Loft extension - proposed steel at an angle??

tostaky

Hello,

The structural engineer has drawn up plans for our loft extension. The plan shows three steel beams, one perpendicular to the external wall and parallel to the street, and two steels at an angle, not longer parallel to the street. It seems very unusual. Justification is: chimney breast on one side and staircase on the other side means they have to be at an angle. 
I have tried google but i am not getting anywhere as it is too specialised. I would like some re-assurance that this is ok.
Also, the engineer said we could put perpendicular steels but we would need to add one more or two more (i cant remember). The builder may have wanted to increase his margin by reducing the number of steel? Of course he says it is fine. 

Why would a structural engineer may prefer steels at an angle rather than perpendicular? 
Thank you!

MikeJXE

tostaky said:

Hello,

The structural engineer has drawn up plans for our loft extension. The plan shows three steel beams, one perpendicular to the external wall and parallel to the street, and two steels at an angle, not longer parallel to the street. It seems very unusual. Justification is: chimney breast on one side and staircase on the other side means they have to be at an angle. 
I have tried google but i am not getting anywhere as it is too specialised. I would like some re-assurance that this is ok.
Also, the engineer said we could put perpendicular steels but we would need to add one more or two more (i cant remember). The builder may have wanted to increase his margin by reducing the number of steel? Of course he says it is fine. 

Why would a structural engineer may prefer steels at an angle rather than perpendicular? 
Thank you!

Because thats what his calculations tell him  is required and is the most economical 

tostaky

Thank you  - But how comes it is so unusual?

MikeJXE

Wait for member section_62 he might explain it better 

stuart45

Put a diagram of the job up to make it easier to see what the mean.

Section62

stuart45 said:

Put a diagram of the job up to make it easier to see what the mean.

^This.

But in the absence of a plan, it sounds like either the chimney/stairs mean the beams can't go in ideal positions, or else the issue is one of lateral support to one of the walls in which case a diagonal beam can be more efficient if there is space to fit it in.

tostaky

This is the drawing

tostaky

Yes as you said, because of the chimney and future staircase, the beams cannot be orthogonal.
i understand that, but why is it so unusual to have steels at an angle? is it because people prefer to add more steels to make it perpendicular, maybe perpendicular is better in some ways?
I just don't want to find myself in 10 years wishing that we had perpendicular steel because something went wrong.
Also the middle steel will be resting above the window in the toilet and although the plan does not mention a padstone, when i spoke to the engineer he said there should be one that is 2 meters long. Is it going to be enough?
Thank you in advance

tostaky

Also, we went with a very large company and although the architect came and took pictures, the structural engineer did not come - so it makes me feel even more worried, that he hasn't got a sense of the building structure.
Finally, my builder want to use a private building control surveyor. Is the private surveyor meant to do a visit and check the struct eng calculations/plan before my builder orders the steels? 
Thank you!

Section62

tostaky said:

Yes as you said, because of the chimney and future staircase, the beams cannot be orthogonal.
i understand that, but why is it so unusual to have steels at an angle? is it because people prefer to add more steels to make it perpendicular, maybe perpendicular is better in some ways?
I just don't want to find myself in 10 years wishing that we had perpendicular steel because something went wrong.
Also the middle steel will be resting above the window in the toilet and although the plan does not mention a padstone, when i spoke to the engineer he said there should be one that is 2 meters long. Is it going to be enough?

Various reasons, one being most rooms are rectangular, so walls are more commonly parallel or perpendicular.  Also, where beams are connected to other beams or columns it is easier to fabricate 'square' connections, so that would be preferred where possible.  It is also much easier to do associated work if you aim to keep things perpendicular and parallel - for example in your case the 47x195 'B' joists will each have to be cut to a unique length. That increases the scope for errors being made and risks the 'that will do' attitude, resulting in a build which departs from the design.

I'm fairly sure the 152x152x23 beam used as a lintel is what the SE is talking about (above the toilet window)... but "Detail A" needs to be checked to confirm.

tostaky said:

Also, we went with a very large company and although the architect came and took pictures, the structural engineer did not come - so it makes me feel even more worried, that he hasn't got a sense of the building structure.
Finally, my builder want to use a private building control surveyor. Is the private surveyor meant to do a visit and check the struct eng calculations/plan before my builder orders the steels? 
Thank you!

Personally I like to visit sites in person to get a feel for whatever it is I'm working on, but increasingly people are working remotely and it isn't unusual for SE's to work from just plans and photos.  Site visits cost money - so won't be done unless the SE thinks it necessary and/or you require one and are willing to pay.  Likewise building control is increasingly done on the basis of plans and pictures, with fewer (or no) site visits done.

tostaky

Thank you - this has been really helpful. 
Now it is how much do i trust the builders to do a good job and not a "that will do" job...!