Low Energy Whole House Refurbishment

4th Nov 2009



In early 2009 Knauf Insulation undertook a project to internally insulate an 1890’s Victorian mid terrace property to current energy standards. The aim was to install systems that could be undertaken by any competent builder to achieve an effective and efficient low energy refurbishment at a modest marginal cost over a normal refurbishment. The attractive brick frontage made the property less suitable for external wall insulation (EWI) but ideal for Knauf Insulation’s Internal Wall Insulation (IWI) system using their patented EcoStud as a replacement for the more traditional timber stud framing. To provide a side by side comparison, a Knauf Insulation insulated metal stud system was also installed in part of the property.

This private rental property had been damaged by a tenant and required renovation. Knauf Insulation assisted the landlord and his builder to enable a ‘whole house - low energy’, refurbishment to be undertaken with an emphasis on a low marginal cost.

Survey Summary:

Walls - solid No insulation Very poor
Floor No insulation Poor
Loft 100mm Inadequate
Boiler New condensing Very good
Heating controls TRV’s Good
Windows Double glazed Adequate
Doors UPVC Adequate
Lighting Incandescent Very poor


Figure 1 Figure 2 Figure 3 Figure 4

Figure 1 shows Stage 1 with all fixtures removed and the plaster removed back to the original 225mm thick brickwork, although in most cases the EcoStuds would be affixed through the existing plasterwork.

Figure 2 shows Stage 2 with the new EcoStud mechanically fixed to the brick wall and 75mm of EcoBatt friction fitted between to ensure a complete coverage of insulation across the whole wall.

Figures 3 and 6 show Stage 3 with the 12.5mm vapour check plasterboard fixed to the EcoStud framework in the bathroom and the living room. The overall reduction in floor area was less than 2 per cent.

Figure 5 Figure 6

THE SYSTEM (figure 4)

  1. EcoStud which has an overall size of 50mm wide x 75mm deep x 2400mm long to replace a typical size of timber stud. This comprises Polyfoam extruded polystyrene laminated to Oriented Strand Board (OSB). EcoStuds were mechanically fixed to the wall with the OSB facing into the room using 130mm screws and plugs, a minimum 40mm fixing penetration into the wall is required.
  2. 75mm thick EcoBatt water repellent glass mineral wool slab with a thermal conductivity of 0.032 W/mK friction fitted between the EcoStuds to ensure intimate contact between the inside of the wall and the back of the plasterboard thereby preventing unwanted air movement and draughts through the system.
  3. 27mm Polyfoam Linerboard, a laminate of 17.5mm Polyfoam extruded polystyrene and 9.5mm Knauf plasterboard fitted around all window and door reveals to limit cold bridging and surface condensation. 27mm Polyfoam Linerboard was also installed at all party wall junctions to a minimum width of 400mm and the full height of the rooms in order to prevent heat loss and the potential for condensation and mould growth in internal corners.
  4. 12.5mm vapour check plasterboard attached to the OSB of the EcoStuds using 25mm drywall screws with all edges sealed with Knauf Multi Purpose Sealant to prevent air movement behind the wall lining reducing the thermal performance of the installed system. Knauf Insulation also used the alternative Knauf metal framing system at the front of the property to assess suitability and timing of the two installations.

Both the Knauf Insulation IWI system and metal system resulted in an improvement of the U-value from approximately 2.00 W/m2K to 0.35 W/m2K, an improvement in thermal performance of almost 80 per cent.

At Doncaster there was little time difference between the installations of both systems, but the Knauf Insulation IWI System proved a more cost effective way to achieve the same level of thermal performance. In total the builder installed 73m2 of internal wall insulation into the property.

Figure 5 shows the existing 100mm thickness of insulation between the ceiling joists, topped up with a second layer of 200mm Loft Roll.


Insulation was also fitted between the timber floor joists and the external wall to ensure continuity of insulation between the two levels. This eliminates any major thermal bridge through the insulated internal dry lining system.


The front of the property had a ¾ height cellar above which was the timber floor of the living room. Knauf Insulation took the opportunity of insulating this area from below with 150mm of glass mineral wool friction fitted between the timber floor joists. As the cellar was prone to seasonal flooding, with a high moisture content in the cellar atmosphere, it was decided to use EcoBatt water repellent slab in 2 layers of 75mm to fully fill the 150mm deep floor joists and ensure the insulation was in close intimate contact with the underside of the timber floor boards to eliminate air movement. Figure 7 below shows part of the cellar ceiling.

A new tightly fitting UPVC door was fitted at the top of the cellar stairs to prevent cold air from entering the kitchen area, and as the internal wall to the dining room abutted the cellar atmosphere, it was also insulated with the Knauf Insulation IWI System. At the same time the underside of the staircase to the first floor was battened out and insulated.

Figure 7 Figure 8


In conjunction with University College London, Knauf Insulation have also installed monitoring equipment to enable measuring of the conditions Figure 5 at the interface of the insulation and internal face of the solid wall. Permanent in-situ sensors have been installed in each room to measure relative humidity and temperature and this data is collected in a logger located in the cellar. University College London will work with Knauf Insulation over coming years to measure and interpret the results generated. Sensors were also positioned within the suspended timber ground floor zone and on the cellar wall.

HoBo type sensors were used in each room to measure the internal conditions as well as installing an external HoBo sensor to monitor weather conditions. Figure 8 below shows the set up of the data logger.

The new tenant has agreed to maintain a daily activity log of the use of washing machines etc to inform the project team when high levels of moisture vapour are being generated.


The Energy Performance of the property prior to the low energy refurbishment (which had a condensing boiler with radiators in each room, UPVC windows and doors and 100mm of glass mineral wool loft insulation) was SAP 63D with a CO2 emission rate of 3.80 tonnes per annum, excluding appliances. The property after the low energy refurbishment achieved a SAP 82B with a CO2 emission rate of 1.80 tonnes per annum, a 52 per cent reduction in CO2 emissions. The calculated energy savings are approximately £300 per annum, however, based on current fuel costs a figure of £400 would be more appropriate, with greatly improved comfort conditions.


U-values before Treatment (W/m2K)

U-values after Treatment (W/m2K)

Walls 2.00 0.35
Roof 0.43 0.13
Floor 0.71 0.21



The Knauf Insulation IWI System is a highly cost-effective system for upgrading existing properties to current Building Regulation thermal standards and beyond. The marginal cost of installing the Knauf Insulation IWI System, over and above the work that was required to bring the property up to a decent standard, was approximately £2800. The reduction in energy bills results in the marginal installation costs being re-couped after approximately 7 years based on current energy prices.

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