Stack Ventilation essential?

[ashthekid]

I don't see any ventilation for the stacks created in my conversion project build.

Is it a Building Control requirement or do you not have to have them?

[Marvin]

2 hours ago, ashthekid said:

I don't see any ventilation for the stacks created in my conversion project build.

Is it a Building Control requirement or do you not have to have them?

I think it depends if there are Air Admittance Valves (AAV's) which would allow air into the pipes but not out, and, if the design requires air to escape the pipes which would mean a pipe would need to terminate outside the building.

 

Good luck

 

M

[Gus Potter]

5 hours ago, ashthekid said:

I don't see any ventilation for the stacks created in my conversion project build.

Is it a Building Control requirement or do you not have to have them?

 

In almost all cases for a domestic dwelling (not flats which often share a common stack) it is a BC requirement. Here is some info which I hope helps BH members.

 

In Scotland for example the regs point you to BS EN 12056 part 2 which is to do with drainage inside buildings. Comply with this code and you are well on your way to complying with the regs. There used to be great stuff and diagrams in the regs to help self builders /renovators but these are getting progressivly stripped out.

 

Here are a few thoughs / observations. If you get a feel for the principles then you can adapt to suit your needs. Often you see a drain pipe poking out the roof..with a grill on top to prevent birds nesting and so on..  the top of the main stack.

 

This open vent serves two purposes. One is to prevent excessive suction building up in the main drain line serving your house the other is to prevent over pressure in the line which will blow the traps.. and worse.

 

Pressure can build up in a main drain line;  if the wind is blowing the wrong way down stream (other folk doing daft things like facing a vent stack into the wind), if you have a blockage and a build up of gas (could be a gas leak too and the gas migrates into the drain! nice to vent outside than into your house) down stream if say your neighbour has been putting nappies down the drain. They get the drain folk in and they put a pressure washer down the pipe.. I'll leave the rest of the description for now as to much information can be uncomfortable.

 

Commonly though it's suction that causes the issue. There are a number of ways you can design a drainage system. Some work on what we call "full bore flow" this is more common in the EU except for some roof drainage systems in the UK... you often see these full bore roof systems described as "syphonic systems" in the UK, some toilets work this way but just within the "bowl".  Mainly though in the UK we design the drains in our houses (system iii) to not run full bore and thus they don't generate this true syphonic effect. But they do still generate some negative /positive pressure.

 

When you pull the plug on the bath the water flows and pretty much fills the pipe. As the water moves down the pipe it compresses the air in front of it. If you don't relieve this compression it can blow the traps on say a sink in another room and thus fumes will enter that room. Some air passes over the top of the water in the pipe as it is not running full bore but often not enough. Commonly a sink trap has a shallow seal of water so we are only taking about a small amount of pressure, much less than say a car tyre or you blowing up a balloon.

 

Once the bath is nearly empty if the pipe run is long then you have this body of water still moving down the pipe and this creates a suction effect behind it which keeps drawing water. This "residual suction" can be enough to stop the bath trap from filling properly at the end of the drain cycle and not creating a proper water seal. This means that when you say next flush the toilet the smells come out the bath trap rather than venting out through the stack. If the seal is completely broken (the trap is not filled enough) then you invite "lingering" odours from your own house and that of your neighbours unless you have your own private sewage system, in which case it's you own personal "gas".

 

One way we get around this is to fit an air admittance valve on branch lines, say on a long run to a kitchen sink or ensuite bathroom. This works a bit like a snorkle in reverse. It is sensitive enough to let air in but not pressure (smells) out. This allows the trap to fill properly from say the last bit of water in the bath and create a seal.

 

Now one problem arises with AAV's is that the regs require them to be set above the level of the spill over point. For example in a bathroom the idea is that the home owner will see the sink spilling over if they have a blockage rather than the AAV leaking and causing hidden damage. Now that all makes common sense. Some of the building regs are really good! But  this does not fit well with modern bathroom and kitchen design as no one seems to want a "box in the corner" of their new sleek vanity unit or kitchen work top.

 

I mentioned adapting previously. Sometimes you can implement an old solution that was commonly found in tenement flats. This is called a "loop vent". Here you create a circuit of pipe in a loop. The top part of the loop does not carry water, it just lets air circulate.  Have a look on the internet for loop vent design.. kitchen designers with island units have picked up on this, reinvented the wheel and are punting this as some kind of great new invention.

 

Ashthekid.. hope this give you and BH folk some background info. Oh, and there have been a few other posts on BH about pipe gradients etc...