Brick House, Block Extension, Rendered - Will It Crack ?

[Renovation]

I have a brick house which I am moving windows, infilling doors etc and as it's old I cannot get an identical match plus it has three different types of brick used. I am also building a 4m x 6m first floor extension.

My cunning plan is to use blocks then render (modern self coloured) the lot.

Will mixing bricks and blocks below the render cause cracking due to differing thermal expansion ?

I intend to use the 7N Stranlite throughout.

http://www.plasmor.co.uk/html/products/plasmor-pro...

Thanks

Edited by Renovation on Monday 20th October 23:16

[B17NNS]

I wouldn't mix Thermalite (or similar lightweight) with concrete or brick and then render. Id do the addition in concrete and infill your window openings/alterations in brick.

Re. the rendering take a look at the building regs. You may need to insulate to comply.

[TA14]

Why not just use bricks for all of the external leaf work and avoid the issue?

[037]

Use concrete block!

[Renovation]

B17NNS said:

I wouldn't mix Thermalite (or similar lightweight) with concrete or brick and then render. Id do the addition in concrete and infill your window openings/alterations in brick.

Re. the rendering take a look at the building regs. You may need to insulate to comply.

The Stranlite is a fairly heavy block (rather than a thermalite that you can cut with a handsaw) or do you mean I need the really heavy dense concrete blocks ?

Why does render affect the need for insulation ?
I intend to do the usual 100mm filled cavity, I'm also improving the house which I thought I could trade against although these days if you touch anything they want it all to be to the latest standards.

Oh - do you mean that if you touch an element they want it to comply - FFS they live in a dream world - if that's the case it simply won't comply.

[Renovation]

TA14 said:

Why not just use bricks for all of the external leaf work and avoid the issue?

I was checking whether cracking was an issue - I've only used all blocks or no blocks before.

You mean render over bricks ? It seems an expensive solution if conc blocks will suffice.

If you mean matching the bricks - I can't - it has to be perfect for the planning consent and there are 3 types - some metric some imperial and ranging in age from 40's 60's 80's

[B17NNS]

Renovation said:

The Stranlite is a fairly heavy block (rather than a thermalite that you can cut with a handsaw) or do you mean I need the really heavy dense concrete blocks ?

You can render lightweights successfully but given the opportunity to specify (from a rendering perspective) I'd go with a dense concrete. I'd advise against mixing the two. Can you not use brick for the infills thus negating the issue?

Renovation said:

Why does render affect the need for insulation?

http://www.planningportal.gov.uk/permission/commonprojects/externalwalls/

[Renovation]

Ok Thanks - the bricklayers will love you !

Yes I've been googling - I remember advising a friend about this a couple of years ago now - I wish I had a better memory.

It has to be rendered to comply with the Planning Consent and there is less than zero budget left so it cannot be insulated.

[Spudler]

Obviously it depends on your Local Authority but not once have I been pulled on usng insulation re the render, and I've done rather a few.
Use concrete block and fibreglass mesh any areas of concern, plain & simple.

[TA14]

Renovation said:

It has to be rendered to comply with the Planning Consent and there is less than zero budget left so it cannot be insulated.

Insulating a wall will have a lot more effect than a floor and you've been jumping through hoops to do the latter.

[EggsBenedict]

it's going to depend on the render to an extent. I have a block built garage that is rendered to match the house. Loads of cracks on the inside walls, none in the render. I can't remember what the guy who did the rendering did, but it was in the makeup of the render as I remember the guy saying that whatever he was putting in was to 'hopefully' prevent cracking later.

[Renovation]

TA14 said:

Insulating a wall will have a lot more effect than a floor and you've been jumping through hoops to do the latter.

I have insulated the walls internally but not to the full spec as I'm unwilling to lose that much space internally and don't have faith in external insulation in the long term.

I probably wouldn't have insulated the floor but it is damp - hence very cold, so it had to be done.

[TA14]

Renovation said:

TA14 said:

Insulating a wall will have a lot more effect than a floor and you've been jumping through hoops to do the latter.

I have insulated the walls internally but not to the full spec as I'm unwilling to lose that much space internally and don't have faith in external insulation in the long term.

I probably wouldn't have insulated the floor but it is damp - hence very cold, so it had to be done.

For future reference note that external inwsulation is better for the building and the occupants so it's best to use it where you can.

[Renovation]

TA14 said:

For future reference note that external inwsulation is better for the building and the occupants so it's best to use it where you can.

When it has a proven history of 30+ years under modern render I'll use it.

I've seen too many "innovative" solutions fail - I'm unwilling to try any until they have been proven.