Ubutressed wall length and lateral support

[OrangeJuice09]

Hi,
I have a couple of questions relating to the approved drawings for a single storey 3m extension.

A new 5.5m wall will be built next to the neighbours house on the left. Some of the wall will be in the existing garage and it will extend by 3m onto the patio.
The original architect added a pier to rest an 203x203 rsj, but after speaking with the SE, he thinks if the inner wall is built with concrete blocks, the pier can be removed as the wall can sustain the load. However SE also thinks a windpost should be added as the wall is unbutressed.
From the attached diagram (yellow box area) it can be seen that one end of the wall has a corner return and on the other end there is also a corner on the inner wall. So I'm unsure why a windpost is needed. How long can a double wall be with approx height of 3m without a butress? and would the vaulted roof provide any support to this wall?

The other question is about the wall nibs which I want cutting away to an internal measurement of 225mm. The brickwork in this section does not have a cavity and is 9 inches thick. The council approved the drawing but the SE thinks that 225mm is inadequate, mainly for the load. Another SE thinks there is inadequate lateral support and a goalpost design is needed in the 'proposed kitchen' area (2x 178 rsj). Happy to not cut back the walls to the 225mm but wanted to know if there is a rule of thumb I can apply.

Thanks for your time

 

[Nakajo]

I would trust a real structural engineer (that I could sue) over an imaginary online pundit (that I couldn't)

 

[^woody^]

I would trust a real structural engineer (that I could sue) over an imaginary online pundit (that I couldn't)

Online pundits are being found and arrested for saying the "wrong" words nowadays, so surely an armchair SE could be sued?

As for the OP's predicament, houses like mine have been up for decades and there does not appear to be any buttressing at the corners and beams seem to be sitting on walls with no nibs ( I know this as I put them there) and bizarrely, the house is still up.

Like when I get my toes tickled, I do tend to chuckle at any mention of lateral support to walls in any domestic house.

 

[tony1851]

You don't need goalposts in your layout; neither do you need the nibs on the side walls.
Your SE needs to try a bit harder.

 

[OrangeJuice09]

You don't need goalposts in your layout; neither do you need the nibs on the side walls.
Your SE needs to try a bit harder.

Its a single storey extention attached to a 2 storey link-detached property, fairly standard. Currently there is a large bay window on the right with an opening of 2.3m (under the proposed 2x 178) and another bay in the existing kitchen (to the left).
I've spoken to 2 SE's and they are telling me that the nibs (middle and right pier) are inadequate for the load and for the lateral support, even though its been approved by the local council, that part I can't understand. I can speak to the SE again but I dont have enough techncal information to go by to make my case. What can I say to the SE's to convince them, any examples would help ?

 

[tony1851]

Is it the case that you want goal posts and are querying why your SE hasn't specified one? And why are you concerned if b/control have approved the scheme?

FWIW:

Middle pier: assuming the inner skin isn't made of hollow cinder block or meringue, that would almost certainly be OK. Are the SEs forgetting that some of the load will be distributed into the 100mm wall running into the pier? and also that said wall will serve to stiffen the pier itself, thus enabling it to carry a higher load than if it was a free-standing pier?

Nibs each side; not necessary - simple spreaders can be used to distribute the load, so you can run your units continuously. Cut-down 6" x 4" pre-cast concrete lintels are ideal for this - especially as they have reinforcing wires.

Lateral stability; this is the mare's nest that some SEs wheel out to justify the additional design costs of a goal post. Nine times out of ten they are just not necessary. You look at the ground floor plan of the house as a whole, and understand that all walls running parallel to the removed walls (ie all those remaining walls and returns running left-to-right) serve to stiffen the house against lateral wind load. There are methods of proving this, but some SEs are either unaware, or can't be bothered.

 

[OrangeJuice09]

I'm happy to go with the current scheme where there are 215mm nibs and no goalposts. My only query was to not to have a nib (located where it states 300mm) on the new wall on the left where the 203 RSJ sits, but because my original architect has gone absent, I asked two SE's and they flagged up the above issues (insufficient piers etc.). Even though b/control has passed off the scheme.

Middle pier, currently 1.1m wide and made from solid brick without cavity.

Nibs each side; - The nib on the left, I can have the inner wall built with 7N blocks and rest a padstone/lintel; WRT the nib on the right, if I was to have no nib, would the padstone/lintel be put across the existing and new wall (where they join) ?

I agree with your statement on lateral stability - I think the SE's are over complicating it. One SE has suggested to add a windpost in the cavity of the new wall so that the pier can be removed. (located where it states 300mm). So now I cannot commence the brickwork as the windpost needs fabricating unless I discover otherwise.

 

[tony1851]

One SE has suggested to add a windpost in the cavity of the new wall so that the pier can be removed.

Nonsense; a windpost is installed to stiffen a cavity wall and provide resistance to lateral wind load.

The masonry pier would provide almost no lateral resistance to wind load as it can take no bending moment; it's function would be to provide an increased bearing area for the reaction from the beam.

Steel windpost and masonry pier serve completely different functions.

 

[Dereekoo]

Cl 2C6 of Doc A building regs give guidance on height/length of walls if certain conditions are satisfied. Running through the various clauses I would suggest that wind bracing is not required (but then I am only an online pundit BSc, C Eng, MICE so it is best that you satisfy yourself and flag up your findings with your SE)

 

[OrangeJuice09]

@Dereekoo I've checked 2C6 and it doesnt seem to refer to a cavity wall, which is where the windpost is to be placed unless I misunderstand. I quote: '2C6 Solid external walls, compartment walls and separating walls in coursed brickwork or blockwork: Solid walls constructed of coursed brickwork or blockwork should be at least as thick as 1/16 of the storey height. Further requirements are given in Table 3.' So not sure if it applies.

Nonsense; a windpost is installed to stiffen a cavity wall and provide resistance to lateral wind load.

My mistake, the SE suggests adding a windpost for the lateral forces and not the load, but wants to position it under the 203 RSJ (located on the left wall inside the cavity) and also tied to the rsj to top level.

 

[Dereekoo]

@Dereekoo I've checked 2C6 and it doesnt seem to refer to a cavity wall, which is where the windpost is to be placed unless I misunderstand. I quote: '2C6 Solid external walls, compartment walls and separating walls in coursed brickwork or blockwork: Solid walls constructed of coursed brickwork or blockwork should be at least as thick as 1/16 of the storey height. Further requirements are given in Table 3.' So not sure if it applies.


My mistake, the SE suggests adding a windpost for the lateral forces and not the load, but wants to position it under the 203 RSJ (located on the left wall inside the cavity) and also tied to the rsj to top level.

Sorry Cl26C was a starter for 10 and is part and parcel of all the other clauses in 2C hence subsequent comment re running through various clauses, it would be nice if regs could be sorted out by one clause but that will never happen, move on to Cl 2C8