Suspended timber ground floors: measured heat loss compared with models

Abstract

There are approximately 6.6 million dwellings in the UK built before 1919, predominantly constructed with suspended timber ground floors whose thermal performance has not been extensively investigated. The results are presented from an in-situ heat-flow measuring campaign conducted at 27 locations on a suspended timber ground floor, and the estimated whole-floor U-value compared with modelled results. Findings highlight a significant variability in heat flow, with increased heat loss near the external perimeter. In-situ measured-point U-values ranged from 0.54 ± 0.09 Wm −2 K −1 , when away from the external wall perimeter, to nearly four times as high (2.04 ± 0.21 Wm −2 K −1 ) when near the perimeter. The results highlight the fact that observing only a few measurements is likely to bias any attempts to derive a whole-floor Uvalue, which was estimated to be 1.04 ± 0.12 Wm −2 K −1 and nearly twice that derived from current models. This raises questions about the validity of using such models in housing stock models to inform retrofit decision-making and space-heating-reduction interventions. If this disparity between models and measurements exists in the wider stock, a reappraisal of the performance of suspended timber ground floors and heat-loss-reduction potential through this element will be required to support the UK's carbon-emission-reduction targets.

Suspended timber ground floors: Heat loss reduction potential of insulation interventions

“…The uninsulated floor point U-values (U p ) were estimated between 0.54 ± 0.09 Wm −2 K −1 further away from the exposed environment, to as much as 2.04 ± 0.21 Wm −2 K −1 near the perimeter wall and airbricks (location 6) -as reported in [38]. This large spread of U p -values and reduced U p -values with increased distance from the perimeter wall was as expected and as also observed across the floor in a thermal chamber [58].…”

“…(2). in Table 2, which is explained in detail in [38]. Sensors remained in place for the bead insulated floor and as such the contact, edge heat loss and instrument errors are identical before and after this intervention and may be excluded when comparing the relative U-values for the uninsulated and bead-insulated floor -see Eq.…”

“…The case study house was a pre-1919 solid wall terraced house located in a conservation area in London and the case study characteristics, alongside instrumentation of the uninsulated floor and research methods, are described in more detail in [38]. The 12.15 m 2 living room floor had a floor void depth of 250 mm below the 100 mm joists, with a 150 mm concrete oversite surface on the soil.…”

“…The 12.15 m 2 living room floor had a floor void depth of 250 mm below the 100 mm joists, with a 150 mm concrete oversite surface on the soil. Airbricks were located between the joists and three sleeper walls divided the void in four void sections, as described in [38]. A total of 27 heat flux sensors (Hukseflux HFP01, ±5% accuracy) were placed on the living-room floor surface, with one sensor on a joist, see Fig.…”

“…The financial payback of retrofit interventions depends on the accurate estimation of the construction's performance and on the actual achieved improvement in thermal performance. In particular, recent research suggests that actual floor heat loss might be underestimated by models, which could underestimate the energy saving potential of measures affecting this building component [38,39]. This paper explores the efficacy of retrofit measures on a suspended timber ground floor in a pre-1919 terraced house in West-London, UK.…”