This presentation Basements are Changing · John Straube Presentation 1 ... zRecent studies – Minn, Chicago, CMHC, IRC. ... backfill soil properties Screened(1)

University of Waterloo www.civil.uwaterloo.ca/beg

John Straube Presentation 1

Building Better Basements, or“How to Build Basements that Don’t Stink”

www.BalancedSolutions.comwww.civil.uwaterlo.ca\beg

BEGBuilding Engineering Group

Dr John StraubeAssistant ProfessorDupont Young Professor

University of Waterloo

1/31/2005 John Straube2 /71


This presentation

Basements– How are they changing– What they do

Performance– Problems– Causes

Solutions


Basements are Changing

Increasingly used as living space– Not a root cellar anymore!– High quality space expected - new and retrofit– Owner can finish herself– Low cost for high density sites (cities)– Can now locate laundry, heating, hotwater elsewhere– Slabs growing (old people) unlikely to make a major dent

Modern basements are different – they need different approaches!




Basements – Part of the Enclosure


Basements

Below grade enclosure– Includes floor slabs, and practically rim joist– Separates exterior (soil/air) and interior

Functions of all parts of the enclosure– Support– Control– Finish (usually)


Functions of the building enclosure

Support – Structure: wind, gravity, earthquake– Below grade – Soil pressure, hydrostatic?

Control– Heat (less extreme than above grade)– Air (less air pressure, but it stinks, Radon?)– Moisture (vapor, free and bound liquid)

Finish – usually, but optionalDistribute (sometimes)


Support (Structural performance)

Structural system– Does not work based on rational analysis– Don’t ask for an engineers stamp

Failure modes– Poorly compacted subsoil– Top-edge Bracing

Raised bungalowsStairwells parallel to wall




Basement Structural System

Foundation Wall

Floor slab

Footing

Above Grade

Below Grade

Similar for Similar for most most basementsbasements

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Basement Structural System

Floor slab

Footing

Above Grade

Below Grade

••Raised BungalowsRaised Bungalows•• StairsStairs

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Control: Moisture

Moisture causes most failures (less spectacular)– Mold (musty smell)– Decay (especially rim joist)– Staining /Paint peeling– Floods and leaks, eventually causing the above– Salt damage to masonry – old basements

Where does moisture come from?– Exterior– Interior– Built in

Recent studies – Minn, Chicago, CMHC, IRC



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Exterior surface Exterior surface waterwater

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Surface Drainage

First step– Common problem

OverhangEavestroughDownspoutsSloped gradePerimeter drain

From: Lstiburek 2002

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Exterior surface waterExterior surface water••Drainage wont help hereDrainage wont help here••Damage recoveryDamage recovery

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Moisture Sources:

built into the Assembly

•Minimize by:• Delay finishing internally• Reduce water in concrete

1. Built-in Moisture (from water in concrete, mortar, wood, etc.)

2. Construction moisture accumulated during construction (ice, snow, rain, etc.)

1. & 2.

1. & 2.



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Initial Drying


Soil cold for first yrExcavation collects waterConcrete is wet

– 25-50 liters/m2

Cannot dry to wet exteriorSolutions = dry in

– No low perm interior– Semi-permeable insulation– Smart vapor barrier

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Basement in a Bag• Tolerable north of Arctic Circle

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Moisture Sources:

from Exterior Environment

Minimize Rain loadsProvide Good SheddingProvide Good DrainageProvide Capillary Breaks

3. Surface water Run-off

2. Rainwater shedding

1. Precipitation

5. Sub-surface Moisture - Groundwater- Vapor

4. Water vapor

5. Sub-surface Moisture 5. 1/31/2005 John Straube20 /71

A wet basement – ground water



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Controlling ground/rain water

Many different acceptable methodsClassification of Groundwater control

– 1. DrainedNeeds capillary break and gap/drain space

– 2. Perfect BarrierOne layer of perfect water resistanceBeware hydrostatic forces

– 3. Storage (mass) Safe storage capacity and dryingDon’t use vapor barriers, do insulate (carefully)

