Pitched Roofs
Issues to Consider Issues to Consider
Design Considerations
Full Fill Between & Under Rafter Insulation
Partial Fill Between & Under Rafter Insulation
Between & Over Rafter Insulation
Over Rafter Insulation
Partial Fill Between & Under Rafter Insulation
Breathable Membrane - Horizontal Installation on Continuous Substrate
Breathable Membrane - Vertical Installation on Discontinuos Substrate
  Refurbishment - Ventilated - Between & Under Rafter Insulation


INTRODUCTION
For this application we recommend the use of Kingspan Kooltherm® K7 Pitched Roof Board (premium performance CFC/HCFC–free rigid phenolic insulation) with Kingspan Kooltherm® K18 Insulated Dry-lining Board beneath the rafters.

Figure 1
Between & Under Rafter Insulation


Premium Performancezero ODP
PRODUCT DATA ACHIEVING U–VALUES

Kingspan Kooltherm® K7
Pitched Roof Board
Board Size 2.4 x 1.2
Insulant Thickness(mm) Refer to local distributor or Kingspan Insulation price list for current stock and non-stock sizes.
Facings Composite Foil
Core CFC/HCFC - free
rigid phenolic

U-value
(W/m².K)
Kingspan Kooltherm® K7
Pitched Roof Board
600 ctrs
400 ctrs
0.30
55
60
0.20
100
110
0.18
120
130
Thermal Conductivity
(l-value) - K7®     45mm 0.022 W/m.K

1 The requirement for a vapour control layer and/or under tile ventilation should be assessed to BS 5250: 1989 (1995). Vapour check plasterboard or a separate vapour control layer can be used as preferred.

2 Kingspan Kooltherm® K18 Insulated Dry-lining Board contains an integral vapour control layer.

3 Calculation based on rafters being underlined with Kingspan Kooltherm® K18 Insulated Dry-lining Board comprising 12.5 mm plasterboard and 25 mm insulation of thermal conductivity 0.022 W/m.K. Thickness shown in the table above is only the between rafter component. Calculations are based on 50 mm wide rafters, assuming a 50 mm ventilated airspace between the rafters above the insulation layer installed between them.

4 The l–value quoted is in accordance with the Harmonised European Standard BS EN 13166 (phenolic) using so called 90/90 principles. Comparison with alternative products may not be appropriate unless the same procedures have been followed.

5 If tiles are to be used then this normally necessitates the use of counter battens and tiling battens over the breathable sarking membrane to allow for water drainage and attachment of the tiles.
FIXING DETAILS
    Between Rafter Insulation
  • To maintain a 50 mm ventilated void above the insulation and to ensure the boards are flush with the bottom of the rafters, side nail battens to the rafters in the appropriate position to provide a stop’.


  • Boards cut individually to fit the rafter spacings and simply install the correct thickness of insulation in such a manner that it is flush with the bottom of the rafters but does not fill the rafter depth.


  • Measure the space between the rafters before cutting the boards as spacings vary. In all cases insure that insulation boards between rafters are fitted tightly. Fill any gaps with expanding urethane sealant.


    • Under Rafter Insulation
  • Fix the Kingspan Kooltherm® K18 Insulated Dry-lining Board at right angles to the underside of the rafters. Boards should be fixed with galvanised clout nails, long enough to allow 25 mm penetration of the timber. These should be placed at 150 mm centres and not less than 10 mm from the edges of the board along all supporting edges.


  • All edges of Kingspan Kooltherm® K18 Insulated Dry-lining Board must be supported. This will necessitate the use of noggings placed between rafters to correspond with the long edges of the boards.


    • General
  • Ensure accurate trimming to achieve close butting joints and continuity of insulation.


  • Ensure the continuity of the insulation at the ridge.


  • Ventilation should be provided in accordance with Approved Document F, F2 Condensation in Roofs) or the Building Regulations or Technical Standard K Ventilation of Buildings, Regulation 23) of the Building Standards (Scotland).


  • To prevent a cold bridge, tightly pack flexible insulation material between the rafters and the cavity closer.


  • Boards should be cut using a sharp knife or fine toothed saw.
Figure 2 (Alternative – Scottish Style Detail)  
Scottish Style Detail