 Winterizing Guide: How to Freeze-Protect Building Drain Piping
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How to protect building drains from freezing: this article explains how to prevent frozen drain piping and freeze-damage or burst drain pipes in buildings and in the building connection to a septic system or to a municipal sewer line. You might think that because plumbing drains slope downwards (or should) that there is not freeze risk - that's not entirely true, as we explain here.
The articles at this website will answer most questions about freeze protection for piping and other building plumbing and heating system components: how to winterize a building to avoid frozen pipes, and how to thaw frozen water supply & drain piping, wells, & water tanks.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
How to Avoid Freeze Damage to Building Drain Piping
Our page top photo shows what might happen if a building drain is clogged, leading to standing wastewater in the pipes which then froze and burst.
Is the building heat going to be left "on" or "off" - the answer determines the extent of freeze-proofing needed.
- If heat is to be left on in a partially winterized building see the procedure at: Winterize - Heat On (continuing below)
- If heat is to be turned off and the building completely winterized, see the procedure at: Winterize- Heat Off
What? My Building Drains Can Freeze Too?
 Freeze damage risk in buildings is not confined to water supply piping or hot water heating piping. Building drains can also freeze and break, including fixture traps and building drains.
Building drains can freeze inside the building and even outside a drain line that is not below the frost line can easily freeze in some conditions which we outline below.
Even if the building water supply piping has not frozen a drain line can freeze. You may first notice the problem when a toilet, sink, or tub simply stops draining.
In a building where water is left on at some plumbing fixtures, be sure that there are no leaky supply valves or running toilets.
In freezing weather a slow drip or water running slowly into a drain pipe can lead to ice build-up, a frozen or even a frozen and burst drain pipe, or a water backup into the building.
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What Causes Building Drain Pipes to Freeze?
- A building main drain or other building drain pipe is exposed to freezing temperatures outdoors
- A building drain is routed through an un-heated crawl space or basement, or an attic or attic knee-wall that is unheated indoors
- A plumbing fixture drain trap extends down into an un-heated crawl space or basement or is in the path of a cold draft even if the crawl space or basement is heated.
- A toilet is running or a faucet dribbles continuously into the drain system
- A water softener or other water treatment equipment is left on and running improperly, perhaps sending a continuing stream of water into the drain system
- A roof gutter drains into the sewer piping (bad), perhaps through a drain line that enters the building (still worse) en route to the sewer connection; clogged gutters that dribble water slowly into the drain system increases the freeze risk.
Handling Roof Gutters that Drain into the Sewer Piping
Some older homes include roof drainage downspouts that are carried to drain pipes which connect to the building sewer drain piping. In some installations the gutter downspouts connect to a drain line inside the building, perhaps running out of the building under the basement floor onwards to a public sewer line.
Such drains can easily freeze in an un-heated home, leading to broken drain lines, frost-heaved basement floors, and severe basement flooding.
We recommend that drain connections between roof gutters and downspouts and the building sewer line be abandoned.
If necessary, install temporary above-ground downspout extensions to conduct roof runoff well away from the building rather than into the sewer line via the basement floor. Incidentally, because the volume of roof runoff sent into a sewer line can overwhelm municipal sewage treatment plants this connection is prohibited in some communities.
What Else to Do to Avoid Frozen Building Drains
- Make sure there are no "running" toilets or faucets or other equipment
- Make sure there are no blocked or clogged drains that will hold standing wastewater (that freezes and breaks the pipes)
- If heat is left off in a building, use a non-toxic antifreeze in plumbing traps
- Find & Fix Water Pipe Freeze-Up Points, including adding insulation and heat in problem areas if necessary
Frequently Asked Questions (FAQs) about Freezing Drain Lines: Cause, Prevention, Cure
Question: What is the required or recommended depth for connecting house drain pipes(such as a bathroom waste pipe) to a septic tank to avoid freezing?
What is the required or recommended depth for connecting house drain pipes(such as a bathroom waste pipe) to a septic tank in New York State in order to avoid freezing?
If a house drain pipe is connected toward the top of a septic tank, is it vulnerable to freezing and, if so, how much soil should cover that pipe to protect it from freezing?
