advice needed please

[diy001]

I need some clear advice on cavity wall construction. Im using concrete blocks on inner skin and bricks on the outer. I need help in deciding what insulation to use and how wide i need to keep my cavity.

Thanks in advance.

 

[noseall]

Go with full fill 100mm dritherm cavity insulation batts.

 

[diy001]

thanks for the reply noseall, my friend has some celotex from previous works, which i can get for discounted rate. its 75mm, would this give better insulation?

if i use this then do i still maintain a 100mm cavity and fill with 75mm celotex

 

[diy001]

just like to ad, i'm going to use concrete blocks on the inside but again im at a loss, there seem to be a few to choose from. What block should i go for and what cavity, insulation set up do i need to go with it.

i value your help.

 

[diy001]

anyone?

 

[noseall]

Why use concrete blocks? Your bricklayer will be dismayed.

The most commonly used are aerated lightweight blocks either the cinderblock variety or the celcon type. These are not only easy and quick to lay but offer a greater thermal resistance.

Using P.I.R. thermal boards means having to build the (inner leaf)blockwork first as this sits tight against the blockwork.

There are several ways of building a cavity but all will have the same objective, which is to achieve a u value of say 0.3 W/m²K or to satisfy the latest building regulations.

The method i have suggested is the simplest, quickest, cheapest and is preferred by builders.

 

[diy001]

I'm going to be hanging cabinets etc on the walls, i've read threads on here that recommend concrete blocks in those circumstances.

what i need to know is

A) is it ok to use concrete blocks, please give reasons for your answer

B) If i do use concrete blocks which do i choose as there are few different ones

C) is the 75mm celotex good/ better to use than dritherm full fill.

D) and lastly what cavity set up do i go for when i use concrete blocks 75mm celotex, and bricks. im guessing 100mm cavity with 75mm celotex leaving 25mm residual cavity.

 

[noseall]

A) is it ok to use concrete blocks, please give reasons for your answer

Yes it is ok to use dense concrete blocks. They will take longer to lay and will need to be kept dry and laid in dry weather using a strongish mortar.

B) If i do use concrete blocks which do i choose as there are few different ones

Just ask for a dense solid 7n 100mm block. All builders merchants stock them.

C) is the 75mm celotex good/ better to use than dritherm full fill.

Your main objective is to achieve a certain u value set out in building regulations. Going down the partial fill celotex method means having to build the blockwork or inner leaf first and is fiddly to fit. So comparisons for the two methods i.e. partial fill celotex v's full fill dritherm are that the latter is easier, quicker and means that you can set out and build the external leaf and any openings accurately.

D) and lastly what cavity set up do i go for when i use concrete blocks 75mm celotex, and bricks. im guessing 100mm cavity with 75mm celotex leaving 25mm residual cavity.

Sounds about right. Have a look here.

P.S. unless your cabinets weigh 15 tonnes then you will be able to achieve a decent fixing into medium density blocks. Otherwise all the wall units in the country will be falling off the walls. It is the man and not the block that leads to a poor fix.

 

[diy001]

thanks ever so much Noseall. To be honest I dont know the different types of blocks, i thought there was concrete and aerated. And medium density was just another name for a aerated block.

i have done a U value calculation and it came up as 0.27 is that better then 0.32? sorry if it sounds a little stupid, im just finding it a little elusive, but it coming to me slowly.

 

[diy001]

anyone?

 

[jeds]

Yes, 0.27 is better than 0.32. The minimum to comply with current regs is 0.28.

 

[diy001]

There are several ways of building a cavity but all will have the same objective, which is to achieve a u value of say 0.3 W/m²K or to satisfy the latest building regulations.

jeds im confused

 

[jeds]

The minimum standard used to be 0.30. It was recently changed to 0.28

 

[Norcon]

Go for dense concrete block with 150mm cavity pumped with bonded bead which will acheive 0.2 W/m²K. This will far exceed building regs and it frees up the builder to concentrate on his job.
Laying blocks!
There are wall ties available for 200mm cavity also.

Some people prefer 6" block on the inside.