Block type for bricking up garage door

[ThamesValley]

I have a detached single leaf brick garage which I'm converting into a home office. It dates from the 1930s like the house I think. It has an up and over garage door with a solid oak(?) lintel. There are piers on either side os the opening - the left one in parallel with the front which means there are two courses where the opening is. The opening is off centre, so on the right side the opening is up against the straight wall, there is no corner. The pier there is in line with the wall, so there are two courses for the first 500 mm or so.
The opening itself is 2350 wide and 2240 tall. I'd like to put a 920 wide UPVC door on the left, so about 1400 wide masonry to brick up. The DPC is about 120 above the floor slab, so I was thinking a block on its side (100 plus 20 mortar bed), then a DPC and then tie the new blockwork into the wall with a wall starter.
The concrete base slab is about 150 thick I think - hopefully strong enough to support a one leaf blockwork? Would 3.6N Aerated block work for this? I would render it to match the rest. The weight of an aerated block is 7.5 kg and I think I'll need about 30 of them, so that is 225 kg plus mortar.
Thanks for your advice.

 

[Notch7]

If you are doing the conversion under building regs, then I’m not the BCO will allow you to build off a slab.

If you aren’t, then you can do what you like, but bear in mind the stability and load bearing capacity of the slab is dependent on the ground beneath.

 

[noseall]

I have a detached single leaf brick garage which I'm converting into a home office. It dates from the 1930s like the house I think. It has an up and over garage door with a solid oak(?) lintel. There are piers on either side os the opening - the left one in parallel with the front which means there are two courses where the opening is. The opening is off centre, so on the right side the opening is up against the straight wall, there is no corner. The pier there is in line with the wall, so there are two courses for the first 500 mm or so.
The opening itself is 2350 wide and 2240 tall. I'd like to put a 920 wide UPVC door on the left, so about 1400 wide masonry to brick up. The DPC is about 120 above the floor slab, so I was thinking a block on its side (100 plus 20 mortar bed), then a DPC and then tie the new blockwork into the wall with a wall starter.
The concrete base slab is about 150 thick I think - hopefully strong enough to support a one leaf blockwork? Would 3.6N Aerated block work for this? I would render it to match the rest. The weight of an aerated block is 7.5 kg and I think I'll need about 30 of them, so that is 225 kg plus mortar.
Thanks for your advice.

Surely you will be building the outer course in brick? Regardless, the (visible masonry below DPC) would be brick, render or no render, as this will still be visible.

 

[ThamesValley]

@Notch7 I'm not planning to make it habitable but I will try to follow modern insulation standards as per building regs.
I'm assuming these lightweigh blocks can be rendered OK? Wickes sell Tarmac Toplite Standard as their lightweight blocks and I'm thinking of using those if they'll take normal render.

 

[Ivor Windybottom]

Nobody can say whether your floor slab can take the weight. It's unlikely to collapse spectacularly, more likely you'll get big cracks in the render where it moves. I pulled up my garage floor and found nothing but fresh air under it - the original soil had sunk so the concrete was spanning the gap between the walls.

You really should dig a foundation and build it properly. Rules are there for a reason, mostly to protect you from yourself.

If you really want a botch job then build a timber frame and clad the outside. Perhaps inset it slightly and use a different surface finish, with flexible sealant where the panel meets the original wall. This is what we have, plastic planks on the outside, done by previous owners. Looks terrible, but less awful than cracked and collapsing masonry.

 

[ThamesValley]

I take your point but with lightweight blocks the weight of 250 kg say (with mortar) would be less than a car driving over the slab?

 

[Notch7]

@Notch7 I'm not planning to make it habitable but I will try to follow modern insulation standards as per building regs.
I'm assuming these lightweigh blocks can be rendered OK? Wickes sell Tarmac Toplite Standard as their lightweight blocks and I'm thinking of using those if they'll take normal render.

my apologies I didnt notice that it is detached

You can take a chance it might not move, its not so much about the weight as the chance the ground will cause movement. light weight blocks would be ok from a weight point of view but theres always a chance of cracking.

You need to pay attention to detailing the damp arrangement if you dont have a cavity wall -that applies to the new wall and the other singles

 

[freddiemercurystwin]

I take your point but with lightweight blocks the weight of 250 kg say (with mortar) would be less than a car driving over the slab?

It makes you wonder why they bother with foundations at all.

 

[noseall]

I'm assuming these lightweigh blocks can be rendered OK? Wickes sell Tarmac Toplite Standard as their lightweight blocks and I'm thinking of using those if they'll take normal render.

Yes they can be rendered, but not down below DPC. The masonry showing above the finished external level and below DPC WILL BE VISIBE and needs to be showing pointed brickwork.

You will need a concrete foundation. Building off an old slab is bonkers, unless its is and engineered raft. Imagine the fun you'll have if ever you need to break some of the floor away.

 

[^woody^]

150mm slab should be fine for building off as you propose. Block bonding to the existing would be best not not essential, otherwise use fishtail ties not wall starters.

A single leaf wall is not ideal for a door, and piers should be built at the jambs.