Do external soil stacks freeze?

[WWilts]

For various reasons including cost-effectiveness, an external soil stack & vent is preferred on a private elevation of the house.

 

Builder fears the external stack might freeze. Might it really?

 

[Temp]

I think its quite rare for a 110mm vertical stack to freeze.  More common for smaller diameter "horizontal" feed pipes to freeze (eg from kitchen sink to the stack).

[markc]

For it to freeze it must be full of standing water … that’s not how a stack works.

or the stack has to be so cold that any water will flash freeze while the water flows through it … that’s not going to happen in UK.

if the underground or lower portion did somehow get blocked then the stack could backup and freeze. Again unlikely.

[Dave Jones]

if the poo is reaching the top of your soil stack you really are in a pickle!

[SteamyTea]

9 hours ago, WWilts said:

Builder fears the external stack might freeze. Might it really

I once had the external waste downpipe freeze and back up into the toilet, was the winter of 86/7.

No idea why it backed up in the first place and it thawed the next day and never happened again.

[WWilts]

12 hours ago, SteamyTea said:

I once had the external waste downpipe freeze and back up into the toilet, was the winter of 86/7.

https://www.netweather.tv/weather-forecasts/uk/winter/winter-history
https://en.wikipedia.org/wiki/1981–82_United_Kingdom_cold_wave

Perhaps something in the drains contributed, together with the temperature. Enough to make me rethink external soil stack. Still ruminating.
 

[PeterW]

Wouldn’t worry - unless there is a downstream full blockage you won’t fill a stack. Downstairs WCs will be the first to show a problem. 

[Marvin]

On 13/08/2021 at 14:10, WWilts said:

For various reasons including cost-effectiveness, an external soil stack & vent is preferred on a private elevation of the house.

 

Builder fears the external stack might freeze. Might it really?

 

The only other possibility is a slow supply of water (like a dripping tap or overflowing loo) down the pipe in freezing conditions, cold enough to freeze the water before it reaches the pipe where it enters warmer ground.

 

For this reason external  condensate pipes have to be insulated.

[WWilts]

5 hours ago, Marvin said:

dripping tap or overflowing loo) down the pipe in freezing conditions

This was what the builder fears

[PeterW]

2 minutes ago, WWilts said:

This was what the builder fears

 
why..?? We’ve had these since the 1900’s and never had issues so why start now ..??

[Marvin]

16 hours ago, PeterW said:

 
why..?? We’ve had these since the 1900’s and never had issues so why start now ..??

a freezing stack would be an extremely rare event in most of the UK

 

However cold bridging due to the cold air in the soil stack rising in the building could be the other problem considered.

Also the termination through the roof can be a leaky problem.  

 

And again the smaller the diameter of the pipe the more likely to freeze so perhaps the 32 and 40mm pipes are the real concern.

[WWilts]

20 hours ago, Marvin said:

cold bridging due to the cold air in the soil stack rising in the building could be the other problem considered.

Also the termination through the roof can be a leaky problem.  

SW England. Mild climate, relatively.

Not understood your meaning fully. Thermal bridge owing to exit of soil pipe is understood. Cold air rising in the building not understood. Decision is internal soil stack vs external. 

Termination through roof might occur with internal stack, although external rodding point with a branch to external vent pipe could help overcome this issue. External vent pipe if needing to be tall can go around the eaves, which project about 400mm or less from the wall face.

Interested to understand the meaning so that it can be factored into the decision.
 

[Marvin]

8 hours ago, WWilts said:

Cold air rising in the building not understood. Decision is internal soil stack vs external. 

Yes, with an internal stack  terminating through the roof cold air can enter the pipe from both ends. Sometimes the pipe can act as a wind tunnel causing the wall of the pipe, in the house, to get very cold.

[Mr Punter]

Some people choose to have an internal stack with a dirgo and an external vent at low level elsewhere on the drain.