Side Extension Brick Work

[AndyMcG]

I am currently building a small side extension to my house under permitted development.

I managed to lay the foundations and build up to DPC last year before the winter kicked in. I am back on the case now and have a few questions if anyone can help.

The house is made out of imperial bricks and therefore I have used 70mm bricks and matched to the top line of the the houses existing courses (shown in photo).



I am hoping to lay the DPC and then lay two more courses of 70 mm bricks. I am then going to block work the rest of the extension with the intent of rendering the extension and the front of my property. My question is I am using this wall starter to tie in the block work to the house. As the blocks are metric the course levels will be out of line with the existing imperial house brickwork. On an aesthetic level i don't care what it looks like as i have the 6 courses of house bricks matched and inline (which will be shown and below the render) and I will be then be rendering the blocks.

My question may seem silly but is this method correct, using the wall starter and not matching courses? Is there any alternative. Many thanks.

 

[tomfe]

Would you not want to render down to the dpc, so you can just use blocks above dpc.
Wall starter above dpc and it does not matter about matching the courses as it won't be seen.

 

[AndyMcG]

Thanks for the reply.

I was working on the basis I needed some kind of gap between the DPC and the Base of the render in case some kind of bridging occurred.

Is that not the case? If not then blocks straight onto the DPC would save me some time and bricks.

 

[tomfe]

Stick the dpc out a bit from the wall then when you put your bellcast bead you can go up to this, if needed you can cut it back.
http://www.rend-right.co.uk/wp-content/uploads/2011/08/Durability-6.gif

 

[AndyMcG]

That sounds good. So on my 100mm wide bricks I can use 112mm DPC and leave the 10 - 12 mm spare DPC extending past the face.

The existing house DPC doesn't protrude but as long as my bellcast bead doesn't bridge it i should be fine?

 

[tomfe]

I am sure others will say different, but that is the way I would do it. You can then literally sit the bell cast on the DPM.
For the existing house yes that's fine, just sit the bead above the DPM.

 

[AndyMcG]

Thanks tomfe. I like this post about fixing batons along the existing DPC to allow the bellcast bead to rest onto allow for rendering up to DPC.

One other question. I am building a one storey extension with a 100mm cavity wall. It would appear block makers indicate that a 3.6N celcon block can be used on the internal and external leaves above DPC. People argue for an against this. Does anyone have thoughts or experiences using this approach?

 

[tomfe]

Aircrete block are notoriously difficult to render, however the manufacture does have a method to render them so it 'should' work.
If you use a thin coat render with mesh and a suction reducing base coat I can see it working. However you do run the risk as many spreds don't like to work on it.
I presume you want to use an aerated block due to it's thermal performance can't you use the money saved in using a light block and upgrade insulation?

 

[AndyMcG]

The existing house brick work has been painted several times over the years so I was thinking of meshing that in order to render it. So I will probably end up using a mesh system on the extension and the existing house and then rendering the lot.

The main reason I thought about using Aircrete blocks for both leaves was for ease of lifting, cutting and laying. The insulation was going to be a slab rock wool type.

Would you mind recommending a block type for the inner and outer leaves of the cavity wall?

 

[tomfe]

If you are using Jewsons that celon block is fine for inner leaf, (I think they have YTongs in stock as there is a short on aerated blocks)
Outer leaf I'd just go for a light concrete block, fibolite etc they weigh around 9kg so not that much more than an aerated one and it will save you around £2 a metre. Just buy a cheap angle grinder if you've not already got one to cut them with.

 

[AndyMcG]

Thanks will be ringing the Merchants tomorrow to place my order in time for a Bank Holiday week of work, Thanks again tomfe

 

[AndyMcG]

Here is update. I ended up using the 70mm bricks for the two courses above the DPC as I had tons left over and thought i may aswell use them.

Can anyone advise on Regs for building out from the house before an opening (is there a minimum width of brick /block? You can see from the Image I have started an opening for the window. The brick work will be tied into the Wall starter but how do I carry on up?

Forgot to say, Its only a single storey extension, using a catnic cavity lintel above window.