Pipe sleeve and under ground conduits through foundation : how big is too big?
I am building a slab foundation, with 4’6″ frost walls and 24″X8″ footings. The front corners of the house and garage are about 20 feet apart. I would like to sleeve the foundation walls so I can run conduits between the buildings, for future services. The questions:
(1) Ideally I want to run 3 separate 2.5″ conduits between the building. As such, a 6″ PVC sleeve through the 8″ wall will not do. I will need an 8″ sleeve. Is that too big for an 8″ poured concrete wall with no rebar? Are there rules that determine how far up it has to be from the footing?
(2) Ideally I would like to run my water line through this sleeve (I would like to avoid digging under the footing for the water line). This means that at the wall it would be about 3.5′ down, and my frost line is 4′. Is there an equivalent insulation I can wrap the pipe with to compensate for the missing 6″ of soil cover?
(3) In the even that insulation is not possible, what is the best way to get the water line into the house? The footings are being poured on “undisturbed” soil, so I hesitate to trench in the footprint. If I have too, how deep to i go below the footing? Do I sleeve the pipe (2 sizes larger)? Do I backfill with compacted gravel?
(4) Is there a grade of conduit I should ask for? I want to make sure I can run everything underground between the buildings (natural gas lines, electrical, water, hot water for heat in insulated pipes, ethernet, cable etc).
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Replies
1. Sleeves that size are very common, especially on the bottom 1/3rd of the wall.
2. Try to avoid going through the wall with the water line. The soil below it will settle and put shear stress on the water line. If you need to go that route install 4" of 25psi foam 6' wide over the line.
3. You should install your water line about 6" or more below the footing and mark it's location so the concrete workers don't spear it with a form pin. You can hand dig through the footing area to minimize the disturbed area, but I wouldn't lose much sleep over it. Sewer and water are typically installed into the house footprint before wall trenches are dug, meaning there is usually a 4-5' wide disturbed area. It's never an issue. Tell the concrete guys to install some rebar in that location.
4. Conduit is cheap. Schedule 40 is most common, but I like the extra strength of schedule 80 for a small price increase.
Thanks Rick.
I was worried about the grade of conduit, after reading a horror story on the web about a guy who did exactly what I am planning, only to find out his conduit was not rated for electrical!
Is there a rule of thumb as to how much concrete I should leave between the top of the footing and the 8" PVC sleeve?
Is there a reason that you are placing all 3 conduits through a single sleeve? When I sleeved for utilities, I used separate ones for each item. I think it will for one it made it much easier to waterproof and seal around them, although I was entering crawl spaces and basement walls.
My other suggestion would be to eliminate the sleeve and just place SCH 80 conduit through the forms. Leave enough length on both sides so that you could cut off fittings and reattach if you needed to make a change. This may be a simpler option since you're already placing conduit. The sleeves are probably more beneficial for direct bury things like gas line.
This is an old but good, interesting and visually appealing (in a retro way) document that includes designing foam to cover water lines.
Don't use a common sleeve. Sleeving like this is commonly done commercially, and I usually work in the commercial realm. I have used 4" sleeves for 3 x 1.25" ducts before, and then seal around the ducts with canned foam or a pourable elastomeric sealant (which is better when you expect a lot of water penetration).
For what you're doing, use seperate sleeves, if you use sleeves at all. Common practice is to come up through the slab, not through the wall, when you place the conduits at the time of construction. Usually you bring the conduits up against the wall with a small gap, usually a cap that is the same as the depth of a strut channel, so you can use "strut straps" as your conduit clamps. This makes for a clean installation, just run one piece of strut on the wall that is the same length as the width of your junction box or panel, then strap all the conduits to that strut wherever they are as they approach the panel. Easy, and clean.
I would stick with schedule 40 PVC here. You don't really need sechedule 80 here. If the runs are longer and you want to avoid open trenching, considure using HDPE pipe here (you need UL listed for power cables, but not for telecom cables), which can be installed by directional drilling in continuos pieces (no couplinegs). I would also either install the entirety of the conduit runs at time of construction, or stub them out far enough from the building to avoid any landscaping or sidewalks, then cap them and mark the surface. Excavate later to get down to the capped conduits when you're ready to extend them to complete the run. Skip the sleeves inside the structure. You could also place a handhole over the stubbed ends to provide an access point. There are various ways to do it.
