Full fill cavity

[DannyT]

Hello.

we have our plot purchased in the mull of Galloway and have just had our first meeting with the architect. 
Looking at block construction as I’m a bricklayer and that’s where my cost savings will come in. Mentioned to the architect I’d like building clad to allow full fill 200mm knauf eco therm 32 batts in cavity. 
He is adamant that we have to maintain a 50mm air gap and use rigid boards. Doesn’t matter if rendered or clad.

I know as a bricklayer how hard rigid boards are to fit without gaps, even if I was doing it.

 

Anyone have any advice on this with latest regs etc? Can I use eco therm 32 with their BBA certification?
Im used of building in England so Scottish way is new to me.

 

Thank you

Dan

[Moonshine]

We did 150mm ecotherm batts fully filled, with render.

 

Building control and architect were fine about it.

 

Only think I would say is I am in the south West, as you could it be an issue with wind penitrating rain?

 

Have a look at the building regs, lso maybe worth a chat with the local building control officer.

 

This document only recommends full fill in sheltered areas

 

https://www.gov.scot/publications/building-standards-technical-handbook-2019-domestic/

Edited June 16 by Moonshine

[DannyT]

Thanks for your reply moonshine

 

Im going to send building control a email

over next week to see what their thoughts are.

With regards to wind penetrating rain, I would have thought a cladded exterior would deal with that as the air gap would be between cladding and outer skin of block. 
we are classed as severe (3) on the uk map. 
Just found a interesting article to argue a case though.

https://www.labc.co.uk/news/full-fill-masonry-cavity-walls-and-exposure-wind-driven-rain

 

Full fill is definitely something I want to push. I believe a much better wall u value can be achieved for the same cavity thickness. I’d rather sacrifice design over using rigid PIR boards and tape.

 

Thank you

 

Edited June 16 by DannyT

[nod]

As a bricklayer the Architect probably knows less about cavity’s than you 

He should have another look on Google It really is personal choice 

We’ve done both methods 

Seven years back we changed to full fill mid build Due to lack of availability after a fire wiped out the factory that makes the fidget boards in Germany 

Which ever way you go BC will only care that it’s installed properly 

 

The Architect is working for you Nog the other way round 

[joe90]

I used the same insulation in a 200mm cavity brick outer and full fill and as you say it has a bba certificate, the bricklayer was not convinced but didn’t argue and BC were fine with it. It was a fairly exposed location and the western wall facing the coast got soaked. When core drilling the wall for the ASHP I found the outer wall wet through but the insulation did not wick anything into itself. I did coat the one wall with waterproofer after but to protect the bricks more than the insulation.

[torre]

6 hours ago, DannyT said:

He is adamant that we have to maintain a 50mm air gap and use rigid boards. Doesn’t matter if rendered or clad.

I know as a bricklayer how hard rigid boards are to fit without gaps, even if I was doing it.

 

Did they explain why? You've a long journey ahead with your architect, at this early stage you'd hope they'd be listening to your point of view in an area where you've expertise and experience.

 

For me as a client it's important to know that an architect or builder is going to listen to what I want and, if something really doesn't work, explain why when suggesting another approach.

[JohnMo]

7 hours ago, DannyT said:

He is adamant that we have to maintain a 50mm air gap and use rigid boards. Doesn’t matter if rendered or clad.

If architect will not or can't explain why, find an architect who you can work with.

 

The architect should be able to produce a U value and interstitial condensation report quite easily, to show you the issues (if there are any). Another option is full fill poly beads, which give a self draining cavity 

[DannyT]

Thank you for all your replies.

 

Ill take on board suggestions.

First on the list is going to be to contact building control for their views on this matter.

Secondly I’m going to drop the architect a email thanking him for the initial sit visit. I will then outline my reasons why I’m “adamant” I want full fill and he can come back with his reasons. However “the planning don’t like it around here” won’t cut it for me.

This house needs to be done right first time.
As far as I’m concerned, what ever is calculated for PIR in a cavity is way exaggerated. 
As joe90 also said, we also used ecotherm 32 on my uncles self build and that’s exposed to driving rain in Staffordshire with no Negative effects.
I’ve been a bricklayer for 23 years, mainly on the mass produced house builder sites and I’m determined to build beyond the “norm” like many on here. I hate working on the poorly insulated and badly designed houses I build. 
It’s just a bit daunting going from the English regs to Scottish and their way of doing things.

 

Thanks again

Dan

 

I have included below the 2 different wall build ups but I’ll start a new thread in correct section for that discussion.
Close on paper though but I’ll never be convinced the PIR partial fill will ever be close to those figures in reality. As well as cost and time negatives over full fill.

 

 

 

 

 

[joe90]

1 hour ago, DannyT said:

However “the planning don’t like it around here” won’t cut it for me.

Insulation is not a planning matter it’s  a building regulations matter 🤷‍♂️

[DannyT]

So I have just finished a conversation with BC in Dumfries.

He says it’s been a while since anyone did block and block construction as all timber framed now.

I explained my reasons.

He says nothing is off the table as long as I can prove a product meets the regs, can show them a BBA certificate that will prove it’s fit for purpose and show condensation calculations.
Did say though that he doubts I’ll be able to find anything that won’t allow driving rain through hence why it’s standard for a 50mm air gap.

Im just going to look at knaufs info whilst banging my head on a wall!

[Moonshine]

12 minutes ago, DannyT said:

Im just going to look at knaufs info whilst banging my head on a wall!

 

https://www.knaufinsulation.co.uk/products/dritherm-cavity-slab-32

 

Quote

Holds an Agrément certificate by the BBA for use in all exposure zones, including those in very severe areas.

 

Just phone the technical department (01744 766666 ) and ask to be emailed the certification, send that to the BCO, get them to confirm its acceptable in an email. Send that email to the architect, then crack on.

Edited June 17 by Moonshine

[joe90]

1 hour ago, DannyT said:

Did say though that he doubts I’ll be able to find anything that won’t allow driving rain through hence why it’s standard for a 50mm air gap.

It’s about its ability to NOT wick any moisture (like I posted about earlier).

[ADLIan]

Even if a cavity batt product is Certified for use as a full fill insulation in any exposure zone there are caveats that should be read, normally in conjunction with the Building Standards, Approved Documents and associated British Standards. Wall may need to be rendered or clad in more exposed locations.