- Jane
Reply: House drains may be above the frost line and depend on proper slope and drainage to avoid freeze-damage.
Plastic drain pipes are usually buried at least 18" and bedded in sand to avoid mechanical damage to the pipe. But building main drains (upper right circle in our photo at left) are often not below the frost line outdoors and in a freezing climate such as New York, the lines depend on proper slope to drain into a septic tank or into a municipal sewer main to avoid freezing.
So the waste piping depth is more determined by using the required pipe slope (1/8" to 1/4" per linear foot) and working backwards from the septic tank or municipal sewer line connection point and the property's own elevation and slope.
Our sewer piping photo (above left, courtesy Galow Homes - click to enlarge) shows a new sewer line (at left and foreground) being connected to an existing house drain (circled areas) in a New York home. You will notice that where the existing main sewer line exits the building the plumber included a cleanout (upper circle in photo) and that the depth of the waste piping is just about 12" below the ground surface. At this particular installation the drain piping slope exceeds 1/4" per foot in the area of the new connection because the ground slope in this area falls rapidly away from the home.
From the point of entry into the septic tank or into a municipal sewer main, drain piping lines need to slope 1/8" to 1/4" per foot to drain properly. Some piping sections may slope more than this due to terrain properties (our photo above) but slope should not be less.
We don't find that in-use septic tanks freeze up - most likely due to the combination of the warmth generated bacterial action, the entry of warm water from the building, and the fact that a good portion of the tank will be below the frost line in most installations. Also see SEPTIC TANK DEPTH.
Watch Out though: the whole theory behind allowing drain lines to be above the frost line in your state, to avoid a freeze-up of the drain line, depends on:
- Proper drain line slope
- Drain lines that are not clogged or blocked
- The absence of any ongoing plumbing supply leaks such as a running toilet
If the outside (or inside for that matter) building drain piping is not properly sloped it will clog.
If the drain line is blocked, the holding of wastewater in a drain line that is above the frost line means that in prolonged cold weather the line will freeze and often will burst
If there is a running toilet or other small plumbing supply leak, that rivulet of slow but continuous wastewater can freeze in the bottom of shallow outdoor drain lines in a freezing climate; over time and without sufficient wastewater passage to thaw out and flush out that freezing of water on the bottom surface of the drainline the whole line can slowly fill with ice, leading to a frozen waste line, blocked line, sewer backup in the building, or a burst sewer line.
Question: how much does it cost to bury a pipe below the frost line
Wonderful information.
I am currently in the process of buying a home in Virginia, and a portion of the drainage pipe is exposed. Any idea how much (typically) it would cost to bury the pipe, or who I would contact to fix this? - Meaghan 5/31/12
Reply:
Meaghan,
if the drain pipe that is exposed is properly sloped and you don't have fixtures that run continuously into it (say a running toilet), the freeze risk is very low, especially in VA.
Speaking very generally, the 2013 cost to dig a 25-foot trench runs between $300. & $400. or about $13. to $16. per foot, with of course many variables such as depth, soil properties, and obstructions. There are online cost estimators that take your zip code and will give closer estimates, but even those can be way off as the cost estimator has no idea about local site conditions at your property. Simply hitting a big boulder, for example, can change the picture.
The cost to bury is something you'd best get from a local excavation contractor or landscaper who can see the actual site conditions, length of pipe to be covered, to what depth, thus estimating yards of soil, hours of machine and labor time, and finish landscaping requirements.
Without that data, an estimated cost to bury something arbitrary. Just be sure that your "burying" does not also bury building siding or you'll be asking for an insect problem.
Question: what is the frost line depth in Nebraska's Platte Valley
Any idea what the specs might be in Nebraska's Platte River Valley? We are not far to ground water. - Gary 8/16/2012
Reply: easy to find frost line data for Colorado, but for Nebraska?
Gary,
The spec is the frost line, right? Any local plumber will tell you.
