Wednesday, February 26, 2014

Freezing and bursting pipes info

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hen water freezes, it expands. That’s

why a bottle of soda explodes if

i t ’s put into a freezer to chill quickly

and forg o t t e n .

When water freezes in a pipe, it expands the

same way. If it expands enough, the pipe

bursts, water escapes and serious damage

results.



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HY PIPES BURST

S u r p r i s i n g l y, ice forming in a pipe does


n o t

typically cause a break where the ice blockage

occurs. It’s not the radial expansion of

ice against the wall of the pipe that causes

the break.

R a t h e r, following a

complete ice blockage

in a pipe, continued

freezing and

expansion inside

the pipe cause

water pre s s u re to

i n c rease downs

t ream — between

the ice blockage and a closed faucet at the

end. It’s this increase in water pressure, literally

thousands of pounds of pre s s u re, that

leads to pipe failure. Usually the pipe bursts

where little or no ice has formed.

Upstream from the ice blockage the water can

always re t reat back towards its source,

so there is no pre s s u re build-up to cause

a break.

Water has to freeze for ice blockages to occur.

Pipes inside a house that are protected adequately

by placement within the building’s

insulation, insulation on the pipe itself, or

heating, are safe.



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EGIONAL DIFFERENCES

G e n e r a l l y, houses in nort h e rn climates are

built with the water pipes located on the



inside



of the building insulation, which protects

the pipes from subfreezing weather.

H o w e v e r, extremely cold weather and holes

in the building that allow a flow of cold air to

come into contact with pipes can lead to

freezing and bursting.

Water pipes in houses in southern climates

often are more vulnerable to winter cold

spells. The pipes are more likely to be located

in unprotected areas outside of the building

insulation, and homeowners tend to be less

aware of freezing problems, which may occur

only once or twice a season.

Pipes in attics, crawl spaces and outside

walls are all vulnerable to freezing, especially

if there are cracks or openings that allow



FREEZING AND BURSTING PIPES



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N


AT U R A L

H


A Z A R D MI T I G AT I O N

P


I P E S I N S I D E A H O U S E T H AT A R E

P R O T E C T E D A D E Q U AT E LY B Y P L A C E M E N T

W I T H I N T H E B U I L D I N G


S I N S U L AT I O N,

I N S U L AT I O N O N T H E P I P E I T S E L F


,

O R H E AT I N G


, A R E S A F E.

A publication of the Institute for Business and Home Safety



cold, outside air to flow across the pipes.

R e s e a rch at the University of Illinois has

shown that “wind chill,” the cooling effect

of air and wind that causes the human body

to lose heat, can play a major role in accelerating

ice blockage, and thus bursting, in

water pipes.

Holes in an outside wall where television,

cable or telephone lines enter can pro v i d e

access for cold air to reach pipes.

The size of pipes and their composition (e.g.,

copper or PVC) have some bearing on how

fast ice forms, but they are relatively minor

factors in pipe bursting compared with the

absence of heat, pipe insulation and exposure

to a flow of subfreezing air.



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H E N IS IT CO L D EN O U G H TO FR E E Z E?

When should homeowners be alert to the

danger of freezing pipes?

That depends, but in southern states and

other areas where freezing weather is the

exception rather than the rule (and where

houses typically do not provide adequate

built-in protection or builders care l e s s l y

place pipes in unprotected areas),


the “temperature

alert threshold” is 20 degrees F.




This threshold is based upon re s e a rch

conducted by the Building Research Council

at the University of Illinois. Field tests of

residential water systems subjected to winter

t e m p e r a t u res demonstrated that, for uninsulated

pipes installed in an unconditioned

attic, the onset of freezing occurred when the



outside



temperature fell to 200 F or below.

This finding was supported by a survey of 71

plumbers practicing in southern states, in

which the consensus was that burst-pipe

problems began to appear when temperatures

fell into the teens.

However, freezing incidents can occur when

the temperature remains above 20


0 F. Pipes

exposed to cold air (especially


flowing a i r,

as on a windy day) because of cracks in

an outside wall or lack of insulation are vulnerable

to freezing at temperatures above

the threshold.

However, the 20


0 F “temperature alert threshold”

should address the majority of potential

burst-pipe incidents in southern states.



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I T I G AT I N G T H E PR O B L E M

Water freezes when heat in the water is transf

e rred to subfreezing air. The best way to

keep water in pipes from freezing is to slow

or stop this transfer of heat.

Ideally, it is best not to expose water pipes to

s u b f reezing temperatures, by placing them

only in heated spaces and keeping them out

of attics, crawl spaces and vulnerable outside

walls. In new construction, proper placement

can be designed into the building.

In existing houses, a plumber may be able to

re route at-risk pipes to protected are a s ,

although this may not be a practical solution.

If that’s the case, vulnerable pipes that are

accessible should be fitted with insulation

sleeves or wrapping (which slows the heat

transfer), the more insulation the better. It is

i m p o rtant not to leave gaps that expose the

pipe to cold air.

