INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS
If you are looking for more details, kindly visit 4 inch ductile iron pipe price per foot.
FIRST NAME
*
LAST NAME
*
*
MESSAGE
*
ADDITIONAL DETAILS
Thanks. We have received your request and will respond promptly.
Log In
Are you an
Engineering professional?
Join Eng-Tips Forums!
*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.
Promoting, selling, recruiting, coursework and thesis posting is forbidden.
Eng-Tips Posting Policies
PVC vs Ductile Iron for water mains?
thread164-365559 Forum Search FAQs Links MVPsForum
Search
FAQs
Links
MVPs
(Civil/Environmental)
(OP)
28 May 14 21:29I work for a water company and the town engineers have decided to replace a percentage of DI mains with PVC through a grant program. Since we don't currently have any PVC mains, what are the pros and cons of going with PVC. I just don't see it as strong enough and easily damaged during excavation and almost impossible to trace and can hydrants be connected? Thanks in advance. Rob
(Civil/Environmental)
29 May 14 15:20Other than what you have stated, it may be less expensive.
(Civil/Environmental)
29 May 14 16:12long term O&M costs may not make it less expensive.
however,
hydrants can be connected to pvc lines
locating pvc lines is relatively simple, but you should be installing tracer wires and warning tape in your trench. with the traceable locator tape, not a big deal
it is certainly strong enough to be used for municipal water distribution service but maybe not on major transmission lines
(Civil/Environmental)
3 Jun 14 00:04fyi http://www.nbcmatoday.org/PDFs/pvcdoc.pdf
(Geotechnical)
3 Jun 14 15:35I'd like to know who commissioned that report, rconner.
(Civil/Environmental)
3 Jun 14 17:07The report just identifies the reason that some municipalities use PVC and others use ductile iron. It is a personal preference, the same as rconner's opinion.
No one should expect the report to be definitive and pass a peer review as there are too many odd assumptions.
There are also errors in the report. Plastic pipe was actually invented during WWII by the Germans because it enabled the piping system to be repaired quickly after it was destroyed by the strategic bombing.
Oddly enough despite all of the assumptions, the report actually supports the use of PVC pipe because it states that PVC pipe is 4.7% less expensive than ductile iron pipe. That may not seem like much money for a small project, but 4.7% adds up quickly.
Some have estimated that the cost to repair and replace U.S. water and sewer pipes is as high as $660 billion. 4.7% of that is $31 Billion which is a substantial cost difference.
It reminded me of the story about automobile daylight running lights. Each automobile light may be only 55 watts or so and DRL's sound like a good idea. But when you add up the cost for 55 watts times 254 million cars in the U.S., it adds up to 27,000 megawatts, which is a tremendous waste of fuel.
(Civil/Environmental)
5 Jun 14 19:26Cool thread! I find it interesting as our town is on a semi aggressive replacement program to get rid of all our cast iron and ductile iron mains. We use only C900/905 PVC DR-18 for all repairs and capital replacements and new subdivision installs. The only exception are crosses. Apparently PVC crosses are not yet adequate to withstand all the forces over time, so we still use cast iron crosses with sacrificial anodes attached whenever a cross is needed. We have been using PVC water mains since about 1981 and have not had any leaks on PVC that were not due to original installation error of some kind (eg. over insertion, dirty joint, etc). Advantages of PVC would include less expensive to purchase, less expensive to install; it's much lighter and easier to install, does not corrode, is flexible, can come with internal restraints (i.e Terra Brute, Cobra-lok, bulldog, et al) and is convenient for directional drilling, easy to tap, blah, blah... The disadvantage to PVC would be that you will no longer be invited to the iron pipe parties anymore (probably not the PCCP parties either)...
It might make a difference, so I will mention that we have a minimum bury of 9 feet.
