Some of the replies above make me realise why there are so many cowboys in the building game or people who do not understand what they are doing.
To work out the size of a lintel, be it steel, timber, concrete you need to work out the loads being applied to it.
I have had many jobs where the loading on a standard or even a heavy duty Catnic/IG off-the-shelf lintel has been to great for it. In these cases we have had to use steel sections UB's UC's or PFC's (for you old school chaps RSJ's)
Working out the loadings is not just the bricks/blocks above the opening but what about that floor joist or the roof rafter or any other indirect load being applied to it.
Just think about the weight of a bath full of water sitting on the joist that sits on the lintel or the weight of a room full of people when your holding a party!
Once you have calculated these DEAD and LIVE Loads, added in a safety factor applied it to the span of the opening, calculated its max bending, shear, deflection etc. You work out the lintel size.
But that's not quite it.....all the loads applied to the lintel have to transfer through the ends bearing on the wall below. What size bearing will you need? 150mm? 200mm? Do we need a padstone? Will the brick or block take the weight? Will the lime/cement mortar take it? Again these have to be checked.
I understand that most of the time we have very simple situations with standard door/window spans of 0.75-1.8m but when it comes to anything wider check it out. Some of the spans on bi-fold doors are 3-6m and off-the-shelf lintels aren't enough.
To work out the size of a lintel, be it steel, timber, concrete you need to work out the loads being applied to it.
I have had many jobs where the loading on a standard or even a heavy duty Catnic/IG off-the-shelf lintel has been to great for it. In these cases we have had to use steel sections UB's UC's or PFC's (for you old school chaps RSJ's)
Working out the loadings is not just the bricks/blocks above the opening but what about that floor joist or the roof rafter or any other indirect load being applied to it.
Just think about the weight of a bath full of water sitting on the joist that sits on the lintel or the weight of a room full of people when your holding a party!
Once you have calculated these DEAD and LIVE Loads, added in a safety factor applied it to the span of the opening, calculated its max bending, shear, deflection etc. You work out the lintel size.
But that's not quite it.....all the loads applied to the lintel have to transfer through the ends bearing on the wall below. What size bearing will you need? 150mm? 200mm? Do we need a padstone? Will the brick or block take the weight? Will the lime/cement mortar take it? Again these have to be checked.
I understand that most of the time we have very simple situations with standard door/window spans of 0.75-1.8m but when it comes to anything wider check it out. Some of the spans on bi-fold doors are 3-6m and off-the-shelf lintels aren't enough.