Exterior Moisture

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Drainage by specific backfill soil properties

Screened(1) Below-Grade Enclosure Wall System

Collection and Exit Drain

Interface with undisturbed below grade environment

Above Grade Level

Below Grade Level

A. Screen (similar to cladding---shed and screen surface moisture-rain)

B. Drainage–crushed stone

C. Drainage plane and

Capillary break

E. Concrete or concrete masonry

F. Insulation (int. option)

G. Interior finish

Drained type:• drainage system with drainage plane, and• capillary break

B. Drainage– draining backfill

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Collection and Removal Drain

Interface with undisturbed below-grade environment

Above Grade Level

Below Grade Level

A. Screen -optional (similar to cladding---shed and screen surface moisture-rain)


Capillary break



G. Interior finish

Drained type:• drainage system with drainage layer& plane,• capillary break

Backfill – not necessarily free draining

Non-soil drainage layer


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Collector and Removal Drain


Above Grade Level

Below Grade Level

A. Screen – optional (similar to cladding---shed and screen liquid moisture-rain and groundwater)


Capillary break



G. Interior finish

Drained type:• drainage system with drainage plane, and• capillary break

B. Backfill – not necessarily free draining

Interior Drainage(often retrofit)




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Barrier (1) Below-Grade Enclosure Wall System



Above Grade Level

Below Grade Level

A. Screen – optional(similar to cladding---shed and screen surface moisture-rain)

B. Drainage (opt) – crushed stone

A. Positive side Waterproofing

B. Concrete or masonry

C. Insulation—heat flow control (int. option)

D. Interior finish

Perfect barrier:• drainage system needed to reduce hydrostatic pressure• waterproofing layer resists 300-600 mm head of water


No Drainage – hydrostatic pressure developed

Lowers water table, reduces hydrostatic pressure 1/31/2005 John Straube26 /71

Barrier (2) Below-Grade Enclosure Wall System

Collector and Exit Drain


Above Grade Level

Below Grade Level


B. Drainage (opt) –crushed stone

A. Negative side Waterproofing

B. Concrete or concrete masonry

C. Insulation—heat flow retarder (int. option)

D. Interior finish

Perfect barrier :• drainage system to reduce hydrostatic pressure• waterproofing


No Drainage – hydrostatic pressure developed

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Storage (1) Below-Grade Enclosure Wall System



Above Grade Level

Below Grade Level


B. Drainage (opt) –crushed stone

A. Rubble or concrete masonry (storage)

B. Usually no insulation to allow drying

C. Usually no interior finish (limewash)

Storage (mass) system:• usually no intentional drainage• often no capillary break


Limited ability to resist moisture loads

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Damproofing• Capillary break = drainage plane, but needs gap• vapour barrier?•NOT waterproofing



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GlassfiberGlassfiber Drainage LayerDrainage Layer

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R k l D i L

RockwoolRockwool Drainage LayerDrainage Layer

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Dimple Sheets

Drainage gapact as vapor barrierSo little water = maybe no capillary break needed

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Controlling ground/rain water

Roof and Surface DrainageClassification of Groundwater control

– 1. DrainedNeeds capillary break & gap/drain space

– 2. Perfect BarrierOne layer of perfect water resistanceBeware hydrostatic forces

– 3. Storage (mass) Safe storage capacity and dryingDon’t use vapor barriers, do insulate (carefully)

Perimeter Drains

Exterior Moisture



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Moisture Sources:

from Interior

1. Water Vapor

2. Localized Flooding (abnormal - Water & Vapor)

3. Localized Flooding(Abnormal)

Control interior vapor levels by:• winter ventilation• summer dehumidcation

Control flooding• floor drains• disaster pans at appliances

2.

3.

