Subsidence or structural movement down to drains? Is this feasible or more sinister?

[Klang180]

Ok last one I promise!

This is the part of the survey we are perhaps most concerned about as it suggests the rear part of the house (mid terrace house with two storey connected rear projection) is tilting downwards and may be due to underground instability. Is this likely and how much of a worry is it? If we get a CCTV survey and find broken pipes is this sufficient to cause a whole section of the house to subside? Is this something we need to be very weary of or is it just surveyor talk and really there is very little wrong with this level of movement?

Thanks so much for anyone with the patience to look at this.


In contrast the rear projection exhibits evidence of typically moderate historic structural
movement although the trend appears inconsistent. There is clear evidence of a drop
along the side wall towards the rear corner and at least some settlement also along the
back gable towards the party wall. Internally there is at least moderate settlement of the
kitchen floor and some further evidence of movement in the area of the rear landing,
bathroom and back bedroom.
3.3 Cracking externally appears mainly negligible, corresponding with at least moderate to in
places more pronounced long-term erosion of what is assumed to largely comprise the
original pointing, there being signs of only fairly localised attention. The notable
exception is to the rear gable over the back bedroom window where there is a
concentration of cracking, with some associated slight dropping of the brickwork and
arched lintel. The damage is not considered major, is fairly localised and does not appear
recent in origin. We are nevertheless unable to state that the movement in this area has
ceased and the cause of the cracking requires further consideration. Internally cracking
appears negligible, corresponding with some discolouration of decorations which have not
obviously received any attention in the more recent past.
3.4 Reference to the British Geological Survey information for ground conditions in the
locality, via GeoIndex Onshore, indicates that the property should be underlain by the
Alphington Breccia formation. Although the geological information does not indicate any
superficial deposits, it is likely that the rock has weathered towards the surface. We
would, nevertheless, anticipate adequate bearing capacity. However, this ground can be
unusually susceptible to a loss in strength on wetting, which can typically arise in the
event of water ingress originating from defective underground drainage. This could
explain the degree and pattern of movement affecting the rear projection, which may then
be explained by predominantly historic differential foundation subsidence. This is having
regard to the concentration of drainage pipework, including a soil and vent stack and gully
against the hand side of the rear projection. It is conceivable that water has been ingressing
the ground for many years.
3.5 It is recommended that the adequacy and condition of the underground drainage is
investigated throughout, to confirm freedom or otherwise from defects. Investigation
could be via conventional water testing (subject to suitable access points) and/or CCTV
survey, supplemented by exploratory excavation as required. It is important to establish
that water is not leaking into the ground at the rear of the property, which might explain
2403-S-4441 - 12 -
the movement patterns. Remedial works should then be carried out to the underground
drainage, if or as found necessary.

 

[^woody^]

The arch has dropped. Common thing, and again I can't see how a supposedly qualified surveyor is associating that cracking with foundation movement.

Does he, in other parts of the report, even explore the many possible reasons for that type of cracking, discount the least likely and conclude by reasoned explanation the most likely cause and the reasons why? If not, he's clueless and not doing his job.

 

[Klang180]

The arch has dropped. Common thing, and again I can't see how a supposedly qualified surveyor is associating that cracking with foundation movement.

Does he, in other parts of the report, even explore the many possible reasons for that type of cracking, discount the least likely and conclude by reasoned explanation the most likely cause and the reasons why? If not, he's clueless and not doing his job.

Hey Woody, he mentions the following in the report about cracking at this location. I am worried he is a bit of a cautious person by nature and in this report but as people who have never had a survey done before it has got us worrying.

Rear Gable Elevation
The wall on the ground floor appears satisfactorily plumb overall, and sighting up to
higher level there are similarly no signs of any substantial deviations from the vertical
on the first floor. There does, however, appear to be an outwards lean at high level
up to the roof apex and we assess that the brickwork may have displaced by a
maximum of 25mm-50mm.
Within the brick coursing the trend is difficult to determine, it being suspected that
the mismatch in alignment about the rear doorway is at least partly as built. Our
impression at low level is of some sloping towards the external corner, although there
is evidence also of a slight drop towards the party wall. The fact that almost complete
repointing has been carried out in between the doorway and external corner suggests
that some historic movement or other damage may have been disguised; however
there is no apparent cracking in this area. Also, the brick arch lintel over the door
appears reasonably uniform and intact (photo 03).
There is diagonal stepped cracking at high level, originating from the top corners of
the first floor window and converging below the roof line. The cracking appears
substantially discoloured and weathered, and we estimate a maximum width of
around 5mm. The cracking must correspond with slight dropping in the brickwork
above the window, although the arch lintel appears to remain reasonably uniform and
intact (photos 04, 05).
Some additional localised diagonal stepped cracking is evident in between the top of
the bedroom window and party wall, in a top left/bottom right orientation (photo 06).
It is assumed that a continuation of the cracking into the neighbouring property has
been disguised by repointing, where there is no obvious damage visible. To the rear
wall of no. 4, however, there is substantial erosion of the mortar joints and some
localised old deteriorating assumed cement based mortar patching, with mortar being
loose, displaced or missing in places. There is again evidence of retro-fitted cavity
wall insulation in the form of a number of filled drill holes.
Photo 5 below. Photo 3 & 4 above

