New construction techniques and modern concepts applied to existing historic building envelopes

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New construction techniques and modern concepts applied to existing historic building envelopes

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New Construction Techniques and Modern

Concepts Applied to Existing Historic

Building Envelopes

by

Madeleine Z. Rousseau

National Research Council Canada, Ottawa for

“Tell Them What You Are Going

to Tell Them…”

3 Blocks:

1. Air, moisture and heat flow – Control strategies 2. Rain penetration - Control strategies

Environmental loads affect the

performance of the building envelope

‰ Degree of deterioration – severity of load effects and dose – response relations

‰ Mechanisms of deterioration

Most common agent

of deterioration?

MOISTURE

‰ Mechanical

-deformation,cracking, spalling

‰ Thermal

-Freeze-thaw action, cracking & spalling

‰ Biological

-wood rot, mould growth

‰ Chemical

Moisture Sources

• Before and during construction & conservation

– Building materials during storage and transportation – Rain & snow accumulation during construction

– Construction processes (e.g. concrete)

• During service life

– Exterior sources: rain, snow, ice, atmospheric water vapour, soil

– Indoor sources: occupants and their activities, HVAC systems

Seasonal phenomena

Wintertime

condensation

Rain penetration and

Factors at Work for Condensation

Moisture

(vapour)

Travel Path

Drive

A Differential …

Temperature

gradient

Climates (wind,

Climates (wind,

temperature)

temperature)

and HVAC

and HVAC

Climates;

Climates;

thermal properties

thermal properties

of materials &

of materials &

assemblies

assemblies

(Indoor, outdoor,

(Indoor, outdoor,

construction)

construction)

Vapour and air

Vapour and air

permeance

permeance

of materials &

of materials &

assemblies

assemblies

Factors at Work for Condensation

Moisture (Vapour)

Travel Path

“Through & between, materials

Drive

A Differential …

Temperature Gradient

Vapour Diffusion

Air

Movement

Air leakage versus vapour diffusion

Air leakage is the most significant water

vapour transport mechanism

into concealed spaces

of the building envelope

Air Leakage

The drive:

• Air pressure differential

The resistance:

• Air permeance of materials • Openings

P

_out

< P

_in

Types of air flow

Air Barrier Requirements

•

It is a

SYSTEM

made of

SEVERAL

materials over

the building envelope

•

Materials of low air permeance

•

Rigid assembly, for small deformations

•

Structural strength, to sustain wind loads

•

Most challenging:

Continuity

at joints and

Air Permeance of ABS Materials

Low air permeance

Max 0.02 L/(s•m

2

_{) at 75 Pa}

– Aluminum foil, polyethylene sheet (negligible),

elastomeric membrane (negligible)

spun-bonded polyolefin (0.004)

– Gypsum board (0.009)

– Plywood (0.008), OSB (0.01)

Structural Requirements for the AB

System

‰ Must sustain and transfer 100% of the

wind loads to the structure

– without damage to itself or to adjacent materials and, – without much increase in system air leakage

‰ _{Limited deflection}

EX: the airtight element of the air barrier system may be a flexible membrane

Quantitative Requirements for AB

System

‰

…Air leakage must be controlled to a level where

the

occurrence

of condensation has

to be sufficiently rare,

quantities

sufficiently

small,

drying

sufficiently rapid to avoid material

deterioration

and growth of

mould

and

fungi

.

NBC Appendix A 9.25.3.1

How m

uch for

how lo

ng?

How m

uch for

how lo

ng?

Evaluation Guide for Evaluation of Air

Barrier Systems for Exterior Walls of

Low-Rise Buildings, by NRC Canadian

Construction Materials Centre (CCMC)

**The least drying potential to the outside,

the more airtight the Air barrier should be

Continuity of the ABS

‰

_{Clear design intent:}

What wall materials are to act as the ABS, the airtight element, the rigidity, etc.

‰

How to carry these properties all over the

building enclosure?

Provide thought-through detailing of all junctions.

‰

Validate buildability

Convey the objective to the trades, with mock-up, and figure out the sequencing of trades.

Location of Air Barrier System

‰

Could be almost anywhere …

‰

More durable when the temperature gradient

across it is small

‰

Depends on the vapour permeance of the main

materials

When ABS material has low vapour

permeance, maintain it above dew

point temperature of indoor air.

