Stub Walls for beam

[Crakkers]

Hi

1930s Semi Detached House.

Looking at extending the lounge area by 2m. This will entail knocking through and a beam installing to support the 1st floor. In order to maximise the size of the room I want the beam to rest on the smallest "stub walls" possible. So, is there a minimum length of stub wall the beam can rest on?

Ultimately I know a SE will need to prove any alteration with calcs, but just wondering if there is a standard / recommended?

Also, if I wan a loft conversion, will this affect the above?

Thanks in advance.

C

 

[^woody^]

The smallest possible is 0

 

[Crakkers]

Zero, ok I wonder if you could explain how that might be achieved please?

 

[John D v2.0]

Cut into the wall, fit or cast a pad stone, rest the beam on it.
Or for a new wall, build the wall, then rest the end of the beam on the inner leaf of block work.

Your local bco will allow a beam on a sub wall down to maybe 450mm without calculations, but with calculations you can do what you like.
The se will take the overall stability of the building into account.
In our case he could even take into account next doors wall providing stability to our side. So the back of the house is basically both of the scenarios I detailed above, with the beams hidden in the ceiling.
The cost of a goal post or a channel in the wall would have been a lot more than his design

 

[^woody^]

Zero, ok I wonder if you could explain how that might be achieved please?

The beam sits on the existing walls

 

[Crakkers]

Can the beam sit on existing wall, even if it's a party wall?

Most people are advising a steel goal post, but say it's expensive. What makes goal posts expensive, the material itself is not expensive and the fabrication techniques used are not complex.

 

[John D v2.0]

The beam knows nothing about whether it's a party wall or otherwise.
You shouldn't ask most people, you should find a good SE and take their advice, as they're insured to give it.
Goal posts are expensive compared with a steel on brick because steel costs more than bricks, is hard to adjust on site, needs the connections designed by the SE and created usually off site. It would also need a suitable footing as it's a point load at ground level. There are also considerations for fire proofing as steel doesn't fare well at all in a fire compared with timber or brick.

 

[Crakkers]

Timber is better than steel in terms of fire?

I also know that the beam does not know if it's a party wall or not, just like the beam won't know if it's legal or not.

If I cut into the existing side wall will the beam sit on both "walls" or just "mine". Whilst I would prefer a flush wall to the extension, I don't mind some stub wall. But would like to restrict it to 6 or so.

Been trying to find more info on this topic. Can anyone recommend any sources of reliable info before I go to an SE?

 

[John D v2.0]

Yes timber is better than steel as it doesn't bend when it heats up.
You can sit the beam where you like, a party wall is jointly owned so you can sit it there although if you get into party wall surveyors and all that, they might stipulate about strengthening work needed. Next door are not likely to sue you for trespass of you go too far, but they would expect you to fix up any damage caused by your building work.

 

[^woody^]

Here's a free extract from my structural memoires to be published in 2035. I think this might be reliable, but I may be biased. Buy the book for more info.

• The bearing required by a beam is determined by the loads on the beam. Yout might be able to balance the beam on a broom stick.
  
  
• A goal post frame is a solution for a different problem. If you manage to balance a beam on a broom stick, it might sway in a draught. A goal post will stop this.
  
  
• Timber is better than steel for burning on a fire, but steel better than timber for not catching fire. It's irrelevant as either will require protection from fire in the first place
  
  
• Whether a beam is placed in/on a party wall or whether it is placed on a nib cut in to a party wall matters not, as the PW Act will still apply. Only 50% of the width of a party wall is owned by the neighbour, so that's the only half of the wall he can use.

 

[23vc]

Slight risk of hijacking this but I think it’s relevant - if I’ve had calcs done for steels, based on it being cut into the adjacent wall (ie no nib) but if I decide to retain a bit of a nib to cut down on the demolition, I appreciate this is likely to maybe need a different padstone, but does the steel calc still apply ie same steel can be used (just a bit shorter)?

 

[^woody^]

Slight risk of hijacking this but I think it’s relevant - if I’ve had calcs done for steels, based on it being cut into the adjacent wall (ie no nib) but if I decide to retain a bit of a nib to cut down on the demolition, I appreciate this is likely to maybe need a different padstone, but does the steel calc still apply ie same steel can be used (just a bit shorter)?

Steel loads will be the same but the transfer of the load to the wall will be completely different - ie is not just a case of leaving a nib, you need to know how much is required as the steel is no longer bearing on the main wall at 90°, just a much less bit of a wall.

 

[23vc]

Cheers woody, is that within bco remit to advise/agree , or is it likely to have to go back to the SE?

 

[^woody^]

Depends if he's a clown or not

 

[noseall]

We have had to leave short nibs in the past but have had to extend the beam all the way onto the flank wall.
The nib is there as a we bit of stability for the wall and the beam is bearing onto the flank wall and not the nib.