What to use when building external wall for render

[Grant]

Having watching tonnes of YouTube videos, I’m starting to feel slightly more confident about the extension I’m planning to build myself  - however I’m unsure about what blocks to use.

 

the house is fully rendered already, so the extension will be rendered also. Does this mean I can build both internal and external leafs in block, rather than having to use engineering bricks and face bricks? 
 

should I use dense block below DPC and aerated bricks above DPC?

 

thanks for your help

[Russell griffiths]

Do not use aerated blocks externally, they are really crap, I personally would not use them inside either. 

Dense concrete under damp proof course, light weight aggregate block above dpc. 

 

If you are building this yourself and dont have much brickwork experience, have you thought about ICF. 

 

[Grant]

Thanks for the info. That’s super helpful 

 

The extension is fairly small and sits behinds the house in a tight area (comprises of of single storey walls and low level wall for bi-folds to sit on) - so I think I could probably do the Blockwork in a week/2 weeks (bricklayer would probably only take a 3 or 4 days). I’d worry about ICF and getting the concrete to the back of the house.

 

i assume I’d lay the DPC tape on the external leaf exactly the same as if using engineering blocks? (e.g between the dense blocks and lightweight blocks)

[nod]

49 minutes ago, Grant said:

Having watching tonnes of YouTube videos, I’m starting to feel slightly more confident about the extension I’m planning to build myself  - however I’m unsure about what blocks to use.

 

the house is fully rendered already, so the extension will be rendered also. Does this mean I can build both internal and external leafs in block, rather than having to use engineering bricks and face bricks? 
 

should I use dense block below DPC and aerated bricks above DPC?

 

thanks for your help

 

 

Nothing  wrong with aeriated internal or external 

Millions are used each year in the U.K. Great to render to 

[ToughButterCup]

That's what is brilliant about BH.

A really experienced, time served professional and a no-nonsense builder giving contrasting advice.

 

I -as a Know Knowt- have come to realise that when that happens the answer is -probably - It doesn't matter.

 

Except it does, sometimes.

What we need to know is the answer AND why. Please.

[Russell griffiths]

I was just going to say the same, two answers and two different opinions. 

 

I have been and and still am involved in lots of committees where 10 people all have a view, it generally leads to nothing getting done. 

 

What i I have done all my life is talk to one guy and get his opinions, then talk to another and get his, but at the end of the day you have to paddle your own canoe in life. 

So get a couple of opinions and then make your own decision. 

 

What i I would say to @nod is what blocks did you use to build your house from and why. 

[nod]

5 minutes ago, Russell griffiths said:

I was just going to say the same, two answers and two different opinions. 

 

I have been and and still am involved in lots of committees where 10 people all have a view, it generally leads to nothing getting done. 

 

What i I have done all my life is talk to one guy and get his opinions, then talk to another and get his, but at the end of the day you have to paddle your own canoe in life. 

So get a couple of opinions and then make your own decision. 

 

What i I would say to @nod is what blocks did you use to build your house from and why. 

solids on the outside Though I built three pikes up in aeriated 

and aeriated on the internal 

The reason being originally the sap called for a light weight thermal on the inside  very expensive and a lot of waste Now they are week 

The aeriated had a higher had a higher thermal value than solid 

From memory about 20 p each more expensive 

[Grant]

In any walk of life, people will have different opinions to what is best, which is great, as I’m now in a much better position than last night:
a) I now know that using blocks is fine for external walls and I can avoid engineering and face bricks entirely 

b) I’ve been introduced to aggregated blocks - so will investigate these compared to aerated blocks

All the work will need to be signed off by building control anyway, but forums really help with the (often obvious) questions that a compete novice struggles to find answers to 

[Construction Channel]

Generally if we're going to render we build with fibolite blocks (lightweight aggregate), but we would also put 3 courses of bricks below dpc on the external skin (not always engineering, depends what the architect asks for). This is just for looks though as render will generally stop at the dpc height and there will be 2 courses showing before ground level. 

 

We also avoid aerated blocks (celcon) as they have a bad reputation for cracks but they may have improved since they got that reputation

Hth

[Grant]

The house is currently rendered top to bottom - but with the lowest section in a black render.

 

are you saying that I can’t match this, and instead need to have exposed brick below DPC? 
 

attached image hopefully clarifies what I’m working with 

[Construction Channel]

Can't is a strong word. I'm sure there will be a way round it but it's not standard practice to render below dpc as it bridges it. 

Dpc is usually set 2 courses (150mm) above ground level so that rain splash / snow won't reach above the dpc. This can sometimes be overcome with a French drain (100mm wide gravel channel around the building) but all these things will come down to what the BCO will accept. 

[Grant]

1 hour ago, Construction Channel said:

Can't is a strong word. I'm sure there will be a way round it but it's not standard practice to render below dpc as it bridges it. 

Dpc is usually set 2 courses (150mm) above ground level so that rain splash / snow won't reach above the dpc. This can sometimes be overcome with a French drain (100mm wide gravel channel around the building) but all these things will come down to what the BCO will accept. 

this is super helpful! Thank you for the advice ?

[Russell griffiths]

You can render below dpc no problem, but you must show that this render is completely separate from the render above dpc. 

So the bit below will need to finish level with the dpc and you need to show a detail of separation  as I’m sitting here having a cuppa I found you a couple of pics    First pic is the sort of detail you need to achieve, ignore the external insulation as it’s the first pic I could find, second pic shows what it would look like very roughly just to give you some ideas. 

[Russell griffiths]

Just did this as it may be easier to see, depends on my poor drawing skills. 

Lots of details missing but it might point you in the right direction. 

[Grant]

17 minutes ago, Russell griffiths said:

Just did this as it may be easier to see, depends on my poor drawing skills. 

Lots of details missing but it might point you in the right direction. 

A picture like this is exactly the sort of info I was looking for online. When I speak with building control, I’ll ask if this is possible, as the ‘full render’ look was what I was hoping for, giving the style of the house 

 

thanks Russell

[Pocster]

Even I used the Thermalite blocks .

Easy to lay and easy to cut . Got it dead straight and flush . As I’d never done it before looked a bit rough . Once rendered ( k rend type thing ) looks spot on !

Edited January 12, 2020 by pocster