What U-value should these insulated foundations give

[Thorfun]

Hi all, 

 

I'm after a little bit of help calculating the U-values for these proposed foundations using the Kore system.

 

this one is 200mm of EPS300 under the basement and up the walls:

 

 

 

 

and this is an example of what's under the rest of the house where there isn't a basement. this is a TSD designed Kore system with 300mm thick EPS which is very similar to the MBC passive slab so I would presume that this will yield a U-value of 0.105W/m2K as stated on the MBC website?

 

 

our architects need to know the thickness of insulation we'll need to achieve 0.10W/m2K on the slab and 0.12W/m2K on the walls and I'm hoping that someone would be able to assist with what these current drawings would yield for U-values.

 

I do use https://www.changeplan.co.uk/u_value_calculator.php to do my normal U-value calculations but I can't see anywhere on there that would take in to consideration the soil at the depth of the basement slab nor what effect the soil has on the basement wall U-value.

 

can anyone assist please?

[Thorfun]

thought I'd better add the spec sheets for the Kore EPS ?‍♂️

 

Declaration_of_Performance_KORE_Floor_EPS_100_White.pdf

Declaration_of_Performance_KORE_Floor_EPS_300_White.pdf

[Thorfun]

so, I've put what I think is correct into change plan and got the following for the basement floor and walls. do they seem correct?

 

 

if so, I'm happy with the floor but the walls aren't quite near to the above ground u-values of 0.12W/m2K.

 

I'm thinking that I really shouldn't be worried about hitting 0.12W/m2K in the basement walls as to get that level I'd need 300mm EPS which seems excessive for a basement, especially when airtightness seems to have a much bigger impact on heat loss.

 

thoughts?

[Edward]

EPS 300 is a Jablite product. Cellcore and Heaveguard is a Cordek product, Cordek also manufacturer EPS, called Filcor. Enter your postcode here and you can discuss this with Cordek directly https://cordek.com/contact/ and they can assist you with your insulation calculations. Its unlikely you will need EPS 300 - its probably overspecced on the vertical, so this could save you some cost.

 

On your second drawing, the slab does not appear to be tied in to the foundations. This wont work with the presence of heaving ground.

[Thorfun]

25 minutes ago, Edward said:

EPS 300 is a Jablite product. Cellcore and Heaveguard is a Cordek product, Cordek also manufacturer EPS, called Filcor. Enter your postcode here and you can discuss this with Cordek directly https://cordek.com/contact/ and they can assist you with your insulation calculations. Its unlikely you will need EPS 300 - its probably overspecced on the vertical, so this could save you some cost.

 

On your second drawing, the slab does not appear to be tied in to the foundations. This wont work with the presence of heaving ground.

Hi @Edward. thanks for the response. I think the architect is already asking Kore about the calculations but this forum has already given so much great advice that I thought I'd seek out the thoughts of the collective hive mind. I'm aware that there are other companies that will offer the insulated foundations and I will approach them for quotes but this is simply for the building regulations drawings and as-designed EPS/SAP.

 

I did ask about needing EPS300 and some of the point loads on our building are high enough to require EPS300 (I'm not going to argue with the structural engineer on this point as I trust their calculations and I am in no way qualified to do it myself) and to avoid confusion where EPS200 could be specified and run the risk of getting the wrong spec in the wrong place they have specified EPS300 throughout. I'm ok with this and would rather it was over engineered than run the risk of issues in the future. 

 

Again, on the second drawing I am not going to second guess the structural engineers and believe they have designed the foundations to deal with any heave. the company, TSD, are insulated slab experts and so I trust them.

[Dan F]

There a different ways to calculate foundation u-value and each approach gives a different result.  It comes down to if you consider it a "cassete" and purely look at the materials and their thermal resistence, or if you look at the foundation system in the ground, in which case the caculation works slightly different and gives better (lower) values.

 

Also, each foundation design will have different size ring-beams and/or areas that need thicker concrete, which will both impact the overall u-value of the foundation.

 

In our case about 60% of the slab needed 250mm concrete which meant EPS was reduced to just 200mm.  This had a non-insignificant impact on the overall u-value meaning it wasn't really very close at all to the MBC quoted 0.105W/m2K.   In the end we added an extra 100mm EPS.

[Dan F]

Talk to Andrew at KORE, he'll run the calulcation for you if you send them foundation design.    I would assume the basement wall needs to be treated in a similiar way to foundation.

 

Your 0.10 target, is that "in ground" u-value or "cassete" u-valye?

