Best blocks for outer skin

[MattPope]

Extension walls going up nicely. The ground floor is brick face and the second floor will be rendered. There is also a parapet wall to be made of block and rendered on the first floor of the extension.

The builders have asked which type of blocks I will use - the SE calcs simply show 4N blocks. I have read elsewhere here that lightweight blocks don't render as well. I guess the inner skin should be lightweight blocks

On a slightly different note, which blocks should I use for internal loadbearing walls and blocking up windows?

Thanks as always,

Matt

 

[noseall]

Fibolites or hemelites render nicely and are still easy on the arm but are 3.5N. Any good?

Either of the above are adequate for load-bearing situations, but would require engineered masonry for point loads.

 

[theoldun]

No such animal as 4N block.
Nearest is 3.6 or 4.2N
If you wish to comply with current U value of 0.28W/m2K, then state your present cavity width and current cavity insulation that you are using.
Regards oldun

 

[MattPope]

We have a 100mm cavity and full fill insulation. At present the builders are lined up to use thermalite shield blocks which seem to satisfy the structural and thermal insulation requirements and but how well do they render? Another part of the house was built from thermal blocks and have cracked.

There is a 2 block course parapet wall to go around the top of the extension. Is it worth sticking with the same blocks or an aggregate based block?

How about blockwork for internal walls? No thermal insulation requirements so better to have aggregate based blocks?

Thanks again.

Matt

 

[^woody^]

Don't people specify these on plans any more, and don't building control check?

If you have paid an engineer for this, then perhaps call him up and ask him why he has short-changed you. If things go wrong in the future and you want to make a claim against the engineer or builder, then you need to know who to blame rather than making the decision yourself

There are several factors relating to choice of appropriate blocks, and its not just about u-values

 

[MattPope]

Just to close this thread. The drawings show 4N blocks but no further detail. Spoke with building control and SE and this seems of little interest. I'm surprised that this is so lax from both sides.

The builders will work with 3.6N Thermalite Shields and hopefully these will take render well enough and will deliver a decent thermal performance.

I would have preferred to have used aggregate based blocks for the parapet wall - just seems these are a bit more durable.

Thanks for the advice.

Matt

 

[simonjay]

Just to close this thread. The drawings show 4N blocks but no further detail. Spoke with building control and SE and this seems of little interest. I'm surprised that this is so lax from both sides.

The builders will work with 3.6N Thermalite Shields and hopefully these will take render well enough and will deliver a decent thermal performance.

I would have preferred to have used aggregate based blocks for the parapet wall - just seems these are a bit more durable.

Thanks for the advice.

Matt

Maybe too late now, but I would never build an external skin from aircrete blocks. And definitely not for an exposed parapet. Just too light weight.
Thermal cracks on a tied in internal skin is not of much consequence, but on a parapet ...

 

[^woody^]

A parapet won't be any more prone to thermal cracking with these blocks.

 

[MattPope]

A large number of dense blocks have appeared on the driveway so that's the way I'm going. Hope this makes some sense - just seems a bit tougher than the thermalites.

Next up - decide on coping stones for the top of the parapet wall.

Cheers.

Matt