Need for thermal insulation on the

outside of ABS

CCMC-evaluated Air Barrier

Systems

‰

AB

Systems

– Two insulation-based systems for placement on the exterior of the stud cavity

• Extruded polystyrene; spray-in-place polyurethane systems

Examined the material and system requirements

‰

_AB

_Materials

– Several breather-type sheathing membranes Examined the air permeance, but no system issues (e.g. the effect of fasteners or structural capability)

Moisture Diffusion

The drive:

•

Vapour pressure differential

–

Moisture content

in air

The path of resistance:

–

Vapour permeance of

materials

–

(ng/Pa•s•m

2

_{) for a given}

Requirements for Vapour Barrier

(VB)

‰

Material

of low vapour permeance

– Polyethylene sheet; glass and metals, foil-faced materials,

– Extruded polystyrene (25 mm) = 23-92 ng/(Pa•s•m2₎

– OSB (11 mm) = 44 ng/(Pa•s•m2₎

– Plywood (6.4 mm) = 23-74 ng/(Pa•s•m2₎

‰

_{Location: warm side of the assembly}

Control of Thermal Gradients

EXT

EXT EXTEXT _EXTEXT EXTEXT

+20

+20°°CC

--2020°°CC

INT

INT INTINT _INTINT INTINT

A

A

B

B

C

C

D

D

+20 +20°°CC +20+20°°CC +20+20°°CC --2020°°CC --2020°°CC --2020°°CC

“Tell them what you are going to tell

them…”

3 Blocks:

9 Air, moisture and heat flow – Control strategies 2. Rain penetration - Control strategies

Vancouver BC

Rain Penetration Problems Occur in Cold

climate and Not Just in Coastal Regions

Wetting/Drying Balance

Inappropriate balance between

wetting

and

drying

mechanisms

– Exposure - walls got wet

– Details let water in

– Sensitivity of assemblies – inability to drain or dry

Wetting

• The 6 D Approach

– D

eflect

– D

rain

– D

ry

– D

urable

– “

D

eal with air

pressure difference”

D E T A I L I N G Sequencing … Think 3D Think cross trading…

WATER

WATER

FORCES

FORCES

HOLES

HOLES

Three Conditions Required for Water

Ingress

Over time, design strategies focused on the control of some of these conditions

Effect of Overhang on Wall Performance 0 10 20 30 40 50 60 70 80 90 100 0 1-300 301-600 Over 600

Width of overhang above wall, mm

Per centa ge of walls with pr oblems

Single Element Protection

Mass walls (masonry)

• Masonry is porous

• Thickness of masonry provides large storage capability and long path for water ingress

• Rain deflection on building facades was extensive (e.g. deep

overhangs

• As structural design evolved toward non-load-bearing facades, masonry walls were built thinner and that

prompted a change in design to control rain ingress ( i.e. cavity walls)

Face Seal Approach: Control the Holes

• Cladding assembly is the

ONLY line of defense against rain penetration (and air leakage)

• No provision for water

evacuation once it gets in

• High on-going maintenance;

reliance on exterior seals

Goal: PERFECTION

To eliminate all openings in the cladding system

Inner wall

Air & water tight cladding

Single Element Protection

Multiple –Elements of Protection

Cavity walls

• Started with masonry, where two layers of masonry were separated by a large air space, flashed and drained at bottom

• Brick veneer with a 1 in. air

space, moisture barrier, flashing and weepholes

• Siding installed on vertical furring strips over a moisture barrier, with flashing drained outside

• Includes a drainage space, a capillary break and a moisture barrier

• Includes some redundancy, and control some of the forces

Rain Screen Walls

WATER

WATER

FORCES

FORCES

HOLES

HOLES

Premises:

¾All holes cannot be eliminated

¾Water may enter past the cladding ¾Need to manage all forces, and

Forces

Holes

Holes

Water

Water

• Gravity • Surface tension • Capillarity

• Rain drop momentum

• Air Pressure Difference

Reduce Forces Acting on Cladding

•Cavity wall

•Rain screen; Drain screen

•equalized; modulated; Pressure-moderated;Pressurized rain screen

Interior

Gravity

Horizontal Joint

Exterior

Forces Acting on Cladding-

Gravity

Gravity

Int. Ext.

