Transcript Title Slide

New Models for
Interstitial Condensation
Chris Sanders
BRE Scotland
New Models for Interstitial Condensation
 Importance of Interstitial
Condensation
 Standards and Regulations
 Available models
 Boundary conditions
 Material properties
 Which model should be used?
Surface Condensation
Interstitial condensation?
Interstitial condensation
Moisture movement within the materials making
up a structure leading to local accumulations
sufficient to cause problems:
 Rot
 Corrosion
 Frost damage
 Wetting of insulation
 Staining of internal surfaces
 Damage to equipment within the building
Standards for Interstitial Condensation
BS5250:1979 - Dewpoint Method
 BS5250:1989 - Appendix D contains a
calculation procedure
 BS5250:2002 references
BS EN ISO 13788:2002
 CEN TC89 WI 29.3 Standard for
‘Assessment of moisture transfer by
numerical simulation’ in preparation

Building Standards (Scotland) Regulations
Regulation 18:
A building of purpose group 1 (i.e. housing)
shall be so constructed as to protect the
building and its users, so far as may be
reasonably practicable, from harmful effects
caused by condensation.
Building Standards (Scotland) Regulations
Standard G4.1
A floor, wall, roof or other building element
of a dwelling must minimise the risk of
interstitial condensation in any part of a
dwelling which it could damage.
Building Standards (Scotland) Regulations
Provisions deemed to satisfy the standards:
Interstitial condensation
(G4.1) The requirements of G4.1 will be met
where the walls, roofs and floors are assessed
and/or constructed in accordance with
Appendix D and Clauses 9.1 to 9.5.5.2 of
BS5250:1989
Draft Approved Document C : 2004
Requirements
Resistance to moisture
C2. The floors, walls and roof of the building shall adequately
protect the building and its users from harmful effects caused
by  ground moisture;
 precipitation and wind-driven spray;
 interstitial and surface condensation; and
 spillage of water from or associated with sanitary fittings or
fixed appliances.
Draft Approved Document C : 2004
External walls (resistance to damage from interstitial
condensation)
5.3.4 An external wall will meet the requirement if it is designed
and constructed in accordance with Clause 8.3 of BS 5250:2002,
and BS EN ISO 13788:2001.
5.3.5 Because of the high internal temperatures and humidities,
there is a particular risk of interstitial condensation in the walls of
swimming pools and other buildings in which high levels of
moisture are generated; specialist advice should be sought when
these are being designed.


Similar requirements for floors and roofs
AD F2 moved into C
Available Models

BRECON - BS5250:1989 but includes
ventilated cavities

ICOND - BS5250:2002 and BS EN ISO 13788

MATCH, WUFI, MOIST …..
Theoretical basis of the BS5250 / EN 13788
method

Both use the ‘Glaser’ method
Steady state 1D vapour diffusion
 Constant material properties
 Materials are dry until condensation occurs at
interfaces when RH=100%
 Ventilation of cavities can be included

Glaser misses out:






Materials are hygroscopic, liquid water stored in
pores
Materials can start wet from built in water or rain
ingress during construction
Water moves by a combination of vapour and
liquid flow
Material properties are effected by moisture
content
2D and 3D flows can be important
Driving forces change on diurnal scales
Three winter days
10
Temperature : C
5
Surface temperature
Air Temperature
0
-5
-10
-15
-20
31-Dec
1-Jan
2-Jan
Three summer days
60
Surface temperature
Air Temperature
Temperature : C
50
40
30
20
10
0
11-Jun
12-Jun
13-Jun
Glaser method

Wall or roof divided into a series of homogenous
layers

Thermal and vapour resistance of each layer used
to calculate the temperature (SVP) and vapour
pressure (VP) profiles