Hardware stores and home centers carry the

n e c e s s a ry materials, usually in foam ru b b e r



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E S E A R C H AT T H E UN I V E R S I T Y O F IL L I N O I S H A S S H O W N

T H AT


W I N D C H I L L,” T H E C O O L I N G E F F E C T O F A I R A N D

W I N D T H AT C A U S E S T H E H U M A N B O D Y T O L O S E H E AT


,

C A N P L AY A M A J O R R O L E I N A C C E L E R AT I N G I C E

B L O C K A G E


, A N D T H U S B U R S T I N G, I N WAT E R P I P E S.

V


U L N E R A B L E P I P E S T H AT A R E A C C E S S I B L E S H O U L D

B E F I T T E D W I T H I N S U L AT I O N S L E E V E S O R

W R A P P I N G


, T H E M O R E I N S U L AT I O N T H E B E T T E R.

or fiberglass sleeves. Better yet, plumbing

supply stores and insulation dealers carry

pipe sleeves that feature extra-thick insulation,

as much as 1” or 2” thick. The added

protection is worth the extra cost.

Cracks and holes in outside walls and foundations

near water pipes should be sealed with

caulking to keep cold wind away from the pipes.

Kitchen and bathroom cabinets can keep

w a rm inside air from reaching pipes under

sinks and in adjacent outside walls. It’s a

good idea to keep cabinet doors open during

cold spells to let the warm air circ u l a t e

around the pipes.

Homeowners in the south need to be alert

to the danger of freezing and bursting water

pipes when the outdoor temperature thre a tens

to drop to 20 degrees F.

That’s the temperature at which ice is likely

to start forming in water pipes located in an

unheated portion of a house.

Once ice forms into a blockage in a pipe, continued

growth of ice in the pipe can lead to

excessive water pressure. It’s pressure of the

water that has no place to go when ice builds

that causes the pipe to burst, rather than ice

pushing against the wall of a pipe.

Although 20 degrees F is well below the

f reezing temperature of water, two factors

make this the critical outdoor temperature:

1. The temperature of an unheated portion

of a house is almost always at least

a few degrees above the outdoor temp

e r a t u re. For example, an insulated

attic may be at 37


0 or 380 F when the

outdoor temperature is 32 degrees F.

2. Water “supercools” several degre e s

below freezing before any ice begins

to form.

In re s e a rch tests at the University of Illinois,

water pipes placed in an unheated, insulated

attic consistently started forming ice

when the outdoor temperature dipped just

below 20


0 F.

The 20 degree F threshold is primarily for

homes in the south and other areas where

freezing may occur only once or twice a season.

Homebuilders in these areas often overlook

the threat of freezing and place pipes in

vulnerable locations.

Builders in the north, where temperatures

in the teens and lower are common, routinely

install more building insulation and usually

do not place pipes in unheated portions

of a building.

There are several precautions homeowners in

the south can take when the temperature is

expected to dip into the low 20s:



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Seal all openings where cold air can

get at unprotected water pipes. It’s

especially important to keep cold wind

away from pipes, which speeds up the

freezing process.



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Cover pipes with foam or fiberg l a s s

insulation sleeves, the thicker the better.



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Install heating tapes or cables on vulnerable

pipes.


Be sure to follow manu -

facturer instructions carefully to avoid

starting a fire.




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Leave cabinet doors open under the

kitchen and bathroom sicks to allow

w a rmer room air to circulate aro u n d

pipes.



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Let faucets drip slowly to keep water

flowing through pipes that are vulnerable

to freezing. Ice might still form in

the pipes, but an open faucet allows

water to escape before the pre s s u re

builds to where a pipe can burst. If the

dripping stops, it may mean that ice is

blocking the pipe;


keep the faucet

open, since the pipe still needs pre ssure

relief.



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A C K FR O S T NI P S AT WAT E R PI P E S

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H E N TE M P E R AT U R E DI P S TO 20 DE G R E E S IN TH E SO U T H

Electric heating tapes and cables are available

to run along pipes to keep the water fro m

f reezing.


These must be used with extre m e

caution; follow the manufactur e r’s instru ctions

carefully to avoid the risk of fire.




Tapes and cables with a built-in therm o s t a t

will turn heat on when needed. Tapes without

a thermostat have to be plugged in each

time heat is needed, and may be forgotten.



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E T T I N G T H E WAT E R RU N

Letting a faucet drip during extreme cold

weather can prevent a pipe from bursting. It’s

not that a small flow of water prevents freezing;

this helps, but water can freeze even with

a slow flow.

R a t h e r, opening a faucet will provide re l i e f

f rom the excessive pre s s u re that builds

between the faucet and the ice blockage when

freezing occurs. If there is no excessive water

p re s s u re, there is no burst pipe, even if the

water inside the pipe freezes.

