Has anybody looked into whether there are any risks (unreasonable risks that is) associated with the routing of the cold water pipes in a well insulated building?

The point is that in old buildings the loft was normally cold and the supply pipework was therefore running at low temperatures. This would mean that there was no 'cold' water sitting about at room temperature. We are planning to build a SIP house, so the envelope of the house will be warm. i.e. the roof space will also be within the insulated envelope and is likely to be at, or near, the living temperature.

Give that Legionnaires is known to like water around 20C I wonder if there is an issue with the routing of the cold pipes within the house. Should I, for example, run all the cold pipes in the ground below the insulated slab rather than through the warm loft? On the other hand does the chlorination in mains water deal with this?

Glad of a steer on this.

Hi Neil, There is a pretty good explanation here http://en.wikipedia.org/wiki/Legionella.

According to the link above, legionella has to be inhaled to be a health risk. How is that going to happen in a domestic situation?

How many deaths from Legionaires have been attributed to domestic water systems?

Not true. http://www.accepta.com/industry_water_treatment/legionnaires-disease-domestic-hot-water.asp

Also if you rent out residential property you are legally obliged to comply with approved Code of Practice under H&S regulations.

Where's yours!!

There is plenty of anecdotal evidence that domestic water systems are a source of legionella its just that they get less publicity than an large scale public outbreak.

This report shows that there is evidence of domestic infection being significant. http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=190637

Some 10% of of infections prove to be fatal. In 2006 there were some 500 infections and 44 deaths. It would be naive to think that there has never been a death from a domestic source just because it has not been reported as such.

Given that it is not that difficult to reduce the risk in a domestic system with modest and simple design criteria then I think it is sensible to do this.
This would be especially true if the occupant is in a higher risk category.

any plumbers from Nottingham able to enlighten us?

"A recent suspected case in Reading caused an in depth search of domestic water systems in flats in Reading -- no legionella was found."
Therefore legionella does not occur in residential dwellings - QED

So nothing you hear on the green building forum that you have not heard elsewhere first is a problem.
If you are never going to learn something on here why bother reading it?

If it is the case tha there is no risk why has the HSE introduced regulations that require private domestic landlords to comply with the code of practice on legionella?
http://www.hse.gov.uk/pubns/indg376.pdf

Thanks for the comments and it has certainly lit a few fuses!. To deal with a couple of point s that have come up:

1. I believe a cleanerd caught legionnaires from the aerosols formed when filling a bucket in an underground station in Gateshead some years ago. The point being that this was a rarely used tap with a pipe in a warm environment. The aerosol was created from the impact of water into the bucket.

2. It strikes me that there is an increased risk now due to the general increase in living temperatures in houses, and also possibly by the routing of pipework within the heated envelope of the buildings. I think Tony is right, and insulation will not stop cold water getting to room temperature... it will just take longer. It will, however prevent additional warming from nearby hot water, so it seems to worth looking at. Luckily the bottom range for breeding bugs is about the top of the houshold temps.

3. I like the idea of trying to route the pipework so that the most used appliances are at the far end of the pipe run, so inducing maximum flushing, and minimising dead legs.

4. As to why Nottingham is popular: No idea, it certianly wasn't warmer when I lived there! :-)

On reflection I intend to route the main pipe run under the slab in the colder ground, and minimise the dead legs. An occasional draw off will also probably be worth putting into the maintenance regime.

The moral is don't fill buckets in underground stations in Gatehead. Personally, I've never felt the urge.

Never mind the Legionaires, I would have thought that having water coming out of the cold tap too cold and out of the hot tap too hot for the bugs would be pretty desirable. Any system that delivered luke warm water out of either tap would be pretty undesirable.