If the VP is less than the SVP at all points no
condensation

VP > SVP at any point  condensation

Recalculate profile

Condensation rate
= Vapour flow in - Vapour flow out
.
Glaser profile through wall
BRECON Cavity Ventilation
But what are the flow rates?
Ventilating cavity - partial cavity fill
Unventilated
Ventilated
Ventilating cavity on the cold side
Air Infiltration from building into structure
No models and no data
Stack effect raises internal air
pressure in upper half of the
building in winter
Wind forces may raise internal
pressure intermittently
Operating theatres etc. operate
at over pressure
Condensation standards


BS5250:1989 - Two months of winter
weather : if condensation predicted the
designer should decide whether it is
important
BS5250 : 2002 / BS EN ISO 13788:2002 Twelve months of condensation and
evaporation : three pass/fail criteria
EN 13788 Criteria
No condensation in any month  Pass
 Condensation in winter, which evaporates
in summer  Pass or Fail depending on
amount and material
 Condensation in winter, which does not
evaporate in summer
 Fail because assumed to
cause accumulation over successive years

.
EN 13788 Criteria
300
Accumulated Condensation g/m2
250
A
B
C
200
150
100
50
0
Oct
Nov
Dec
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Boundary Conditions
BRECON
External - January and February mean T & RH
Internal - Any T & RH appropriate to the building type

ICOND
External - 12 monthly means of T & RH
Internal - T = 20°C + 12 monthly RHs determined by internal
humidity class

Internal Humidity Classes
Dv
3
kg/m
Dp
Pa
0,008 1080
5
0,006 810
4
3
0,004 540
2
0,002 270
1
0
-5
0
5
10
15
20
Monthly mean outdoor air temperature, q e
25 o C
Internal Humidity Classes
Humidity
class
Building type
1
2
3
4
Storage areas
Offices, shops
Dwellings with low occupancy
Dwellings with high occupancy, sports halls,
kitchens, canteens; buildings heated with
unflued gas heaters
Special buildings, e.g. laundry, brewery,
swimming pool
5
Relative humidity at internal
temperature
15 C
20 C
25C
<50
<35
<25
50 – 65
35 – 50
25 – 35
65 – 80
50 - 60
35 - 45
80 – 95
60 – 70
45 – 55
>95
>70
>55
Boundary Conditions
MATCH requires
 Internal – Monthly means or hourly values of T & RH
 External – Years of hourly values of :
• Temperature
• Dewpoint
• Wind speed
• Cloud cover
• Global, diffuse and direct solar radiation
EC TRYS for Kew, Aberporth, Eskdalemuir, Lerwick
METEONORM??
Central England Temperature 1950 - 2050
12
Eskdalemuir
Kew
Annual Mean
Number of years
10
8
6
4
2
0
7
7.2
7.4
7.6
7.8
8
8.2
8.4
8.6
8.8
9
9.2
9.4
9.6
9.8
10
10.2
10.4
10.6
Annual temperature
10
Kew
Eskdalemuir
9
8
January Mean
Number of years
7
6
5
4
3
2
1
0
-2
-1.5
-1
-0.5
0
0.5
1.5
2
2.5
3
3.5
January Mean Temperature
4
4.5
5
5.5
6
6.5
Material properties
BS EN ISO 13788 method requires

Thermal conductivity – widely available with
corrections for moisture content and information on
likely variability

Vapour permeability – wet cup and dry cup values
available for many materials, but little information on
variability
Material properties
Match requires