 

[Harry Bloomfield]

The arch has dropped. Common thing, and again I can't see how a supposedly qualified surveyor is associating that cracking with foundation movement.

Does he, in other parts of the report, even explore the many possible reasons for that type of cracking, discount the least likely and conclude by reasoned explanation the most likely cause and the reasons why? If not, he's clueless and not doing his job.

My guess would be that a new window had been fitted, which disturbed/didn't support the arch quite so well as before.

 

[Klang180]

My guess would be that a new window had been fitted, which disturbed/didn't support the arch quite so well as before.

Thanks for this, so not something too much to worry about and in needing of special attention? If we repointed it would that be enough or should we be looking to strengthen it do you think?

 

[Harry Bloomfield]

Thanks for this, so not something too much to worry about and in needing of special attention? If we repointed it would that be enough or should we be looking to strengthen it do you think?

Me, personally, I would just repoint it as is - but woody will have a better idea.

 

[Klang180]

Me, personally, I would just repoint it as is - but woody will have a better idea.

Chers, yes Woody has been very helpful with this stuff but thanks for your input too, it has been very useful.

 

[Klang180]

We can get a CCTV survey of the drains done fairly easily and inexpensively but if this finds nothing then what would be the likely reason for this 'movement'? Is the drain really a likely candidate or are we now saying it is unlikely to be subsidence at all?

 

[Klang180]

Just saw this in the report and thought it might be more important for this issue:

There is minor ceiling cracking, 0.5mm wide or less. To the walls there are no signs
of any structurally significant defects showing through the decorations. There is
minor diagonal stepped cracking emanating from the top left hand corner of the
centre bedroom doorway, less than 1mm wide and in relation to what appears to
comprise an original timber stud, lath and plaster partition, only around 105mm thick
overall (photo 09). The top of the door frame drops towards the front by around
12mm and there is a tapered gap along the top edge of the door, which is otherwise a
reasonable fit in the frame. The front bedroom door frame appears reasonably square
and there is minor localised diagonal cracking, 0.5mm wide or less emanating from
the top right hand corner (photo 10).

In the built-in cupboard, where inspection could be locally carried out at high level,
there is minor discoloured cracking along the wall and ceiling junctions and also
across the corner of the ceiling in relation to decorations of extreme age, not
appearing to much exceed around 1mm wide.

Into the zone of the rear projection there is moderate misalignment of the bathroom
and rear bedroom 3 doorways. The top of the bedroom door frame rakes down by
around 15mm away from the party wall (photo 11) and there is a similar slope down
towards the rear across the bathroom opening. In the latter instance there is also
minor diagonal cracking emanating from the top right hand corner of the frame,
discoloured and 0.5mm wide or less (photo 08). In both instances there is little if any
evidence of opening up of the timber frame/architrave joints since last redecorated.
Both doors also appear to be a reasonable fit in the frames.

The floor appears moderately out of level towards the front end, dropping from the
bedroom 1 doorway alongside the built-in cupboards by around 20mm alongside the
stairwell and otherwise becoming fairly level. The construction appears free from
any significant springiness under footfall. There is moderate flexure and creaking of
the boarding, which also appears at least locally loose towards the bedroom 1
doorway. The flexure and creaking appear fairly widespread, although are most
pronounced towards the bedroom 1 doorway. In the rear section in the zone of the
back projection there is evidence of a minor drop towards the rear and also extensive
substantial flexure and creaking of the boarding.

 

[Ivor Windybottom]

It would be unusual if a house of that sort of age hadn't moved.

Its sounds like a load of fuss about not much, with a back-covering pasted in paragraph about the drains.

 

[Klang180]

Just for clarification this was a 'Full visual Structural Engineer’s report' done by a structural engineer and NOT just a survey.