NHBC Flow Rates Standards (8.1.5)

[blangotti]

Hi, I have a question related to NHBC flow rate standards. Does this standard apply when using a flow regulator? I have a new building without sufficient water flow while using the outlets simultaneously. But the builder insists that it is according to NHBC guidelines and the low flow is because of the flow regulator in front of the tap. Could you please help me? Our house is a 3-story, 4-bedroom house. Even after using a flow regulator, the flow is hardly reaching 4 l/min. This is where I think the builder is trying to deceive.

 

[John.g]

It (NHBC) states in part that:

• be based on a minimum 1.5 bar dynamic pressure at the stop valve inside the home
• ensure a minimum 20L/min flow rate is available at the stop valve inside the home

Is the flow regulator a pressure reducing valve (PRV) installed after the stopcock? Suggest also opening every mains supplied tap in the house and summate their flowrates and see what you come up with.

 

[ShaunCorbs]

Best to test straight off the stop tap

Not uncommon to have blocked filters / strainer gauze

 

[king of pipes]

The water supply company is responsible for the supply of water to your external stopcock at the pressure stated below if it meet this criteria then it's a plumbing issue internally if your builder employed a sub contractor to install the internal plumbing then it is their problem to sort out.

 

[Ric2013]

Looks like KOP and John.G are discussing slightly different criteria. From reading what they are both saying, it seems the NHBC is discussing the flow and pressure at the internal stopcock. The flow and pressure could be quite different from the flow and pressure at the water board's external stopcock which is normally close to the public boundary of the property.

So it is interesting that the NHBC standard is higher than the waterboard standard as you would usually expect the dynamic pressure to be very slightly lower at the internal stopcock and certainly not higher, due to frictional resistance in the supply pipe between the two stopcocks. Perhaps the NHBC standard requires some form of pumping to improve pressure if the water undertaker's supply is not good enough to allow for the NHBC standard to be met without this?

 

[John.g]

I think water boards, in general, are saying that their "duty" is really only to supply water at ~ 10LPM to fill your CWST, the rest is up to you then to pump it or whatever.
I would agree that their responsibilities should end at their stopcock and a dynamic head of 1.5bar @ 20LPM wouldn't be too bad. Based on my run of 22M between stopcocks then a 1 ins (ID)pipe at a flowrate of 20LPM will only have a friction loss of 0.47M (0.05bar) but a lot of piping here is "hydrodare"? with a ID of 11.6mm so the friction loss in that 22M run will be ~ 2.1bar, the static head at my outside (waterboard) stopcock is ~ 3.6Bar so I don't have any real problems even with a upstairs shower running at 10/12 LPM even with this 50 year old piping.

 

[blangotti]

It (NHBC) states in part that:

• be based on a minimum 1.5 bar dynamic pressure at the stop valve inside the home
• ensure a minimum 20L/min flow rate is available at the stop valve inside the home

Is the flow regulator a pressure reducing valve (PRV) installed after the stopcock? Suggest also opening every mains supplied tap in the house and summate their flowrates and see what you come up with.

To answer your question, I did a quick search on stopcocks. It looks like the reducers are fitted in front of the taps. Are the readings above normal? I am going to get a pressure gauge tomorrow to get the static and dynamic pressure. To take dynamic pressure, I just need to connect this gauge to the outside tap and then run the kitchen tap. Is this correct?

 

[blangotti]

It (NHBC) states in part that:

To answer your question, I did a quick search on stopcocks. It looks like the reducers are fitted in front of the taps. Are the readings above normal? I am going to get a pressure gauge tomorrow to get the static and dynamic pressure. To take dynamic pressure, I just need to connect this gauge to the outside tap and then run the kitchen tap. Is this correct?

In my report builder said "All taps have flow restrictors or water saving devices fitted as standard meaning it isn’t
possible to exceed the maximum flow rate regardless of the pressure." However when I measured readings on my own there was significant difference from what they measured.

 

[John.g]

It (NHBC) states in part that:

To answer your question, I did a quick search on stopcocks. It looks like the reducers are fitted in front of the taps. Are the readings above normal? I am going to get a pressure gauge tomorrow to get the static and dynamic pressure. To take dynamic pressure, I just need to connect this gauge to the outside tap and then run the kitchen tap. Is this correct?

Yes, do that first, and then maybe carry out same individual tests on any other mains only supplied taps or shower(s).

 

[Ric2013]

It (NHBC) states in part that:

To answer your question, I did a quick search on stopcocks. It looks like the reducers are fitted in front of the taps. Are the readings above normal? I am going to get a pressure gauge tomorrow to get the static and dynamic pressure. To take dynamic pressure, I just need to connect this gauge to the outside tap and then run the kitchen tap. Is this correct?

Given that your outside tap will (should) have a non-return valve on it, connect the gauge, get your kitchen tap running (try to measure litres per minute, or how long it takes to fill a container of known quantity) and then loosen the gauge thread so a bit of water leaks out around it before gently retightening and taking a reading. If there is a non-return valve fitted, this will help give a more accurate reading when looking at the working (i.e. dynamic) pressure.

 

[Timmy D]

Sounds like you should get an independent plumber in to take and record readings.