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Air and vapor

Surface condensationInterstitial condensationSolar driven summer condensationDrying retardersPsychrometric Chart

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Special Exterior Conditions

Exterior soil is almost always at 100%RH– Plus liquid water can press against wall

Never gets as cold or as hot as above gradeSignificant vertical temperature gradients– Top is different than bottom

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Moisture – not ground water



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Measured Soil Temperatures

-5

0

5

10

15

20

25

Jan Feb Mar April May June July Aug Sept Oct Nov Dec

Date

Tem

pera

ture

(C)

0.1 m

0.5 m

1.0 m

3 m

2.0 m

Note: open field values. No house to add heat

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Measured Soil Temperatures

5 10 15 20 25

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Soil Temperatures at University of Waterloo Weather Station (1999)

-5

0

5

10

15

20

25

30

0 4 8 12 16 20 24 28 32 36 40 44 48 52

Time (weeks from January)

Tem

pera

ture

(C)

soil temp (50 mm)soil temp (200 mm)

Waterloo Measured Soil Temperatures

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Exterior Temperature and Moisture Conditions

• Soil Relative Humidity almost always =100%

• Liquid water may be present

Temperature200 10

SummerJuly

WinterJan.



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Temperature ( °C)

0

500

1000

1500

2000

2500

3000

3500

4000

Vap

our

Pre

ssure

(Pa

)

100% RH75% RH50% RH25% RH

Psych Chart: Air Vapour Content vs Temperature

Saturation

50%

RH

25%RH

75%

RH

100%

RH

100%RH

Temperature

Air

Moi

stur

e C

onte

nt

= va

pour

pres

sure

(Pa,

in H

g),

hum

idity

rat

io (g

/kg,

gra

ins/

pd)

-10 ºC14 º F

0 ºC32 º F

10 ºC50 º F

20 ºC68 º F

30 ºC86 º F

40 ºC104º F

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Basement Vapour Movement

Vapor moves by Diffusion & Air movementDiffusion

Water vapor moves from more to lessCommon rule:– place vapor retarding layers on moist (i.e. high

vapor pressure) side to control vapor diffusionAir Leakage

Vapor moves with air flow (high to low pressure)– Stop air flow or flow from dry side

1/31/2005 John Straube44 /71-10.0 -5.0 0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0

Temperature ( °C)

0

500

1000

1500

2000

2500

3000

3500

4000

Vap

our

Pre

ssure

(Pa

)

100% RH75% RH50% RH25% RH

Below Grade Basement Psychrometrics

Summer

Winter

-10 ºC14 º F

0 ºC32 º F

10 ºC50 º F

20 ºC68 º F

30 ºC86 º F

40 ºC104º F

Since soil is at nearly 100%RH, the vapor drive is almost always inward except at very top during winter in humid houses

Janu

ary

top

foot

ing

July

foot

ing

top

Flow out

Flow in

Flow in



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Basement Vapour Diffusion

Water vapor is moving from soil to interior – for almost the entire year – over all but the top foot of basement

Hence, place vapor barrier on outsideBut we put it on the inside!Moisture moving by diffusion from drying concrete and soil is trapped by interior vapor barriers

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Air M

oist

ure

Con

tent

Air

Moi

stur

e C

onte

ntTe

mpe

ratu

re

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Basement Air Movement

Water vapor moves along with airflowIf moist air touches a cold surface, condensation occursControl?– Include an air barrer– Avoid air loops– Avoid pressures

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Condensation: Cool air contains less vapor

Cool air – increase RHHeat air – decrease RH



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Air leakage

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Internal Stack Effect & Insulation

Hot air = lightHot air = light

Cold air = heavy

• Gaps in batt insulation on both sides•Wrinkles inevitable

Air gapsBatt

Inside

OutsideCommon basement problem

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Internal Stack Effect

Cold WeatherCold WeatherHot air = lightHot air = light

Cold air = heavyCold air = heavy

Result: Air Result: Air FlowFlow

• Gaps in batt insulation on both sides

• closed circuit

• energy cost

• cold surfaces

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Air movement (Stack Effect)

Cold concrete = summer & winterCold concrete = summer & winter

Result: Air Result: Air FlowFlow

Hot air = lightHot air = light

Cold air = heavyCold air = heavy



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Wall w/ only Batt Insulation

Air leakageAir leakage

Air permeable Air permeable insulationinsulation

CrackCrack

Cold

Condensation

Winter

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Wall w/ Insulated Sheathing

Air leakageAir leakage

Air permeable Air permeable insulationinsulation

CrackCrack

Warmer

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Materials to use?