It's common to bring water lines through the wall in residential structures, but you should keep it under the frost line. I would not try insulating it to compensate for a lack of depth.
Regarding going under the footing, the easiest way to do this is just to dig out a notch in the bottom of the footing trench prior to the pour, then run all your conduits/services through that notch. When you pour the footing, the notch will just make a thick spot in the footing over and around the service conduits. That avoids the disturbed ground issue, lets you bring your stuff in in a nice spot, and just costs another cubic foot or three of concrete.
Regarding the types of conduits:
1- HUGE SAFETY NOTE: you CANNOT run a NATURAL GAS line in a shared trench and a NATURAL GAS LINE CANNOT ENTER A STRUCTURE BELOW GRADE. You MUST bring that gas line up above grade on the exterior of the building, then enter the structure. This is because gas leaks have been known to follow along on the exterior of underground lines, and enter structures if the line enters the structure. I would use yellow HDPE gas line for this, and the appropriate steel connections to bring it above grade at the ends of the run. This is the same way the gas companies run these lines, and some gas companies will make up the underground assemblies for you. Don't skimp here.
2- For hot water lines, I'd use the ThermaPEX stuff the outdoor boiler guys like to use. This is a corrugated poly pipe filled with spray foam that has a PEX pipe inside of it. Don't use "wrap pipe", that has a spiral insulation that looks like bubblewrap inside. Make sure the line you use is NSF rated for potable water use here if the hot water line will supply a sink or shower.
3- For potable cold water lines, use regular polyethylene pipe, NSF rated for potable water, which is commonly used for water wells. This stuff is tough, cheap, and readily available. No need to use anything else.
4- For power, use schedule 40 PVC conduit if you'll be open trenching. Use UL listed HDPE duct if you'll be installing by directional drilling. I like to bury down 24" for some extra protection. Regarding size, you need to check the fill tables in the code book for the size conductors you are using. Outbuildings fed from the main structure will usually use four wire services (two hots, a neutral, and a ground). The ground can be smalled than the other three conductors (i.e. #8 copper is good for the ground for up to a 100A circuit).
5- I'd run a seperate power conduit for switched lighting between buildings. Putting path lights on 3- or 4-way switches so that they can be turned on or off from ANY of the buildings is a really nice feature to have. I like to use 1" conduit for this, to provide some extra room for future additions.
6- For communications cables, this depends on what you want to run. For Ethernet, you're limited to 100 meters (328 feet) for copper cabling. I'd use shielded dry direct bury cat6 cable here. DO NOT USE CCA wire. ANY CCA cable is NOT cat-anything, per IEEE specs, regardless of what shady sellers might say. You MUST use ONLY pure copper conductors here. There are fill tables that will tell you how big a conduit you need, but I wouldn't go smaller than 1". I would not go bigger than 2". Ideal is usually 1" to 1.5", as larger conduits can actually be more difficult to pull through.
If you have long runs, consider using fiber optic cable. OM3 will run 10G Ethernet out to 500+ meters. Singlemode can go 10km with cheap optics. Most people will need to contract to have that cable terminated though (but it's easy to pull in yourself), which can add some money to a job since you'll need a telecom contractor for that. It's not hard to do yourself, but it needs some special tools, and a lot of the polishing is done by feel which takes practice before you don't break the connectors (and the glue on, so you get one chance to do it right or you have to cut it off and start over). Fiber is my preference here for a lot of reasons. I'd run 6 or 12 strand depending on your layout and what you're doing. Use "tight buffer" outdoor cable, which is easiest to work with for smaller projects. This stuff is pretty cheap, especially singlemode. I usually get it from The Light Connection in New York State.
BTW, 2.5" is a bit of an oddball conduit size, although available. 2" and then 4" are the most common. There is also a 3" size, but it's less common than 2.5".
Bill