Opinions - 450mm or 300mm inspection chambers (aka manholes)

[Malc]

Hi,

I need to add 2 inspection chambers to my drains because of new connections. One is a new stack which I will probably run at 45 deg to existing drain for better flow and so I don't have 2 manholes almost next to each other. The other is an outlet from a downstairs bath room that turns 90 deg before in run to existing manhole (so I need manhole at the 90 deg). Invert depth is around 500mm.

I need to decide whether to go for the more expensive 450mm or use the 300mm but I wonder how easy it is to get rods into a 300mm.

Opinions?

BTW I assume nobody would suggest using old style concrete manholes for new manholes?

 

[Hugh Jaleak]

The 300mm chambers are for shallow drainage, where the invert is less than 600mm, and whilst it may be possible to get rods in, I suspect these are designed with the use of jetting hoses rather than rods in mind for cleaning purposes.

Rather than 2 chamber next to each other could you use a 450mm chamber, using the 90 and 45 connections may allow both connection to be made on the one chamber? Then the 90° turn for the downstairs bathroom, these are often done using 2 x 45° bends either side of the main channel on a plastic chamber base to allow better flow or use something like this, https://www.drainagesuperstore.co.u...degree-shallow-access-chamber-base-110mm.html

Preformed plastic chambers are usually used now for ease of installation, (and in fact the larger concrete chambers for main drainage also appear to be coming to site ready made now!), but if you have the time and skill to make your own chamber, then feel free.

 

[Malc]

I didn't explain it very well. The 2 new chambers are on opposite sides of the house and connect to other existing pipework. In one case if the new stack came out at right angles from the house the new chamber for that wouldn't be that far from the old chamber (about 1.8m centre to centre I think so 1.4m between them). Hence I think it would look better if I pointed the stack downstream so the new chamber was further away, especially as it would be a different lid. But it's a service passage so looks are not that important.

My gut feel is that 450mm would be cheaper in the long run rather than paying for a jetting hose to come to clear a blockage.

 

[Hugh Jaleak]

I think, especially given the lateral is going to a stack, the 450mm chamber may be the better option.