ᐅ Which conduit pipes should be installed under a precast concrete garage with strip foundations?

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!

I don’t fully understand the situation yet. Pictures are always very helpful in these cases. It’s always difficult to add anything later when cables or pipes are already installed. I would simply pull through some additional spare conduits now and run everything at once, bundled together.

Teimo1988 schrieb:

I don’t fully understand the situation yet. Pictures are always very helpful. It’s always difficult to add anything later when other cables are already in place. I would simply install additional empty conduits now and pull everything through at once, bundled together.

Hi, thanks for your answer. The situation is as follows. The strip foundation is already in place, and before the garage is built, I want to prepare everything as best as possible. A power distribution box will be installed in the garage. The cables come from the basement, pass through the front two foundations, and then go through the garage floor to the distribution box. Next year, during garden work, power cables will be routed from the distribution box under the garage through both the front and rear foundations into the garden.

The landscaping contractor who built the foundations cast various empty conduits into the foundations. Since these can become blocked between the strips, I was considering connecting these sections before the garage is delivered to make it easier to pull cables later. For this, I outlined the options mentioned above.

1) Flexible drainage pipe without connectors but corrugated.
2) With PVC pipes and elbows. Smooth surface. Unfortunately, the PVC pipes need to be connected end-to-end at the foundations since there is no protruding section to use a coupling.
3) HT pipes DN75, since this is the smallest pipe size in the 4th foundation and it protrudes. This way, I could run it "seamlessly" through the other openings. In the middle, a 45-degree elbow would direct the pipes into the garage.

Attached is a graphic.

Hmm, what diameter does the drainage pipe have then? With pipe-in-pipe, you inevitably get a sharp edge or, even worse, the connection moves.
In principle, 45-degree bends are not recommended. I would use a maximum of 30 degrees. How do you go through the garage floor— is it a concrete slab?

The purpose of the multi-duct system is to enable a watertight and gas-tight house entry. This applies not only to the passage of your numerous cables through the foundation, floor slab, or basement wall but also at the point where the cables exit the conduit, with a seal for each individual cable. If the gas supply is introduced through the multi-duct system, it definitely hits the mark.

Teimo1988 schrieb:

Hmm, what diameter does the drainage pipe have then? With pipe-in-pipe setups, you usually get a ridge or, even worse, the joint moves.
In principle, 45-degree bends are not recommended. I would use a maximum of 30 degrees. How are you passing through the garage floor? Is it a concrete slab?

At the hardware store, there are DN80 and DN100 drainage pipes, both solid and perforated. I would try the 100 mm (4 inch) first, and otherwise go with the 80 mm (3 inch). Perforated, since I’m laying underground cables anyway.

The precast concrete garage sits on the foundations, and the floor slab has a 10 x 10 cm (4 x 4 inch) opening configured.