickness and has a thermal conductivity of 0.034 W/mK or better you will achieve at least the same result.

The brand of the high performance glasswool insulation roll or batt 35 (layer 2) is not important. If the insulation is the same thickness and has a thermal conductivity of 0.034 W/mK or better you will achieve at least the same result.

Rothoblaas Traspir 150 R (layer 7) is a high-performance breathable roofing underlay.

Pitch Roof Type 3; Option 3

• The insulation thickness applied between the roof rafters is 180mm
• The insulation thickness applied between the timber battens fixed below the roof rafters is 50mm

Roof Build-up;

9:  Roof tile or slate.

8:  Roof tile battens.

7:  Rothoblaas Traspir 150 R breathable roofing underlay.

6:  Crossflow ventilated airspace.

5:  180mm Knauf Earthwool OmniFit Stud Roll 34 applied partially filling the roof rafters.

4:  Rothoblaas Vaporvlies 120 airtight membrane.

3:  50mm Knauf Earthwool OmniFit Slab 35 applied between timber counter battens.

2:  50mm Timber counter battens.

1:  Plasterboard.

U-value (rounded) 0.18 W/m²K

• Minimum roof rafter depth. 205mm
• Minimum crossflow ventilated airspace. 25mm
• Roof rafter centres. 400mm
• Insulation type and thermal conductivity in layer 5, High performance glasswool insulation roll with a thermal conductivity of not less than. 0.034 W/mK
• Insulation type and thermal conductivity in layer 2, High performance glasswool insulation roll with a thermal conductivity of not less than. 0.034 W/mK
• Roof rafter centres set at 600mm will show a marginal improvement on the U value result.

Rothoblaas Vaporvlies 120 (layer 4) is a fixed sd airtight membrane and is suitable for ventilated roof spaces. Crossflow Ventilated Air Space (layer 6)

The brand of the high performance glasswool insulation roll 34 (layer 5) is not important. If the insulation is the same thickness and has a thermal conductivity of 0.034 W/mK or better you will achieve at least the same result.

The brand of the high performance glasswool insulation roll or batt 35 (layer 2) is not important. If the insulation is the same thickness and has a thermal conductivity of 0.034 W/mK or better you will achieve at least the same result.

Rothoblaas Traspir 150 R (layer 7) is a high-performance breathable roofing underlay.

Pitch Roof Type 3; Option 4

• The insulation thickness applied between the roof rafters is 220mm
• The insulation thickness applied between the timber battens fixed below the roof rafters is 50mm

Roof Build-up;

9:  Roof tile or slate.

8:  Roof tile battens.

7:  Rothoblaas Traspir 150 R breathable roofing underlay.

6:  Crossflow ventilated airspace.

5:  220mm Knauf Earthwool OmniFit Stud Roll 34 applied partially filling the roof rafters.

4:  Rothoblaas Vaporvlies 120 airtight membrane.

3:  50mm Knauf Earthwool OmniFit Slab 35 applied between timber counter battens.

2:  50mm Timber counter battens.

1:  Plasterboard.

U-value (rounded) 0.15 W/m²K

• Minimum roof rafter depth. 245mm
• Minimum crossflow ventilated airspace. 25mm
• Roof rafter centres. 400mm
• Insulation type and thermal conductivity in layer 5, High performance glasswool insulation roll with a thermal conductivity of not less than. 0.034 W/mK
• Insulation type and thermal conductivity in layer 2, High performance glasswool insulation roll with a thermal conductivity of not less than. 0.034 W/mK
• Roof rafter centres set at 600mm will show a marginal improvement on the U value result.

Rothoblaas Vaporvlies 120 (layer 4) is a fixed sd airtight membrane and is suitable for ventilated roof spaces. Crossflow Ventilated Air Space (layer 6)

The brand of the high performance glasswool insulation roll 34 (layer 5) is not important. If the insulation is the same thickness and has a thermal conductivity of 0.034 W/mK or better you will achieve at least the same result.

The brand of the high performance glasswool insulation roll or batt 35 (layer 2) is not important. If the insulation is the same thickness and has a thermal conductivity of 0.034 W/mK or better you will achieve at least the same result.

Rothoblaas Traspir 150 R (layer 7) is a high-performance breathable roofing underlay.

