If i read this correctly you need to make a hole in your what was originally your exterior wall or your new exterior wall, either way it’s an exterior wall yes?.
Not at all familiar with US building practice but at any rate external walls of any construction are not something to mess about with unless you know what you are doing for two reasons:
- It’s probably two leaves either side of a cavity. Not a huge problem but does make it more awkward.
- Unless you have some very unusual house construction then it’s pretty much a given thats it’s loadbearing.
Now of course it’s possible to make a hole in a loadbearing wall, however depending on how big the hole needs to be it can be pretty complicated. For a small hole then chances are the existing brick/block work will be capable of ‘arching’ somewhat. That is to say that a few block can be removed without any supports being put in place and the wall will still stand fine.
If it’s a larger hole thats required then what needs to happen is something called a ‘slapping’. The arching effect is exploited to make several small ‘pockets’ (holes) through which ‘needles’ (normally steel beams) are placed. The tops of these beams are then packed (or in heavy duty applications actually jacked) up against the underside of the pockets. The wall beneath can then be removed with the wall load now arching onto the beams instead of the brickwork between them. After the wall is removed as required, a lintel can be placed and the wall above built back as required, the needles removed and the pockets infilled.
Sounds simple when you say it quick enough but this is definately one of the riskiest operations in building for my money. Especially when you are dealing with older buildings. I was once involved in a huge slapping on an old Georgian building in Edinburgh. These building have walls three feet thick of solid sand stone and we were opening up the entire frontage of the building. Boy did that make a noise when we jacked up what, maybe 500 tons that hadn’t moved for about 200 years. The jacking actually raises it by a fraction of an inch. Anyway, i digress…
Regards your first question. It will depend on a lot of factors, mainly wall construction and design but i’d guess the new external wall is probably less heavily loaded than the original (which presumably takes full load of roof, upper stories etc?). Also, may be of a construction that is easier to get through? On the downside it would require to be left in a weatherproof state.
As to your third question, you can use a circular saw on the mortar joints or just chisel away at them if they are wide enough, or smack the blocks with a hammer. I suspect you wont find this as hard as you imagine and it becomes much easier once the first block is out.
BIG DISCLAIMER - In case it isn’t obvious from what i’ve said above, this isn’t likely to be an easy job and the actual facts of what will and wont work will depend hugely on various factors that an engineer would need to see first hand so i really wouldn’t recommend you tackling this unless you are really sure what you are doing. You may get away with just punching a few blocks out, wriggling through the gap to do your work and just leaving it at that. On the other hand you may cause a major collapse or at the very least significant damage to your house.