(Civil/Environmental)
5 Jun 14 23:05PVC Pipe Association (PVCPA) staff will present information on a 20-year-old AWWARF research study titled “Evaluation of Polyvinyl Chloride (PVC) Pipe Performance.” The study includes the following:
• Survey of utilities, consulting firms, and government agencies
• Results of testing of excavated pipe that had been in service
According to the “Discussion” chapter of the report, the objectives of the study were:
• To perform a comprehensive evaluation of the use and performance characteristics (including performance limits) of PVC water pipe
• To conduct the necessary research and analysis to resolve problems and concerns raised by the first objective
• To report results of analyses along with conclusions and recommendations
This half-hour webinar will address:
•Survey planning
•Survey data for various pipe products
•Survey data for PVC pipe
•Results of laboratory tests on excavated PVC pipe
•What 1994 results mean for 2014
Date: Wednesday, June 25, 2014
Time: 10:00 a.m. – 10:30 a.m. Central Time
PDHs: 0.5
Price: $49.00
(Civil/Environmental)
6 Jun 14 17:29I discovered the linked file I provided in a Google search some time ago when I was looking for comparisons of pipe materials, and I supplied same as I felt it was responding to what the OP requested (and it appeared to enforce to enforce prior good response of others). This is clearly a report from a consulting engineer (whose firm/name is there) to a municipal authority (per URL also there) for a pipeline project. While I frankly do not even know what pipe was selected for this project, but I guess I wouldn't be a bit surprised if responsible selectors chose the one that had the higher installed cost.In this regard, and while I am otherwise rather thick-skinned, I furthermore do feel that saying selection of pipe material is simply a matter of "personal preference" is at best a gross over-simplification and at worst an affront or insult to those utility folks and consulting Engineers in many countries (and in ours in the USA who frankly have done the best job of supplying the best quality water to the most folks and at the lowest real cost of anywhere in the world, and for a very long time.) While no doubt many have their favorites for piping based on their experience/level and other factors as for any capital etc. asset, a whole lot goes into any arguably rigorous selection process beyond this. While I guess it is true all pipes do indeed have at least a similarly sized hole in both ends, beyond that similarity the most common pipe materials that have been around for a long time are really apples and oranges. A whole lot of factors are involved in achievement of a successful pipe system and life cycle (the cheapest is certainly not always the best), and the linked evaluation touches on at least many of them.As to historical "error", by multiple accounts I've heard ballyhooed from the pvc pipe industry pvc pipe was actually first produced in Germany in the 1930's, and before the (bombing etc.) of WWII. While I have seen in the ditty at http://www.sewerhistory.org/articles/compon/pdfs/p... that "damage" to some of the 1930's lines (I thought when I read this to explain why many old pipe/line testimonials were hard to come by?) was in fact blamed on the subsequent WWII, while I guess I'm not surprised this thread is the first I have heard of the claim that it was invented because of that bombing! What might be most interesting/revealing is how much pvc pipe (e.g. percentage relative to other pipe materials) was selected by the inventing country with most long-term experience in the decades that followed the 1930's and 1940's??As to the post from I see a newcomer to these forums suggesting a utility apparently wants to "semi-aggressively" pursue replacement of all iron piping in their system. I hope for the benefit of tax/rate payers they proceed cautiously, While there have been some problems with some of huge quantities of particularly relatively brittle and often also unlined gray cast iron piping out there, iron piping has overall been providing (even with the technology of the day) overall pretty good service for hundreds of years, and in some cases continuously! On the other hand, I am aware of a good many relatively young pvc and other plastic pipelines that have been replaced in their veritable infancy over the last 40 years. I suspect those folks that originally bought those pvc lines also thought highly of the promise of the new material. It seems funny to me however that when folks are promoting plastic pipes, they want to exclude from consideration multiple categories of breaks or leaks from considerations of pipe materials (e.g. "those due to original installation error of some kind ("eg. over insertion, dirty joint, etc", tapping explosions blamed on procedures or tools, third-party damages etc. ) In my opinion, and while I agree with as throughrecordsas possible, all these things and others should be "on the table" as differing pipe materials are considered, as when such problems occur it makes little or no difference to the tax/rate payer and/or other inconvenienced public who/what caused same.I would like to welcome "IronDogg" to these forums. I believe the experiences you presented are indeed atypical (by any chance you are located e.g. in Canada/Alberta? or the very far Northern United States, as I think I have heard some equally strange report from that direction for many years?)[and p.s. to bimr I have a family member who has a 2000 model Toyota Corolla with daylight running lights/DRLs. I guess I have to admit I kinda liked this really safety feature myself in at least some driving conditions, as it is hard to put a price on safety and security. While I have thought this could well wear out bulbs quicker, I never thought about the aggregate power consumption; however, while I guess a cheaper-type car could have been purchased many years ago it still gets more than 30 mpg and has been quite reliable for now approaching 300,000 miles. Everyone have a good weekend ;>)]
(Civil/Environmental)
11 Jun 14 19:35Thanks for the welcome! :) Yeah, I am in the great white north. By semi-aggressive, I just mean that the water main replacement program focuses on those two pipe types. It’s mainly based on things like leak frequency on areas or sections of main, and of course over 90% of our main leaks are on iron. We do have sections of cast iron that is about 100 years old with no recorded leak frequency and we also have had ductile with corrosion leaks after only 20 years. Soil conditions make a big difference.
