Blocks - so many choices! What do you recommend?

kingandy2nd · 2 Jan 2020

I’ve done a search on the forum about which blocks to use, but most of the threads are 10+ years old, so I wondered if things have moved on at all?

We have PP for a double extension, which will be rendered so blocks are the way to go.

7nm foundation blocks will start, with a couple of courses of blue engineering bricks above ground but below the dpc - purely for a nice look before the render starts.

But the actual blocks to use from there upwards is where I’m stuck!

Seems like aerated blocks are suitable for both skins, but lm wondering if lightweight agg blocks might be better for the external skin.

I’m considering attempting the build myself so I’m leaning towards aerated blocks to make life easier...but I do want to get it right, so I’d be interested to hear people’s views on which blocks to use?

Also, I see for whichever type of block there is quite a variation in the price from about £1.30 per block to £3.5 per block (all same sizes)... is there value in not using ‘cheap’ blocks?

Thanks
Andy

23vc · 2 Jan 2020

I wouldn’t go thermalites on the outer skin full stop.
I’ve done the thermalite turbo (long) blocks inner, dense 3N on the outer. Bother manageable weight wise on your own. I know a few people who can’t stand the turbos tho, so could go dense block both skins.
But seen on this forum good things said about “fibolites” (?) recently, think it was from the man who nose all.

I pay about a quid for a standard dense block, more for thermos.

kingandy2nd · 2 Jan 2020

Thanks - will definitely do some research on the fibolites.

^woody^ · 2 Jan 2020

Are you just picking random blocks, or designing a wall to meet required u-values - ie selecting blocks, insulation and internal lining?

kingandy2nd · 3 Jan 2020

^woody^ said:
Are you just picking random blocks, or designing a wall to meet required u-values - ie selecting blocks, insulation and internal lining?

It's a very good question of course Woody. The spec the designer has written is as follows:

To achieve minimum U Value of 0.28W/mÇK
Provide 103mm facing brick or lightweight concrete block with sand and cement render. 50mm clear residual cavity,
45mm Kingspan Thermawall TW50 or 45mm Kooltherm K8
Lightweight block K value 0.11 (Celcon solar, Thermalite turbo, Toplite GTI, Supablock.)
Internal finish 13mm lightweight plasterboard on dabs. Walls to be built with 1:1:6
Cement mortar.

I will design to meet the u-values, however my view is that selecting the correct blocks is the starting point and then I can work the rest of the materials to meet it. Or is that a stupid way of looking at it?

Even if I stuck with the spec's about (concrete block externally, aerate blocks internally) there is still a great variety in actual blocks to use so I'd be interested to know recommendations.

Thank you

cdbe · 3 Jan 2020

There isn't much variety for your inner skin in the 0.11 blocks - it's pretty much those listed, and you would buy the cheapest you can find locally - I used toplite GTi then ran out and managed to find some super blocks at a good price so changed to them (half as long again as normal blocks so quicker to lay). Don't know about the outer as I used brick but would suggest something that render sticks too and is available cheap and local.

Leofric · 3 Jan 2020

kingandy2nd said:
lm wondering if lightweight agg blocks might be better for the external skin.

kingandy2nd said:
To achieve minimum U Value of 0.28W/mÇK
Provide 103mm facing brick or lightweight concrete block with sand and cement render. 50mm clear residual cavity,
45mm Kingspan Thermawall TW50 or 45mm Kooltherm K8
Lightweight block K value 0.11 (Celcon solar, Thermalite turbo, Toplite GTI, Supablock.)
Internal finish 13mm lightweight plasterboard on dabs. Walls to be built with 1:1:6
Cement mortar.

Lightweight aggregate block seems pretty clear for external skin and aerated concrete block for inner leaf

kingandy2nd · 3 Jan 2020

Leofric said:
Lightweight aggregate block seems pretty clear for external skin and aerated concrete block for inner leaf

Thank you I can read it, however I don’t have to follow the specs as long as I meet all the regulations do I?

Lots of ways to skin the cat...so was seeking views on what might make my life easier.

John D v2.0 · 3 Jan 2020

45mm PIR insulation would be a bit random, I'd be surprised if 50mm isn't cheaper. Presumably means minimum 45mm.
Once you go to 50mm you might have a bit more flexibility on blockwork u values.

^woody^ · 3 Jan 2020

I can't understand why you have got someone to specify materials, had the specification approved (or sending for approval) and then are taking about doing something completely different. That makes no sense.

If you are talking about changing blocks, then it will potentially involve choosing between 100 and 110mm blocks, altering the cavity, changing the insulation and changing the internal finish - and then getting that new specification approved.

So why would you want to do that when you've just paid someone to design this and got/get it approved.

kingandy2nd · 3 Jan 2020

John D v2.0 said:
45mm PIR insulation would be a bit random, I'd be surprised if 50mm isn't cheaper. Presumably means minimum 45mm.
Once you go to 50mm you might have a bit more flexibility on blockwork u values.

Thank you. I had found it difficult to find 45mm Insulation locally, so your comment makes a lot of sense!

kingandy2nd · 3 Jan 2020

^woody^ said:
I can't understand why you have got someone to specify materials, had the specification approved (or sending for approval) and then are taking about doing something completely different. That makes no sense.

If you are talking about changing blocks, then it will potentially involve choosing between 100 and 110mm blocks, altering the cavity, changing the insulation and changing the internal finish - and then getting that new specification approved.

So why would you want to do that when you've just paid someone to design this and got/get it approved.

Like I’ve explained, I wanted to make the build easier for myself if I can and there are lots of different blocks (of the same size), so looking for user experiences.

The designer has spec’d this yes, but I’m pretty sure stuff like this is just copy pasted for most builds...I had no input at the time and I value the input from people on this forum if I choose to go down the self build route.

kingandy2nd · 3 Jan 2020

Also the downstairs rooms are a kitchen and garage.

From some of the reading I've done, I believe aerated blocks aren’t good for wall fixings. Therefore wall units in the kitchen and various hooks, shelves, etc in the garage might mean a non-aerated block are preferable for the internal skin?!

23vc · 3 Jan 2020

They can be fixed to fine, just a bit more of a knack to it

23vc · 3 Jan 2020

Or the wall could be battened at the right fixing points rather than dabbed

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Blocks - so many choices! What do you recommend?

Leofric

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