Soil Stack & Building Regs

[lostforwords]

Just want a little direction on this one.

Moved into a new home and have discovered that the downstairs sub stack and main soil stack (serving 1st and 2nd floors) have been connected into horizontal drain runs from downstairs WHB and utility room sink respectively.

Both have been joined using a "sideways" short equal branch.........effectively an inverted "T". Toilet waste is backflowing up the branch towards the sinks.

Both joints are UNDER the house.

ANy comments on this and Building Regs ?

Builder seems to thinks its fine and it meet the requirements of the Building Regs (Adequate system of drainage). This is the bit at the start of the Approved Document (Part H). They are adamant that they do not need to follow the Guidance included in the Approved Document.

If you can Ignore the guidance what can be passed as an "adequate system" ?

Thanks

 

[Hugh Jaleak]

An adequate system is one that works and meets Building regs and Building Control officers approval!! Effluent should be removed without causing any smells or blockages. From your description it does sound a bit of a bodge, I would have expected the stacks to be at the head of the drain and any connections downstream joined obliquely in direction of flow. Am I correct in thinking the connections have been made to either end of the Tee, and the centre branch connection used as the outlet?

Also what is the floor construction? Drains are usually buried under the floor slab, so not sure how you are aware of the arrangement you describe.

 

[lostforwords]

Thanks Hugh

Building Control undertaken by NHBC Am chasing them down as it would appear they have no records of what was inspected on the plot and have stated " It is not possible to confirm whether the connections described in your email were in place at the time our inspection took place"

effluent is being left UPSTREAM of where the stacks join the horizontal drain run, I think as result of solids catching on the shoulder of 45 degree bends. Anyhow waste is trapped in the system and upstream of the soil stack. We initially complained of smells in both the downstairs WC and the utility room.

The connections used are sink waste straight through to outlet, centre branch (facing upwards) input from soil stack.

The drains are under the floors which are block and beam. I have worked out the layout from CCTV surveys which have been undertaken. The CCTV also shows a lot of "material" stuck to the sides and top of drains due to the splatter effect of a 5m odd freefall !

What is puzzling me is that Para 1.26 of Part H states "All stacks should discharge to a drain. The bend at the foot of the stack should have as large a radius as possible and at least 200mm at the centre line". However I have read elsewhere that this is just guidance and only the REQUIREMENT of the Statutory Instrument is mandatory i.e. "an adequate system of drainage" !!

Whats the feeling of other members ?

 

[doitall]

Quite simple, it works or it doesn't, if you're getting a backflow then it's wrong.

Can you do a drawing/sketch and post it.

 

[Hugh Jaleak]

I understand what you mean now. I was always under the assumption that a long radius bend must be used at the base of a stack, there again I havent read the detail of the regs lately!

Obviously it was easier for the builder to do things this way, quite why the sink and basin werent connected via a boss above ground im not sure, probably for aesthetic reasons. If solid matter is collecting upstream then it suggests there may not be adequate fall on the pipes, although the other appliances might not get used as often as the W.C.'s some discharge should be sufficient to wash away anything lurking.

Difficult to offer a solution without major works, the beam and block is screeded over so one hell of a job to access whats underneath now, and its difficult to say what, if anything could be done to alter the arrangement.

 

[kevplumb]

i'm no artist (some would say otherwise)

but is this what you mean ?
View media item 16472

 

[lostforwords]

Admit it does seem a big job to alter system and hence why Builder is making out all is ok.

I also expected to see a long radius bend at bottom of stacks (as do many other people). I think it is actually a case of the groundworkers being left to bodge and cover. For many weeks Builder was saying there are two pipes out to each inspection chamber.......? (It is a large National company). Still dont think I should have to inherit their mistakes as I believe it was designed otherwise.

I think the Building Regs if followed will demonstrate compliance, OTHER methods need to demonstrate that they work to meet the requirement (of the actual regulation in this case "an adequate system of drainage". From inferring what is in the Approved Document this would be many aspects not just it carries the waste to the sewer.

Heres the pics

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You can see the base of the soil stack at the top of the picture. You are of course looking up the run to the head of theh drain where the whb joins.

It takes about a bucket of water down the sink to clear the build up of solids........and it collects at the very next flush !

SVP serves two bathrooms (1st Floor and 2nd Floor)

WC is ground floor toilet.

 

[doitall]

Are the sink wastes below ground in 110mm and reduce at ground level, which is the normal way, or have they reduced in the end of the tee and run 40mm from that point.

Where is the SVP and stud stack positioned.

 

[lostforwords]

Hopefully schematic above will help answer your question.

Had to edit my address away !

Sinks are 40mm to ground level and enter 100mm pipes via a boss and radius bend.

 

[doitall]

So all the pipes in the schematic is 110mm.

In that case to get a back up, the pipes must be running the wrong way, or there's a blockage up stream.

 

[lostforwords]

Not sure of the terms but when the toilet flushes and the discharge hits the "T" the flow divides in two. Half goes where it should to the sewers the rest flows backwards up the drain (due to the speed with which it hits the bottom of the drain from above). I have called this backflow. Also all of the flow hits the bottom and effectively stops for a moment and then relies on the drain fall to get it moving again.

It then appears either through lack of water or a shoulder in the 45 degree bend, that the solids etc get "caught" as they start to resume a more normal dircetion of travel.

I have tested a mock up and with 1.8m of height about 30% of the flow is actually going uphill ! Yes it does reverse but compare this arrangement with what a rest bend does, it transfers all of the vertical kinetic energy into horizontal energy and directs 100% of the flow immediately to the sewers.

 

[doitall]

Can't see how it can from the drawing, can you do a 3d one.

 

[lostforwords]

Tried to draw the layout as basically as I can.

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• lostforwords
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This photo may also help to show what I think the arrangement is (it is the other way round to my drawing):

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• lostforwords
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Stack from above.

Upstream left, downstream right. The equal branch is deceptive as despite appearance the side "arm" in no way tuns the flow entering from this direction.

Does anyone know if the branch would be recommended in any other orientation than with the main flow vertical - as opposed to horizontal in this case ?

Stream from stack hits bottom of branch and heads in both directions (force of falling vertically). About one third heads UP the drain despite fall. This stream should reverse back down drain but is partially obstructed .See the paper in this photo. It is held back UPSTREAM of where the stack joins.

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[Norcon]

A 5m discharge into a T contravenes building regulations IMO.

The base of the discharge stack should have either two 45 degree bends or what is more commonly used, a long radius swept bend with a center line radius of not less than 2 times the pipe bore!

 

[picasso]

do you think the tee has been put on facing the wrong way ?