Are you interested in learning more about ductile iron pipe price per foot? Contact us today to secure an expert consultation!
(Civil/Environmental)
11 Jun 14 21:14Thanks for setting us straight on the bombing story, rconner.The AWWARF research study noted above should be the best reference source to answer the poster's query.
(Civil/Environmental)
20 Jun 14 10:38rconner
I just joined, we are a water main contractor and we are installing HDPE DR11 8" Water Main with Mechanical Joints at the Gate Wells and Hydrants, along with ductile iron sleeves, tees etc.....
From what I have researched, can you tell me the correct or acceptable hydrostatic test method to be used on this pipeline, or pressure testing procedures. From what I have researched and found out that there is no pressure testing other than the normal test procedure for make up water used after an hour for pvc, or ductile systems. I have seen that a hydrostatic test or pressure test in NOT a leak test, and that Totally fused systems with electrofusion couplers or mj adaptors you can use ASTM F2164, in which I dont think is applicable to our case. We have successfully tested HDPE systems built as I described above with many engineering firms using the same procedures as ductile. But I have One firm that in my view wants to make me use something that is not necessary.
Thanks in advance
(Civil/Environmental)
20 Jun 14 14:09Just a couple questions that might help you get advice (and from perhaps more knowledgeable folks than I).
In what country are you located? What exactly is this firm asking you to do that you feel is unnecessary?
(Civil/Environmental)
21 Jun 14 11:29USA
I believe that a leak test procedure with 5% pressure loss is not the proper test. ??? (astm f2164) I have been testing similar situations with the PVC or Ductile Specificaiton in a pipe bursting situation with HDPE and Ductile Mega lugs, inserts, tees, etc... gal/hr, per inch per mile etc.. all this with two other engineering firms, I am having a situation with this one engineering firm, although we had passed the leak test i am reluctant to use this as a standard on this particular project.
(Civil/Environmental)
22 Jun 14 21:18Here is the link for HDPE pressure and leaking testing:Leak testing is described in ASTM F2164, “Standard Practice for Field Leak Testing of Polyethylene (PE)Pressure Piping Systems Using Hydrostatic Pressure.”
(Civil/Environmental)
24 Jun 14 23:50It appears at least some USA manufacturers of polyethylene pipe are indeed promoting specifications requiring field hydrotesting per ASTM F2164. You can read at least the overview/entre' to the latest version of this standard,, and certainly purchase same if you wish and are responsible for knowing the details therein, at the portal http://www.astm.org/DownloadStandardA.html?ASTM%20... . It appears a historical 2002 version of this standard, not controlled as I believe there is a 2013 version available, can even be read for at least the time being at http://nutmeg.easternct.edu/sustainenergy/EnergySe... . A few points to consider in looking at what is meant by field testing of pipelines. The most common basic types of piping used for water service, including polyethylene, pvc and ductile iron all go back to near WWII or thereabouts. However, it is some interesting that while I'm sure various manufacturers and AHJ's have had their own and likely differing opinions concerning same, no sort of widespread utility consensus USA field testing protocols for plastic water pipes e.g. ANSI/AWWA standards have really been available until quite recent years.1. Note first from the aforementioned first portal that this web page for ASTM F2164 leads off with the statement, "5.1 If required by the authority having jurisdiction, hydrostatic pressure leak testing may be conducted to discover and correct leaks or faults in a newly constructed or modified polyethylene or crosslinked polyethylene pressure piping system before placing the system in service.") While the the very first prepositional phrase of this ad (I believe verbatim from a "Significance and Use" section of the original F2164 standard circa 2002) appears to indicate that field hydrostatic testing of pipelines is optional, in my opinion a well-run field hydrostatic test on a new pipeline is instead absolutely critical to provide some degree of protection for all parties to any pipe material piping design and installation, and ultimately the tax/rate payers. This language may be contrasted e.g. with that e.g. of ANSI/AWWA C600 for ductile iron piping systems that reads more unequivocally in Sec. 5.1.2 Workmanship, "All pipe and appurtenances shall be installed and joined in conformance with this standard and tested under pressure for defects and leaks in accordance with Sec. 5.2 of this standard..." then per Sec. 5.2.1.2, "...Following the