Swept Bend Radius -Service Ducts Into Slab

[Barney12]

I've just been pondering my slab insertions and thinking about which services I need to bring into the slab.

 

We made the mistake when doing the garage of making the radius of the ducting too tight and then had an absolute nightmare of a job getting the water pipe and SWA cable in.

 

So what's the collective opinion on a perfect radius for a 60mm duct coming into the slab?

 

i was even thinking of making a really simple 'jig' out of ply which would ensure all the ducts are correct in terms of radius and are supported during the pour. Would take minutes to make and potentially save lots of stress!!

 

Overthinking? Almost certainly!

 

Edited April 8, 2017 by Barney12
Typo

[Steptoe]

A general rule of thumb is 8x diameter

So for a 60mm duct you'd have a 20" radius

[Jeremy Harris]

I found that the 100mm and 50mm duct just naturally adopted a bend radius that was fine for pulling big cable (25mm² three core SWA) and MDPE water pipe through.  Bearing in mind the depth these ducts need to be, there is quite a bit of room to accommodate a gentle bend before they come up vertically through the insulation and slab. 

 

I was surprised at how easy it was to pull the heavy SWA through, the biggest problem (because I was working on my own for that bit) was the weight of the cable, and going from pushing at one end to pulling at the other to get it through.  With two people this would have been a lot easier; one to pull and the other to guide the cable in from the roll at the other end.  The same applies to getting MDPE pipe in, it would have been a lot easier with two people.

[Barney12]

5 minutes ago, JSHarris said:

I found that the 100mm and 50mm duct just naturally adopted a bend radius that was fine for pulling big cable (25mm² three core SWA) and MDPE water pipe through.  Bearing in mind the depth these ducts need to be, there is quite a bit of room to accommodate a gentle bend before they come up vertically through the insulation and slab. 

 

 

Thanks. I assume it's best practice to have the ducts fairly vertical through the EPS to minimise insulation loss? 

[Jeremy Harris]

Yes, all ours came up vertically through the insulation.  Under our 300mm insulation layer there is 150mm of type 3 stone, with the bottom of the service trenches being around another half metre or so below that, so the bends are all below the stone layer.

[dogman]

Mbc will make a frame for you on site. However my water pipe is 32mm and it is in 68mm duct ( i am on my own borehole) 

We had to come from below the compacted stone layer to get a comfortable bend that allowed the MDPE pipe to move. I put it in the duct so i didn't need to struggle to get them through. I did this with power and hot and cold water to the kitchen island as well. 

[dogman]

this is mine

 

 

[MikeSharp01]

We put the water pipe in the duct before we laid it because I was worried about getting it through! Could have done the SWA as well but kept radius at 400mm so I am hopeful.

[Oz07]

Really struggled on last build as used some left over 4" duct for water and kept catching on corrugated sides. Tried a few tricks which didn't work before I noticed some 10mm speedfit knocking about. Straight through with rope on end, rope tied to mdpe, mdpe pulled straight through 

[Triassic]

I had the same problem last week, I used a large vacuum cleaner to suck a string through.  I started by taping a Plastic over the end of the pipe and made a small cross slit in it, then forced the Hoover hose through the slit, so as to get a good air seal. I tied a large peice of kitchen roll to the end of the string and turned the vacuum on and within a minute the string was through.

[Onoff]

To get a draw string through I favour a square of plastic bag with a small hole in the centre. I thread a string through and knot / tape it back to the bag. I then form it into a sort of cone and insert in one end of the pipe. Then attach the vac the other end with some duct tape to make a seal. Job done.