4 Dec 2019
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United Kingdom
hi folks.

this is my first post on here.
i really need some help on sorting out this problem.
im hoping someone can explain the cause as to why the walls around this upstairs bedroom bay window have cracks in them.
ive attached a link to some photos of the bay window.

the 4 main things ive noticed are:

1. the gap under the external UPVC window sill and pebble dashing.
2. the external crack from the right hand side of the window sill.
3. the internal crack which follows the same path as the external crack (diagonally downwards towards the skirting board).
4. several cracks across the top of the internal wall.

could the pebble dashed support under the bay window be loose causing it to drop slightly???
what can be done to fix this - strengthen the support with new timber / steel brackets maybe???
would i require a structural engineer to come take a look???
has anyone managed to fix a similar issue in the past???

many thanks for reading my post.
any help / advice would be greatly appreciated.

thank you all.
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Have you just bought the place or been in for a while? When was the double glazing done, have both bays got proper support poles in?
MR V, good evening.

As "oldbutnotdead" above some more basic information will be of use.

Initial consideration could be the cantilever system [whatever it is] could be failing?? below the window, this in turn could be allowing the window and indeed the entire bay to in effect "rotate" outwards and down, the pattern and position of the cracks, especially internally, could point to the foregoing??

we have lived at the property for almost 35 years. we had the original timber bay windows replaced with the current PVC bay windows in 2005.
i do believe there are metal bay poles in both the upstairs and ground floor bay windows.
we have had no issues with the ground floor bay window since installation.
i noticed the internal cracks around the upstairs bay a couple years ago - but i have only recently noticed the gap outside.
im now worried that the external bay support is coming away from the wall - and taking the bricks with it.
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yes - i think the cantilever / support has somehow loosened off the bricks and is now wanting to rotate downwards.

it is the original support that was there when the timber windows were removed.

its strange that this has only happened after almost 15 years since installing the PVC bay windows though!!!!!
I'm no expert on complex cracking but I'd be interested in the state of the lintel above the ground floor window. Hard to tell from the pics, if the internal low cracks upstairs are at the same height as the external cracks then it is less likely that the upstairs sill thing is rotating outwards, more likely the whole thing is sinking gently as the downstairs (timber) lintel sags.
The gap between pvc sill and pebbledash is probably rubbish fitting- is there a silicon bead under there that has pulled apart or is it just a gap? Hard to tell with pebbledash but a plumb line might be useful (strung from the soffit & measure at various points to the wall, see if there's any significant bulges)

yes - the lower internal crack from sill to skirting is identical to the external crack.

the outside gap under the pvc sill is all the way around the bay - and seems to have occured within the last 12 months i think.

i think there may have been a silicone bead but there was no such 'gap' there before.
the gap seems to have happened due to the bay support shifting downwards for some reason!!!!

to check the state of the lintel - i will need to remove some floorboards - which i will try to do.
do u think it might be worth removing the pebbledash on the bay support to see the condition of the timber framing - and to see if it has somehow worked itself loose.

maybe it could be fixed more securely using masonry bolts etc.
MR V, good evening again.

Suggest you have a look at removing the internal timber sill, if possible???

Reason is that that access route may give sight of what the structure is, and the opening up internally will not allow the winter weather to get at the structure below the window??


good evening sir.

i agree - the better option may well be removing the internal sill - and having a look at what is underneath.

that is if it is possible to remove it in the first place!!!!

i think the support is constructed from timber framing with chicken wire and finished with pebble dash.

thats just an educated guess as its never been opened up before!!!!!
MR V, good evening again.

The internal investigation option appears best, removal of the window sills, starting with the trim around the sill / wall will assist??

Most common defect will be wood rot? or a joint failure?

Attacking from the external, given the shapes and the very, very high "probability" of a mesh is not really a ood idea at this time of year, also an external hole will forever be a patch and as such very unsightly.

Must admit I would be interested in any findings that you can post following your investigations?

my two pee says you need a SE on site - to say whats happening, and what to do about it.

the window board appears to be in two pieces, and perhaps sunk into the reveals?
removing the window board will not be easy, and could possibly result in the w/board splitting.
plus any heavy duty levering down to lift the board might force down the timber cradling structure below the board?

a couple of observations - observations not certainties:

1. thats a very wide soffit overhang - 600mm?
2. the bay is not cantilevered out - above or below.
3. the Bressumer beam crosses an extremely wide opening - is it an RSJ or timber?
4. the B/beam is presumably carrying some short framing which in turn is carrying the roof rafters wall plate, and ceiling joists.
5. the roof might be somehow involved - eg some kind of odd roof thrust or point (overloading)loading?
6. there's no signs of water staining - which would indicate moisture had entered the bay?
7. that front elevation has very slim supporting columns of masonry - the elevation is essentially a large opening.

OP, why not go into the loft above the bay, and take photos? seeing the construction might confirm or demolish my two peesworth about any roof influence?

have any neighbour's in similar houses experienced similar problems?
your immediate neighbour seems to have copy cat construction, and Pvc replacement frames?
Contact your Buildings Insurer for an inspection before you loose the front of your house.

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