Steel plate to timber lintel

[messimagician]

I've got 3 timber lintels that need 10mm steel plates bolting to them. 2 of them seem straightforward as they are not built into the cavity. However the front bedroom one which is 3m long sits below the ceiling with the rafters resting on it to the bay window. Now one end is built into the party wall. The SE sent me the drawings and calculations that shows the steel needs 5 bolts fixing at the ends where it's supported.

Is this going to require a large section of the party wall to be removed to get a drill in for the end fixings?

The second question is that the timber lintels are flush with the brickwork, does the steel normally rest on the brickwork as well? The timber lintel is 175mm while the steel is 150mm but on one drawing it shows the steel being placed on the centre of the timber giving 12.5mm top and bottom, Is this the correct way of fixing it?


One more question which is probably easier to answer is how do you go about fixing plasterboard to this afterwards as you'll have bolt heads protruding ect?

Thanks

 

[freddiemercurystwin]

Post a pic of the SE's details.

 

[wessex101]

1. Right angle attachment on drill, still need part of party wall cutting out though.
2. Steel plate central on the timber lintel. The steel is just to take out the "bendyness" of the timber, it doesn't need a bearing as such.
3. That is probably the hardest question. You would probably have to box out the lintels to clear the bolt heads. Also opens a can of worms regarding fire resistance of the lintels.

I have never seen this done before, I'm guessing you need to strengthen the lintels for a loft conversion or something. I can't help feeling it would be easier to just replace the timber lintels.

 

[messimagician]

 

[messimagician]

Yeah a new floor is going in the loft so all timber lintels need reinforcement. The front bedroom is the only one I can see which is causing an issue as it's got the rafters resting on it also as well as one end being in the cavity

 

[tony1851]

How will you get the nuts on the bolts for the 5 bolts that are at the party-wall end?
Why not use 10mm coach screws instead? They can carry a higher shear load than bolts (surprisingly!)
and be easier to fix.

 

[John D v2.0]

If all else fails it might be cheaper to go back to the SE and ask for an alternative detail. Perhaps there's a way of trimming out around it . Although 3m is very long, but the structural design is what you're paying the SE for so they might have a better way.

 

[tony1851]

1. Is the bay window at the front of the house?
2. Is this loft conversion having a dormer, or just using the existing roof void?

 

[messimagician]

1. Is the bay window at the front of the house?
2. Is this loft conversion having a dormer, or just using the existing roof void?

Yes the bay window is at the front. No dormer.

 

[tony1851]

Looking at the figures, I would say the engineer has considerably over-estimated the loads on the beam, as below;

Assuming your front bedroom is - say - 3.5m deep between the window and the internal load-bearing wall. The total area of floor supported by the beam would be ½(3.5 x 3) = 5.25m² (this is because half the load is supported by the internal brick wall, and the other half supported by the beam).

The live load for a domestic floor is 1.5kN/m² and a reasonable dead load is 0.5kN/m². This means that your beam will be supporting a floor load of approx 10.5kN. (in practice, the floor load won't be anywhere near this because in a loft, you physically can't load the floor to its maximum because of the diminishing headroom at the eaves; classified as 'loft storage', the prescribed live load comes down to 0.25kN/m² for this area.).

The beam will also be supporting the lower part of the roof: assuming you have one purlin approximately half-way up the slope, the additional roof snow load + dead load would be approx. 4kN.

So the beam would be carrying approx. 14.5kN - say 15-16kN tops allowing for self-weight of the beam itself and a small dwarf wall. So it's a puzzle as to how your SE gets it as 25.3kN?

Assuming the beam was C24 grade timber - or even C16 - you would almost certainly be OK just by screwing a piece of 50x225 timber to the room side of the existing beam. Manhandling a piece of steel plate that size would be tricky and totally unnecessary IMO.

 

[messimagician]

Hi Tony

The way the load bearing walls run in the house is odd. Basically where you would have two separate steel beams across a spine wall, I can only use 1 steel beam that's nearer the rear of the property as the load bearing wall runs straight down in a line at the point. The front part of the house the wall supporting the roof is offset by 35cm from the ground floor wall and is sat on the living room joists.

So because of this the largest span in the loft is 3600mm using 75x150 at 300 centres

The timber beam in the front bedroom runs right across the entire room. It drops down below the ceiling and is boxed in, It's a large bay window

The floor has been calculated to 0.50 using trada software looking at the pictures sent

 

[tony1851]

The front part of the house the wall supporting the roof is offset by 35cm from the ground floor wall and is sat on the living room joists.

Is this one of those houses in the Flixton/Urmston area?

 

[messimagician]

Actually in Hazel Grove, Stockport. I take it you've come across this or something similar before? Are you an SE or builder?

 

[tony1851]

SE: why not post your full calcs (minus your address) so that we can have a look?

 

[messimagician]

The first picture is just the timbers calcs being used in the loft. The other 5 pictures are the steel for the front timber beam