Lintel advice please

[walkingman]

I need to install two lintels in the front wall of my new garden building for the door and window. The building is constructed of 140mm dense 7N concrete blocks in a single leaf. There will be one layer of blocks above the lintels. 7x2 roof joists plus firrings spanning 3.6m will sit on those blocks supporting a forward sloping, flat (3 degrees) roof of plywood deck, insulation, and metal box profile sheeting. The window gap is 1860mm and the door 810mm.
I propose to use 140mm wide concrete lintels 2.4m in length for the window and 2.1m for the door. My depth choices would appear to be either 100mm or 140mm.
My question then is would 100mm depth easily cope with the load or should I go for the 140mm?
Any and all help much appreciated.

 

[tony1851]

You need to check whether these are 'composite' lintels or 'non-composite', as there is a difference.
Composite lintels are intended to be built in with several layers of block/brick above, which work together with the lintel and give it additional strength. With non-composite lintels, that doesn't matter.
Personally I would go for the 140. Concrete lintels are not the most reliable of components and can easily crack if mishandled; this is less prevalent with deeper lintels.
(Do you need a 2.1m lintel for the door or was it to be 1.1m?)

 

[walkingman]

Thanks Tony, I think I'll plump for the 140mm, as you say, to be on the safe side.
Sorry that was meant to be 1.2m for the door - dyslexia strikes again!

Are there any other types of lintel you would preferably use in my situation?

 

[tony1851]

Other than use a piece of steel angle (which would be heavy and will eventually give rust stains), can't see any practical alternative to concrete.

edt; just realized, the concrete will of course be heavier! - but stick with that -more practical.