Hi mango7
We are remote from this here on AAM and cracking is not my specialty, but I've prepared this response
This is not a simple issue and the consequences of not addressing it could have long term implications, so I have put some time into this reply.
Before I start I'll say you will probably need a chartered structural engineer to inspect this issue and you may need to undertake limited opening up work to determine its cause and extent.
There are three possible causes of structural cracking that spring to mind:
1. Pyrite.
Please refer to
this thread on AAM for an extensive discussion of it.
Since written descriptions are at a disadvantage to pictures,
this link may be of help. In general Pyrite causes the fill under the slab to expand and depending on how severe this is, it can crack rising walls, internal walls and affect partitions for reasons discussed in the links above. Unless you are seeing the symptoms described in the AAM thread and the link, Pyrite may not be indicated, but the only way to tell for certain is to drill a core and have it sent off for analysis.
2. Settlement, Generally.
This is the main source of cracking I come across and it can be caused by many things. The thread link I posted above has
this post in it discussion a lot of the main points.
Inadequate foundations being a common or a contributory factor. Even where there is what's called "bad ground" you can usually design a foundation to deal with it, so foundation design is really important.
Equally important is poor workmanship which, allied to poor site preparation/ de-watering/ compaction of trenches and hardcore, can negate the effects of good foundation design, leading to settlement.
However even where good design and site preparation can be relied upon, building elements of similar construction but different storey heights and therefore different overall weights can settle differentially, leading to cracking at or about the point where the change in height occurs.
3. Differential Settlement
This is common where extensions or projections are added on to houses. I have come across the following situations.
(i) Where projections from the main building have been built at the same time, either the house or the projection may settle more relative to the other, leading to cracking. The nature of the settlement depends on the issues noted above, but can be mitigated where the house and extension have the same foundation width and depth and are on similar ground. Good bearing ground with foundations at the same depth may prevent most settlement, unless there is unusual groundwater conditions or frost heave issues to deal with.
(ii) Where the projection or extension has been added on later, whether after 1st occupation or even at different times during the build because of work scheduling, differential settlement can occur.
Two conditions seem to arise
(a) There is a structural difference or actual disconnect between main house and extension, for example where a smaller foundation strip was used, and/or where the link between foundations of the main building and foundation was not properly connected structurally. The house may settle more than the extension due to weight, or the extension may settle more than the house due to lesser care in site and trench preparation or smaller foundations strip being used.
(b) The connection between the main house and projection/extension is properly made, but the far corners of the extension may have settled more through one of the reasons noted above. The far corners settle, but the connection point does not, so in section the extension may rotate around the joint where the house and extension meet, causing cracking.
4. Suggested Strategy
As it stands it appears that your house maynot comply with the Regulations in relation to -
Part C Site Preparation and Resistance to Moisture
Part D Materials and Workmanship
In particular your house may have a torn Radon Gas Barrier.
You are perfectly free to chart your own course but it would be prudent to address this issues sooner rather than later.
These defects should be inspected by a chartered structural engineer with experience of domestic scale investigations. An architect may also be required.
The cracking you describe may be indicative of something like the situation at 3 (ii) and 3 (b) above, but only an investigating engineer can determine this. The damp at the crack strongly suggests that either water is lodging in the defect, after finding its way down into it from outside, or the Damp Proof Membrane/ Radon Gas Barrier itself is broken, leading to damp penetration of your floor slab. Damp ingress can give rise to follow-on structural and health issues not related to the original defect.
Filling the crack may only be a temporary solution at best. Its an approach favoured by builders who hope they won't be called back. However a crack that is this wide and deep suggests something more serious is going on and I strongly recommend you take advice from a chartered engineer who will inspect and monitor the situation.
Because of the extended timeframe over which settlement normally occurs, definitive action may take some time. It is normal to investigate the crack to see whether the building is stable or whether the crack is symptomatic of and ongoing problem. This may be done by fixing what is known as as Demec Gauge across the crack and monitoring it for an extended period.
Its important to determine the following -
- what damage has occurred at foundation level and above
- is the condition of the building stable or getting worse
- what is the best remedial approach for the defect
- what is the most cost-effective means to do this
- will your house insurance cover this
I am familiar with the work
Downes Associates in relation to carrying out detailed inspections and proposing remedial work on private dwellings, should you wish to ask someone to call out and offer a qualified opinion.
Malone O'Regan Engineers have also advised us in relation to the design of domestic properties.
ONQ.
[broken link removed]
All advice on AAM is remote from the situation and cannot be relied upon as a defence or support - in and of itself - should legal action be taken.
Competent legal and building professionals should be asked to advise in Real Life with rights to inspect and issue reports on the matters at hand.