12mm crack in room above new RSJ

[KLHD]

I would really appreciate some advice. I am having a single storey extension and creating a kitchen diner which has included removing supporting wall at back of house. In the bedroom above the RSJ I noticed a crack appear within 24 hours of the acros being removed. Within 48 hours it had developed to a 12 mm crack. The builder says this is settlement and is normal and filled it with filler. Over the weekend it seems to keep on moving. I have noticed that the bedroom window also sticks. A friend has advised me to call the building inspector to check it out ... But I am worried this will cause tension with the builder. Does this sound like settlement? Or should I get it checked out? I will try and upload a pic ....

Untitled

• KLHD
• 20 Oct 2012
• 1

For some reason pic has uploaded upside down! Crack goes down not up.

 

[freddiemercurystwin]

12mm is way too much, consider spending the next few nights in a B&B.

 

[Static]

Yer 12mm is a structural crack and should be inspected by a structural engineer.. first check with building control as they should probably view it first..

 

[KLHD]

I've got a meeting with building inspector and builder this afternoon - so hopefully will get something sorted. Thanks for advice. Scary times when you're handing over 50k and have no idea about building.

 

[tony1851]

Did an SE do calculations for the beam and bearings?. You need to check if the beam is too small for the span, or if it's the builder hurrying and not packing/supporting properly. What size was the beam and what is the span?

 

[Static]

Did an SE do calculations for the beam and bearings?. You need to check if the beam is too small for the span, or if it's the builder hurrying and not packing/supporting properly. What size was the beam and what is the span?

Possibly those are the questions to ask the building inspector..

 

[Jase750]

Have you put your acros back in?

 

[KLHD]

There are two RSJs . One that spans the gap from the old back wall and a little one that spans the old wall between the kitchen and dining room. The little one is welded into the big one. The inspector told the builder the spec he expected to see in there.

He was quite happy with everything today. He said he doesn't like to see 12mm cracks but will allow up to 15 mm as deflection/settlement - he prefers it to be around 5mm. He reassured me - but I have a builder friend who keeps sucking his teeth and shaking his head! I'm assuming that the inspector won't sign something off that is wrong or dangerous. (?)

 

[KLHD]

Jase - I was so worried on Sunday I called builder at home and asked if acros needed to go back in. I was told that it wasn't necessary and there wasn't a problem

 

[Static]

What kind of span is the larger beam doing?

 

[KLHD]

5m for the big one and 3 m for the smaller one

 

[chapeau]

Yer 12mm is a structural crack and should be inspected by a structural engineer.. first check with building control as they should probably view it first..

At what width of crack would you bring an engineer in with a 5m beam as in this example? Or does the beam size matter?

 

[Static]

Any crack over about 3-5mm should be investigated to ensure no further movement will occur.. but for this instance where a new beam is going in then some deflection is inevitable, would be allowed total deflection of 20mm.. 12mm is a lot for dead load deflection but can be repaired with hopefully no further issues (wouldn't say that sticking in a bit of polyfiller is the right way to repair)..

Would have to assume the beams have been adequately designed for live load and no further serious movement will occur and that the props weren't removed prematurely etc as said above..

 

[tony1851]

[quote="Static";p="2550925" some deflection is inevitable, would be allowed total deflection of 20mm.. 12mm is a lot for dead load deflection but can be repaired with hopefully no further issues (wouldn't say that sticking in a bit of polyfiller is the right way to repair)..

[/quote]

We don't know how much the beam has actually deflected; all we know is the width of the crack.
The SE has to allow for a maximum deflection of span/360 under live load. Maximum dead load deflection is left to the discretion of the designer. My guess is that the SE has forgotten about this. Deflection is an important consideration with longer beams.

 

[gissle]

Definitely right to be concerned, this isn't just a settlement crack. Get the builder back to put it right.