Foundations??

[lizzieuk1]

2 minutes ago, Nickfromwales said:

That’s going to be for you to find out tbh. That’s one for lots of googling and ringing and emailing of specs.  
 

Maybe someone on here has bought some like this and can provide a link to the supplier? 

Thanks Nick, its not easy, I've been  trawling for hours hence the post, thought there may be someone on here who's done similar.

[lizzieuk1]

5 minutes ago, Nickfromwales said:

I think for Georgian style the glazed units just come pre fitted with the bars?

Found these and I think the may do 3g so will enquire. 

[Nickfromwales]

12 minutes ago, lizzieuk1 said:

Thanks Nick, its not easy, I've been  trawling for hours hence the post, thought there may be someone on here who's done similar.

Maybe start a new thread in the doors and windows forum to wake the gods, vs hoping someone finds this in the foundations thread 👌. Prob get more responses that way, specific to the windows 👍👍

[Iceverge]

OK here are some numbers for our 185m2 house after having a play with PHPP.

 

Out annual heat demand is 2625kWh. Passiv windows with 3G , 200mm EPS in the floor (u = 0.16) , 250mm EPS bonded beads in the walls (0.15) , 400mm Cellulose in the attic. (0.1)  Airtightness 0.31 ACH50. 

 

 

Here are some Airtightness figures. 

 

• 0.31 ACH = 2625kWh
• 1 ACH = 3012kWh
• 2 ACH= 3586kWh
• 3 ACH= 4170kWh
• 4 ACH= 4716kWh
• 5 ACH= 5537 kWh
• 6 ACH= 5861kWh

 

Now I play the same game but step back the other fabric of the house individually to say a bregs basic house of a few years back. 

 

• Floor U 0.3 = 3103kWh
• Wall U 0.235 = 4005kWh
• Roof U 0.175 = 3159kWh
• Double Glazing = 3387kWh
• Lose MVHR = 5365 kWh

 

Keep the airtightness and MVHR but use the poorer figures everywhere else

• 5918kWh

 

MVHR and  airtightness are the biggest wins. 

 

 

Then come glazing and U value. This isn't as straightforward to generalise as window areas vary, a bungalow will have much more wall than a 3 story town house. Insulation has to be improved all together really. Not much point in adding 50mm to the attic insulation when its already at 500mm. It only reduced the U value by 0.008W/m2K. However if you add 50mm to 100mm wall insulation it takes it from 0.4 to 0.26. 16 times more of a difference. 

 

I concluded in our house for the above insulation types the ratio of increasing the insulation in the following ratio was the most economical. YMMV depending on construction specifics. 

• 4 Floor
• 5 Walls
• 8 Roof

Hope this helps. 

 

 

[Iceverge]

As an aside 3G, Airtightness and MVHR were always going to be included for the comfort, noise, air quality and building health aspects. 

 

Payback was considered but it wasn't really ever up for discussion given the other benefits.  

[JohnMo]

10 hours ago, Iceverge said:

Out annual heat demand is 2625kWh. Passiv windows with 3G , 200mm EPS in the floor (u = 0.16) , 250mm EPS bonded beads in the walls (0.15) , 400mm Cellulose in the attic. (0.1)  Airtightness 0.31 ACH50

Shows how much difference form factor makes as well, we are long thin single storey with all vaulted ceilings. Again MVHR, 3G passive spec windows (but quite a lot of them)

 

Our U values

Floor 0.09

Roof 0.12

Walls 0.14

 

Our heating usage is near double yours.

[Iceverge]

Our actual measured heat usage was a bit more, 3.2MWh/annum. Not sure of why the difference to PHPP. 

 

The insulated envelope of our house is essentially a 8.5mx13.5mx5.5m box so a good form factor like you say. We're quite a distance further south than you too.

 

What was your blower door result and window spec?

 

 

 

 

 

 

 

[JohnMo]

16 hours ago, Iceverge said:

The insulated envelope of our house is essentially a 8.5mx13.5mx5.5m box

 

70m perimeter, approx 8x25m and average of 3m tall except lounge which is 6m tall.

 

16 hours ago, Iceverge said:

What was your blower door result and window spec?

Average window U_w 0.6, our glass doors came double glazed (krypton filled) and are 1.2, front door 1.0.

 

We had a blower test prior to plasterboard at 2, fixed all the leak areas (mostly at DPC), but at final test it still came in a 2. But the MVHR wasn't sealed very well during test. So suspect better than 2 by a decent margin, could feel a definite breeze where the MVHR units are located. Couldn't be bothered doing a further test.

[lizzieuk1]

On 06/03/2025 at 22:08, Iceverge said:

Hope this helps

Many thanks Iceverge, that's a great post.

[lizzieuk1]

OK, so the SE has come back to say happy to detail a raft for us. I asked for an example he has done before but, his reply was:

"I have done insulation below ground bearing slab for the industrial building working in the previous company and I do not have such a detail. I have been running my company for 6 years and no one from my 1200 projects has done XPS below the slab. It's a shame because this is a correct way to insulate the building. You should assume 200mm XPS if you wish to have a well insulated building."

 

Then he's put a link to Isoquick as an example of a foundation he feels is ideal. 

 

Now, we're not suggested he can't design one but, a bit concerned whether it will be the best option.

 

Help! Should we go to one of the raft suppliers or elsewhere to get it designed?

[IanR]

8 minutes ago, lizzieuk1 said:

Help! Should we go to one of the raft suppliers or elsewhere to get it designed?

 

Yes.

 

Isoquick is an option, but they are not optimised. You'll pay more than you need to for steel and concrete and you'll have more mass to heat up for the UFH. 

