Author Topic: Developer & NHBC position on incorrectly installed DPC & floor void ventilators  (Read 6904 times)

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DKR

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There have been a few posts by members on DPC installed at the incorrect height from ground level, lower than the industry standard and NHBC's own standards and requirements. It would be good to know the outcome of claims / chasing / disputes with either builder or NHBC on this. Some 10 years on from such historical posts reporting on NHBC and builders rejecting this being a constructional problem, this mistake is still happening on new builds.

In our case, the problem is bigger in that the floor void below the beam and block ground slab is not appropriately ventilated because the original ventilating airbricks have been covered up by the carport paviours and mock ones, not connected to the telescopic ventilating tubes, have been installed right above the submerged ones. Unscrupulous construction standards, dishonesty and lack of conscience at their utmost manifestation.

I'd be grateful if anyone could share their experience on how similar situations have been resolved as precedent is important and if positive, could help us. We were having progress with the developer, infamous Countryside, having admitted wrong construction and willingness to rectify after months of emails, only to stumble on a detail they haven't considered in their proposed remedial works (which we practically drafted ourselves for them, we're architects). At that point they referred the matter to NHBC whom we were trying to avoid getting involved with having experienced their utter incompetence and lack of ethics. As a result Countryside withdrew their admittance to wrong doing, and changed their minds to say, with the backing of NHBC, that the low level DPC is not a problem, and only the obstructed ventilating airbricks are on which they submitted some shoddy method to rectify.

All this is after 17 months from us having pointed out this constructional error to Countryside during the snag visit one day before exchanging, and still no resolution, if anything we are now back to square one.

Many thanks for any insight or experience anyone may have on this.
DKR


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NHBC Technical Extra says:
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Ground level and dpc.
NHBC inspection staff have noted, and are concerned, that the well-established best practice of the finished ground level being 150mm below the dpc is being ignored on an increasing number of sites.
At the accessible entrance, the landing will be less than 150mm from the dpc. This is inevitable if an accessible threshold is to be provided. However, this need only apply at the threshold and this raised ground level should not be maintained for the
remainder of the perimeter of the dwelling.
Where homes have multiple entrances with accessible thresholds, there may be a greater temptation to ignore best practice and maintain a raised ground level around the dwelling between the entrances. This is not acceptable; the dpc should be 150mm above ground level, except next to the entrances.
An additional dpc can also be introduced where there is a risk that the primary dpc will be less than 150mm above ground level.

Ventilation
It is important that air bricks do not become obstructed. By having the finished external ground level 150mm below dpc, air bricks are usually at least 75mm above the ground.
If the ground level is less than 150mm below dpc, air bricks can easily become blocked with debris and may also allow water from adjacent ground

Clearly the 150mm above ground level for the DPC is not only "well established best practice" and "desirable" as far as I can remember, it is a Building Regulation requirement.

In addition, air bricks must be at 2m centres and cannot be covered or near or below ground level so water does not drain under the floor.

Presumably as Architects you knew this and Countryside, having acknowledged it was wrong should have put it right by now. Each case will be judged on its merits but be aware that each air brick will be considered an individual claim and fall below the NHBC's minimum claim value anyway. As with most insurers they try to avoid paying for claims!
As for the resolution of other cases with other housebuilders, each has their own attitude towards customer care and defect resolution.

What you have is not right but should be put right by Countryside Properties.
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DKR

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Many thanks for your comments 'New Home Expert' especially on what may happen with the claim being broken down to cover each air brick.

The thing is an inadequately ventilated floor void is not lawful and there is no doubt about this.
On the other hand, the 150mm height of the DPC from ground level is a technical solution and not statutory in its own right. What's statutory is the prevention of damp and moisture migration into the building ie the Building Regulations that are in the green box in the Approved Documents. The Approved Documents as a whole are in effect recommendations, best practice, proposed solutions. Hence NHBC / Countryside avoiding rectifying it. Having said that, we're open to suggestions as to how the statutory requirement of preventing damp migration is mitigated, when it's not being achieved by the incorrectly positioned DPC. So far neither Countryside nor NHBC have been able to put forward any alternative solutions. This is why the Technical Solutions in the Building Regulations should really be enforced in some way as it takes years of tests, trials etc to prove that any other solution would work. And such openness in interpretation leaves people like us and many others out on a limb.

I hope NHBC would have no leg to stand on when it comes to dissecting the claim to link it to each air brick, as pointed out above regarding inappropriately ventilated floor void. It would take rectifying all the air bricks as part of one claim to achieve the required ventilation of the floor void (there is a minimum clear area of inlets / outlets dependent on the area of the void, or something along these lines.)

I am aware of NHBC's technical notes which you extracted above, which I sent back to Countryside in my reply before I posted in this forum. I am more interested in their published Standards and Requirements given to developers and builders, which come at a hefty price. How come they were able to re-package the Building Regulations and some British Standards extracts and sell these, I don't understand. Their technical notes don't even reference the Building Regulations drawings which were plucked and inserted in their own text. Anyway they are saying that the electronic version will be freely available in the summer. I read in the past they dispute the 'should' in the regulation text regarding the 150mm DPC height from ground level. If it was a requirement the text should have said 'must'.

