New doorway in Masonary block wall

My home is elevated at the front and has a garage underneath (at ground level) that is constructed of masonry blocks (old style besser blocks I think - they are not solid concrete blocks) with an in-situ cast reinforced concrete roof (approx 200mm thick) and part of the house is built on top of that in-situ slab.
I want to put a 1200mm doorway in one of the garage walls and will need to remove some of the concrete blocks, this will require steel lintels etc. I have done some research but my situation doesn't seem to fit any standard senario's provided by steel merchants etc.
I was intending to use two 150x100x10mm standard gal angle sections, would this be adequate?
I suspect that this probably significant overkill for the situation but it's better to be sure than sorry!

I did a bathroom reno (split old bathroom into two and added a ensuite) in a block house and cut a 720 mm door in. I got a 1200mm lintel from buntings (galv 5mm thick), brought a steel door frame from Spence doors http://www.spencedoors.com.au (also available at buntings). the block thickness was only 100mm but that shouldn't make a difference.

Process I did was roughly this.

1. checked wall and found two pipes routed in doorway. rerouted plumbing
2. made up a plastic tent so that fine mortar dust didn't go everywhere
3. donned a mask (P2 rated halfface)
4. hired wet saw and marked out and cut block passage.
5. knocked out blocks (king big hammer)
6. after predrilling lintel for door frame head holes, cut in lintel along an existing mortar line in approx half a block width so that the lintel sat over the middle of a block in the head flush down on the block. also recessed the lintel so it didn't sit proud on wall face.
7. industrial adhesive (sikaflex), put in a temporary door head (75mm upright studs with a pine head, slightly narrower than width) and waited for it to go off.
8. mortared (with plasticiser/pva) over the gaps and filled in any holes
9. fitted steel door frame and put in csk dynas to secure to blocks (door comes with these holes already in)
10. after priming the door frame, hung my $25 internal hollow core door (keeps the weight down).
11. got a chair and a beer and sat down and admired my work.

took me about 2-3 days including waiting time.

try and make the hinge side of the door frame along the vertical edge/joins of the blocks on one side. this gives a secure base to dyna the frame to.

as long as the wall isn't structural/load bearing and you're not taking out a pier, things should be fine.

mine was 100mm block. if you're doing it in 200mm block, maybe you can slot the lintels into the middle of the block cavity and back fill with mortar somehow? (might be a bit tricky) I'm pretty sure when they build they put them in as they go and mortar across the top. I'm no brickie.

anyway see how it goes, snap a few shots and maybe the gurus here can have a crack (i'm no guru)

cheers

Sounds like enough to hold up the Opera House but it depends on the load, any point load & the number of courses obove the lintel.
i.e. the distribution of the load [if any] above the opening.

As Ausdesign says the load is really going to be the block work that remains sitting above the new lintel level. With an opening of just 1200mm the concrete floor/ ceiling would stay put if all blocks were removed to make a an opening that wide (and wider too if it was properly constructed with appropriate steel reinforcing).

It will be best to place the lintel across an existing mortar line - so at the next one above the height of the opening you are after. Remove the mortar from between the blocks and make sure you extend over the sides of the opening by at least 1/2 a block (ie: ~200mm) - so the length of you lintels will be 1600mm if the opening is evenly spaced at a half block. Do one side and insert the lintel then do the other side - when both are in pace you can cut down the sides of the opening and remove the blocks below the lintel.

The sizes you suggest are probably overkill. You would be OK with a single lintel using the 150mm on the flat and simply remove the mortar from the inside to a little more than the depth required knock the lintel into place then remove the blocks below. I have used plastic wedges to hold the lintel in place (internal only - they don't like UV exposure) and cast zinc alloy axe/ hammer handle wedges on external uses. If fitted properly they should be tight fit anyway.

Unless you are close to the coast and get direct salt spray etc you don't really need gal either. Standard structural steel with a good coating of red or grey steel primer will last for 40 years or more.