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Internal Wall Insulation on Solid Wall Buildings Some challenges. Neil May. INTERNAL WALL INSULATION – WHY?. INTERNAL WALL INSULATION – WHY?. ?. INTERNAL WALL INSULATION – WHY?. Any one for EWI ?.

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slide4

?

INTERNAL WALL INSULATION – WHY?

any one for ewi
Any one for EWI?

Assessing the execution of retrofitted external wall insulation for pre-1919 dwellings in Swansea (UK); Joanne Hopper et al2011

slide6

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

slide7

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

slide8

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
slide9

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
slide10

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 (inclRdSAP (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.
external insulation versus internal
External Insulation versus Internal

Energy loss through external wall in %

External

insulation

Thickness of internal insulation in cm

slide13

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
slide14

Thermal Bridges: Party Wall Issues

Before After

13,1 °C

13,1 °C

12,6 °C

15 °C

  • Partial fixed internal wall insulation:
  • Displacement of isotherms, surface temperature sinks on the non-insulated side of the wall
    • Risk of mould / mildew
moisture research background
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 13788 as per BS5250) is inappropriate for IWI unless walls are absolutely dry and protected. EN 15026 is correct standard at present
modelling protocols
Modelling Protocols
  • BS EN 13788 (BS 5250) versus EN 15026
slide17

Driven rain and internal VCLs: Average water content of an external (German) wall

Driven rain absorption 100%

Variant 1:

without VCL

water content in kg/m2

Driven rain absorption 50%

Variant 2:

with VCL

Driven rain absorption 0%

Insulation thickness (k-value 0.040) in mm

Source: Dr. A. Worch: Innendämmung: BauphysikalischeAspekte, Probleme und Grenzen und Lösungswegefür die Praxis

(engl: Dr. A. Worch: Internal insulation: structural-physical aspects, problems and limits and solutions for the practice)

conflicting understanding of risk
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%
slide19

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 (68800-2) says 250g/m2 into structure; UK?
  • Durability of different materials under moisture (ie gypsum plaster)
  • Consequential effects on whole building performance and occupant health
ktp approach
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

modelling
Modelling
  • Use of WUFI Pro 5 1D
  • Also use of Build Desk

Modelling can tell you a lot, however…..

problems with modelling
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
slide23

Swansea, SW

London, SW

Pavadentro on 9” solid brick, 1%DR

slide24

Swansea, SW

Swansea, N

Pavadentro on 9” solid brick, 1%DR

slide25

London, N

London, SW

Pavadentro on 9” solid brick, 1%DR

impact of density
Impact of density

On 9”solid brick Swansea 1% DR

case studies
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

Neil May, February 2012

case studies1
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
trinity college
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

Neil May, February 2012

slide31

Laboratory testing

  • Test methodology
  • Laboratory test update
  • Proposals for future tests
    • Investigate the dry-out potential
    • Liquid moisture ingress – wind driven rain
slide32

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
slide33

MOISTURE TRANSFER

Moisture convection:

leaks

Liquid transport:

Wind driven rain

Vapour diffusion

Construction moisture

summer

winter

slide34

MOISTURE TRANSFER – TEST 1

Moisture convection:

leaks

Liquid transport:

Wind driven rain

Vapour diffusion

Construction moisture

slide35

T

[ºC]

T

[ºC]

INTERNAL WALL INSULATION – LIMITS

EXT

INT

EXT

INT

Low temperature at the wall-insulation interface

Risk of interstitial condensation and mould growth

slide36

INTERNAL WALL INSULATION – LIMITS

Low temperature at the wall-insulation interface

Risk of interstitial condensation and mould growth

slide39

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)

slide40

Settings:

  • Driving force: vapour pressure differential
  • External conditions: Manchester TRY file from CIBSE, diurnal temperature variation into account
  • Internal conditions: WarmFront data (UCL), 80th percentile bedroom RH
  • Rain is not simulated

TEST 1

Δ VP

ΔVP

ΔVP

slide41

TEST 1

The wall is exposed to:

  • November, December – winter: vapour adsorption due to diffusion
  • May, June – spring: vapour desorption due to diffusion
slide42

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

slide43

TEST 1

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)

ΔVP

ΔVP

slide44

Settings:

  • WUFI Pro 1D
  • Climate file from chamber
  • Only diffusion (rain is off)
  • Initial conditions from chamber (trends comparison)

COMPARISON OF MONITORING AND MODELLING

slide45

RH - simulated

RH - monitored

COMPARISON OF MONITORING AND MODELLING

Dry-fit Pavadentro

Wetting well simulated – drying underestimated

slide46

RH - simulated

COMPARISON OF MONITORING AND MODELLING

RH - monitored

Pavaclay and Pavaflex

slide47

RH - simulated

RH - monitored

COMPARISON OF MONITORING AND MODELLING

PIR

slide48

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

COMPARISON OF MONITORING AND MODELLING

Do we know the properties of materials in traditional buildings?

some specific problems in practice
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
some interactions to be considered
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
key findings so far
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
way forward for iwi on solid walls
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.
thank you

Thank you

www.natural-building.co.uk