Internal Wall Insulation on Solid Wall Buildings Some challenges Neil May

Internal Wall Insulation on Solid Wall BuildingsSome challenges

Neil May

Performance of breathable materials in UK dwellings

INTERNAL WALL INSULATION – WHY?





?

Any one for EWI?

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



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

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

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.

Thermal Limits (German house)

Ener

gy lo

ss th

roug

h ex

tern

al w

all i

n %

Thickness of internal insulation in cm External

insulation

External Insulation versus Internal

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

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 wallRisk of mould / mildew

13,1 °C 13,1 °C15 °C

Before After

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

• BS EN 13788 (BS 5250) versus EN 15026

16

EN 13788 EN 15026Steady state DynamicMonthly (averaged) HourlyLimited materials criteria Full materials criteriaNo driven rain Driven rainNo orientation Orientation

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

wall

wat

er c

onte

nt in

kg/

m2

Insulation thickness (k-value 0.040) in mm

Variant 1:without VCL

Variant 2:with VCL

Driven rain absorption 0%



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)

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%

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

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

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

Modelling can tell you a lot, however…..

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

40 60 80 10010

15

20

25

30

35 Moisture content - location

Insulation Thickness [mm]

Moi

stur

e co

nten

t [kg

/kg]

Liverpool, SW

Manchester, SW

Swansea, SW

London, SW

Pavadentro on 9” solid brick, 1%DR

40 60 80 10010

15

20

25

30

35Moisture content - orientation


Moi

stur

e co

nten

t [kg

/kg]

Swansea, SW

Swansea, N


40 60 80 10010

15

20

25

30

35Moisture content - orientation


Moi

stur

e co

nten

t [kg

/kg]

London, N

London, SW


London-N London-W Swansea-N Swansea-W15

17

19

21

23

25

27

29

31

33

35

Moisture content – different membranes

0

5

100

sd-value [m]

Moi

stur

e co

nten

t [kg

/kg]

100mm Pavaflex on 9”solid brick, 0 DR

Impact of density

0-10mm 10-20mm 20-30mm 30-100mm0

5

10

15

20

25

30

35

100mm Pavaflex

100mm Pavadentro

20mm Pavaclay & 80mm Pavaflex

Depth in construction

Moi

stur

e Co

nten

t (M

-%)

Ρdentro = 175 kg/m3

Ρclay = 380 kg/m3

Ρflex = 53 kg/m3

Ρflex = 53 kg/m3

On 9”solid brick Swansea 1% DR

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

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

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

Laboratory testing

• Test methodology

• Laboratory test update

• Proposals for future tests– Investigate the dry-out potential– Liquid moisture ingress – wind driven rain

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


MOISTURE TRANSFER

Vapour diffusion

Liquid transport: Wind driven rain

Construction moisture

Moisture convection: leaks

summerwinter


MOISTURE TRANSFER – TEST 1

Vapour diffusion

Liquid transport: Wind driven rain

Construction moisture

Moisture convection: leaks


INTERNAL WALL INSULATION – LIMITS

INTEXTINTEXT

Low temperature at the wall-insulation interface

Risk of interstitial condensation and mould growth

T[ºC]

T[ºC]


INTERNAL WALL INSULATION – LIMITS

Low temperature at the wall-insulation interface

Risk of interstitial condensation and mould growth


To what extent breathable materials

can reduce the risk of interstitial

condensation?


TEST METHODOLOGY


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)


TEST 1

Δ VP

ΔVP

ΔVP

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

The wall is exposed to:

• November, December – winter: vapour adsorption due to diffusion

• May, June – spring: vapour desorption due to diffusion


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


ΔVP

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


COMPARISON OF MONITORING AND MODELLING

Settings:

• WUFI Pro 1D

• Climate file from chamber

• Only diffusion (rain is off)

• Initial conditions from chamber (trends comparison)


COMPARISON OF MONITORING AND MODELLING RH - simulated

RH - monitored

Wetting well simulated – drying underestimated

Dry-fit Pavadentro



RH - simulated

RH - monitored

Pavaclay and Pavaflex


COMPARISON OF MONITORING AND MODELLING RH - simulated

RH - monitored

PIR



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

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

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

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

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

Thank you

www.natural-building.co.uk

Documents

Internal Wall Insulation on Solid Wall Buildings Some challenges Neil May