Forces Acting on Cladding-

Surface

Tension & Capillarity

Surface tension Interior Capillarity Exterior Control of cracks Control porosity ??? 10 mm

Rain drop momentum

Interior Exterior

Forces Forces Acting on Cladding

-Rain Drop Momentum

Vertical joint

Control of Forces-

Air Pressure Difference

Air Pressure Difference

Air pressure difference P_o P i P o> Pi Interior Exterior o P o P = Pi P_i

?

P_c P P o o

=

=

PPc_c

“Tell them what you are going to tell

them…”

3 Blocks:

9 Air, moisture and heat flow – Control strategies 9 Rain penetration - Control strategies

• Different materials and construction techniques • Little/no insulation in place • No designated air barrier

• No designated vapour barrier • Different detailing

• No humidification

• Depressurization with several stacks and combustion systems • May have been subjected to poor

maintenance, poor alterations and “improvements”

• Little concern over energy

efficiency, thermal comfort and air quality

• Buildings last centuries

Applying these principles to “upgrade”

older masonry buildings

Old Buildings - Appreciating the differences:

Typical scenario: “the building will be converted to new use. Can we add some thermal insulation on the inside

Concerns over adding thermal insulation

inside

• Adding thermal insulation on the interior side will result in colder masonry in wintertime

• Colder masonry may be more susceptible to:

– interstitial condensation, mould and water damage, & frost jacking

– differential movement with other adjoining elements, and crack formation or displacement

– more freeze-thaw cycles on sunny facades, possibly resulting in spalling where masonry is water saturated

– Less drying potential (and increased time of wetness) which can affect moisture sensitive materials embedded in the

• If the only thing you were going to do is to add thermal insulation, yes all these risks could materialize…

A holistic approach needs to be adopted

Minimize external moisture loads transport:

¾Minimize rain and melting snow deposition on masonry ¾Preserve the integrity of the first line of protection against rain infiltration

Minimize internal moisture loads transport:

¾Control indoor relative humidity

¾Provide effective barriers to moisture flow into the assembly

¾Minimize pressurization of the B. E. ***Identify problem areas and treat those separately/differently

Minimize External Moisture Loads

Transport to Interior

¾ Assess the roof integrity at managing water, melting snow and ice (detailing, flashing, slopes, condition of eave troughs and downspouts, air leakage in roof spaces) ¾ Minimize rain and melting snow deposition

on masonry elements (drip edge projection, flashing over & under openings, slope for drainage)

¾ Preserve the integrity of the first line of

protection against rain infiltration (condition of mortar, need for repointing with

compatible mortar) without reducing its breathability

¾ Decode existing damage to target problem areas, and address the cause

¾ Control relative humidity indoors- Do you even know what it is likely to be, based on occupancy requirements? How will it be controlled?

¾ Minimize pressurization of the building envelope; this means less drive for exfiltration of humid air. Do you even know what it is likely to be? -interact with HVAC engineering for acceptable solutions

¾ Provide effective barriers to moisture flow into the assembly. Air barrier continuity at junctions and interfaces will likely be your challenge

¾ Opt for reversible interventions

¾ Identify problem areas, and address the cause

¾ Recognize unknown and manage the risks, e.g. add redundancies,

tighter quality control during construction, monitoring problematic areas during several years of service, modelling prediction??

Minimize Internal Moisture Loads

Transport to Exterior

Case Studies

Several design professionals have studied & published :

• Patenaude-Trempe: conducted field review and test

openings on 10 energy retrofitted masonry buildings in different fashions, and reported satisfactory performance.

– In 8 cases 25 to 37 mm SPF was sprayed onto the back of the masonry, acting as both air barrier and thermal

insulation. Typically vapour barrier was independent part of an uninsulated steel stud assembly

SPF sprayed directly on masonry is practically not reversible. One better practice is to first apply a sacrificial parging on the masonry before applying the SPF (J. Diodati case

Case Study

• NRC-IRC monitored a 4 storey warehouse built in 1911 and converted in 1993 to offices and workshops and laboratories

Energy Retrofit Approach

16 mm drywall 90 mm steel stud 30-35 mm air gap 55 mm foil-faced insulation Concrete floor Main support floor beam Steel column in brick wall Sand-lime brick Clay brick 765 305 235 100 16 mm drywall

