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How many blocks do i need to build a extension 3.5mx3.5m x 2.4mhigh with a cavity

7 Answers from MyBuilder Bricklayers

Best Answer

Hi, the amount of blocks you would need ,would be 588. its 10 blocks per square metre.

3.5 x 3.5 = 12.25m (lenth)
12.2 5x2.4 = 29.4 m (lengh x height)
29.4 x 2 = 58.8 m (x2 for cavity so two skins)
58.8 x 10 = 588 blocks (x10 -10 blocks per squre metre)

Also add 5% for wastage.


Answered 28th Feb 2011

standard blocks are 450mm x 225mm high so its 10 to a square mtr. so i expect your extention has 3 side so 3.5 trs x 2.4 mtrs = 8.4 mtrs x 10 blocks = 84 blocks x 3 walls = 252 blocks skin x 2 = total 502 blocks. and then you need to take away the area of your windows and door.
hope this helps you.


Answered 28th Feb 2011

I would agree with Tom .
If you get the higher amounts at least you will have some spare blocks to sit your spot boards on.


Answered 1st Mar 2011

520 blocks will cover the job ,


Answered 28th Feb 2011

you would need 50.4 metres=504 blocks less windows and doors


Answered 11th Mar 2011

If i was you i would add another
3.5 +3.5 +3.5 =10.5 length
0.9 depth of footing (depending on ground conditions)
sub total =9.45 x 2 skins =18.9m2
@10 block m2 =189 without waste
call it 3packs @ 72= 216 allowing for waste,

unless your not having any footings on your extension.
Even better get someone who knows what they are doing to come round and have a measure up unless it probably will cost you in the long run.


Answered 20th Mar 2011

10 blocks per m2


Answered 18th Mar 2011

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