Soil Pipe - Thermal Bridging Passiv

[Dave Jones]

Looking at our soil pipe layout and it occurs to me this is a large 110mm sized cold radiator running all over the building sucking nice cold air through it from the roof.

 

While I cant find any requirements in SAP to mitigate it, need to do something. Easiest fix is the council house option of putting the stack outside. Obviously a no go.

 

I think I will lag using something like this rather than rely on rockwool.

 

Then there is the issue of venting, standard is to run it to a tile vent in the roof to breath nice freezing cold air. Dergo air admittance at the top of the pipes at ceiling level. 

 

BUT we have a combined foul and grey water so the gutters are going into the same run, wonder if the regs would allow the downpipes to act as a vent as they will be the highest point on the run anyway ? 

 

[Jenki]

I worked on a 80's architect design house several years back, warm air receivers in floors and walls etc. quite futuristic  for the time, but the veneer ply walls did date quickly,😂. back to the topic this house had zero external pipes, the rain water came inside and into soil stacks, (A disaster in the waiting in my view) but this was how the soil was vented, via the running outlets, not sure this is acceptable, but it worked.

[Big Jimbo]

Might be worth asking them. I had 4 internal soil stacks in my last house. I used dergo's on all of them. B.C.insisted that i had One to fresh air. I said that as i was on a run of 10 houses, there was plenty of ventilation to the system.  They agreed after having a right old ding dong with them. The only thing i would say is that all the rain water pipes will have traps to stop leaves etc entering the system. So not really vented.

[Dave Jones]

ive emailed NHBC technical to see what there opinion is.

[Crunchynut]

I can’t help with your question specifically but I wonder why the insistence that at least one vent is to open air. We know air admittance valves work and they obviate the need for a cold bridge. So what’s the problem?

 

I can think of only 2 objectives : firstly to ensure the drainage system (ie everything after the drains leave the property) is vented, though this can be achieved by vents to the drains  elsewhere outside of the house. Secondly because there may sometimes be pressure back up the stack which needs to go somewhere- but can’t think why.

[JohnMo]

2 hours ago, Crunchynut said:

can’t help with your question specifically but I wonder why the insistence that at least one vent is to open air. We know air admittance valves work

Would think because air admittance valves only let air in not out. Otherwise your house would stink. If you only breath inwards a pressure build-up occurs, hence need for an external open air vent.

[Crunchynut]

I get that they only let air in to ensure the waste moving down the pipe doesn’t suck out the traps, but in what circumstances does air need to move in the other direction (other than reasons mentioned)?

[JohnMo]

20 minutes ago, Crunchynut said:

, but in what circumstances does air need to move in the other direction

 

Change of temperature, sewage giving of gases, changes in air volume within the piping (you flush the loo etc), etc. It's not designed to be a pressurised system, it's designed to be open vented. Hence a need for a two way open vent external to the house.

[JohnMo]

11 hours ago, Dave Jones said:

option of putting the stack outside. Obviously a no go.

Why is it a no go?

 

All our pipes are under the floor insulation, each toilet, shower, and sink has its own pipe into the underground pipes, any cold air trapped by a water trap. One pipe internally goes up vertical for an air admittance valve, very well insulated with rockwool.

 

External vent at back of house in black same as the gutter drain pipes. Job sorted

[Conor]

The air in sewers is generally warm, the the losses are minimal. All three of our stacks are on internal AAVs. No issues. All wrapped in rockwool anyway as it's a sound requirement for BC.

[Mike]

6 hours ago, JohnMo said:

sewage giving of gases

Worth mentioning that they can include methane, which is explosive.

[Dave Jones]

16 hours ago, Conor said:

The air in sewers is generally warm, the the losses are minimal. All three of our stacks are on internal AAVs. No issues. All wrapped in rockwool anyway as it's a sound requirement for BC.

 

not so sure about that. heat goes to cold. would like to see real world heat loss calcs having many meters of cold bridge running through a warm zone.

[JohnMo]

Thought your showers ran all the time, your pipes will never be cold

[Dave Jones]

44 minutes ago, JohnMo said:

Thought your showers ran all the time, your pipes will never be cold

 

showers yes. bath and sinks no.

[Kelvin]

My SVP comes up through the roof in the detached garage so no penetrations through the house. 

[Dave Jones]

8 minutes ago, Kelvin said:

My SVP comes up through the roof in the detached garage so no penetrations through the house. 

 

so you dont crap in the house ?

[Kelvin]

13 minutes ago, Dave Jones said:

 

so you dont crap in the house ?

The garage is connected to the foul pipework. 

[Iceverge]

I worried long and hard about this. 

 

We have an AAV in the internal soil stack in the house and vent externally on a soil pipe on the garage. Seems to work ok.

 

However you really won't loose as much heat as I thought. Here's a study. Basically is states that 25mm of insulation will make it a non issue. 50mm if you're bothered. 

 

https://www.elementalsolutions.co.uk/wp-content/uploads/2012/08/Heat-loss-via-internal-drainage-vent-pipes-full.pdf

 

The dual function of the stack can be split. 

 

1. Use a small (maybe 50mm or smaller) soil stack vent to air to allow for gases to escape and prevent pressurisation while minimising the chimney effect. 

 

2. Add an AAV internally to ensure the traps don't empty. 

[Dave Jones]

very interesting read, good find!

 

In the conclusion they suggest treating the SVP as a cold bridge to ground confirming my suspicions. Will vent through tile vent and insulate as much as possible. probably a bit OTT but we have a long runs throughout the house.

 

"In our uninsulated SVP the average temperature increases by up to 2K, but
when insulated the air temperature will be <1K above ground temperature, so we suggest
treating this as a thermal bridge to ground rather than air."