Foam Board: EPS, XPS, PIC– water tolerant– vapour barriers to vapour retarders

spray foam – Semi-rigid (Icynene) and rigid (Spray polyurethane)– airtight – May allow some drainage– R values of 4 to 4.4/inch– vapour semi-permeable (Icynene much more)

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ICFs

If you afford it, use them – cap break, insulation, vapor retarder



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Better

Add layer of:– foam or– spray

foam

Insulation & service distribution space

2x framing

Gypsum wallboard

Plastic baseboard

Keep bottom of drywall ¾" off of finished floorInstall capillary break or ½" plastic wood spacer under bottom plate

pre-manufactured drainage layer (shown) or free draining material

Site sloped away from building

Urethane foam airsealSill gasket air seal

Poly vapor barrier

Continuous sealant joint over bond break

Damproofing

Sealant airseal

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Best?Insulation & service

distribution space

Gypsum wallboard

Plastic baseboard

Keep bottom of drywall ¾" off of finished floor

Draintile in crushed stone wrapped in geotextile




Poly vapor barrier


Damproofing

1x2 horizontal strapping

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Foam onlyVertical strapping



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Solar Drives at Grade

Wet concrete from rain, grade, built-inSun shines on wall and heats itWater evaporates and diffuses in & outCan condense inside of cold and impermeable

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2.Vapour drives inward (& out) 3.Condensation

on “cold”surfaces

1. Temperature and solar heating

warms wet material

WettingIf impermeable

DryingIf permeable

3.Vapour dries to inside

Inward Diffusion @ grade

1/31/2005 John Straube63 /71-10.0 -5.0 0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0

Temperature ( °C)

0

500

1000

1500

2000

2500

3000

3500

4000V

ap

our

Pre

ssure

(Pa

)

100% RH75% RH50% RH25% RH

Hot Wet materials

• 30-60 C• 90-100% RH•VERY high vapour pressure

SummerWinter

-10 ºC14 º F

0 ºC32 º F

10 ºC50 º F

20 ºC68 º F

30 ºC86 º F

40 ºC104º F 1/31/2005 John Straube64 /71

Rim joists

Scenario– Wood generally on exterior– 38 mm Wood is a vapor barrier– Practically difficult to stop air leakage

Result– Condensation on rim joist in cold weather– Decay if it can’t dry in or out

Solutions– Insulate on exterior



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Basement Floors

Basement floors – Part of enclosure

Concrete alone fine but when you finish…– Comfort (cold and hard)– Water under finish flooring– Water condensing on top (summer)

Solutions– Install finish over small amount of insulation– Install vapor barrier

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Slabs

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Summary

TolerableRiskyBe perfect..& lucky



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Summary

good

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Summary-best

best


This is theoretically best, but thermal mass of walls requires good summer humidity control and floor should be insulated

Insulation & service distribution space

Gypsum wallboard

Plastic baseboard

Keep bottom of drywall ¾" off of finished floor

Draintile in crushed stone wrapped in geotextile




Poly vapor barrier


Damproofing

1x2 horizontal strapping

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Conclusions

Building in a hole in the ground is hardDon’t forget about built-in moistureand remember summerMoisture comes in liquid AND vapor Insulation and drainage are the best tools, not vapor barriers and waterproofing

www.civil.uwaterloo.ca/beg publicationswww.balancedsolutions.com

1/31/2005 John Straube72 /71

Addition

Repair– Wall leaks groundwater

Retrofit/Reno– Risk reduction

Documents

This presentation Basements are Changing · John Straube Presentation 1 ... zRecent studies – Minn, Chicago, CMHC, IRC. ... backfill soil properties Screened(1)