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Internal Wall Insulation on Solid Wall Buildings Some challenges Neil May.

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Presentation on theme: "Internal Wall Insulation on Solid Wall Buildings Some challenges Neil May."— Presentation transcript:

1 Internal Wall Insulation on Solid Wall Buildings Some challenges Neil May

2 Performance of breathable materials in UK dwellings INTERNAL WALL INSULATION – WHY?

3 Performance of breathable materials in UK dwellings INTERNAL WALL INSULATION – WHY?

4 Performance of breathable materials in UK dwellings INTERNAL WALL INSULATION – WHY? ?

5 Any one for EWI? Assessing the execution of retrofitted external wall insulation for pre-1919 dwellings in Swansea (UK); Joanne Hopper et al 2011

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8 Background Government/EU commitment to 80% reduction in GHG by 2050 All buildings to be near to zero GHG/ Carbon emissions by 2050 = One building every 50 seconds from now on Green Deal/ ECO programme starting this autumn (?) with particular emphasis on solid wall buildings 6 million plus solid wall buildings in UK, most in England, most are brick. Minimum 2 million expected to use Internal Wall Insulation Many cavity wall and other buildings to use IWI as well

9 Research Concerns Thermal performance – Background issue of U values of traditional walls – Effect of IWI on thermal resistance of masonry – Thermal bridging issues – Overheating issues Moisture performance – Effect of internal moisture – Effect of driven rain and other liquid moisture sources Health – Effect of above on occupant health – Interaction with other factors especially ventilation

10 Thermal issues: Traditional walls Do not conform to type of wall suited to BR 443 (using BS 9496) – ie discreet layers of known materials Consequently in –situ testing of traditional wall U values show that most walls perform better than under BR443 (incl RdSAP (2009) default values. Typically traditional walls have U values of 0.9 to 1.6W/m2K for walls over 225mm wide. The thicker the wall the better the U value. Performance is much affected by moisture. More moisture leads to lower thermal resistance. U value calculations given for IWI on traditional walls need to take these issues into account.

11 Thermal Limits (German house)

12 Energy loss through external wall in % Thickness of internal insulation in cm External insulation External Insulation versus Internal

13 Practical limits: Thermal Bridges Refurbishment of a traditional stone wall with 60 mm insulation on the inside Reveal not insulated Reveal now insulated with 40 mm insulation

14 Thermal Bridges: Party Wall Issues 12,6 °C Partial fixed internal wall insulation: Displacement of isotherms, surface temperature sinks on the non- insulated side of the wall  Risk of mould / mildew 13,1 °C 15 °C BeforeAfter

15 Moisture – research background Experimental work of Tim Padfield, Brian Ridout and others based on material qualities and site testing – no or little modelling used German work of IBP based on laboratory testing and modelling Masses of good conservation work and even more bad work on old buildings (no modelling or material testing, just observation) Everyone agrees that Glaser (ie EN as per BS5250) is inappropriate for IWI unless walls are absolutely dry and protected. EN is correct standard at present

16 Modelling Protocols BS EN (BS 5250) versus EN EN 13788EN Steady stateDynamic Monthly (averaged)Hourly Limited materials criteriaFull materials criteria No driven rainDriven rain No orientationOrientation

17 Driven rain and internal VCLs: Average water content of an external (German) wall water content in kg/m2 Insulation thickness (k-value 0.040) in mm Variant 1: without VCL Variant 2: with VCL Driven rain absorption 0% Driven rain absorption 50% Driven rain absorption 100% Source: Dr. A. Worch: Innendämmung: Bauphysikalische Aspekte, Probleme und Grenzen und Lösungswege für die Praxis (engl: Dr. A. Worch: Internal insulation: structural-physical aspects, problems and limits and solutions for the practice)

18 Conflicting understanding of risk? Driven rain is not so important in Germany as UK IBP sees presence of oxygen as critical RH limits in IBP – Max RH with air = 85% – Max RH without air = 95% Part F limits – 1 day 85% – 1 week 75% – 1 month 65%

19 Some Knowledge Gaps Material data (thermal and moisture) for traditional buildings Modelling (thermal and moisture) of traditional buildings Thermal performance of traditional buildings Moisture performance of all buildings esp traditional Weather data – particularly wind driven rain Mould formation processes and limits Construction fault modelling? New DIN ( ) says 250g/m2 into structure; UK? Durability of different materials under moisture (ie gypsum plaster) Consequential effects on whole building performance and occupant health

20 KTP approach Aim is to find a safe, effective, saleable solution for mainstream application. So focus on 9” to 13” brick buildings in England. Three legged strategy: Modelling Case studies, real life monitoring Laboratory testing Comparative testing of breathable and non-breathable systems

21 Modelling Use of WUFI Pro 5 1D Also use of Build Desk Modelling can tell you a lot, however…..

22 Problems with Modelling Human error Manipulation Data errors/ unknowns (ie OSB µ = 30/175) Simplification of complex structures Problems at junctions/ bits you can’t model Issue of how to model bad application False certainty

23 Swansea, SW London, SW Pavadentro on 9” solid brick, 1%DR

24 Swansea, SW Swansea, N Pavadentro on 9” solid brick, 1%DR

25 London, N London, SW Pavadentro on 9” solid brick, 1%DR

26 100mm Pavaflex on 9”solid brick, 0 DR

27 Impact of density On 9”solid brick Swansea 1% DR

28 Case Studies Very few available 2 year KTP, but problems may take 10 or 20 years to develop So many variables between each case study 28Neil May, February 2012

