Insulated raft done

[kandgmitchell]

Just to add to the wealth of knowledge on here.

 

We have just completed our insulated raft using xps with concrete 250mm thick at 100m2. Installed the foul drains and surface water out to a soakaway.

 

All in,  including labour it's come to £26K and a bit. Hope this might help with others budgeting.

[Mr Punter]

Any pictures?

[kandgmitchell]

Yes, I'll post a few.

[mike2016]

How did you handle door openings, any special shuttering / detailing required? 

[kandgmitchell]

This is to take a DanWood timber frame. The frame sits on the edge of the slab with the exterior insulation overhanging. More insulation goes ontop of the slab and an insulated former is used at door openings (from what I can see from the details provided). No special shuttering although we backed the vertical insulation with scaffold boards just in case. Be honest I doubt if they were needed though. It was a Green Raft that uses a vertical plastic joining strip between the horizontal and vertical insulation panels.

[Duncan62]

Did Mark install or did you DIY?

[kandgmitchell]

Mark? It was a "self" install with groundworkers doing the heavy stuff and me making sure the details were done properly. Took a while simply beacuse of the number of wet days when the site was just too muddy to work in.

[Dunc]

@kandgmitchell May I ask: how big is the raft (square meterage) and roughly what shape (simple rectangle vs something fancy)?

I've just had my quote from MBC for ours and nearly fell off my chair...

thanks

[scottishjohn]

On 26/02/2024 at 16:15, kandgmitchell said:

Just to add to the wealth of knowledge on here.

 

We have just completed our insulated raft using xps with concrete 250mm thick at 100m2. Installed the foul drains and surface water out to a soakaway.

 

All in,  including labour it's come to £26K and a bit. Hope this might help with others budgeting.

Idid look at that 

but as we have 700mm original granite walls  it was not possible 

webasically have a modern wood framed house inside granite walls

so we went for concrete sub floor --100mm of pir and up the walls then ufh and going screed ontop of that 

 

Edited February 28, 2024 by scottishjohn

[kandgmitchell]

44 minutes ago, Dunc said:

May I ask: how big is the raft (square meterage) and roughly what shape (simple rectangle vs something fancy)?

Nigh on 100m2 simple rectangle but with two pairs of 200mm x 850mm "outshoots" which support an open gable feature on the rear and front elevations.

[kandgmitchell]

We had MBC price the job last year. Their quote (April 2023) for an insulated raft for the same building design was £34K. Just a note, DanWood add their own insulation ontop of the slab so we used 150mm xps under.

[kandgmitchell]

As asked for here are some photo's. 8043 is the stone base done. 8046 the sand blinding, 8047 the sub raft insulation under way. 

[kandgmitchell]

Final two photo's 8053 is the steel, sorry it was getting dark when I rembered to take this. Layer of A393 mesh in bottom and top with a further layer of A393 min 1.0 m wide around the upper perimeter (we just used the 1.4m offcuts from the main mesh). A couple of embedded beams using 16mm bars where the main load bearing walls are.

8059 is the finished raft with a muddy surface due to the state of the ground whilst the rain water drainage was being done. I'll power wash it off before the frame arrives.

[jack]

Thanks for the photos.

 

Is your stone base MOT1 or similar? I've more commonly seen large no-fines stone specced - something like railway ballast.

[tuftythesquirrel]

On 26/02/2024 at 16:15, kandgmitchell said:

Just to add to the wealth of knowledge on here.

 

We have just completed our insulated raft using xps with concrete 250mm thick at 100m2. Installed the foul drains and surface water out to a soakaway.

 

All in,  including labour it's come to £26K and a bit. Hope this might help with others budgeting.

 

Could you tell me how thick was the XPS as it will affect the budget if I go thicker. Thanks.

[kandgmitchell]

The stone was MOT1 type stuff which I think is max 30mm downwards. It packed tight with a 2T vibrating roller.

 

I used 150mm xps for the insulation because the Dan Wood spec uses 90mm of insulation across the top of the raft. I could have added more but it was diminishing returns really.

