Unbroken wall longer than 6m

[L.Lam]

Hello,

We are building an 2 storey side extension which is 3.8m x 6.5m using solid wall construction (celcon foundation blocks). On the ground floor, we are building an internal wall using blocks. On the 1st floor, the side wall is spans the length of extension without any internal partition. The structural engineer has added a steel column on the 1st floor with a steel beam connected to the edge of the column. When we questioned this with the SE, they said it was needed for lateral restraint because it is unbroken and longer than 6m. It doesn't make sense to me but I am not a builder or SE so I have tried to find more information about this on the internet but failed and struggling to understand it.

There seems to be some very knowledgeable people on this forum and hope someone can help either to explain why it is needed and if there are any alternatives.

 

[^woody^]

Walls are restrained by the floors and roofs they support so that the whole house acts as one rigid unit.

 

[stuart45]

You need movement joints in blockwork over 6M in length, never heard of a steel column required in a normal run.

 

[Bouy]

Cl 2C6 of Approved Document A gives guidance on this

 

[tony1851]

6.5m is not excessive considering that the wall will be bonded to return walls at each end and will be restrained by the rigidity and weight of the floor and roof. The only lateral stability issue is on the first floor panel; the Code of Practice for design of masonry walls gives simple guidance on how to check these things without resorting to steel. We don't know the overall layout of the house, but I strongly supect that no additional restraint would be required in this case.

What might be an issue is the potential for shrinkage cracking, but that is a separate problem.

How does the SE propose fixing the base of the steel column to the blockwork, and also how is the other end of the beam going to be held? Seems like an idea copied from the undergraduate textbook "Wind posts for Dummies".

 

[Notch7]

I've had building inspectors insist on a wind post or pier when wall over 6 metres.

A wind post has wall ties built in and can usually be fitted inside a cavity. It has to be fixed to foundation at bottom and wall plate at top.

 

[Notch7]

What might be an issue is the potential for shrinkage cracking

Thermalites seem awfully prone to cracking anyway, they don't seem to need much of a reason!

 

[tony1851]

A wind post has wall ties built in and can usually be fitted inside a cavity. It has to be fixed to foundation at bottom and wall plate at top.

Agreed, though OP says it's solid wall constuction (no cavity?), and the windpost seems to be installed at 1st floor chamber level? Can't see how they can effectively secure the bottom of the post, unless I've misread it. Could do with seeing the drawings really.

 

[L.Lam]

Here is a drawing of the side extension showing the steel column and beam. SE propose plates at the bottom which is then bolted to blocks. The blocks are fitted inside flanges of column. The beam is bolted to the edge of column (not on top) and the other end of the beam is to be fitted into the existing wall of house sitting on a padstone.

The design seems to weaken the house rather than strengthening it. It is also worrying that the ceiling joists run parallel to the beam. Builder and architect assumed it would be perpendicular until we checked the plans.

 

[^woody^]

I've had building inspectors insist on a wind post or pier when wall over 6 metres.

That's every house gable wall, and front and back walls too then, some garages, all bungalows, some rear extensions, some garden offices and outbuildings.

How bizarre.

 

[^woody^]

Here is a drawing of the side extension showing the steel column and beam. SE propose plates at the bottom which is then bolted to blocks. The blocks are fitted inside flanges of column. The beam is bolted to the edge of column (not on top) and the other end of the beam is to be fitted into the existing wall of house sitting on a padstone.

The design seems to weaken the house rather than strengthening it. It is also worrying that the ceiling joists run parallel to the beam. Builder and architect assumed it would be perpendicular until we checked the plans.

Find a proper engineer - or one that is not just making work for himself

 

[tony1851]

(The ceiling joists usually do run parallel to the flank wall and in line with the roof rafters (assuming its a normal gable-type roof?) - nothing wrong with that as long as the usual metal straps are added connecting the ceiling to the existing and new walls).

But good luck to the builder trying to fix that windpost!

1. why such a heavy section of column? - wind posts are usually much smaller.
2. How is he going to cut the blocks to fit into the web of the beam?
3. Has the SE heard of cold bridging? - you will get condensation on the room-face of the beam, which will show as a dark vertical line.
4. Bolting the base of the beam will mean the bolts are too near the face of the block; there will be shear force and a bending moment at the base of the column, which the block may not be able to resist.

It would be interesting to see the connection details/figures for the base of the column.

With all due respect to the SE, frankly, IMO this is a poor design, unnecessarily complex, expensive to install, and as much use as a chocolate teapot.

 

[L.Lam]

I am not happy with the design especially now some of you have confirmed that it may not be unnecessary but not sure what we can do. To go to another SE will mean delays and cost.

Here is a view of the front elevation. Tony, so the ceiling joists are correct?

 

[^woody^]

Why do you need a structural engineer for a basic extension?

 

[L.Lam]

Why do you need a structural engineer for a basic extension?

Don't you need to submit structural calculations for building control? Is this something you can easily do yourself?