Garage expansion with concrete panels

[crispy]

Hello all.

I'm planning a garage upgrade this year and could do with some pointers as I'd like to do a lot of it myself if possible including working out the costs in advance where posible.

 

My existing garage is on a 6x3m slab and I have the space to extend it by 3m or more into my garden and out to 5m wide to the property boundary.

For budget reasons, I only want to add to it, not remove and replace it.

 

I have already bought nearly enough concrete pebble dash panels and want to set them on a single course of blocks to give a decent headroom.

 

First question is how do I calculate the correct block to take weight? 

The blocks I'm looking at have a load rating of either 3.6N/mm2 or 7.3N/mm2. Is it just the actual weight of the walls and the roof plus a bit for safety or something more?

 

Secondly, I have what I can only describe as a brick chimney in the garden which could limit how long the garage can be. It's about 1.8m deep and has an in and out pipe that only ever seems to flow a small amount of water, fortunately not under where I'm planning to build. The manhole cover and surrounding area of about 4x5m is about ½m above the garage floor level. My local water company don't have it on their plans, even though the house was built in the 1960s.

Any advice on how close I can put my new slab to it without any issues?

 

Thanks in advance. 

 

 

[crispy]

Any advice or opinions gratefully received 

[ProDave]

Some pictures of what you have might help.  Trying to understand how you widen and lengthen a garage without knocking any of it down?