Based in Unit 102 Coolmine Ind Est

Kooltherm K7 Sarking Board

General Description

Kooltherm K7 Sarking Board is a CFC free phenolic foam laminate with a tough composite foil facing on each surface. The closed-cell foam core gives the board outstanding thermal performance, while the fact that it is phenolic leads to excellent fire characteristics and low smoke emission.

We are a dublin based insulation company. For more info regarding our energy saving solutions, get in contact with Usher Insulations today!


K7 Sarking Board is designed for use in pitched roof applications and allows an increased level of usable space compared with insulation applied at ceiling level. It eliminates the risk of condensation within the roof space and avoids all problems attendant with it. It is possible to use K7 either on top of the rafters when the roof timbers are exposed, or between the rafters when applying the boards from beneath (often in a retrofit attic conversion). In the latter case, it is necessary to retain a ventilated airspace of 50mm above the insulation. K7 is the only product currently available, that can retain this airspace and achieve the 0.25 U value required, using standard rafters with depths of 113mm.


K7 is manufactured in a range of thicknesses from 20 to 70mm and in standard widths of 600mm or 1200mm. The standard lengths of board are 1200 and 2400mm.

Technical Data

K7 is manufactured in a range of thicknesses from 20 to 70mm and in standard widths of 600mm or 1200mm. The standard lengths of board are 1200 and 2400mm.

Typical Values 



 20 - 70mm


 600, 1200mm 



Compressive strength @ 10 % deformation

 175 kPa min 

Dimensional stability (40mm board): 


a/ 7 days @ 20°C

 no change

b/ 7 days @ -20°C

 no change

Moisture vapour resistance


Foam Core



Thermal conductivity @ 10°C 

 0:018 W/mK

Closed cell content

 90 %

Fire/Smoke properties:


*BS 476 1989:Part 6 

 S<12 s<6 

*BS 476 1993:Part 7

 Class 1 

*BS 5111 1974: Part 1

<5 % obscuration

* The combination of these two tests gives a Class 0 to the Building Regulations

For more info regarding our energy saving solutions and insulation producst, get in contact with Usher Insulations today!


The insulation shall be Kooltherm K7 Sarking Board with a CFC free phenolic foam core and a thermal conductivity of 0.018W/mK. The board thickness should be . .. . . . mm which will achieve a U value of . . . .

K7 Thickness

U Value











The boards are laid directly over the rafters and are held in place by counter battens which are placed over the line of the rafters and secured by nailing through into the rafters using fixings such as the Inskew fixing from Helifix. The number of fixings will depend on a variety of factors such as location, pitch of roof, slate/tile load etc. Detailed advice is available from the fixing supplier.

Vertical joints between boards should be supported by the rafters. All joints between boards should be sealed with a self adhesive aluminium foil tape. A breathable non bituminous sarking membrane is laid across the counter battens and stretched tight. The membrane is held in place by the slate/tile battens which are secured by nailing into the counter battens.

NB The boards themselves are not suitable for trafficking unless fully supported. The use of ladders or crawling boards is recommended until counter battens and tile battens are fixed.

K7 Thickness

U Value











The insulation board is fitted between the rafters in such a way that a minimum airspace of 50mm is left between the insulation board and the sarking felt. The exposed inner surface of the insulation board is then protected by a sheet of plasterboard that is fixed to the underside of the rafters. The plasterboard is to be fixed by means of wide head clout nails, penetrating at least 35mm into the rafters, at 150mm separations.

NB In retrofit applications where the standard rafter depth is 113mm (4.5 inches), only a insulant with a 'k' value of under 0.019W/mK will give the 0.25 U value demanded by the Building Regulations. To date only phenolic foam insulation satisfies this condition.