Groundworker for Insulated Raft - Highlands

[Dunc]

Can anyone recommend a groundworker with experience of installing an insulated raft fondation in the Highlands (Inverness) region?

Really struggling to find anyone who has even heard of this, never mind done it. 

[JohnMo]

Define exactly what you mean by insulated raft, many meaning used by different people.

[Kelvin]

John is right and I had the same issue as you. I spoke with Greenraft (Phil Grove) They were keen do one in Scotland and said they’d work closely with whichever groundwork company I was using. Unfortunately we were too far along the process to make such a big change. We did build a trench foundation using insulated blocks with an insulated upstand so not a bad outcome. 

[Dunc]

Apololgies for lack of clarity @JohnMo Insulated raft as in Kore/AFT/GreenRaft type system, such as https://www.kore-system.com/products/kore-insulated-foundation/

 

Similalry to you @Kelvin am in conversation with Greenraft and they claim to have worked with a couple of installers up here, but have failed repeatedly to provide contact details.

While several suppliers are keen to assure me that it's so easy as to be DIY-able I'm not prepared to take the risk on such a critical component!

 

MBC's quote is eyewatering so I may have to resort to something more traditional with a trench, insulated blocks and upstand. Do you have any idea on the thermal performance you achieved? (U, psi?)

[Kelvin]

If Greenraft claim that then it’s been in the last two years as they said they hadn’t done any up here when I spoke with them. Primarily because they struggled to find groundworkers. 
 

I’ll dig the U value out from my notes. The psi values were calculated as part of the energy performance pack but that was based on concrete blocks rather than insulated blocks and I never bothered having them updated. 
 

I used 300mm wide insulated trench blocks. What surprised me was how hard it was to source these in Scotland. I tried every manufacturer and they all said the same thing that there’s no demand for them. My wall build up is unusually wide for a timber kit. In the end I convinced a local Mannok dealer to bring me them from Ireland as part of their weekly delivery. 

[saveasteading]

The insulation can be anything you like with trad construction. The perimeter needs attention too. 

Quality slab work is a skill that few groundworkers have.

However I would go for a  groundbearing slab with minimal mesh, then pir then a pumped screed by a specialist. The base slab can therefore  be a bit rough as it's all covered.

 

I'd love to know the cost level for a kore system. I'm thinking 50% more than trad.

[Kelvin]

The greenraft quote wasn’t too bad all things considered. 
 

I have a pallet and a half of those Mannok insulated trench blocks left (had to order a minimum amount) If you do go down that route and happen to need 300mm wide trench blocks then you can have these FoC for a donation to Buildhub. 
 

https://mannokbuild.com/aircrete-thermal-blocks/mannok-aircrete-seven/

 

[JohnMo]

We couldn't find anyone up here so decided to do a modified version of some more traditional. We are on a sand hill so lots of belts and braces added. But a simplified version of this is doable with local labour for not much cost wise. Pretty much thermal bridge free. Not shown is a 70mm upstand I added to screed edge. Used 200mm of PIR insulation under a fibre reinforced concrete screed 100mm thick.

 

 

 

[Dunc]

@Kelvin that's very generous of you, thanks! Will keep this in mind, though we're months away from digging.

@JohnMo thanks for sharing this, appreciated! It is looking like I'll probably have to go in this direction ultimately.

 

Cost wise, it's interesting.

The EPS formers aren't really very expensive (<£10K from all the suppliers who quoted on my 138m² GF build) and really I'd be buying nearly as much sheet EPS for standard foundation insulation, other than the thickness of the upstand.

Suspect this will be more than ballanced by the cost of insulating blocks (marmox, mannok etc) - roughly £2k for my permieter, assuming I only need 1 block wide (MBC frame is 300mm wide - maybe it can overhang and I can have more upstand insulation internally?)

The concrete slab component may be 40mm thinner in the diagram above than a kore raft, which on my build would only be 5.5m³ , so £825 less.

Both require 2x A393 mesh layers.

The underbuild for the kore raft would be 800mm deep MOT3 & 50mm sand blinding on my plot. For me that's 110m³ so about £5k. No idea what trench dimensions or blockwork would be required for a more traditional found (my perimeter & internal load bearing walls are about 80 linear meters).

Then there's the top screed layer in the trad build.

 

I really wonder if it will work out pretty similar materials wise, and I'd be happy to pay a small premium for the easy to achieve U value of 0.1W/mK. It's just the lack of experienced contractors that causes the issue. Or my lack of bravery to go DIY 😕.

[JohnMo]

1 hour ago, Dunc said:

Suspect this will be more than ballanced by the cost of insulating blocks (marmox, mannok etc) - roughly £2k for my permieter,

Did all the calcs and just couldn't justify Marmox as they adding nothing in real terms from the design I posted. The Thermolite blocks are in a dry space so thermally stable and twice the height of marmox.

 

Ours came out at 0.09 U value. As I said our was a standard ground work contractors, doing most of it, but I did all the insulation and UFH, they can back concreted over the top.  I then built the walls.