installation of any new pipe or any valved section thereof shall be subjected to a hydrostatic pressure test." [I would particularly note e.g. that per AWWA C906 governing requirements for USA polyethylene pipe manufacture, individual polyethylene pipes are not required to be pressure tested by the manufacturer/at the factory, not even considering all that conceivably can happen to the pipe later/before final installation and burial!]2. This as well as the criteria from the linked document bimr provides seems quite liberal in the overall scheme of things. Lets say we are going to test a normal new 2,000 feet long 8" diameter underground water distribution pipe line that has been fully installed in the buried position it is intended to serve, and in our first case say it is polyethylene pipe to be field tested say to 160 psi.When I pull up the "Technical Note 802" on the website at http://www.performancepipe.com/en-us/Documents/PP8... , the first thing I see are all kinds of caveats with regard to tests and exactly what tests do and do not mean (though I wonder a little bit why, that is another story and I'll not worry about that here). As I know my required test pressure is 1-1/2 times my maximum service pressure, I will choose "Alternate 2", that I see is lead off with, "Immediately following the initial expansion phase, monitor the amount of make-up water required to maintain test pressure for one (1), or two (2), or three (3) hours. If the amount of make-up water needed to maintain test pressure does not exceed the amount in Table 2, no leakage is indicated." I choose 2 hours duration, as I know from my experience that that has long been the MINIMUM required/vetted for many years duration of AWWA C600 (for other material), so I look at their "Table 2 Test Phase – Alternate 2 – Make-Up Water Allowance". I see that for my two hour test the allowable make-up water is 1.0 U.S. gallon for every 100 feet of 8" pipe in my testing extant. For my 2,000 feet long project, I thus run the not too hard calculation (2,000 ft/100 ft)(1.0 Gal.) and come up a full 20 gallons (most of the bottom half of a 55 gal drum) of water they say I should allow the Contractor to pump back into this small hdpe pipeline if necessary to maintain pressure etc. Let’s now look at case two, that I had chosen instead ductile iron pipe for this project. Looking at Table 11-6 of AWWA M41, AWWA C600 (or tables in any number of major utility testing specifications re-created there from on the web) you will find that at 160 psi the testing allowance to maintain pressure is no more than 0.77 U.S. gallons per hour testing duration per 1,000 feet of pipeline involved (meaning I must multiply this amount by (2,000 ft/1,000)(2 hr/1 hr) ft or 4 to get the total testing allowance for such modern ductile iron piping installation that is in fact ~3.1 gallons, or milk jugs, of water). Now before we proceed further, let me add some more information, also from AWWA standards. Unlike ductile iron pipe, some folks may not know plastic pipe manufacturers are not now necessarily required by minimum AWWA standards e.g. AWWA C906 to hydrostatically leak or pressure strength test each piece of pipe at the factory, and I daresay little or no for hdpe water pipe is likely so tested. Also and on the other hand, anyone who has been around field installations of pipes very long understands that reasonable field testing allowances from the practical standpoint are necessary for the real world. It is virtually impossible to make sure all pipelines are laid precisely like profile lines on a CAD drawing, or that air release devices end up located precisely at every high point as shown on drawings (so that no air is trapped in pipelines), said air goes into and out of solution as it will, temperatures heating or cooling over the test duration have an effect on pressure (particularly on trapped air in accordance with Boyles, Charles, and Gay Lussacs etc.), pipes can settle or move at least slightly as they are pressurized (changing test volume some), water can soak at least a little into e.g. cement mortar linings, and indeed particularly for hdpe pipes there is also some rather complex change in test volume due to Poisson as well as Bourdon behaviors of the viscoelastic material (that are frankly more dependent on the pipe embedment and layout, as well as variations in piping, than some numbers in a table!) etc. In other words, pumping 3 gallons of water back into a ductile iron pipeline or seven times that allowable amount back into a polyethylene pipeline (the latter claimed outrageously by the vendors to be "jointless" and "leak-proof")"after the same two hour test doesn't mean either one of them has leaked that amount of water.
Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.
Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.
