loft insulation

[nanuuk]

Hi, I am rather puzzled by the following note (extracted from our drawing):

"Provide 100mm thk kingspan k7 between joists with kooltherm k18 to the underside of the ceiling joists."

Is 100mm the total of k7 and k18? If so what should be the thickness of each? And in what order do I place them on top of plaster board. (Plaster board is the ceiling for 1st fl rm, insulation will separate 1st fl rm from loft.)
Many thanks.

 

[freddiemercurystwin]

Like this:

Untitled

• freddiemercurystwin
• 8 Jun 2010
• 20

ask your designer how thick the layer beneath needs to be, the regs have changed slightly since I drew that detail.

 

[PrenticeBoyofDerry]

K18 is an insulated backed plasterboard.
K7 is just an insulation board.
They will expect you to insulate between joist with 100mm K7
Then board out with K18
or visa versa

Kingspan Kooltherm® K18 Insulated Dry–lining Board may be
used to line ceilings. Installation is similar to that of standard
plasterboard. Boards must always be placed with the long
edge running across the joists, rafters or battens and all edges
must be supported. Timbers must offer a minimum 20 mm
support to all four edges of the board. This will necessitate the
use of noggings placed between the joists / rafters to coincide
with the long edges of the board. Dry wall screws or,
alternatively, large–headed galvanised / sheradised clout nails
should be used to fix the board. These must be long enough
to allow a minimum 25 mm penetration of the supporting
timber, and be placed not less than 10 mm from the edges of
the board and be spaced at 150 mm intervals along all
supporting timbers.

From kingspan K18 spec

 

[ajrobb]

You'll need about 120 mm to get below the required U-value of 0.18 W/m²/K for a flat roof, or 150 mm to get below 0.16. With joists bridging the K7, you'll need more.

 

[nanuuk]

Hi,
I found the details within the drawing i.e. 2 x 12.5 plasterboard shts. I worked out I need a k18 board 37.5mm thk (i.e. 25mm plus 12.5mm of foil) so including K7 the insulation will total 137.5mm.

The joists are 175mm. Does this mean I need to top up with another 75mm of insulation to avoid bridging? I must admit I am slightly confused as I've come across
1. "Insulation should be increased to compensate for the joist bridging effect" as well as
2. "good vapour barrier is required below the insulation" and
3. "Excellent vapour control is also required, especially when electrics may penetrate."
So WHICH is correct?

Many thanks.