Full fill in very severe area of driven rain

[Lewis88]

Im soon to be starting my new house build. It is going to block, cavity, block design with a 150mm cavity space. hoping to use a 150mm mineral wool batt full fill, my house design will be rendered however I have two columns faced in natural stone that I believe would count as ‘fair faced’, does this mean that I can’t use 150mm mineral wool batts? If the natural stone will count as fair faced is there anyway to make it not fair faced with a stone facad over the top?
 

I have yet to get the foundation and structural designs finalised so can make adjustments if necessary to allow for a bigger cavity, I really want to use full fill Mineral wool batts due to cost, ease of build and air tightness.

 

I live in an area of very severe driven rain so I’m looking at ways to do it that won’t affect potential warranties later on down the line. Home will be as airtight as I can make it with underfloor heating and MVHR.

[joe90]

I used mineral batts in a full fill 200mm cavity, brick outer skin, the west wall facing the sea did get wet and whilst core drilling for the ASHP the brick was wet right through but the mineral wool had not absorbed any wet. The batts had a bba cert for full fill but as a preventative measure I treated the wall with water proofer and rain ran off it like glass afterwards. Rendering should negate the need to waterproof like I did.

[Lewis88]

Thanks for the reply Joe, are you also in an area of very severe driven rain? And did you get a structural warranty? Currently feeling that I’m out of my depth with the wall makeup and floor insulations. I had planned on getting an insulated raft however I’m now going to go for a standard raft with insulation and screen on top. This is purely down to not being able to find anyone willing (or reasonably priced) to do it. 

[Redoctober]

@Lewis88  Not sure if this would help but have you considered Surecav? - https://www.surecav.co.uk/

 

 

 

 

[Lewis88]

@Redoctober no I hadn’t seen that before that is interesting! I can’t imaging it works with mineral wool batts but it could be a good compromise on that part of the house!

[joe90]

6 hours ago, Lewis88 said:

Thanks for the reply Joe, are you also in an area of very severe driven rain? And did you get a structural warranty? Currently feeling that I’m out of my depth with the wall makeup and floor insulations. I had planned on getting an insulated raft however I’m now going to go for a standard raft with insulation and screen on top. This is purely down to not being able to find anyone willing (or reasonably priced) to do it. 

My build was a few miles away from the north Devon coast so near the Atlantic. No structural warranty, I had intended to have an insulated raft but was in hospital when the builder was doing it so had insulation on top of the raft  then 70mm flowing screed with UFH pipes within it so heat up times should be a little quicker. 
 

note, if you put a @ in front of my name and choose from the drop down I will be informed you have quoted me 👍

[Redbeard]

Might this help a little as you formulate your thoughts? https://www.nhbcfoundation.org/wp-content/uploads/2016/05/RR10-Full-fill-cavity-wall-insulation.pdf. I can't find any other papers specifically relating to using full fill or not. The only other one I found was w.r.t. 'brick creams'.

 

If we were talking retrofit CWI I would definitely not use mineral wool in an exposed area. Have you thought (subject to prior consultation with potential contractors as to the suitability of their product for use in exposed areas) of building the cavity empty and retrofitting graphite EPS beads?

[Lewis88]

@Redoctober no I hadn’t seen that before that is interesting! I can’t imaging it works with mineral wool batts but it could be a good compromise on that part of the house! 
 

@joe90 thanks for the tip👍

 

@Redbeard I’d considered it but I think that MWB would be cheaper.

 

I’m now thinking that the part of the house where the glass gable is located can’t be full fill so it will probably be easier to treat this an extension and give it a larger cavity (maybe an extra 50mm) than the rest of the house to maintain the same levels of insulation but allow for a cavity of 50mm. Does this sound logical or am I missing something?

[joe90]

1 hour ago, Lewis88 said:

but allow for a cavity of 50mm.

The problem with mineral wool batts is you have no way of keeping the batts on the inner face to allow for the cavity next to the outer skin. 

[ADLIan]

Plastic retaining discs that fit onto the wall tie will do the job. Standard practice.

[joe90]

https://insulationgo.co.uk/blog/does-mineral-wool-need-air-gap/#:~:text=As a result%2C mineral wool,wool on its outer side.

[Lewis88]

@joe90 I’ve probably not explained it as well I’d hoped, essentially I’m looking for full fill to stop the air movement, make it easier to build and more cost effective.
 

My issue isn’t that I could pass building regs with 150mm cavity of full filled mineral wool batt insulation. The issue I have is that if I built it to this spec it would mean that I couldn’t get a structural warranty through NHBC due to them not allowing full fill insulation on fair faced masonry in an area of very severe driven rain. 