Click Here to join Eng-Tips and talk with other members! Already a Member? Login
What may be a cost-effective solution is not always what it seems. I was involved in the plumbing design for an eight-story residential assisted living facility in Cambridge, Mass., where the architect insisted on using Polyvinyl Chloride (PVC) piping throughout for the sanitary and storm systems. The architect had convinced himself that PVC piping, on a cost-per-linear foot basis, was so much cheaper than cast iron and copper that it was ludicrous to consider cast iron as a material of construction for his project. He was quite justified in his thinking, given that lengths of PVC Schedule 40 piping are about one-fourth the cost of hubless cast iron.
My main concern at the time, however, was PVC's lack of sound attenuation. I finally succeeded in convincing the architect to accept cast-iron piping from the basement up to the second floor. Because the first floor contained all of the public areas and common living areas, the architect conceded that the flow noise of water cascading through the sanitary and storm piping would be unacceptable. In hindsight I've found that cast-iron piping probably could have been used for all of the vertical risers up to the eighth floor for nearly the same cost as PVC, with much quieter results. The following article is a qualitative and quantitative comparison between PVC and cast-iron installations.
Polyvinyl Chloride is a common thermoplastic that has become the leading pipe material for both pressure and non-pressure applications. Resistant to electrolytic, chemical and biological attack, PVC piping holds a great advantage over metallic piping. The smooth inner surfaces help prevent fouling or clogging, which is very important in gravity drain applications.1 Polyvinyl Chloride piping has become the predominant material of choice for plumbing in single-family residential dwellings. It is so popular, in fact, that if you walk into many home improvement outlets, such as Home Depot, you can't even find cast iron or DWV copper next to the racks of PVC piping and boxes of PVC fittings.
The use of Polyvinyl Chloride pipe and fittings is often restricted by code. In Massachusetts, for example, the use of PVC pipe is restricted by the plumbing code (248 CMR) to residential dwellings, hotels, motels, inns, condominiums and similar buildings up to and including 10 stories in height.2 Even then its application is restricted to drainage, waste and vent (DWV) piping and storm drainage.
Because PVC is not fire retardant and can release noxious fumes when burned, it is not permitted for installation in return air ceiling plenums. Special conditions such as photo labs and soda fountains (carbonated water) permit the limited use of PVC.3
In all other applications, common non-plastic materials for DWV systems include service weight cast iron with poured lead or neoprene gasket joints, no-hub cast iron with stainless steel band clamps (commonly referred to as CISPI clamps), threaded galvanized steel and DWV copper with soldered joints. The most popular of these non-plastic systems appears to be no-hub cast iron and DWV copper, mostly because of the ease of installation.
Perhaps the two most attractive features of PVC are low cost and ease of installation. A 10-foot length of 4-inch hubless cast-iron pipe can be purchased for about $58. A 10-foot length of 4-inch Schedule 40 PVC costs only about $18.4 This amounts to a 70-percent savings. There is also a difference in fittings. A 4-inch sanitary tee, for example, costs about $5.50 in PVC and $11.50 in cast iron. The stainless steel band couplings required to join cast-iron fittings and pipe sections further add to the cost of cast iron. Such a coupling in 4-inch costs about $5.10.5 Because three such couplings are required to make the joints for a sanitary tee fitting, the overall cost for the 4-inch cast-iron sanitary tee increases to $26.80. PVC is simply joined with socket joints and solvent cement, which at any home supply store costs about $8 a quart.
At first glance, it would seem to make perfect sense to install PVC for a DWV system where the plumbing code allows. In the case of a single-family dwelling, PVC DWV is by far the least expensive plumbing package. However, there are four factors that must be considered before jumping into a complete PVC system for a large multistory residential project such as a condominium or hotel. These factors are (1) firestopping of plastic pipe penetrations through walls and floors, (2) thermal expansion relief, (3) hangers and supports, and (4) sound transmission.
First consider firestopping. The Massachusetts Building Code Chapters 6 and 7 define the requirements for firestopping and draftstopping for structures. In the case of the assisted-living facility in Cambridge previously mentioned, the plumbing risers were installed in concealed wet wall spaces between units. According to the architect, the code requires a minimum one-hour fire resistance rating between dwelling units and floors.6 Cast-iron pipe is fire resistant and will not burn away or otherwise deform when exposed to fire.
