New extension cracking - advice please

[John543219]

New double floor extension, just had windows fitted and noticed crack from the top window on the first floor vertically down to bifold below after they went in and were installed.  Very good deep foundations with the build at 2.5m so don’t think movement or subsidence (hopefully not)…

Should we be concerned???

The exterior is about to be rendered so want to ensure all ok before this is done

Any advice appreciated so we can get a good feel for what this might be 👍

[Dave Jones]

what type of lintel was installed above the bifold ?

[John543219]

Steel RSJ 

[Iceverge]

I wouldn't worry about that. How long since it has been built?

[John543219]

About 2 weeks since appeared, extension has been up couple of months 

Edited July 9, 2023 by John543219

[Dave Jones]

wouldnt worry if its an RSJ on a padstone. That blockwork is rough as feck mind.

[Iceverge]

 

Put a couple of these on it, take regular pics of it and save it to the cloud. 

 

Delay rendering until all movement has stopped. 

[John543219]

Thanks for this, great advice and will get a few of these on it next week 👍

[George]

This is most likely due to the concrete blocks shrinking slightly. This happens post manufacture and continues for some months, conditions depending. It can be dealt with by putting in movement joints when blockwork walls are 6m+ (although unusual in domestic settings), but cracks can happen in other circumstances. The line of the wall with a window is a relative weak point so has cracked along that line.

 

Now the crack has occurred, ongoing movement should be minimal. But monitoring will help confirm that.

 

The cracks should be ground out and repointed. If the crack has gone right through I would consider adding in stainless steel helical bars to crack stitch (aka helifix bars)

 

 

Edited July 10, 2023 by George

[John543219]

Thanks for this George, appreciate advice and makes sense 

Think expansion / contraction of RSJ with heat etc has also come up on a few searches and info

will look at sorting with helifix bars 👍

 

[Gus Potter]

What is on the inside? another masonry leaf? If so does the crack appear on the inside. If so you may have a problem on your hands as the tying together of the building needs to be checked.

 

How long is the wall?

 

On the other hand it could just be the blocks shrinking and the crack manifests at the weak spot.