Process for building a cavity wall with insulation

[oliverdupuy]

Hi everyone

I'm new here so thought I'd firstly say hello. I'm a wannabe DIYer, in the early stages of trying to build an extension on the front of my house, so doing lots of research. I will be using professionals to do some of the work, but I'm really keen to find out as much as I can about the process so I can do as much DIY on it as possible, and take on a some experience for the future. Hopefully some of you kind folk can help point me in the right direction on a few things, and hopefully I'll also be able to help a few other people once my experience level goes up a bit!

I'm through planning permission, which wasn't too much of a drama, but now into the far more complicated world of building control. So I've been learning all about foundations, cavity closers, wall ties etc!

My build is relatively simple. My neighbours have a front extension already, and I'm just looking to come out to match what they've done (pic below).

I've been reading the building regs and understand I'm going to need wall ties and insulation in the cavity, and I've been researching how it gets constructed. It looks like the inside leaf gets built up a bit, then the insulation is added, then the outer leaf is built up to the same level as the inside leaf, and then the process starts again. Is there a kind of standard as to how much of the inside leaf gets built before the outer leaf is built up to match it?

And if the inside leaf is built up with the wall ties mortared into it, how does the insulation attached to the inside leaf? Does it need holes drilled into the batt so that the batt slides over the wall ties?

And finally, the outside leaf on one side will be my neighbours existing brick outer leaf, so our inner leaf will need to be tied into that. I gather there are wall ties I can attach to the existing leaf by screwing onto the brickwork, but how does the insulation get fitted into the cavity? Does it slide over the wall ties once they're screwed onto the existing leaf, then just get pushed flush with the inner leaf once it's built to the height of the batt? Does the insulation need to be attached to the inner leaf (e.g. with adhesive) or just pushed flush?

Thanks and sorry for so many questions on my first post!
Oli

 

[noseall]

Outer leaf - inner leaf?

Depends what method of insulating the cavity is preferred as to which gets built first. It's more practical either way to set out the brickwork and the subsequent openings first. However, partial fill cavity build does not allow this.

We generally build up to lintel height then back it in with blocks. Small brick panels sometimes require propping/securing whilst curing especially when the weather is like it is today!

 

[oliverdupuy]

Thanks! It will be a partial fill cavity with the batt flush against the blockwork, so I guess blockwork first, up to lintel height, batt on and secured, and then brickwork?

 

[noseall]

Thanks! It will be a partial fill cavity with the batt flush against the blockwork, so I guess blockwork first, up to lintel height, batt on and secured, and then brickwork?

Correct. Partial fill is not DIY friendly. It's not even skilled bricky friendly!

 

[garyo]

I've never really grasped why anyone uses partial. You don't seem to save any meaningful space by the time you include the cavity, or get a better U value, and the chance of it being badly implemented seems significantly higher than with cavity bars.

 

[^woody^]

I've never really grasped why anyone uses partial

Exposure, damp issues, longetivity, performance.

 

[noseall]

I've never really grasped why anyone uses partial.

Me neither when you consider that the full fill cavity batt suppliers guarantee their products are water repellent etc.

 

[stuart45]

Given the choice I would go for batts. Never had any problems, even living in an area of loads of wind driven rain.