Max cavity size before engineer needed

insular1

I was just reviewing insulation options with a friend who is also in design phase for a new build. He was saying they're planning a 175mm cavity with 150mm partial fill insulation.

Firstly I'm pretty sure I read somewhere that any cavity over 150mm had to be certified by an engineer but he tells me he has not hired one and does not plan to as his architect said it's not needed. Is this true? Can anyone point me to the regulations where this is covered?

Secondly that would only leave him an air cavity of 25mm. Is this way to little? Can anyone point me to the regs around what air cavity is needed for partial fill?

Thanks in advance!

Calahonda52

AFAIR, its in Eurocode 6. (IS EN 1996)
Just get you pal to ask Architect is he complying with Eurocode 6. (IS EN 1996)
I doubt it as he is not in a position to design one unless he is a structural engineer
The issue is that once you go beyond 150, the ties need more design including the type and frequency because the walls are no long treated as one wall.

insular1

Thanks a million! Googling those now.

Johnnyhpipe

Cavity width aside - who is designing/certifying the rest of the structural elements if there is no engineer involved?

Is the architect capable of undertaking structural analysis and design calculations? Does his PI cover same?

Just curious.

Gumbo

insular1 wrote: »

Secondly that would only leave him an air cavity of 25mm. Is this way to little? Can anyone point me to the regs around what air cavity is needed for partial fill?

Thanks in advance!

I won't answer the cavity width questions as there's nothing more I can add to Hondas post. He is 100% correct.

I can comment on the air cavity. There is no regulation to keep the cavity. He would be better off using a 150mm cavity and fully filling it with xxtratherm full fill insulation of he is going down that route.

insular1

Johnnyhpipe wrote: »

Cavity width aside - who is designing/certifying the rest of the structural elements if there is no engineer involved?

Is the architect capable of undertaking structural analysis and design calculations? Does his PI cover same?

Just curious.

That's what I was wondering too! But he's going with a building contractor and is under the impression the contractor will provide sign off or hire an engineer to do so.

kceire wrote: »

I can comment on the air cavity. There is no regulation to keep the cavity. He would be better off using a 150mm cavity and fully filling it with xxtratherm full fill insulation of he is going down that route.

Yeah that's exactly what I was saying to him as thats what I'm planning on doing! Unfortunately my engineer is out of the office for the rest of the week and I was unable to ask him so thought I'd seek wisdom on here. The rationale his approach is that it would be cheaper or the same price to go 175mm partial fill than 150mm full fill while allowing the option of pumping the cavity later on if he wanted to beef up insulation.

insular1

Ive been digging through that eurocode 6 and can't find anything specifically limiting cavity size, but it's quite possible I missed it. However some more searching and I found a few documents stating limiting cavity width to 150mm per "I.S. 325 Use of Masonry Parts 1 and 2" I can't seem to track down a copy of this online. Any idea where I could get it or is it an older standard superceded by the eurocode 6?

He's also just told me of a mutual acquaintance who apparently built 200mm cavity and fully pumped it. He's involved in the building trade and went direct labour, no architect, no engineer!! Is that even possible? How could he have gotten that approved or signed off or is that only an issue if you need mortgage sign off? I'll be taking to him over the weekend to find out the truth in this!!

Gumbo

insular1 wrote: »

Ive been digging through that eurocode 6 and can't find anything specifically limiting cavity size, but it's quite possible I missed it. However some more searching and I found a few documents stating limiting cavity width to 150mm per "I.S. 325 Use of Masonry Parts 1 and 2" I can't seem to track down a copy of this online. Any idea where I could get it or is it an older standard superceded by the eurocode 6?

He's also just told me of a mutual acquaintance who apparently built 200mm cavity and fully pumped it. He's involved in the building trade and went direct labour, no architect, no engineer!! Is that even possible? How could he have gotten that approved or signed off or is that only an issue if you need mortgage sign off? I'll be taking to him over the weekend to find out the truth in this!!

Your doing a lot of research for your 'friend'.
I've come across these wider cavities and I always request engineers certification to say they have inspected them, designed the walls accordingly and are satisfied with the constrcution in site.

insular1

I don't want to see him get shafted to be honest. Plus I kinda went out on a limb and told him he wouldn't be allowed do that without engineering sign off and he could get in trouble. But now I'm not sure!

I'll report back what my engineer says when I get in touch with him next week and what the fella with the 200mm cavity did if I get to talk to him over the weekend.