Extension to Increase Garage Size

[CanIEat]

Hi all. I had a garage door fitted in the opposite gable end of my garage to where the original door was. Instead of bricking up the old door opening, I am going to build a small extension to make the garage long enough to fit my van inside. I have laid blocks on the ground to show the rough layout - see pics.

I've built a few walls before so happy with laying the blocks, but wanted to ask advice on how best to do the footings? My plan is to dig a trench 600mm wide by 600 deep then pour 250mm concrete, reinforced with steel bar. Then lay courses of flat concrete blocks to bring above ground level. Continue building with blocks (upright) to the height of the old door opening. Then finish with a single pitched roof against the wall above the opening.

Does this sound reasonable or anything I'm missing? A couple of other questions... at what height should a DPC be put in? To attach a wall starter to the existing walls is it best to chip off the old roughcast and attach them direct to the blocks?

Thanks!

 

[23vc]

Foundations may need to go deeper and not need mesh. Arguably no dpc required. Yes to hacking off for wall starter. Dont use the thermalite type blocks in the pic.

 

[CanIEat]

Foundations may need to go deeper and not need mesh. Arguably no dpc required. Yes to hacking off for wall starter. Dont use the thermalite type blocks in the pic.

Thanks. I have proper concrete blocks to use, just used those ones to mark it out. Can I use the thermalites further up the wall? It appears that one side of the original door opening might be further back than the other side. What's the best way to deal with that? Cut blocks shorter on one side?

 

[23vc]

If it’s single skin I wouldn’t use thermalites. How’s it further back? the top looks straight and you’d build square to the existing wall

 

[CanIEat]

If it’s single skin I wouldn’t use thermalites. How’s it further back? the top looks straight and you’d build square to the existing wall

Just looks like that as the blocks I've laid out don't meet up. I haven't measured anything yet and just laid them down roughly to get an idea of size, hopefully all is ok

 

[CanIEat]

Was looking at this again today, having marked out where the trench is going. The block corners are square and the blocks are square to the walls either side of the opening. As can be seen in the pic it looks like wall on one side is approx 70mm out of alignment with the other side. Just wondering what the best way to deal with it is. Thanks

 

[Deluks]

Insert a small piece of cut block to make up the difference.
Once you've hacked off the render it might end up being a smaller offset.

 

[robinbanks]

My plan is to dig a trench 600mm wide by 600 deep then pour 250mm concrete, reinforced with steel bar.

Dig 450 and show us a picture of the ground

250 is quite thick; I can't see you needing more than 150 for a single skin, single storey garage

Rebar isn't needed

Rest sounds reasonable

What height is the existing DPC? If absent, 150mm min above finished ground level

If the rough cast is solid no need to chip it off. The mortar will key to it. If it's parting company with the wall, remove it

We don't build with only full blocks, by the way. Nearly every wall built has cut masonry units in it somewhere. You build a wall to the length you want the wall, not a multiple of the length of its constituent masonry units plus mortar perps

 

[CanIEat]

Insert a small piece of cut block to make up the difference.
Once you've hacked off the render it might end up being a smaller offset.

Dig 450 and show us a picture of the ground

Thanks for that - might go for cutting a block shorter on one side rather than inserting a cut piece on the other - as I only need a couple of feet extra space inside the garage and still have to fit the caravan behind it!

Will dig the trench out to 450 and see if I hit solid ground.