Insulation and Associated Building Materials; Pack sizes, Roll sizes.

Contact Your Local HPC Builders Providers for Pricing

Rothoblaas Breathable Roofing Underlay

Traspir Evo 150

Roll size: 1.5mtr x 50mtr (75m2 per roll)

Price per roll €

Eaves tray/eaves carrier

Tray length: 1.3mtr Price per length €

Knauf Insulation Earthwool OmniFit Stud Roll 34

100mm Knauf Earthwool OmniFit Stud Roll 34

Insulation thermal conductivity 0.034 (W/mK)

Insulation thermal resistance 2.942 W/m²K

Roll size: 1.2mtr x 5.2mtr (6.24m2 per roll)

Price per roll €

150mm Knauf Earthwool OmniFit Stud Roll 34

Insulation thermal conductivity 0.034 (W/mK)

Insulation thermal resistance 4.412 W/m²K

Roll size: 1.2mtr x 3.5mtr (4.2m2 per roll)

Price per roll €

180mm Knauf Earthwool OmniFit Stud Roll 34

Insulation thermal conductivity 0.034 (W/mK)

Insulation thermal resistance 5.294 W/m²K

Roll size: 1.2mtr x 3mtr (3.6m2 per roll)

Price per roll €

220mm Knauf Earthwool OmniFit Stud Roll 34

Insulation thermal conductivity 0.034 (W/mK)

Insulation thermal resistance 6.471 W/m²K

Roll size: 1.2mtr x 2.5mtr (3m2 per roll)

Price per roll €

Knauf Earthwool OmniFit Slab

50mm Knauf Earthwool OmniFit Slab 35

Insulation thermal conductivity 0.035 (W/mK)

Insulation thermal resistance 1.428 W/m²K

Sheet size: 1200mm x 600mm (8.64m2 per pack)

Price per pack €

50mm Knauf Earthwool OmniFit Slab 35

Insulation thermal conductivity 0.035 (W/mK)

Insulation thermal resistance 1.428 W/m²K

Sheet size: 1200 x 400mm (5.76m2 per pack)

Price per pack €

Rothoblaas Airtight Membranes, Tapes, Sealants, Primer & Airtight Foam

Vaporvlies 120 (fixed sd airtight membrane)

Roll size: 1.5mtr x 50mtr (75m2 per roll)

Price per roll €

Clima Control 80 (variable sd airtight membrane)                (variable sd - sometimes refferred to as an itilligent airtight membrane)

Roll size: 1.5mtr x 50mtr (75m2 per roll)

Price per roll €

Flexi Band Airtight Tape

Overlaps, joints, penetrations and abutments. (25 linear mtrs per roll)

60mm Price per roll €

Flexi Band Liner Airtight Tape (internal and external use)

Split tape (split 50mm+50mm) (25 linear mtrs per roll)

100mm Price per roll €

Seal Band Airtight Tape (internal use)

Split tape (split 48mm+12mm) for window/door frame to block or plaster reveal. (40 linear mtrs per roll)

60mm Price per roll €

Plaster Band In - Plasterable airtight Tape (internal use)

Split tape for window/door frame to block reveal and membrane to block. (25 linear mtrs per roll)

  75mm (split 63mm+12mm)     Price per roll €

100mm (split 88mm+12mm)     Price per roll €

150mm (split 138mm+12mm)   Price per roll €

200mm (split 188mm+12mm)   Price per roll €

Superb Glue - Airtight Sealant (310ml tube)

Price per tube €

Superb Glue - Airtight Sealant (600ml sausage)

Price per sausage €

Hermetic Foam - Airtight Closed Cell Acoustic Foam (b2 fire rated) (750ml tin)

Universal Primer Spray (750ml tin)

PIR Insulated Plasterboards

PIR Insulation bonded to 12.5mm plasterboards

PIR = Polyisocyanurate foam insulation.

37.5mm x 1200mm x 2400mm

42.5mm x 1200mm x 2400mm  

50.5mm x 1200mm x 2400mm

52.5mm x 1200mm x 2400mm

62.5mm x 1200mm x 2400mm

72.5mm x 1200mm x 2400mm

82.5mm x 1200mm x 2400mm

92.5mm x 1200mm x 2400mm