To seal the penetration of a cast-iron pipe through a fire rated floor, all that is needed is some mineral wool batting and fire-resistant caulking or mortar. Firestopping assemblies from various manufacturers can be found in the Underwriters Laboratories standard UL 1479 (ASTM E814). All firestopping assemblies must be listed and approved by ASTM E814 (UL 1479) and E119 standards. The typical cost of firestopping materials for a 4-inch cast iron pipe is about $18 and the time of installation averages about 32 units per day.
Because PVC piping is not fire resistant, it will quickly melt and burn away, leaving an opening that will permit the spread of smoke, heat and flame. To counter this, the firestopping materials for plastic piping must be intumescent.7 When exposed to the heat of a fire, intumescent materials will expand more than 20 times their original volume to fill and seal the floor penetration. A test sample of a PVC pipe and firestop collar displayed by a firestopping vendor showed little evidence of the original PVC, but the intumescent material had completely sealed off the inside of the pipe penetration. A common firestopping assembly for plastic piping through concrete floors consists of a ring of intumescent material held in place around the pipe with a metal collar. This assembly is more labor intensive to install as it involves shooting in masonry anchors, clamping the collar in place and installing a smoke seal with a bead of the same type of fire-resistant caulking or mortar used for cast-iron pipes.
Proper installation of this assembly can be further complicated due to the maximum annular space allowed between the pipe and the floor opening. In the case of a 4-inch PVC pipe, the maximum annular spacing is limited to a half-inch.8 This means a 4-inch pipe penetration requires a maximum 5-inch core. This leaves little or no room for error when the contractor locates and drills floor openings through concrete slabs. This opens the door for costly errors for mis-drilled holes and misaligned piping passing through the slab. The cast-iron pipe assembly, on the other hand, is allowed to have an annulus ranging from point of contact to 2-inch maximum, allowing for some misalignment error. The cost of materials for the PVC firestopping assembly is about $32, and the time of installation averages about 20 units per day, 12 units fewer than the cast-iron firestopping.9
The Massachusetts plumbing code requires that a Polyvinyl Chloride DWV system allow for a thermal expansion of a half-inch for every 10 feet.10 Thermoplastic materials such as PVC have a rate of thermal expansion six to 10 times greater than that of metal pipe.11 The stresses of expansion are relieved in a PVC-DWV system with changes in direction or expansion fittings that are basically a pipe within a pipe that telescopes in and out as the piping expands and contracts. The joint is sealed with rubber O-rings lubricated with a water-resistant lubricant such as petroleum jelly. Expansion joints are required in vertical stacks at every other branch interval and on horizontal runs exceeding 20 feet.12 According to a quote from Portland Pipe in Boston, a 4-inch expansion joint costs about $72.60. This added expense drives up the cost of PVC piping, especially when running long waste and vent risers up a multistory building.
Expansion joints can create headaches during pressure testing. "When we tried to pressure-test the (DWV) piping, the expansion joints kept leaking," says Eric Aronson of the J.C. Higgins Corporation in reference to the Cambridge assisted-living facility. "I had guys running around trying to fix leaks until the plumbing inspector finally signed off on the piping." In a system spanning eight stories with 12 vertical risers, the expansion joints caused costly man-hours to fine-tune.
Another factor that drives up the relative cost of PVC piping is hanger spacing. Horizontal runs of PVC piping are required by code to have supports every 4 feet on center.13 Cast-iron piping, on the other hand, needs to be supported at every pipe length with an approved hanger no more than 18 inches from the joint or couplings between sections.14 If cast-iron piping is installed in 10-foot sections, hangers are needed every 10 feet on center. So the cost of hangers for PVC piping is about 2.5 times than that of cast iron in horizontal installations. Remember the costs for 10-foot lengths of PVC and cast iron? PVC was about a third the cost of cast iron. However, for long horizontal runs (pitched according to code, of course), PVC drains can cost as much as, if not more than, cast-iron no-hub piping when expansion joints and hangers are taken into account. Even though the PVC is cheaper and lighter, it takes much longer to install and adjust the hangers and properly install the expansion joints every 20 feet. The playing field is evened out in vertical stacks, however, because both PVC and cast-iron piping need to be supported with a riser clamp at every floor.
