G ENERACIÓN DE NIVELES DE ABSTRACCIÓN

Shorrock (2005) estimated that there are nearly 10 million uninsulated suspended ground floors in the UK and Power (2008) argues that floor insulation is essential alongside other fabric intervention measures to achieve significant overall dwelling energy reductions. About 8000 floors were recently insulated under the ECO and the Green Deal policies, though this represents only a small proportion of overall measures - see Chapter 1.2.3. However, no literature was found that identifies the proportion of insulated floors in the UK's pre-1919 housing stock.

Insulating floors might provide many benefits, including reduced energy use and energy bills with reduced associated carbon emissions (Power, 2008), though this depends on

space-heating fuels used. An additional benefit of floor insulation might be increased dwelling airtightness as well as better occupant thermal comfort - see Chapter 6.5. EST (2006b) suggests that up to 60% heat loss reductions might be achieved by insulating suspended timber ground floors. Floor insulation was also highlighted as a cost-effective carbon reduction measure by Shorrock (2005), Rickaby (2014a) and Mackenzie (2010), with estimated carbon reductions of 1.82 million tonnes of CO2 per year for the UK housing stock, excluding any compensating occupant behaviour such as 'take back'⁶(Mackenzie, 2010). It is unclear what these estimates are based on and estimated carbon reductions will be lower when low carbon space-heating supply increases.

However, some dwelling retrofits estimated significant energy reductions without insulating floors by using higher fabric standards elsewhere, for example 'Cottage Retrofit' at the Isle of Wight (TSB, 2012). Furthermore, Friedman (2014) found that floor insulation was, together with doors, one of the least considered energy efficiency upgrades to conservation properties from a sample of 116 industry respondents. Forty one percent said improving floors was not a major objective; while only 9% to 18% said it was considered in most if not all projects respectively (Friedman, 2014).

6 The 'temperature take back factor' is "the degree to which fabric and ventilation changes could result in increases in

The upgrade of existing ground floor structures is regulated by Building Regulations Part L1B, which recommends insulated floor U-values of maximum 0.25 Wm^-2K^-1 for the entire floor when at least 50% of the floor surface is upgraded or replaced or where 25% of the entire building envelope is renovated (NBS, 2015). Exceptions exist for listed buildings and other relaxations exist to take account of practical and technical constraints (such as maximum 15 year payback, difficult floor level differences between parts, structural issues). In these cases a maximum U-value of 0.70 Wm^-2K^-1 is allowed (NBS, 2015). New ground floors are to be built to the same maximum U-value of 0.25 Wm^-2K^-1 in England and Northern Ireland and maximum 0.18 Wm^-2K^-1 in Scotland and Wales. These are improvements from 0.45 Wm^-2K^-1 in 1990, prior to which no recommendations were specified for floors (Dowson et al., 2012).

Other sources also recommend upgrade of floors with maximum U-values of 0.20 to 0.25 Wm^-2K^-1 (for example EST (2004, 2007)); Rickaby (2014a) recommends 0.25 Wm^-2K^-1 as good practice and 0.15 Wm^-2K^-1 for advanced practice. Such advanced U-values of 0.16 Wm^-2K^-1 and 0.13 Wm^-2K^-1 are reported by Baeli (2013) for the Shaftesbury Park Terrace with

fully-filled floor void with EPS beads (p37) and for Midmoor Road (p 41-42) respectively. The latter design value was achieved with a combination of 100 mm rigid insulation on top of joists and 100 mm mineral wool insulation between the joists. In another case study in Brent, spray foam floor insulation was predicted to lead to a U-value of 0.12 Wm^-2K^-1 but no further information was provided regarding the material or application depth (Baeli, 2013, p 65-66).

Large thermal improvements were also predicted for replacement of suspended timber ground floors with an insulated concrete ground floor: for example in Hawthorn Road, a U-value of 0.12 Wm^-2K^-1 was predicted with 200 mm EPS on top of a new concrete floor (Baeli, 2013, p 46), and 0.13 Wm^-2K^-1 in Greenwich (LEB, 2011a). In Liverpool, a U-value of 0.12 Wm^-2K^-1 was estimated by rebuilding a suspended ground floor with a proprietary product called Supafloor (LEB, 2011b).

The above floor U-values are based on modelled design predictions, not on actual in-situ measured performance, of which there are only a few published. Currie (2013) reported a 70% U-value reduction from 2.4 to 0.7 Wm^-2K^-1 in one pre-post measured point U-value; the floor was insulated with 80 mm woodfibre between joists. Harris (1997, 1994) observed up to 50% heat-flow reduction by insulating a test-cell floor and by stapling a radiant barrier under the joists of a test-cell; increased void airflow reduced the U-value reduction achieved. In New Zealand, Cox-Smith (2008) investigated the performance of foil insulation over time and observed that newer reflective foil draped over joists performed slightly better than when draped under joists and when soiled after several years. Isaacs (1985) conducted large-scale in-situ heat-flux monitoring of 63 houses in New Zealand and observed that foil-insulated floors with enclosed floor voids generally met the (then) stipulated building standards, while floors with no perimeter walls (i.e. exposed to the outside) and foil insulation did not meet those standards.

