Internal Wall Insulation on Solid Wall BuildingsSome challenges
Neil May
Performance of breathable materials in UK dwellings
INTERNAL WALL INSULATION – WHY?
Performance of breathable materials in UK dwellings
INTERNAL WALL INSULATION – WHY?
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
Assessing the execution of retrofitted external wall insulation for pre-1919 dwellings in Swansea (UK); Joanne Hopper et al 2011
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%
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)
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
Insulation Thickness [mm]
Moi
stur
e co
nten
t [kg
/kg]
Swansea, SW
Swansea, N
Pavadentro on 9” solid brick, 1%DR
40 60 80 10010
15
20
25
30
35Moisture content - orientation
Insulation Thickness [mm]
Moi
stur
e co
nten
t [kg
/kg]
London, N
London, SW
Pavadentro on 9” solid brick, 1%DR
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
Performance of breathable materials in UK dwellings
MOISTURE TRANSFER
Vapour diffusion
Liquid transport: Wind driven rain
Construction moisture
Moisture convection: leaks
summerwinter
Performance of breathable materials in UK dwellings
MOISTURE TRANSFER – TEST 1
Vapour diffusion
Liquid transport: Wind driven rain
Construction moisture
Moisture convection: leaks
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]
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
Performance of breathable materials in UK dwellings
To what extent breathable materials
can reduce the risk of interstitial
condensation?
Performance of breathable materials in UK dwellings
TEST METHODOLOGY
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)
Performance of breathable materials in UK dwellings
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
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
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
Performance of breathable materials in UK dwellings
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
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)
Performance of breathable materials in UK dwellings
COMPARISON OF MONITORING AND MODELLING RH - simulated
RH - monitored
Wetting well simulated – drying underestimated
Dry-fit Pavadentro
Performance of breathable materials in UK dwellings
COMPARISON OF MONITORING AND MODELLING
RH - simulated
RH - monitored
Pavaclay and Pavaflex
Performance of breathable materials in UK dwellings
COMPARISON OF MONITORING AND MODELLING RH - simulated
RH - monitored
PIR
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
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