Another negative factor associated with installing PVC piping is its unforgiving nature once a joint has been cemented. To make field alignments, cutting the piping to length and temporarily assembling the fittings dry works to a point. But have you ever pushed the end of a PVC pipe too far into the socket of a joint without cement and not been able to pull them apart? The tolerances between pipe and fitting are made to allow the solvent to act as a lubricant when setting the joint. Once the joint has set after a few seconds, there is no opportunity for adjustment. Hubless cast-iron joints are mechanical and can be assembled loose and then torqued down to specifications after critical alignments have been made. In other words, there is a higher potential for costly errors when installing PVC pipe if not done with a great deal of planning.
The last, and probably most meaningful factor to end users, is sound attenuation. Even though the light weight of PVC piping makes it easier to transport and install, it is the low density of PVC that makes it so poor at attenuating flow noise. Cast iron, on the other hand, is much quieter because its mass absorbs far more sound energy. You can always tell who has PVC piping installed in their home when someone flushes the upstairs toilet and it sounds like a rain storm inside the living room or kitchen wall. This is probably the greatest negative against PVC piping. Some of the noise can be muffled with wrap fiberglass insulation, but it doesn't compare to cast iron. The associated material and labor costs for insulating the piping only adds to the total cost of PVC.
The noise problems associated with PVC piping are well known in the plumbing trade and most plumbers insist on installing cast-iron no-hub piping in areas of a home where noise would be an issue, such as when passing through living spaces on its way down to the basement. In other areas with short runs of horizontal drains, such as the toilet discharge or shower drain, noise isn't as much as an issue, since it is localized and intermittent. But if the drain pipe is directly above the ceiling of a living room, bedroom or other living space, cast iron should be considered.
So the question at this point is: When all factors have been taken into consideration, is it worth specifying PVC-DWV systems in multistory residential buildings in terms of cost and performance? To compare the total installed costs of PVC and cast iron, consider a single floor-to-floor section of a waste and vent riser system in a multistory building. Assume the floor-to-floor height is 12 feet, and the 4-inch waste stack receives a 4-inch horizontal waste branch through a 4-inch sanitary tee fitting and the 3-inch vent stack receives a 2-inch vent connection through a 3-inch by 2-inch sanitary tee fitting. Two separate scenarios can be compared-built completely of PVC pipe and fittings and built with PVC rough plumbing and vertical waste and vent stacks of no-hub cast iron. When comparing costs, the associated plumbing fixtures, hangers, coring and PVC branch piping are identical for both scenarios so they are not included in any cost estimating for comparison sake. Only the vertical stacks are considered. The estimated costs for both scenarios are summarized in Tables A and B.
According to the estimates, the lower cost of PVC pipe and fittings is offset by the higher costs for expansion joints and firestopping. The only uncertain variable in these estimates is the labor cost. Equal costs were assumed for installing a straight, 12-foot section of risers. But when working with rough plumbing in walls where there are many cuts, bends and fittings, the overall labor cost for installing PVC should be significantly lower because of the ease of installation. "When you just consider the vertical risers," Aronson says, "you're not looking at a big difference in labor costs for just the vertical piping."
Also, the time and expense for rigging bundles of piping up several stories has not been taken into account, but this has to be factored in for a specific project. These cost estimates, of course, do not address the sound attenuation issue. In a multistory apartment or condominium building, the accumulated water flow can be significant on lower floors and make noise levels higher and nearly continuous. If fiberglass wrap insulation is considered to cut down the noise for the PVC stacks, the overall cost of installation is increased. Therefore, given the fact that the installed cost of uninsulated PVC and cast-iron riser sections is nearly equal, a DWV system consisting of PVC branch piping with cast-iron vertical risers and offsets would be the better choice. It offers both the labor and material savings that PVC provides and minimizes flow noise through the use of more massive cast iron while minimizing the cost of firestopping and thermal expansion fittings.
There are no exact costs for each material, and everyone's estimates will vary. But it seems clear that the 70-percent to 75-percent savings people see at first glance when buying PVC piping and fittings isn't always realized in the final installed cost. When installing vertical waste, vent and rainwater stacks down several stories or when there are long horizontal runs to be installed, the PVC/cast-iron combination described has the following advantages:
Of course, each individual situation must be assessed to find the factors that will be significant. Even if PVC comes out ahead on a particular project, how much is an owner willing to pay for quieter plumbing? Or are the savings worth sacrificing comfort levels? You will have to discuss with your clients. So when an architect on one of your projects insists on PVC piping to save money, you can discuss at least four important factors that make PVC waste and vent stacks less attractive.
For more information, please visit 4 inch ductile iron pipe cost per foot.