DPC and air bricks below the ground level

[ls523]

We've recently moved into a new-build (completed in May 2023) and been made aware of an issue with the DPC and the air bricks to the rear of the house (with bi-fold doors opening to a patio). Both DPC (above the air bricks) and air bricks are below the ground level and covered by gravel (see image attached).

We talked to the developer who said that they are below the ground level because the patio has to have a level threshold. To allow sufficient ventilation, the developer suggested to cut back the patio 150mm from the rear house wall on both sides of the bi-fold doors, dig out below the air bricks and then fill the bottom of the trench with gravel so that the top of the air bricks will be 150mm above the gravel.

I am not happy with the proposal by the developer, because 1) I am not sure if 150mm wide trench is sufficient, as NHBC Technical Guidance says "air bricks below general ground level are acceptable with continuous strip of lowered ground extending at least 600mm away from front of air brick(s)". and 2) The proposal didn't solve the issue that the DPC below the bifold doors are still below ground level. The Building Regulations about a level threshold and the DPC being 150mm above ground level seem to contradict with each other.

Could anyone advise what is the best solution to fix this issue and whether it would impact the value of the house?

(On a related note, the house passed Building Control during construction. I emailed Building Control, who basically admitted that they didn't check air bricks at all. I wonder if I could do anything about it).

All suggestions are highly appreciated. Many thanks!

[New Home Expert]

DPC below the bi-fold doors is normal. It should be 150mm above finished ground level at either side of the door. Clearly this is not the case.
It would appear the NHBC warranty inspector and the Building Control final inspector are not doing their job.

Not only does the NHBC warranty standards state the dpc should be (at least) 150mm above the finished ground level but this is also contained in the building regulations. The crucial words being "should be" which is not "must be"

The developers solution" is a bodge job that is easier and cheaper for them.
WHO IS THE BUILDER/DEVELOPER?
It may (or may not) solve the problem. But as you clearly state, the NHBC standards suggest what can be done in this instance and the solution is not that.

My opinion is any water in the 150mm trench" will drain away under the PCC beam and block floor which will probably cause dampness in the house at some point.

This same issue is posted time and time again over the last ten years and it appears that those working on housebuilding sites still even now have no clue as to how to sort their levels out properly to avoid this.

As for the house value, it is a new build and they tend to devalue over the first few years anyway. they are also less desirable to buyers for many reasons. A good buyers survey should highlight this clear defect and any offer you do get may be reduced because of it.

Keep going with the complaining and you could use the New Homes Ombudsman Service in about 6-9 months once you have worked you way through the housebuilder's customer complaints service procedures and jumped through all the NHOS hoops.

[ls523]

Thank you so much for the reply. You said that "DPC below the bi-fold doors is normal. It should be 150mm above finished ground level at either side of the door." Does it mean that DPC at either side of the doors doesn't need to be at the same level as below the bi-fold doors? I've been told by the developer that "a bridge of the DPC should be avoided", which is why they had the DPC below the bi-fold doors and below the ground level at both sides of the doors. I am very confused, as obviously the DPC needs to go below the bi-fold doors, which require a level threshold hence the ground level is now above the DPC. If the DPC goes straight from one side of the wall through the bottom edge of the doors to the other side, how could it be 150mm above ground level? Or is it that the DPC could be 150mm above the ground level at either side, go around the bottom of the doors, and then go back up to the other side 150mm above the ground level?