Movement in 1930's Bay Window...

[PhilEdT]

Evening all,

This really has been a source of worry for me, so any help would be much appreciated.
First off all, I know that 30's Bay Windows are just going to move at some point. We are on clay.

What I'm really, really keen to avoid is underpinning, which could devalue the house.
This house was bought in late '14, and the survey at the time highlighted a fine crack to the Bay Window. The report said that differential settlement could occur over a period of years due to its construction. The crack was plastered/painted so no ingress nor damp. It corresponded to an internal crack in the upstairs bay window, which has changed little in the last 7 years.

However I recently noticed at the start of September, that the crack had opened to around .5mm. Looking at it today, its expanded to 1mm. I put a 6cm strip of paper in the crack, it went in all the way.

I know .5mm expansion in 2.5 months isn't loads and we've had a very dry summer. But clearly something has changed, as this wasn't happening in the previous 7 years we've been here.

Any thoughts on this really appreciated.


Update, a surveyor said its not much to worry about and most probably signifies movement following the dry summer and then rain, as opposed to subsidence.

He recommended looking into the Helifix method to remedy.

 

[manchestermonkey]

Hi. It sounds like you might have some ongoing movement. Generally speaking, bay windows in houses built in the 1930s were built straight off the ground whilst the main house will probably be on a brick spread footing (or possibly a concrete strip footing). This leads to the potential for differential movement.

Initially, you should contact a structural engineer to assess whether the movement is structural or cosmetic, and indeed if it is ongoing. You also might need to dig a trial house at the junction of the bay window and main front wall to determine the extent and type of the foundations. If underpinning is required then piled RC needle beams work well, compared to old way of using mass concrete blocks.

BTW, underpinning certainly won't devalue the house; quite the opposite - depending of course if you have any structural movement going on.

Having said all of that, it is equally possible that it's seasonal movement but this might then suggest that you have clay with a medium or high plasticity (i.e. more susceptible to movement caused by changes in the moisture content of the clay).

All ifs-and-buts until further investigation is carried out.