From a quick historical search about the frost line in Nebraska I learned from the Colorado Climate Center that for Colorado the frost line data is:
Typically the frost line in Nebraska in your area is around 10-14-inches from the ground surface
The deepest frost penetration in Nebraska in the last 20 years was at 20-inches. But watch out: more extreme variations are occurring in weather patterns everywhere so deeper frost penetrations may be in store.
In the 1930's in a cold winter with little snow cover the frost line extended down to 30"
So to be safe, and if you plan to move to Colorado, assume the frost level there is at least 20-inches and 30-inches would be safer.[8] OK, let's look for a better answer.
Take a look at the Air Freezing Index to Guess at Frost Line Depth for Your Area
Can we translate that data to Nebraska? Not directly. When you cannot find local frost line depth data, building codes adopted by your community still will have the answer. For example, the International Residential Code (IRC) for 2012 gives Air Freezing Index data for each U.S. state.
Figuring the Frost Line Depth for Nebraska
Most of Nebraska has an index of 1500 or less, except for Boyd, Burt, Cedar, Cuming, Dakota, Dixon, Dodge, Knox, Thurston counties where the air freezing index is 2500. Now we can do a little extrapolation and arm-waving:
The same IRC explains in Table R 403.3(1) that we can translate an air freezing index into a required footing depth. That data is in our table quotation just below. You can see that for an air freezing index of 1500 or less the minimum footing depth is 12-inches, and for an air freezing index of 2500 you'd have to make the footings at least 16-inches deep. Not very deep, right? Since the intent of footing depth is to protect a footing from frost heaves, I figure this is a good approximation of the frost line depth for your area: 12-16-inches.
| 2012 IRC, excerpt from TABLE R403.3(1) MINIMUM FOOTING DEPTH AND INSULATION REQUIREMENTS FOR FROST-PROTECTED FOOTINGS IN HEATED BUILDINGS [Italics ours] [9] |
AIR FREEZING INDEX
(°F-days)b |
MINIMUM FOOTING DEPTH, D
(inches) |
| 1,500 or less |
12 |
| 2,000 |
14 |
| 2,500 |
16 |
| 3,000 |
16 |
| 3,500 |
16 |
| 4,000 |
16 |
Watch out: local frost line data and local codes prevail; rules about minimum building footing depth, which you can use to guess at a safe frost line, may be different in your area from those assumed by and in the area addressed by teh IRC. Best bet is to ask your local building department.
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Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.
- [1] "New Electric Heat Tapes Help Prevent Fires," US Consumer Product Safety Commission (CPSC) #00936
- Mark Cramer Inspection Services Mark Cramer, Tampa Florida, Mr. Cramer is a past president of ASHI, the American Society of Home Inspectors and is a Florida home inspector and home inspection educator. Mr. Cramer serves on the ASHI Home Inspection Standards. Contact Mark Cramer at: 727-595-4211 mark@BestTampaInspector.com
- John Cranor is an ASHI member and a home inspector (The House Whisperer) is located in Glen Allen, VA 23060. He is also a contributor to InspectApedia.com in several technical areas such as plumbing and appliances (dryer vents). Contact Mr. Cranor at 804-747-7747 or by Email: johncranor@verizon.net
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides:
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- [5] "Freezeproof Your House," Mike McClintock, Rodale's New Shelter, p. 30, October 1985 (approximate date)
- Eric Galow, Galow Homes, Lagrangeville, NY. Mr. Galow can be reached by email: ericgalow@gmail.com or by telephone: 914-474-6613. Mr. Galow specializes in residential construction including both new homes and repairs, renovations, and additions.
- [7] "How to Winterize Your Pipes," Mike McClintock, Homeowners How-To Magazine, p. 59-62, Nov-Dec 1979.
- [8] Colorado Climate Center, "How deep is the frostline in the winter in various parts of Colorado?", website http://ccc.atmos.colostate.edu/questions.php, retrieved 3/1/13
- [9] Cyber Regs, " ICC Subscriptions
International Residential Code for One- and Two-Family Dwellings". R403.3 Frost-protected shallow foundations, citing 2012 IRC, http://publicecodes.cyberregs.com/ icod/irc/2012/icod_irc_2012_4_par033.htm retrieved 3/1/2013
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