 

Im trying to work out how I should compromise, whether that means changing my plans and use another form of insulation or slightly change my plans in that part of the building to a different cavity setup. This will be my first self build so it’s all a learning curve to me.

 

could the block work behind the stone be wrapped in a membrane like timber frames are done?  That way it wouldn’t be classed as fair face masonry as there’s a water barrier (I presume)

[joe90]

Ah I understand now, I wonder why NHBC are so strict when the insulation has a bba certificate for cases like this? Perhaps ask NHBC what they will accept 🤷‍♂️

[ADLIan]

NHBC requirements always trump BBA Certs. That’s just the way it is!

[joe90]

Not had time to read it all but skimming through it I saw no mention of rendered walls 🤷‍♂️

 

https://www.nhbcfoundation.org/wp-content/uploads/2016/05/RR10-Full-fill-cavity-wall-insulation.pdf

[ADLIan]

The report doesn’t cover rendered brick/block wall as it covers worst case scenario of pretty poor quality brick outer. It was also a study to ensure the BBA test rig could still be calibrated and used.

[saveasteading]

I've used full fill as my preferred option on several cavity wall projects. I much prefer it because it is idiot proof,  doesn't need a gap, and prevents spots falling in the gap.

No problems anywhere. Were they exposed? I can't recall if any seaside jobs had it but I wouldn't hesitate to use it.

Even if damp got through a brick, it would have to be sucked into the insulation. Full fill won't do that.

If still in doubt, phone BG or Knauff, who I find very helpful.

[Lewis88]

Hi @saveasteading I’m not on the coast, but at 1300 ft above sea level so i believe that’s why my area is counted as ‘very severe driven rain’.  I will definitely the two companies and see what advice they can come up with, no harm in a call or two. 
 

like you say the full fill method looks easier and if it looks easier I’m sure that I’ll end up with a better final result 

[Iceverge]

3 hours ago, Lewis88 said:

changing my plans and use another form of insulation

I would stick with what you're at.  Have a look at the denby dale video's for best practice. Its a very good series.  

 

 

 

We're 250mm full fill here (I would do more if I had the chance again!) with EPS beads in the SW of Ireland, so plenty driving rain. No issues so far. EPS beads are the norm here. 

 

However we're rendered (sand+cement) throughout. I would just get your plasterers to do a simple coat of render behind the stonework contigious with the rest of the render if you're bothered. 

Practically speaking, if your stonemason points the stonework properly you'll be fine. 

Overall take care of the detailing around windows ( permanently flexible sealant done well ) and use a good paint and some brick cream/waterproofer and I wager you'll have zero rainwater making it past the first mm.

 

If you build with a half assed mason, leaving open perp joints, balled up insulation that gets wet in construction and cavity trays that are covered in mortar ( AKA mass housing estates) of course you're inviting trouble. 

 

[joe90]

34 minutes ago, Iceverge said:

I would stick with what you're at. 

I agree but @Lewis88 problem is the HSBC won’t pass any full fill insulation for his warranty.

[Iceverge]

 

Knauf do a partial fill detail as do Rockwool. 

 

Personally I would always prefer to spend my energy making sure the job was done properly rather than spending money on a warranty that may or may not pay out later. Perhaps it's needed for the lender. 

 

[saveasteading]

9 hours ago, joe90 said:

HSBC won’t pass any full fill insulation for his warranty.

As if BG and Knauf don't know what they are doing? If this was me I would investigate further for some misunderstanding, and esp phone the suppliers.

[joe90]

I didn’t have a warranty but when I HAD to sell got a retro one.

[Lewis88]

Unfortunately I warranty is a must for me, my partner is adamant. I’m not opposed to making the cavity larger with more insulation but the NHBC strictly rules out full fill with fair face masonry.

 

@Iceverge are you saying that I should do the stone and glass gable as the following internal block, full fill insulation, external block (with render applied) then a cavity and stonework? If so that could work. I suppose that the render would mean that it is no longer considered ‘fair faced’ and just had a stone skin?? 
 

I’m really not au fait with any other form of building than brick and block, but that all any of the trades do around here. Could it be easier to do this part in timber frame? My architect tells me that build systems can be joined/interchanged.

[joe90]

2 minutes ago, Lewis88 said:

but the NHBC strictly rules out full fill with fair face masonry.

But if memory serves from their document they don’t say how big the cavity should be? (Best to check) so make it 10mm bigger and use the methods @Iceverge suggests above (but if it were me I would still put in more insulation, you only buy it once and save heating costs forever. With my 200mm full fill cavity the heating only came on occasionally for a couple of months a year (and was only 4KW).