Thermal conductivity and Vapour permeability
Density and specific heat – generally available
Water sorption coefficient – standard test, but data
not generally available
Sorption Isotherm – standard test data catalogues
available.
Liquid water diffusivity – no standard test and no data
available
External Insulation
External Insulation - January profile
External Insulation - ICOND Results
100
Condensation rate : g/m²/month
80
Accumulation : g/m²
Rate & Accumulation
60
40
20
0
Oct
-20
-40
-60
-80
Nov
Dec
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
External Insulation
Render
Outer 5mm XPS
Inner 85mm XPS
Outer 5 mm AAC
Inner 185mm Celcon
Plaster
6
Moisture content: %
5
4
3
2
1
0
Sep
Oct
Nov
Dec
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
External Insulation - MATCH no liquid
100
Mortar
Outer 5mm EPS
Inner 85mm EPS
Outer 5mm Celcon
Inner 185mm Celcon
Plaster
Moisture content : %
80
60
40
20
0
1
2
3
4
5
Years
6
7
8
External Insulation - MATCH liquid
40
35
Mortar
Outer 5mm EPS
Inner 85mm EPS
Outer 5mm Celcon
Inner 185mm Celcon
Plaster
Moisture content : %
30
25
20
15
10
5
0
1
2
3
4
5
Years
6
7
8
Partial Cavity Fill
Partial Cavity Fill - January profile
Partial Cavity Fill - ICOND Results
150
Condensation rate : g/m²/month
Accumulation : g/m²
Rate & Accumulation
100
50
0
Oct
-50
-100
-150
Nov
Dec
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Partial Cavity Fill - no liquid transport
20
18
16
Brick:outer 97mm
Brick: inner 5mm
Polyurethane: outer 4mm
Polyurethane: centre
Moisture Content : %
14
Polyurethane: inner 4mm
Celcon
12
Plaster
10
8
6
4
2
0
Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug
Partial Cavity Fill - with liquid transport
20
Brick:outer 97mm
18
16
Moisture Content : %
14
Brick: inner 5mm
Polyurethane: outer 4mm
Polyurethane: centre
Polyurethane: inner 4mm
Celcon
12
Plaster
10
8
6
4
2
0
Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug
Full Cavity Fill
Full Cavity Fill - January profile
Full Cavity Fill - ICOND Results
1400
Condensation rate : g/m²/month
Accumulation : g/m²
1200
Rate & Accumulation
1000
800
600
400
200
0
Oct
-200
Nov
Dec
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Full Cavity Fill - MATCH no liquid
400
350
Moisture Content : %
300
Brick : Outer 97mm
Brick : Inner 5mm
Mineral Wool : Outer 5mm
Mineral wool ; Inner 95mm
250
200
150
100
50
0
Sep
Oct
Nov
Dec
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Full Cavity Fill - MATCH liquid flow
8
7
Brick : Outer 97mm
Brick : Inner 5mm
Mineral Wool : Outer 5mm
Mineral wool ; Inner 95mm
Moisture Content : %
6
5
4
3
2
1
0
Sep
Oct
Nov
Dec
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Internal Insulation
Internal Insulation - January profile
Internal Insulation - ICOND Results
300
250
Condensation rate : g/m²/month
Accumulation : g/m²
Rate & Accumulation
200
150
100
50
0
Oct
-50
-100
Nov
Dec
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Internal Insulation - MATCH no liquid
26
Brick:outer 97mm
24
Brick: inner 5mm
Moisture Content : %
22
Celcon: outer 95mm
Celcon: inner 5mm
20
Polyurethane: outer 5mm
18
Polyurethane: inner 60mm
16
Plasterboard
14
12
10
8
6
4
2
0
Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug
Internal Insulation - MATCH with liquid
26
Moisture Content : %
24
Brick:outer 97mm
Brick: inner 5mm
22
Celcon: outer 95mm
20
Celcon: inner 5mm
18
16
Polyurethane: outer 5mm
Polyurethane: inner 60mm
Plasterboard
14
12
10
8
6
4
2
0
Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug
Timber Framed Wall
Timber Framed Wall - January profile
Timber Framed Wall - ICOND Results
4500
4000
Condensation rate : g/m²/month
Accumulation : g/m²
Rate & Accumulation
3500
3000
2500
2000
1500
1000
500
0
Oct
-500
Nov
Dec
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Timber Framed Wall MATCH no liquid
350
Brick: outer 97mm
Brick: inner 5mm
300
Plywood:outer 10.5mm
Plywood:inner 2mm
Moisture Content : %
250
Glasswool: outer 5mm
Glasswool: inner 95mm
Plasterboard
200
150
100
50
0
Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug
Timber Framed Wall MATCH with liquid
35
30
Moisture Content : %
25
20
Brick: outer 97mm
Brick: inner 5mm
15
Plywood:outer 10.5mm
Plywood:inner 2mm
10
Glasswool: outer 5mm
Glasswool: inner 95mm
Plasterboard
5
0
Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug
Timber Flat Roof
Timber Flat Roof - January profile
Timber Flat Roof - ICOND Results
2000
1800
Condensation rate : g/m²/month
Accumulation : g/m²
1600
Rate & Accumulation
1400
1200
1000
800
600
400
200
0
Aug
-200
Sep
Oct
Nov
Dec
Jan
Feb
Mar
Apr
May
Jun
Jul
Timber Flat Roof MATCH no liquid
50
30
20
10
Fe
b
M
ar
Ap
r
M
ay
Ju
n
Ju
l
Au
g
Se
p
O
ct
N
ov
D
ec
Ja
n
Fe
b
M
ar
Ap
r
M
ay
Ju
n
Ju
l
Au
g
0
Se
p
O
ct
N
ov
D
ec
Ja
n
Moisture Content : %
40
EPDM
Plywood: outer 2mm
Plywood: centre 16mm
Plywood: inner 2mm
Rockwool: centre 170mm
Rockwool: inner 5mm
Plasterboard
Timber Flat Roof MATCH with liquid
50
30
20
10
Ju
n
Ju
l
Au
g
Ju
n
Ju
l
Au
g
Se
p
O
ct
N
ov
D
ec
Ja
n
Fe
b
M
ar
Ap
r
M
ay
0
Se
p
O
ct
N
ov
D
ec
Ja
n
Fe
b
M
ar
Ap
r
M
ay
Moisture Content : %
40
EPDM
Plywood: outer 2mm
Plywood: centre 16mm
Plywood: inner 2mm
Rockwool: centre 170mm
Rockwool: inner 5mm
Plasterboard
Concrete Flat Roof
Concrete Flat Roof - January profile
Concrete Flat Roof - ICOND Results
160
Condensation rate : g/m²/month
140
Accumulation : g/m²
Rate & Accumulation
120
100
80
60
40
20
0
Aug
-20
Sep
Oct
Nov
Dec
Jan
Feb
Mar
Apr
May
Jun
Jul
Concrete Flat Roof
MATCH - no liquid transport
Moisture content : %
8
XPS: inner 5mm
Concrete: outer 10mm
Concrete: inner 10mm
XPS: middle 90mm
Screed
Concrete: centre 140mm
XPS: outer 5mm
180
160
7
140
6
120
5
100
4
80
3
60
2
40
1
20
0
0
Sep Jan May Sep Jan May Sep Jan May Sep Jan May Sep Jan May
Outer 5mm XPS Moisture content : %
9
Concrete Flat Roof
MATCH - with liquid transport
14
Moisture content : %
12
10
180
XPS: middle 90mm
XPS: inner 5mm
Screed
Concrete: outer 10mm
Concrete: centre 140mm
Concrete: inner 10mm
XPS: outer 5mm
160
140
120
100
8
80
6
60
4
40
2
0
Sep Jan May Sep Jan May Sep Jan May Sep Jan May Sep Jan May
20
0
Outer 5mm XPS Moisture content : %
16
Moisture flows from house to loft
Conclusions

Boundary conditions should represent ‘extreme’
rather than ‘mean’ years - once in ten years?.

We need information on air flows in cavities

We need models that can take account of air
infiltration from within a building into the structure and
we need the data to run them
Conclusions



Simple ‘Glaser’ models are adequate for many lightweight
structures, with little storage capacity
More complex models are needed for ‘heavy’ constructions
that store water
We need the material properties data and the climate data to
run these models.
Questions
What is your experience of interstitial condensation
problems?
 Do you use prediction models?
 What guidance documents are needed
 Regulations are starting to require more thermal
complex calculations – should moisture be going the
same way?