[kandgmitchell]

Just to add to this with a bit of experience of what I would do differently "next time".

 

I had installed 50mm twin wall duct for the electric supply. After completing the raft that duct was extended by the groundworkers to the electric kiosk with the meter some 20 odd metres away.

 

Only later did I consider the cable needs - 3 phase 25mm. Upon picking it up from the suppliers I could immediately sense a problem coming. A) it was heavy and B) it didn't bend well.

 

This week I discovered drawing it through a 50mm duct was not practical - should have used 80mm at least. Also the bends in the duct made pulling the cable through a nightmare. Luckily, after a struggle we got it outside the raft (all of 3 metres) but had to dig down to it and cut it open to get past the first (of several) too tight bends. Finally have strained back trying to pull it the last 5 metres - can't even bend over at present! Resourceful wife asked two random men in a family of four passing by to help and they very kindly stepped in and pulled it the last bit while I sat on the floor in a lot of pain.

 

So, 1) work out cable needs in advance.

       2) use a bigger duct than you think you need

       3) consider running the cable through the duct laid out in a straight line, then placing both duct and cable in place in one go so you know it will bend where you need it to!

       4) just get someone else younger and fitter to do it!

[joe90]

14 minutes ago, kandgmitchell said:

just get someone else younger and fitter to do it!

🤣

[kandgmitchell]

True, but one doesn't realise the years have caught up until you're caught out!

[AartWessels]

Just out of curiosity, how did you 'sleeve' any of the ducting through the insulation? 

[Alan Ambrose]

Congrats, you must feel that’s a major step forward. Thanks for posting the images and the ‘what not to do’ hints.

 

Any chance of an anonymised drawing? I’m interested in the position of dpcs, barriers etc. I think xps a much better choice than, say, Kore. Mind if I ask how you got the drains and ducts (a) in the right place and (b) held in the right place during the pour?

[Russell griffiths]

50 minutes ago, AartWessels said:

Just out of curiosity, how did you 'sleeve' any of the ducting through the insulation? 

Why would you sleeve the ducting through the insulation. 
the duct is the sleeve, the cable or pipe passes through the duct, the duct should be sealed tightly to the insulation. 

[AartWessels]

14 hours ago, Russell griffiths said:

Why would you sleeve the ducting through the insulation. 
the duct is the sleeve, the cable or pipe passes through the duct, the duct should be sealed tightly to the insulation. 

 

Well, that's basically what I mean, my apologies, English is not my first language. I was curious about the way is has been sealed.

[Nick Laslett]

15 hours ago, Alan Ambrose said:

I think xps a much better choice than, say, Kore.

I believe there are pros and cons for both XPS and EPS. You just have to pick your trade offs. It was back in 2019 when I was researching this, so please forgive my hazy memory. If I remember correctly it was the way the two materials behaved after they get very wet and how they dry out. It could have been propaganda from either side. Very hard to find honest brokers in materials science.

 

I had one groundworks outfit that wanted to use XPS and I had already got a quote for Kore with MBC installers. I went with MBC installers because I wanted the UFH installed in the raft. 
 

I don’t want to be misunderstood, they are both great materials for an insulated foundation, no one should be concerned with either approach. It is a challenge with discourse on this kind of a forum because of the financial costs in any decision, people can quite reasonably be upset, if they have spent a lot of money. 

 

The biggest take away is that you can source the XPS or EPS direct from the manufacturer as long as you know the specification. Charlie Luxton covers this point on his insulated raft video see the comments. This would be a dramatic cost savings vs material marketed as special insulation raft product. 
 

https://youtu.be/0kXrj8RGtBI?si=f3xf5hUpwi8sS08e

 

[Russell griffiths]

51 minutes ago, AartWessels said:

 

Well, that's basically what I mean, my apologies, English is not my first language. I was curious about the way is has been sealed.

Ok cool. 
so the duct is sealed to the insulation. 
the pipe or cable travels through the duct. 
at both ends of the duct you seal with a wire mesh to stop vermin and seal with some sort of foam sealer, you can put a string on the metal mesh so it is easy to pull out.