Irrespective of attitudes, knowing of any factual outcome of past resolutions to such similar problems would have been most useful to us.

Regards
DKR

New Home Expert

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The NHBC Standards are quite clear on the DPC height:

Quote
DAMP-PROOF COURSE
5.1 - S9
Moisture from the ground shall be prevented from reaching the inside of the building.
A damp-proof course should be positioned at least 150mm above finished ground or paving level and should link with any ground floor dpm.
The dpc should be of the correct width and fully bedded
.

Regarding the Building Regulations, measures suggested in the Approved Documents are as you say "recommendations, best practice, proposed solutions"  in other words design criteria measures that would enable compliance with the actual regulation. I agree that the contents Approved Documents should be mandatory not guidance or optional designs.

Installing a DPC 150mm above ground level would obviously be one method meeting the Prevention of Damp regulation.
Then an injected damp proofing system would also work, as would fitting an impervious barrier to the external wall although seldom done in practice.

A "low" dpc (below 150mm above FGL) could mean that your home does not meet the Building Regulations for "prevention of damp." The NHBC warranty would step in if damp did start as their own Standards have been breached.

In any event, a surveyor worth his salt would almost certainly note the low dpc in his report when you come to sell and your buyer would probably base their offer lower as a result.

The NHBC Standards for suspended ground floor ventilation are:
Quote
5.2 D10
(b) ventilation of underfloor voids
A minimum void of not less than 75mm should be provided below the underside of floor slabs and beams.
On shrinkable soil where heave could take place, allowance should be made for the void to accommodate the following movements according to the shrinkage potential of the soil:
high potential - 150mm 
medium potential - 100mm
low potential - 50mm.

In all regions except Scotland, all underfloor voids should be ventilated by openings providing not less than 600mm² of open area per metre run of external wall, equivalent to one 225mm x 75mm clay air brick to BS 493 at 2m centres.

In Scotland, all underfloor voids should be ventilated by openings providing not less than 1500mm² of open area per metre run of external wall, equivalent to one 225mm x 150mm air brick at 1.5m centres.

Ventilation openings should be provided on at least two opposite sides. Where this is not possible, effective cross ventilation from opposite sides should be provided by a combination of openings and air ducts.

Where the finished level below the floor is lower than the finished adjoining ground level, appropriate drainage should be provided.

The reason the NHBC use the word "should" rather than "must" is because there are several ways of achieving compliance with their Standards and the Building Regulations and an infinite number of designs. (Basements come to mind.)
If it "should" and "doesn't" it is not complying!

As for past factual outcomes, these are irrelevant as wrong is still wrong and what you have must be addressed.

Regarding the NHBC standards, I am surprised as an architect you do not have access to have a copy.
The Building Regulations are all noted and referenced in the Appendix section for each NHBC Standard requirement.
Quote
STATUTORY AND OTHER REQUIREMENTS
5.2 - D2  Design of suspended ground floors shall comply with all relevant statutory and other requirements

A list of statutory references applicable to this Chapter is given in Appendix 5.2-A.
[/b]

In my opinion, the NHBC Standards in the most part, exceed the basic requirements of the Building Regulations .
They are written in clear, easy to understand, plain and unambiguous English.
Even so, it would appear that large plc housebuilders such as Countryside, are totally incapable of building their homes to meet the Standards and when they are 'found out', will put in every effort to find justification and excuse to avoid rectification works at all costs.

If the NHBC refuse your warranty claim, you can take the matter to the Financial Ombudsman Service.

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DKR

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Thank you New Home Expert for your response.

Yes Countryside should own up, and they aren't. NHBC are not helping by siding with Countryside and offering suggestions that are technically flawed, even going against their own Standards and saying well in fact, the lower than needed DPC is not wrong.

Yes retrospective and remedial injection of DPC has been put forward but this is not what we bought. It has a much shorter life span than a properly installed sheet DPC which lasts the design life of the house.

We are aware that the house value may be affected because of someone's dishonesty and mis-selling (with the mock ventilating air bricks which are deceptive), we are having sleepless nights about it. We are aware of the Financial Ombudsman Service and also are aware of this being a route to be the last resort as it is long, painful, and convoluted.

The main issue is that fabric deterioration may well be underway because of the constructional errors and this needs to be remedied as soon as possible. We were wondering how other home owners in similar situation may have managed to speed matters up and which routes they followed to get their problem sorted.

NHBCs Technical Extras do not reference the diagrams they 'borrowed' from the Approved Documents.

We are architects and non-registered professionals (with NHBC) and therefore do not have free access to their published standards - I presume registering would incur a yearly fee of some sort, which we are not contemplating.. I still think the NHBC repackaging and selling what they term as their Standards is not right, when the Building Regulations are freely available online. It would appear public pressure changed their mind to make their online version freely available at least, *sometime* this summer they say.

Just to warn you, I will be away from this forum for a while with work and family commitments and will visit it intermittently. If any reader with a similar situation who managed to reach an acceptable resolution to their advantage, please do get in touch.

All the best as always
DKR

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As you say, the NHBC Standards will be freely available online from "Summer 2015" giving free access to the published Standards for everyone.

This will be a marvellous resource for all new home buyers.
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