Treatment unit sizing - professionals disagreeing!

[Randomusername]

Sorry, it’s another treatment plant thread from me...

 

Projected build is 4 bedroom house with possibility of single bedroom annexe in roof of garage. 

 

Surveyor number 1 states that 8 PE Marsh Ensign will be sufficient (in fact more than). 
 

Surveyor number 2 does not agree with maximum 8 PE projection, and would fit larger 11 PE WPL Diamond unit (as this is the next size up in the range that their company fits). 

They are basing this on a directive from British Water, suggesting that as the house/annexe would be classed as two separate buildings, the actual PE would need to be 9 as a minimum. 
 

To me, the 9 PE equivalent assertion by the second surveyor appears excessive?
 

[PeterW]

Sizing is as per page 4, section 5 of this document. 

 

An oversize unit can be a bad thing as they need a minimum flow to “survive”

So a 4 bed would be counted as 6P, and depending on how you count the annex, you could either say it is 5 bed and therefore it is 7P, or if you said it was a self contained unit and also has kitchen etc then it would be counted as 3P on its own so would be a total of 9P..

 

Clear as mud..??

 

[joe90]

31 minutes ago, PeterW said:

An oversize unit can be a bad thing as they need a minimum flow to “survive”

yes that is what I have read/understood. However I was told a 3 bed house (which we have) should be counted as 6 person (three double beds!!,)

 

48 minutes ago, Randomusername said:

Projected build is 4 bedroom house with possibility of single bedroom annexe in roof of garage. 

I would read that as 9 person (but I have not read the above doc) but does “single bedroom” mean a Single bed as in fir one person?? Or a one bed annexe?

[PeterW]

5 minutes ago, joe90 said:

yes that is what I have read/understood. However I was told a 3 bed house (which we have) should be counted as 6 person (three double beds!!,)

Minimum size for a house is 5P, and you add one 1P per room over 3 rooms, so yours is technically a 5P but you may find the smallest unit avaialbale was a 6P unit. 
 

 

[ToughButterCup]

We are a 2 person house (in a 2 bedroom house) using a 13 person tank. The unit is working fine. We plan to connect another 4 bedroom house to the same tank in the new year. The tank will more than cope with two houses full of guests.

 

Fat chance this year.