Rock-a-bye baby: What a nursery rhyme teaches us about pipe supports
Fair warning — As I write this article I have been up since 2:45 a.m. because, apparently, my 20-month-old daughter hates me and felt I did not require a full night’s sleep heading into Monday morning. A lot of things go through your mind during that late-night/early morning period when you are trying to convince a toddler who is inexplicably wide awake to go back to sleep so daddy can function like a normal human being at work later.
As I spent “bonding time” with my daughter, I remembered the issues I had with several of the common nursery rhymes we sing to our children to comfort them. Some of them are ridiculous and some of them are even horrifying when you take a moment to pay attention to the lyrics. For example, doesn’t it seem a bit extreme to swap out a mute mockingbird with a diamond ring? No wonder kids today have such a sense of entitlement.
On the other hand, we have “Rock-A-Bye Baby,” a nursery rhyme only Stephen King could love. In this lovely gem, we sing about a baby who has been put in a cradle … in the branches of a tree. According to the song, this seems to have been done by the parents looking for some sort of automatic rocking mechanism; in this case, utilizing wind power. Although this shows some progressive thinking in some ways, our tale turns south after the bough the cradle is on breaks and the cradle and baby come crashing down to suffer some unimaginable fate.
And then we wonder why our kids don’t immediately fall back to sleep.
If we assume the parents, in this case, were not completely insane, we can point out the technical flaws in their plan. Harnessing the power of the wind to rock your child so you don’t have to do it manually seems innovative, but these parental engineers failed to take into account whether the boughs and branches of a tree could support the weight of the cradle and baby as well as the stress from the wind load. If the branches had been properly supported, perhaps this nursery rhyme would be less traumatizing. The same can be said for piping throughout a plumbing system. Whether in a small residential home or a massive skyscraper, piping of all kinds needs to be properly supported to maintain the proper function of the system and prevent failure of piping materials.
All parts of the plumbing system must be supported with reference to this code, the manufacturer’s installation instructions and any other requirements of the AHJ. Hangers must be located so that the pipe is supported independently of fixtures, appliances and appurtenances; and fixtures, appliances and appurtenances are supported independently of the pipe. Examples of appurtenances are meters, pressure-reducing valves, strainers and backflow prevention devices.
Data regarding the weight of pipe is available in engineering manuals or manufacturers’ literature. Plans and specifications must be checked to determine the pipe’s wall thickness as per pipe schedule. The weight must include the contents of the pipe. This is calculated as the weight of water contained within a given size of pipe. The weight of flanges, bolts, valves and fittings (plus insulation) must also be calculated. The proper size of anchors, rods and hangers must be selected for the weight and size of the piping. See Table 313.6 for one method of selecting hanger rod size.
Where anchors and supports are attached to the structure, the structure must be strong enough to support the additional load of the piping system, fixtures or appliances. This is most critical when renovating commercial and industrial buildings.
Pipe and its supporting hangers should be one compatible system. If the supports are of a different material than the pipe, care should be taken to isolate the pipe from incompatible materials; otherwise, corrosion may occur and cause pipe failure. The isolation may be something as simple as taping the pipe with 10- or 20-mm black tape or using an isolating hanger.
Table 313.3 is a very extensive table containing the requirements for vertical and horizontal support for most of the piping materials and applications used in the plumbing system. Distances between supports will vary depending on the size, type of material, type of joint and use of the pipe. For example, Schedule 40 PVC DWV pipe will have supports placed closer together than threaded steel water pipe.
The parameters of the table — distances between supports both vertical and horizontal — were developed based on the ability of the piping material and type of joint, when full, to remain level or plumb without sagging, and properly aligned. Therefore, the table should be followed at all times. The improper placement of the supports will cause the installation to fail inspection and, even worse, may cause the piping system itself to fail. You can easily use your favorite search engine for examples of pipe hangers and supports.
One of the most important elements of Table 313.3 are the notes at the bottom of the table. These five notes are very important to the proper support of piping materials in the plumbing system. Notes 1, 2, 3 and 4 pertain mostly to cast iron pipe. It is important to understand when installing either compression gasket or hubless cast iron pipe with shielded couplings (or no hub couplings) that if the pipe is over 4 ft. (1,210 mm) in length, there should be one support at every joint (see Figure A).
An explanation for each note contained in Table 313.3 follows:
1. The hanger or support must be placed next to the pipe joint, not more than 18 in. (457 mm) from the joint (see Figure A).
2. A brace to prevent horizontal movement of horizontal piping shall be placed at 40-ft. intervals of piping. This is especially critical in areas of earthquake activity. Buildings are now built to withstand extensive ground movement, so the piping system must also be able to withstand this movement (see Figure A).
3. The intersection at tees or wyes in horizontal pipe must be supported by a hanger on the branch also placed within 18 in. of the joint.
4. It does little good to support piping on the joint itself. The hanger will not be taking the weight of pipe if placed on the joint. The joint itself will have all the weight, which will lead to the failure of that joint.
5. Consideration for expansion and contraction of piping is contained in other areas of the code; however, vertical water piping is sometimes forgotten. This note creates a requirement for the expansion and contraction of vertical water piping to be addressed by the design professional.
Another consideration for designing a system of pipe hangers, supports and riser clamps is to determine whether the pipe is scheduled to be insulated. Whenever insulation is applied, the type and thickness of the insulating material must be considered. The size of the hangers must be increased if the pipe is insulated, and the hangers are to be placed externally over the insulation. Also, there must be sufficient space for installers to apply and repair the insulation (see Figure B).
There is one last thing to consider when installing piping supports. There are other sections of the code that pertain to supporting piping or equipment. These depend on the type of installation — water, gas, DWV and medical gasses. All of the code must be taken into account when installing the plumbing system for proper piping support and other aspects of the system. Failing to do so could put you in a situation where … down comes the system, piping and all.