I am putting a new opening through a 400mm thick solid wall. The lintel for the opening will have a point load on one side from a roof beam. That's ok ....I'm going to go OTT with the first 2 100mm lintels and then using 2more 100mm lintels to support the stone work above the remainder of the 400mm opening. (2 x Catnic CN5CX and 2x standard Catnic lintels). My question is over the side support for the lintel, I originally thought that I could use the existing stone work to support the new lintels at the side. However I now doubt the the centre of the wall is solid stone but is rather rubble infill between the outer stone. My question is: do I need to build engineering brick supports for the lintel?
As a structural alteration this question should be put to the building control officer of your local planning dept but the general practice is to insert concrete padstones on the ends of the wall to make sure the load is carried equally over the full width of teh wall. The padstones are usually 100mm thick and extend back the full length on the lintels bearing which in all cases should be an absolte minimum of 150mm. Please check this advice with your local authority as, if the wall in question is on dubious foundations they may insist on much more bearing each side.