While insulation of floors should lead to reduced heat loss and increased space-heating energy savings, it might also lead to increased moisture build-up as found by Airaksinen (2003) in Finland. Airaksinen (2003) observed that floors with a typical U-value of 0.2 Wm^-2K^-1 had average void relative humidity (RH) almost 10% higher than floors with U-values of 0.4 Wm^-2K^-1; the latter floors lead to 2ºC warmer void air temperatures on average - see Section 2.7. Despite slow uptake of floor insulation, thousands of floors have already been insulated - see Chapter 1.2.3.; yet the impact on heat loss reductions, occupant thermal comfort and on floor void conditions are unknown, which hinders informed retrofit decision-making.

2.6.1. Typical floor insulation methods

In the UK typically a fibrous insulation is installed in between joists (Figure 7. option a) (BRE, 2000, EST, 2005, EH, 2010, Rock, 2013). Insulating floors with limited void access, such as the floors subject of this thesis, usually requires lifting of the floorboards, which is a disruptive process (Rickaby, 2014a). Access to floors from below is less disruptive (Roberts, 2008) though not always possible due to health and safety concerns. Despite potential large carbon savings (Shorrock, 2005), the disruptive potential of full floor insulation might lead to little uptake according to Dowson (2012), Shorrock (2005) and Killip (2011), who argue that full floor insulation in between joists makes only sense when taking up the floorboards anyway.

Figure 7. Typical floor insulation methods identified, including typical floor insulation installed in between joists (a.), under joists (b.) or a combination of insulation in between and under the joists (c.), on top of joists (d.) or on top of the floor boards (e.). Other methods include insulation sprayed to the underside of the floor boards and/or joists (f.), full-filling the floor void with insulation (g.) and installing insulation on the ground in the void and/or on the foundation perimeter walls (h.).

Little is published on insulation methods in terms of heat-loss reduction, thermal comfort improvements or any unintended consequences. There are several fixing options and combinations, usually aiming to improve airtightness with vapour permeable membranes at the underside of joists or with radiant barriers; sometimes membranes are also placed directly on top of the joists, or in both locations (see Figure 7.). The effect of insulation on dwelling airtightness is discussed in Chapter 6.5. Placing insulation on top of the joists reduces the joist thermal bridging effect but is more disruptive (Harris, 1997), and door openings, skirting boards and electrical sockets need adjusting (see Figure 7.d and e ).

Some novel insulation methods have recently been tested, most focusing on insulating the floor by lifting the fewest floorboards, thereby minimising disruption and intervention times.

For example, Retrovive (2015) blow cellulose fibre into a breather-membrane strategically installed by lifting only specific floorboards (Collings, 2015, Retrovive, 2015). Some systems include full-fill EPS bead insulation (Figure 7.g), as was undertaken at Shaftesbury Park Terrace (Baeli, 2013, TSB, 2011).

To avoid beads spilling out and to reduce moisture being brought in from the outside, airbricks are permanently sealed, though this is considered controversial as it is assumed airbricks regulate moisture in the void (see Douglas (1998c), BRE (1991) and Singh (1998)) and as discussed in Section 2.7.2.). The long-term impact of sealing airbricks in general or of these EPS bead-filled floor voids are however unknown.

Other innovative methods include remote spraying of insulation in floor voids (Baeli, 2013, p 65-66) (Figure 7. f), allowing simultaneous encapsulation of the joists, which otherwise tend to remain uninsulated and become a thermal bridge after insulating between the joists.

Q-bot (2015) are trialling robotics to survey the floor and apply insulation in this manner⁷ (Lipinski, 2015) while U-Floor Technologies, developed by Sustainable Venture Development in London, is a new innovative device deployed through the airbricks and using a natural, sprayable insulation material (Czako, 2015).⁸

The different installation options can be achieved with different insulation materials, some of which are listed in Appendix 2.B. Insulating timber floors is likely to increase the floor's

thermal mass: typically the thermal mass of an uninsulated suspended floor is between 5-7 kJ/m²K (carpet/vinyl floor finish on floorboards respectively; excluding foundation walls and the ground); which can increase to 17-19 kJ/m²K with 100 mm mineral wool in between the joists (CIBSE, 2015, table 3.53). This is however, still a relatively small thermal mass compared to solid concrete floors (38-58 kJ/m²K carpet/vinyl, uninsulated)(CIBSE, 2015) and the presence of the soil underneath the floor (1285 kJ/m²K based on 1 metre depth of common earth (CIBSE, 2015, table 3.37). Thermal mass is important in moderating temperature fluctuations and shifts temperature variations. Hence material conductivity, thermal mass and time constant (i.e. the time it takes to respond after a change) are

important material characteristics to consider in relation to heat-loss reduction interventions.

Generally, insulating floors reduces the heat-flow from the internally heated spaces to the floor void (and hence to the external environment) and the sub-floor void air and surfaces will become colder and closer in temperature to the external environment. This in turn affects the thermal mass equilibrium of the ground and foundation walls and the moisture content of the sub-floor void might increase to critical moisture levels for mould growth in summer - see the following Section 2.7.

7 The author was involved with q-bot for early research design in 2013/2014, based on the research design tested and developed in this PhD research to support q-bot in thermal performance monitoring, however no pre-post data was shared for analysis to be included in the thesis at the time of writing.