Temperature gradient in Jan 1994

765 mm -10.5 C 235 mm C la y b ri ck fa ci n g -31.1 C Exterior Steel column 305 mm 0 C 32.2 C Air space Dry wall In su latio n 5 5 m m S te e l s tu d 9 0 m m Interior 24.8 C 18.9 C 23.9 C 765 mm 265 mm 305 mm C la y b ri ck fa ci n g -29 C Exterior Steel column 0 C 32.9 C Interior 24.8 C 15.3 C Uninsulated Insulated

Comparative Temperature Regime

-40 -30 -20 -10 0 10 20 30 40

Aug-93 Dec-93 Apr-94 Aug-94 Dec-94

Tem per a ture (°C ) UNINSULATED T6 INSULATED T41 Max Min Max Min INTERIOR SURFACE Interior face of masonry

No moisture problems were detected

in wintertime – A contributing factor

-50 -40 -30 -20 -10 0 10 20 30 0 5 10 15 20 25 30 December 1994 P res s u re di ff er enc e (P a) Weekend

The building operated mainly in negative pressure (laboratories and workshops), leading to cold air infiltration, not exfiltration of indoor air)

The Dynamic Buffer Zone- the Mechanical

Weapon

• The goal: avoid

exfiltration of indoor humid air and keep masonry warm

• Strategy: create a double wall or use an existing cavity and blow warm dry air to pressurize that cavity above

outdoors and above indoors pressure

Indoor space at 50%RH

DBZ _Masonry

Typical Applications

• Most warranted: buildings of high heritage significance where the indoor humidity level requirements are high, and the complexity of the building geometry/construction or the preservation of the interior finishes make the use of “passive” approach of installing interior insulation and air barrier impractical

• Examples: McCord Museum Montreal; Musée des beaux-arts Montreal; Musée du Québec Quebec city; Federal

heritage properties on Parliament Hill Ottawa; Nature Museum Ottawa

DBZ- variations on the theme

Reported to be less effective as negative pressure can prevail in the DBZ near the return air plenum

DBZ: Things to consider

• Need for an effective air barrier to form the interior layer of the BDZ cavity

• Evaluate impact on indoor air quality e.g. Not suitable when contaminants such as asbestos is present in exterior walls

• Need a monitoring & alarm system, and back up plan if air handling system breaks down

• Need training building manager • Evaluate energy consumption

In a nutshell

• In the conservation field , every case is unique

• Effective moisture control is a must for ensuring durability of the building. Air tightness more critical and challenging to achieve than vapour diffusion control.

• Effective intervention on the INTERIOR of the building envelope does require effective control of EXTERNAL moisture sources

• No one magic bullet solution for adding thermal insulation to interior of existing older masonry envelopes. Several documented case studies showed a holistic approach to air, heat and moisture flow control can work.

Thank You!

Madeleine Z. Rousseau

National Research Council Canada, Ottawa E-mail: madeleine.rousseau@nrc.ca

Water

Water

Forces

Forces

Holes

Holes

•

• Regional & local climatesRegional & local climates •

• Geometry of building envelopeGeometry of building envelope •

• “Direct” water management“Direct” water management •

• Shielding (projections, Shielding (projections, soffitssoffits) ) •

• Properties of cladding Properties of cladding materials

materials

Reduce exposure to rain

• Protection during construction • Overhangs

• Eavestrough and downspout system to manage water from top to bottom

Holes

Holes

Forces

Forces

Water

Water

•

• Unintentional holes Unintentional holes

(during design, construction

(during design, construction

and service life)

and service life)

•

• Intentional holes (vents)Intentional holes (vents) •

• Porosity of the claddingPorosity of the cladding

Re duc e H ole s (unobst ruc t e d

Choosing the Destiny of the Walls

Control of holes Control of holes Control of forces Control of forces

•

•

Face

Face

-

-

seal wall

seal wall

also known as Barrier wall

also known as Barrier wall

or Surface

or Surface

-

-

sealed wall

sealed wall

•

•

Cavity wall,

Cavity wall,

•

•

Rain screen wall,

Rain screen wall,

•

•

Pressure

Pressure

-

-

“controlled”

“controlled”

wall

Keep Going!