A dripping faucet wastes some water, so only

pipes vulnerable to freezing (ones that ru n

t h rough an unheated or unpro t e c t e d s p a c e )

should be left with the water flowing. The

drip can be very slight. Even the slowest drip

at normal p re s s u re will provide pre s s u re

relief when needed.

W h e re both hot and cold l ines serve

a spigot, make sure each one contributes

to the drip, since both are subjected

to freezing.

If the dripping stops, leave the faucet(s)

open, since a pipe may have frozen and will

still need pre s s u re relief.



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F YO U SU S P E C T A FR O Z E N PI P E

If you open a faucet and no water comes out,

don’t take chances. Call a plumber.

If a water pipe bursts, turn off the water at the

main shut-off valve; leave the faucet(s) open

until repairs are completed.

Don’t try to thaw a frozen pipe with an open

flame; you may start a building fire.

You might be able to thaw a pipe with a

hand-held hair dry e r.


Slowly apply heat,

s t a rting close to the faucet end of the pipe,

with the faucet


open. Work toward the

coldest section.


D o n ’t use electrical appliances

while standing in water; you could

get electrocuted.



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O I N G O N A TR I P

When away from the house for an extended

period during the winter, be careful how

much you lower the heat. A lower temperat

u re may save on the heating bill, but there

could be a disaster if a cold spell strikes and

pipes that normally would be safe, freeze and

burst.

A solution is to drain the water system. This

is the best safeguard. With no water in the

pipes, there is no freezing. This re m e d y

should be considered even when the homeowner

is not leaving but is concerned about a

serious overnight freeze.

To drain the system, shut off the main valve

(usually at the water meter or where the main

line enters the house) and turn on every

water fixture (both hot and cold lines) until

water stops running. It’s not necessary to

leave the fixtures open, since the system is

filled mostly with air at that point and not

subject to freezing.

When re t u rning to the house, turn on the

main valve and let each fixture run until the

pipes are full again.



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F T H E R E I S N O E X C E S S I V E WAT E R

P R E S S U R E


, T H E R E I S N O B U R S T P I P E,

E V E N I F T H E WAT E R I N S I D E

T H E P I P E F R E E Z E S


.

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Pipes in attics and crawl spaces should

be protected with insulation or heat.

Pipe insulation is available in fiberglass

or foam sleeves. Home centers and

hardware stores have sleeves providing

1/8 to 5/8 inches of insulation; specialty

dealers have products that pro v i d e

up to 2 inches of insulation. (Check the

Yellow Pages under “Insulation” or

“Plumbing Supplies” for sources.) The

extra thickness is worth the price and

can save a pipe that would freeze with

less insulation.



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Heating cables and tapes are eff e c t i v e

in freeze protection. Select a heating

cable with the UL label and a built-in

thermostat that turns the heat on when

needed (without a thermostat, the cable

has to be plugged in each time and

might be forgotten). Follow the manufacturer’s

instructions closely.



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Doors on cabinets under kitchen

and bathroom sinks should be left open

during cold spells to allow the warmer

air of the room to circulate around the

pipes.



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Exterior pipes should be drained or

enclosed in 2” fiberglass insulation

sleeves.



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Pipes leading to the exterior should be

shut off and drained at the start of the

w i n t e r. If these exterior faucets do not

have a shut-off valve inside the house,

have one installed by a plumber.



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Hoses should be removed and store d

inside during the winter.



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O U T H E R N HO M E O W N E R S FA C E

T


H R E AT O F FR O Z E N PI P E S

Water damage from frozen pipes that burst can be a major problem for homeowners in southern

states, maybe even a bigger problem than in the colder north.

Home builders in the south often do not consider the threat of freezing weather and thus place

water pipes in vulnerable locations.

Houses built on slab foundations, common in the south, frequently have water pipes ru n n i n g

through the attic, an especially vulnerable location.

In addition, southern homeowners experience relatively few severe cold spells, so they don’t

consider freezing a problem and don’t bother checking the condition or location of pipes in their

homes.

In the north, by contrast, home builders know freezing is a threat, and they usually do not place

water pipes in unheated portions of a building or outside of insulated areas.

Southern homeowners should be aware that pipes in attics, crawl spaces and outside walls are all

subject to freezing and bursting. If these pipes don’t have insulation or heat to protect them, a

strong overnight freeze can cause trouble.

Changes in building codes will require homes built in the future to have adequate protection for

pipes, but many plumbing installers are not aware of the changes. Houses already built re m a i n

vulnerable.

These suggestions for homeowners in southern states will help them prevent freezing pipe damage:



73 Tremont Street, Suite 510, Boston, Massachusetts 02108-3910



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N S T I T U T E F O R BU S I N E S S A N D HO M E SA F E T Y

The Institute for Business and Home Safety (IBHS) is an independent, nonprofit

o rganization created by the pro p e rty-casualty insurance industry

to reduce deaths, injuries and pro p e rty damage through natural hazard

loss mitigation.



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