29 Case Studies Solid brick and Pavadentro – 1 with external render – 1 without render Solid brick and Celotex, without render, but brick impregnated LEAF funded project – 2 solid stone terraces with Pavadentro system & one new breathable system (not started) Trinity College Cambridge (not directly linked to KTP) ERDF Aim High 10 solid wall brick houses in Birmingham 29

30 Trinity College WUFI modelling with 3 different companies in 4 iterations, giving very different results Material Property Testing (GCU) Site survey (blower door, in situ U-value, RH monitoring, core samples for density and initial MC) 2 times with very different results Extensive monitoring planned after application 30Neil May, February 2012

31 Laboratory testing Test methodology Laboratory test update Proposals for future tests – Investigate the dry-out potential – Liquid moisture ingress – wind driven rain

32 Test methodology 8 different internal insulation systems 4 conventional systems – the most common IWI systems in the UK market 4 breathable systems from NBT – development of two new systems

33 Performance of breathable materials in UK dwellings MOISTURE TRANSFER Vapour diffusion Liquid transport: Wind driven rain Construction moisture Moisture convection: leaks summer winter

34 Performance of breathable materials in UK dwellings MOISTURE TRANSFER – TEST 1 Vapour diffusion Liquid transport: Wind driven rain Construction moisture Moisture convection: leaks

35 Performance of breathable materials in UK dwellings INTERNAL WALL INSULATION – LIMITS INTEXTINTEXT Low temperature at the wall-insulation interface Risk of interstitial condensation and mould growth T [ºC] T [ºC]

36 Performance of breathable materials in UK dwellings INTERNAL WALL INSULATION – LIMITS Low temperature at the wall-insulation interface Risk of interstitial condensation and mould growth

37 Performance of breathable materials in UK dwellings To what extent breathable materials can reduce the risk of interstitial condensation?

38 Performance of breathable materials in UK dwellings TEST METHODOLOGY

39 Performance of breathable materials in UK dwellings TEST METHODOLOGY Monitoring interstitial condensation by measuring the RH at the wall-insulation interface 6 RH capacitance sensors each section Additional test: comparison between monitoring and hygrothermal modelling (WUFI Pro)

40 Performance of breathable materials in UK dwellings TEST 1 Δ VP Settings: Driving force: vapour pressure differential External conditions: Manchester TRY file from CIBSE, diurnal temperature variation into account Internal conditions: WarmFront data (UCL), 80 th percentile bedroom RH Rain is not simulated

41 Performance of breathable materials in UK dwellings TEST 1 The wall is exposed to: November, December – winter : vapour adsorption due to diffusion May, June – spring : vapour desorption due to diffusion

42 Performance of breathable materials in UK dwellings TEST 1 – COMPARISON OF RELATIVE HUMIDITY Breathable materials: 22% average RH reduction Non-breathable materials: 8% average RH reduction Higher speed of desorption in breathable materials

43 Performance of breathable materials in UK dwellings ΔVP Higher speed of desorption in breathable materials (measured at the wall-insulation interface) Possible reasons: Low vapour permeability (vapour movement on both sides) The capillary suction moves the moisture away from the critical interface Breathable materials can store moisture (hygroscopicity) TEST 1

44 Performance of breathable materials in UK dwellings COMPARISON OF MONITORING AND MODELLING Settings: WUFI Pro 1D Climate file from chamber Only diffusion (rain is off) Initial conditions from chamber (trends comparison)

45 Performance of breathable materials in UK dwellings COMPARISON OF MONITORING AND MODELLING RH - simulated RH - monitored Wetting well simulated – drying underestimated Dry-fit Pavadentro

46 Performance of breathable materials in UK dwellings COMPARISON OF MONITORING AND MODELLING RH - simulated RH - monitored Pavaclay and Pavaflex

47 Performance of breathable materials in UK dwellings COMPARISON OF MONITORING AND MODELLING RH - simulated RH - monitored PIR

48 Performance of breathable materials in UK dwellings COMPARISON OF MONITORING AND MODELLING Do we know the properties of materials in traditional buildings? WUFI calculations agree with the measured data during vapour adsorption (“winter”) The simulation underestimates the dry-out potential of the materials Possible reason: – Underestimation of liquid transport coefficient in clay blocks and insulation materials – Incorrect algorithms in model

49 Some Specific Problems in Practice Rising damp. Different moisture levels at different parts of walls (ie corners). Joist ends Window reveals Partition/ party walls Uneven walls Gypsum plaster Knowing what walls are made of Quality of workmanship/ bad application Services Application in wet areas (bathroom, below DPC,…) What are extreme conditions/ limits? Human behaviour issues Long term maintenance of fabric and building services 49

50 Some interactions to be considered Internal Wall Insulation and thermal performance due to changing moisture levels Overheating Indoor air quality Ventilation requirements and systems Heating systems Occupant behaviour 50

51 Key findings so far No one really understands moisture movement. BR443 and BS 5250 currently inappropriate for modelling solid walls and possibly any wall with internal insulation Correct modelling and testing indicates that – External wetting is much more important than leakage of moisture into the structure – Location and orientation are critical for capillary open walls – Breathability of IWI systems is vital where walls are wet – Density of insulation is also vital – Too much vapour openness is sometimes a problem – In some situations only minimal or no insulation is possible 51

52 Way forward for IWI on Solid Walls? Must take into account faults and failures short and long term of both IWI application AND other building maintenance (incl external fabric, rain water, drains, ventilation) Need useful safe and buildable solutions, not over-optimised solutions to allow for unknowns, faults and human behaviour Pointless and dangerous going for U values better than 0.40W/m2k (?) Need much more evidence, as well as proper data sets for materials and weather Move towards simplified guidance rules and structure No “one size fits all” solution. Accept uncertainty and move forward with awareness. Its as much about process and people as technologies. 52

53 Thank you


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