Lintel calculation check please

[liftfan]

Hi,

I’d like to increase the size of an internal wall opening and was wondering what lintel size I need. I was hoping to get away with a 65mm x 100mm but now not sure!

In the opening below I’d like to replace the existing 1m lintel (red) with a 1.8m (red plus blue) to give a 1.5m clear span.

The wall is lightweight block. Above it is the loft with the joists running like below. The black rectangle is the new opening.

These are my calcs:

UDL for ceiling below a sloping roof:
Dead load x factor = 0.3 KN/m2 x 1.5 = 0.45 KN/m2
Live load x factor = 0.25 KN/m2 x 1.35 = 0.34 KN/m2. (Figures from a steal beam calc website)
Total = 0.79KN/m2

Ceiling joists: 4.5m off each side , so half total span = 4.5m (9m divided by 2)

Lintel: 1.5m clear span

Total load: 1.5 x 4.5 x 0.79 = 5.33 KN


I think the Supreme Concrete website shows I need a bigger 100x140 beam as shown below.


Is that right?

Thanks

 

[oldbutnotdead]

Not sure about your calcs, think there might be a decimal in the wrong place.
Real question- why not open it out all the way (except for nibs either side). You'll regret it later if you don't.
Building Control may (if you're lucky) advise on lintel suitability- put a Building Notice in & then ask

 

[tony1851]

For that span, a 100 x 65 is too flimsly and liable to crack (though it won't fall apart) even by just manhandling it up; the 100 x 140 would be more appropriate. Having said that, a concrete lintel that size is very heavy - why not consider a steel beam instead? a 127 x 76 steel 'I' beam would be fine, or a lightweight Catnic box lintel, or even a length of 4" x 4" angle iron - if you can live with a thicker bit of plaster in the other side of the wall?

(BTW, in your calculations, you have the factors the wrong way round - it's x1.35 for dead load and x1.5 for live load if using the Eurocodes, though it won't make much difference in your case; and don't forget the weight of the blockwork plastered both sides - approx 1kn/m². Also, manufacturers of concrete and steel lintels tend to give un-factored loads in their tables, so you might have over-estimated the load).

 

[liftfan]

Why not open it all the way? Good question. I’m going to build a stud wall add on so it will be full size for that. I have full plans Building Regs for other stuff in the house including structural calcs and whatever I do I’ll run it by them as the chap has been very helpful.

Thanks Tony! That’s brilliant advice. Looks like my local builders merchant has the Catnic box lintel in stock so I’ll go for that. Looks much easier!