• Assume some water will get in, and design ways to get it out quickly and through a route that can handle wetness

• Rainscreen wall approach provides such a second line of defense

• Face seal wall approach provides only one line of defense. When that fails...

One more!

• Rainscreen wall includes an air barrier system, a capillarity break (cavity), a water-resistant drainage path to the outside, large vent area, some

compartmentation

The “Lack of” syndrome

• Lack of design detailing

• Lack of communication between field and design teams

• Lack of field supervision & coordination and quality control

LEAD to

Air Convection Loops Without

Through-Flow

Air flow in and out of an external air cavity

INT. EXT.

Air flow into a stud cavity, and back inside

Cold air circulation between materials

INT. EXT.

Vertical wall section External

air barrier system

Insulating sheathing

Cold air circulation between materials

INT. EXT.

Vertical wall section External

air barrier system

Insulating sheathing

Airtightness of the AB System

15-60 60- 170 170-800 > 800 0.05 0.10 0.15 0.20

Max. Air Leakage Rate

at 75 Pa (L/(s

•

m

2

)

For 35% RH, 22°C indoors

Water vapour permeance of outmost

unvented wall layer (ng/Pa•s•m

2

₎

R value on Outside of Low Air & Vapour

Perm Materials, as a Function of Climate

Heating Degree-Days (HDD)

< 4999

5000s 6000s 7000s 8000s 9000s 10000s11000s12000 & up

Increasing period+ intensity of cold temperatures

Ratio of outboard to inboard

R value 0.2 0.3 0.4 0.5 0.6 0.7 0.1

Increasing R value on the outside of low perm material

Fredericton Edmonton

Then the Open Rain Screen was Born…

• In 1962 Norwegian Building Research Institute published

Curtain Walls, in which Mr. Birkeland wrote:

– “The only practical solution (to the problem of water

leakage) is to design the exterior rain-proof finishing so open that no super-pressure can be created over the joints… The surges of pressure created by the gusts of wind will then be equalized on both sides of the exterior finishing.”

• In 1963 Kirby Garden at NRC Canada wrote Canadian Building Digest Rain Penetration and its Control.

– Control of ALL FORCES acting on exterior wall – Importance of air leakage control to gain rain

penetration control and pressure equalization • In 1971 the Architectural Aluminum Manufacturers

Association published “The Rain screen Principle and Pressure-equalized wall design

Plane of

airtightness of the wall

Interior Interior

Face-seal approach applied to a precast concrete panel cladding wall

Face-seal Approach

One-stage joint Two-stage joint Horizontal section

Towards Rainscreen:

Rainscreen:

• • • • • Rain screen

• Effective vent area • Vent location

• Design loads • Stiffness

Wind driven rain _{Air Barrier System}

• Effective leakage area • Design loads

• Stiffness

Chamber

Depth & Volume Air permeability

Drainage (flashing & drainage holes)

Delimiters •

Exterior Interior

Features of a Pressure-equalized Rain

Screen Wall

Water resistance of inner boundary

Wrap Up 1/4

• Barrier walls: Single protection without any redundancy. Watertightness based on perfection of exterior seals.

Once exterior seals fail, water cannot get out. High maintenance costs for sealants, too often triggered by water damage

• Mass walls: single protection but with some redundancy.

Weatherproofing based on absorptive property of large mass of masonry or concrete and evaporative drying. Problems tend to be corrosion of metals embedded in masonry, freeze thaw damage or rain ingress at joints

• Cavity walls: dual protection by means of a drained and

flashed clear cavity behind cladding and second line of defense (moisture barrier). Has been successful when combined with careful detailing and where wind-driven rain pressures were not high

• Variation: Ventilated cavity walls, which provide the dual protection of cavity walls, with the addition of vents top and bottom of compartment to promote drying of wall. Several modelling studies underway in this area

Wrap Up 3/4

• Rain Screen walls: Multiple protection & redundancy of the cavity wall, with addition of the control of air flow .

– Requires an effective air barrier system inside the wall.

– Requires more venting than typically provided in cavity walls. – Requires control of lateral air flow behind the cladding with

compartment separators

• Has been used successfully in panelized wall systems and curtain walls exposed to high wind-driven rain

pressures. Can reduce wind loads on cladding. • Several terms used in industry:

Pressure-equalized; moderated ; pressure-compartimentalized