Garage wall cracks - Serious ?

[jim1955]

Hello,

Suddenly found a crack in the free standing garage wall and need some advise on how much of a problem it may be, though a bit of a tale on its construction.

The main garage was self built 40 years ago, with full depth foundations to the inspectors requirements etc.
As there was some waste space at the back of the garage, we removed to loose top soil and put a layer of hardcore down so any excess concrete from the laying of the main base could be used to make a storage area, it ended up about 4" thick of concrete.

Some 30 years ago we wanted a bit more space in the garage for a little workshop so we knocked a doorway though the rear wall and added the 3 foot extension with the same blocks onto this rear slab.
( though yes, we should have done proper footings !)

Its all been fine for all these years, but last week be suddenly noticed a line of cracks in the blockwork joints on one side as the red line shows.
Also the extensions dpc looks like theres a movement crack all around it.

We can just get a 1mm spacer in the top area of the cracks and in where the dpc is.

There have been no changes to the surrounding land /properties, so wonder if this is just a small 'settlement' crack we can live with or possibly something more serious ?

We are on the hills in the north of England, but not an area known for subsidence.

 

[^woody^]

It wont be a settlement crack after 40 years. It may be a subsidence crack after 40 years though - especially if the foundations are like you have drawn.

The ground changes every few months of every year. Sometimes more than other years.

 

[jim1955]

It was a mistake , though surprised it lasted so long without any movement.

Its only a 4ft long extension; trying to decide which will be the best solution -

Underpinning, would seem simpler as the inside 'workshop' area has been insulated / panelled etc though outside access space around it is rather limited.

To remove and rebuild properly with full foundations or just remove and replace with a lean to shed ?

Either way, one outstanding question would appreciate some advice, the existing blocks ( 18 x 9 x 4" dense concrete) in the main garage area that have now have these joint cracks, once the actual cause has been removed, do they need removing and re-laying or can the joints be drilled out and repointed with mortar or use some joint mastic ?

 

[^woody^]

If you are happy that you know the cause, and the solution is underpinning, and this will stabilise the wall, then yes any cracks can just be repointed and they should not progress any further.

If that is not the case, and there is potential for further ground movement, then its a different repair.

The most common causes of foundation movement are leaking drains, or moisture extraction by large trees or shrubs, or both. These causes should be discounted before devising any repairs.

 

[jim1955]

Yes, thanks for the good advice, have been making some more checks, reference points / markings and spirit level checks on the walls to see how far things are going and in what direction / exact cause.

Despite the cracks not able to see anything out of vertical plumb, horizontal alignment, bowing etc, so while the weather is too wet and cold will continue to monitor things.

No drains to worry about but a large shrub on the opposite wall to the crack, but that may be coming out anyway.

If we do have to underpin that raft section is rebar a must and if so any recommendation as it its diameter and spacing eg 150mm between bars ?

thanks.

 

[jim1955]

Well a bit more evidence today.

On the rear garage wall the dpc joint had been covered in mastic and it and the rest of the wall downwards had been covered in thick bitumen to help protect it from the elements over the years, so had not seen this fault clearly until lots of rubbish etc had been removed.

Seems the slab and blocks below the dpc have slipped on the bitumen /felt old type of dp material and moved away from the upper blocks by about 6mm, this was confirmed by removing the inside panels and insulation which shows the same.

Also on the other lengthwise wall, which has a window close to the extension and originally thought was ok, can just see the very, very small traces of similar cracks in the masonry paint.

So it looks like the extension slab is moving, but the question now is with that degree of movement on the rear wall / dpc , even if the walls were underpinned, will the wall itself be sound enough with that 6mm displacement ?