[lizzieuk1]

1 minute ago, IanR said:

 

Yes.

 

Isoquick is an option, but they are not optimised. You'll pay more than you need to for steel and concrete and you'll have more mass to heat up for the UFH. 

Is that because Isoquick use a level, constant 200-300mm concrete slab rather than an integrated ring beam Ian? 

 

Have had a high level cost from Greenraft for material supply, worth asking them for design??

 

My worry is the SE doesn't have enough experience and will just design the easiest option, which, inturn will mean its sub-optimal. 

 

Don't want to upset the SE but need a diplomatic way to tell him we're going elsewhere for the raft 😬

[IanR]

28 minutes ago, lizzieuk1 said:

Is that because Isoquick use a level, constant 200-300mm concrete slab rather than an integrated ring beam Ian? 

 

Yep.

 

28 minutes ago, lizzieuk1 said:

Have had a high level cost from Greenraft for material supply, worth asking them for design??

 

I don't know Greenraft. The image on their website appears similar to Isoquick, but without the bespoke insulation pieces.

 

I'd recommend Advanced Foundation Technology, and use them as a baseline to compare others to.

 

28 minutes ago, lizzieuk1 said:

Don't want to upset the SE but need a diplomatic way to tell him we're going elsewhere for the raft 😬

 

He doesn't specialise in insulated rafts, he shouldn't be upset if you choose to use a specialist.

Edited Monday at 14:22 by IanR

[lizzieuk1]

4 minutes ago, IanR said:

 

Yep.

 

 

I don't know Greenraft. The image on their website appears similar to Isoquick, but without the bespoke insulation pieces.

 

I'd recommend Advanced Foundation Technology, and use them as a baseline to compare others to.

 

 

He doesn't specialise in insulated rafts, he should be upset if you choose to use a specialist.

Yes, I think you're right, the greenraft looks similar to isoquick- hadn't noticed that last week when I looked at it. 

 

Will make contact with AFT and have a chat, need to make sure we start things in the right way, literally the foundations of the project!

 

Thanks Ian! 

[JohnMo]

So what's so special about a raft, that suitably detailed normal strip foundations and slab cannot achieve?

 

I just started the structural engineer and architect in the direction of travel to get thermal bridge free design that any ground worker can follow.

[lizzieuk1]

6 hours ago, JohnMo said:

So what's so special about a raft, that suitably detailed normal strip foundations and slab cannot achieve?

 

I just started the structural engineer and architect in the direction of travel to get thermal bridge free design that any ground worker can follow.

It's a fair point JohnMo but, we feel, as we will likely do much of the works ourselves that,  the detail may be simpler to achieve.

Also, SE has said on the hedge side we will need  1.7m deep foundation (if medium vcp), with all the usual hassle of clay boards etc, not to mention the sticky mess of excavating all the clay! I think a raft may be a better solution. 

[JohnMo]

But would you not be excavating approx 5 to 600mm from the whole area of the house to replace with MOT anyway even for a passive slab?

[lizzieuk1]

12 minutes ago, JohnMo said:

But would you not be excavating approx 5 to 600mm from the whole area of the house to replace with MOT anyway even for a passive slab?

Yes, but the upper 400mm is topsoil so easier as less clay to excavate - after digging a large 'pond' out in the field we've experienced the grimness of excavating the clay too 😆

[Iceverge]

 

34 minutes ago, lizzieuk1 said:

t's a fair point JohnMo but, we feel, as we will likely do much of the works ourselves that,  the detail may be simpler to achieve

 

I'd be putting that in the "pro" box for conventional footings. Nobody will care as much about details as you. 

 

Can you trench fill for the footings in dry weather? With good digger operator and it's one of the simplest footings you can make. 

 

Superb performance can be achieved with any kind of foundation so long as you look after the thermal bridging which isn't rocket science. 

[lizzieuk1]

1 minute ago, Iceverge said:

 

 

I'd be putting that in the "pro" box for conventional footings. Nobody will care as much about details as you. 

 

Can you trench fill for the footings in dry weather? With good digger operator and it's one of the simplest footings you can make. 

 

Superb performance can be achieved with any kind of foundation so long as you look after the thermal bridging which isn't rocket science. 

Yes we could, and will, work in the drier weather (so long as the uk summer plays ball!) but with a 1.7+m trench in clay I'm not convinced it is any cheaper than the raft. Did a quick high level costing and there was very little difference. Will do a more detailed cost once I hear back from the raft suppliers to see how things compare. 

 

It's a nightmare trying to decide as everyone has different preferences and all perfectly viable reasons for those preferences!

Will have to make a decision at some point or we'll never get our regs drawings submitted!

[Iceverge]

What about strip foundations and ICF rising walls? 

 

 

[Nickfromwales]

5 hours ago, Iceverge said:

What about strip foundations and ICF rising walls? 

 

 

Do you really want a woodcrete ICF block under DPM and rising up? EPS is fine, done this before very successfully, but I'm not so sure that's a good idea with WC.

[Iceverge]

Internet thinks woodcrete would be fine underground........

 

I was thinking of EPS however, it will perform every bit as well as an insulated raft as a foundation provided you get your thresholds right. 

[JohnMo]

16 minutes ago, Iceverge said:

Internet thinks woodcrete would be fine underground........

 

I was thinking of EPS however, it will perform every bit as well as an insulated raft as a foundation provided you get your thresholds right. 

Durisol install manual says 

[Nickfromwales]

11 minutes ago, JohnMo said:

Durisol install manual says 

Did you install any below grade?