ᐅ Which conduit pipes should be installed under a precast concrete garage with strip foundations?
Created on: 4 Oct 2025 14:19
M
mk_2021
Hello everyone,
Soon our precast concrete garage will be installed directly adjacent to the house. We have already planned an opening in the floor to allow for a power distribution box for the garden electricity to be mounted inside the garage. In addition to the power cable, other cables will be routed there, such as network cables. All cables will be underground cables coming from the multi-utility supply.
The strip foundation has already been built. The subcontractor laid three DN110 (4-inch) KG pipes through the foundations and cut them flush. In the last foundation, a DN75 (3-inch) HT pipe was installed with a slight overlap. To make matters worse, the distances to the edge of the garage vary by up to 10cm (4 inches).
What can I do to make cable pulling as easy as possible afterwards and to prevent the pipes in the foundations from clogging?
1) Run an 80mm (3-inch) slotted flexible drainage pipe completely through, to avoid water accumulation, and secure it to the HT pipe with cable ties? I would only bury the pipes slightly so they remain stable. Or would it be impossible to pull cables through these pipes afterward?
2) DN110 (4-inch) KG pipe. Because the pipes in the foundations are cut flush, I cannot connect them with couplings. Is there another way to connect them? Maybe butt-joined and secured against slipping with a bit of mortar?
3) DN75 (3-inch) HT pipes? Of course, this reduces the diameter immediately and I would also have to work with bends and calculate carefully in advance.
Or is there an even simpler solution? In total, it’s only about 9m (30 feet), fairly straight but not completely. Since everything is under the garage, the stress from external forces should be minimal.
Many thanks for any ideas and experiences!
Soon our precast concrete garage will be installed directly adjacent to the house. We have already planned an opening in the floor to allow for a power distribution box for the garden electricity to be mounted inside the garage. In addition to the power cable, other cables will be routed there, such as network cables. All cables will be underground cables coming from the multi-utility supply.
The strip foundation has already been built. The subcontractor laid three DN110 (4-inch) KG pipes through the foundations and cut them flush. In the last foundation, a DN75 (3-inch) HT pipe was installed with a slight overlap. To make matters worse, the distances to the edge of the garage vary by up to 10cm (4 inches).
What can I do to make cable pulling as easy as possible afterwards and to prevent the pipes in the foundations from clogging?
1) Run an 80mm (3-inch) slotted flexible drainage pipe completely through, to avoid water accumulation, and secure it to the HT pipe with cable ties? I would only bury the pipes slightly so they remain stable. Or would it be impossible to pull cables through these pipes afterward?
2) DN110 (4-inch) KG pipe. Because the pipes in the foundations are cut flush, I cannot connect them with couplings. Is there another way to connect them? Maybe butt-joined and secured against slipping with a bit of mortar?
3) DN75 (3-inch) HT pipes? Of course, this reduces the diameter immediately and I would also have to work with bends and calculate carefully in advance.
Or is there an even simpler solution? In total, it’s only about 9m (30 feet), fairly straight but not completely. Since everything is under the garage, the stress from external forces should be minimal.
Many thanks for any ideas and experiences!
Or does anyone have a better idea?
The option with the perforated drainage pipe is probably the easiest to install.
With PVC sewer pipes, it generally feels easier to pull cables through later, right? The only issue is the joint connections. Possibly, I could align the PVC sewer pipes in the gaps directly butted against those in the foundations and then fix them to the foundations using metal brackets, for example by securing the “free” pipe with a screw and nut and attaching the bracket to the foundation with a screw and anchor?
The option with the perforated drainage pipe is probably the easiest to install.
With PVC sewer pipes, it generally feels easier to pull cables through later, right? The only issue is the joint connections. Possibly, I could align the PVC sewer pipes in the gaps directly butted against those in the foundations and then fix them to the foundations using metal brackets, for example by securing the “free” pipe with a screw and nut and attaching the bracket to the foundation with a screw and anchor?
T
Teimo198810 Oct 2025 10:49KG pipe is great for pulling cables through. The joints must, of course, be 100% watertight since they will be embedded in concrete. If concrete gets inside, that’s really bad. I would also secure it mechanically and, for extra safety, properly seal around it from the outside with polyurethane foam.
M
Molybdean10 Oct 2025 11:44mk_2021 schrieb:
Or does anyone have a better idea?Fränkische Kabuflex R is made exactly for something like this and is available in numerous diameters.
Teimo1988 schrieb:
KG pipe is great for pulling cables through. Connections must of course be 100% watertight since they will be embedded in concrete later. If concrete gets inside, that’s really bad. I would also mechanically secure it and, for extra safety, seal around it thoroughly with polyurethane foam. Hey, thanks for the info. No, only the sections within the strip foundation are embedded in concrete and have already been installed. The garage actually “floats” above, and the other pipes lie on the soil, meaning between the ground and the underside of the garage floor. At most, sand, soil, and animals could get inside. Since I’m using underground cables anyway, I assumed the pipes are just to make it easier to pull cables later. So I don’t think waterproofing is necessary.
But your tip about mechanical fixing is good. Maybe I’ll drive some metal rods into the ground and secure the pipes with wire and soil.
Molybdean schrieb:
Fränkische Kabuflex R, that's exactly designed for this purpose and comes in many diameters.I have found those as well, but I would need to order them separately, and they are only available in 50m (165 feet) coils at a corresponding cost. I thought that since I basically only need a conduit for the space between the ground and the underside of the garage, I could use any pipe. It also does not need to be waterproof because underground cables are planned. With a DN110 (approximately 110mm / 4.3 inches) pipe, you could also add a garden hose or similar later on. That’s where the idea of using a drainage hose came from. I would bury it about 10cm (4 inches) deep (no deeper is possible). Unlike sewer pipes, water does not accumulate inside.Similar topics