We thermally insulated six different areas each requiring a different solution:

  • Roofs over occupied areas – 110mm Kingspan Kooltherm phenolic foam board over rafters and 100mm between.
  • Roofs over unoccupied areas (cold roof spaces) – 430mm Rockwool insulation was laid between and above the floor joists of these areas.
  • Flat roof – 210mm Kingspan Thermaroof 
  • Walls
    • 230mm Permarock expanded polystyrene on external walls that could take this thickness without unduly restricting the width of the adjoining passageway for people bringing their bikes and wheelie bins through,
    • 130mm and 180mm Permarock phenolic on walls adjoining narrow passageways.   Phenolic performs much better for a given thickness than polystyrene but is more expensive.  However, it was necessary for space reasons on this rather cramped site. 
    • Special grades of expanded polystyrene insulation below the damp proof course to the thickness of the insulation above.
    • The sheets of insulation were first stuck to the existing pebbledash wall with ribbons of adhesive to eliminate any air flows behind the sheets.
      EWI Pattresses
      They were then mechanically fastened into the brick with a type of steel and plastic screw with a plastic disk holding the sheets in place.  
                                                                                The picture alongside shows these fasteners.  It also shows a vertical line of plywood pattresses recessed into the insulation to hold the rainwater down-pipes and other  mountings onto the building.


  • Upstanding insulation on internal edges of parapets, external walls and other junctions to eliminate cold bridges – 25mm Kingspan expanded polystyrene and phenolic as appropriate.
  • Ground – 25mm Vacupor vacuum insulation sheets over the existing concrete slab and below the underfloor heating system

Throughout, careful detailing around floor and wall junctions, windows, doors and in the roof spaces was provided by the architects McHugh Stoppard to prevent cold bridges causing unnecessary heat loss and the risk of condensation and damp patches.  It was a superb effort by our architects Dan Smith and Mike Young, who produced a much more detailed and comprehensive design than most builders are used to.

In addition, Hush acoustic floor insulation  was used to reduce noise between the offices and the flat above.

Insulating the Ground Floor

The floor was a particular challenge.  We didn’t want to dig up the existing 100mm concrete slab.  Nor did we want to build up the floor level with insulation to leave an unacceptably low ceiling height without room to put in a service void.   We wanted the thinnest possible insulation to go beneath the under floor heating pipes. Fortunately we’d come across the Vacupor vacuum insulation product exhibited at the annual Greenbuild exhibition in Manchester.  Whilst normally we have deliberately chosen UK manufactured product, on this occasion we ended up in Kempten, Bavaria for a highly effective vacuum insulation product  via the Cumbrian low-carbon building company Envirohomes. 

Whilst the u-value of 0.15 for a 25mm thick sheet is exceptionally good, the fragility of the product meant that enormous care had to be exercised in laying it.  Once punctured, its insulation value is almost nil.  So it was sandwiched in foam and then temporarily overlaid with correx  to protect it.  The site briefly became a hard hat and carpet slipper zone, with boots taken off and left at the front door.

On top of the insulation, red plastic crating was laid into which the under floor pipe-work was clipped, and then overlaid with a 75mm self-levelling liquid screed.Floor Screed  The three stages of floor preparation can be seen in the photo to the right.  The silver encased Vacupor can be seen over the existing slab at the front, covered in a thin white protective foam, then the pipework in its red crating, partially screeded, and then the final fully screeded floor.  Dalliam , who are supplying the office heating and cooling system, then installed the manifold for the under floor pipe-work and successfully pressure tested their pipework.

A potential future problem is the concentration of pipework routed along the corridors to the individual offices, which could mean the corridor floor becomes uncomfortably hot, and may need insulating our finished corridor floor to keep the heat in.   Geoff Morgan, our building services consultant, notes that this is a common problem with underfloor heating systems.