I am building over a flat roof garage which has a cavity wall except for the front. Wall to be brick outer and block inner. I need to put a cavity lintel over the front and this will be 3450mm long. There is a choice of standard or heavy duty.
Which one do I need? The HD one is £200+ dearer than the standard. It's no good asking the manufacturer as they just say have a structural eng. decide. So can anyone tell me a typical application for each grade of lintel?
Thanks
mark
Hard to say without knowing what it needs to hold up!
It's to do with the loads on the lintel. The catalogues usually give a safe working load (SWL). Wall loads are about 4.5kN/m^2, floors (in dwellings) are about 2.0-2.25kN/m^2, roofs are between 1.5-2.5kN/m^2. Multiply by the areas bearing onto the lintel, add a bit more to be on the safe side, and you have you SWL.
If you only have a couple of rows of blocks over it, the light one will be sufficient. If it is the full triangle you will need the heavy one.
Very important. Before you start piling blocks on a long metal beam, support it in the middle off the ground with a bit of timber (4"X2"). Remove when the cement has set. If you don't do this, the beam will sag.
It will have a bedroom above, brick and block wall with a conventional tiled roof. Wall will have a large window.
I'll remember the tip. Or maybe let it set for a few days before loading.
mark
I think I understand what your saying but working out areas is the tricky bit for me. I can do the maths but determining the areas of wall and roof bearing down on to the lintel is where I come unstuck. Thanks
mark
That's the simple bit. How tall is the wall? Multiply by the width of the opening. Do the floor joists bear onto this lintel (directly or indirectly)? If so, take half their length ('cos they're supported at both ends), and multiply by the width of the opening. Do the rafters and ceiling joists bear onto this lintel? ...
The floor joists run parallel to lintel so I presume have no bearing on the lintel. The wall will be about 2.4m and the width 2m of which will be a window 2m by 1.2m. So about 2.4sq. m of brick/block wall directly above. I don't think it's that easy because of triangulation which I'm aware of but my understanding of which is a bit woolly. Is it an equilateral triangle with a base, in my example of 2m wide?
Thanks for bearing with me.
mark
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