 

 

Edited November 24, 2020 by Dan F

[Thorfun]

15 minutes ago, Dan F said:

Talk to Andrew at KORE, he'll run the calulcation for you if you send them foundation design.    I would assume the basement wall needs to be treated in a similiar way to foundation.

 

Your 0.10 target, is that "in ground" u-value or "cassete" u-valye?

 

 

 

the architects have already been in contact with KORE (albeit a chap called Steven) and we are awaiting a response from them. I just wanted to put it out to those on here who also know what they're talking about. ?

 

the 0.10W/m2K target is overall floor U-value for EPC/SAP calculations really. tbh, I plucked the figure out of the air based on the MBC passive slab. it seemed like a good target to get to at the time as I was (and still am) pretty ignorant of the whole thing. same with the walls. 0.12W/m2K seemed like a good figure and the as-designed SAP reflects those target values. Once I actually get the house built and budget becomes a factor I have the option of reducing the wall insulation a bit which will give a 0.14 or 0.15W/m2K figure and then the as-built SAP will change. but for now I just want to get the BR drawings finalised so I can get the submitted and crack on! it seems that the SE is awaiting the final thickness of EPS required to get the U-values I requested of the architects.

 

probably should've done this all sooner but you know how it is. ?

 

25 minutes ago, Dan F said:

In the end we added an extra 100mm EPS

 

did that add a huge amount to the overall cost or was it pretty negligible? 

[Dan F]

Initially I thoght you wouldn't achieve 0.10W/m2K on basement foundation, but seems you are achieving this via 30mm of some kind of PIR product under the screed.  The problem with this is that, the basement walls aren't insulated in the same way so:

 

i) You won't achieve same u-value for walls.

iii) You'll have a situation surely, where the heat in the concrete in the walls will bridge to some extent to the concrete under the floor PIR, making the foundation not quite a effective as the numbers might make it seems. 

 

Can you use the same 30mm PIR on the walls too?  Or simplify things and just use 250mm EPS everywhere.  What function does the PIR sirve?

 

On a seperate note, wondering why you need the screed?

 

 

Edited November 24, 2020 by Dan F

[Thorfun]

33 minutes ago, Dan F said:

Initially I thoght you wouldn't achieve 0.10W/m2K on basement foundation, but seems you are achieving this via 30mm of some kind of PIR product under the screed.  The problem with this is that, the basement walls aren't insulated in the same way so:

 

i) You won't achieve same u-value for walls.

iii) You'll have a situation surely, where the heat in the concrete in the walls will bridge to some extent to the concrete under the floor PIR, making the foundation not quite a effective as the numbers might make it seems. 

 

Can you use the same 30mm PIR on the walls too?  Or simplify things and just use 250mm EPS everywhere.  What function does the PIR sirve?

 

On a seperate note, wondering why you need the screed?

 

 

 

good catch. yes, the architect has specified 30mm PIR above the internal waterproofing system. I'm not 100% sure why but maybe something to do with not being able to or maybe not wise to screed directly on top of the waterproofing membrane. or maybe he just took it from this drawing supplied by the waterproofing contractor.

 

 

either way, I'm actually ok with the extra 30mm PIR. The screed is because of the waterproofing membrane. we can't put UFH pipes in to the slab due to the fact as well, so we need something to go under the finished flooring to house the UFH.

 

we could use 30mm PIR on the walls but that will reduce the room size and so maybe adding extra EPS outside the walls would be the best way to go.

 

thanks for the responses so far. definitely giving me food for thought.

[A_L]

@Thorfun , Here is a slightly out=of-date document which describes the methods for calculation of U-values for below ground walls and floors. Replace the Building Regs U-values and ignore the references to Elemental and Carbon Index methods

 

 

Basement U-values.pdf

[Oz07]

I'd be less concerned about basement walls than gf slab u value. My simpleton brain tells me there will be lower losses due to a more stable ground temp below say 600mm ground level. Sorry can't help with the details

[Thorfun]

1 hour ago, A_L said:

@Thorfun , Here is a slightly out=of-date document which describes the methods for calculation of U-values for below ground walls and floors. Replace the Building Regs U-values and ignore the references to Elemental and Carbon Index methods

 

 

Basement U-values.pdf 301.32 kB · 3 downloads

Thank you so much. I’ll go through it once GBBO is finished!

[Thorfun]

2 hours ago, A_L said:

@Thorfun , Here is a slightly out=of-date document which describes the methods for calculation of U-values for below ground walls and floors. Replace the Building Regs U-values and ignore the references to Elemental and Carbon Index methods

 

 

Basement U-values.pdf 301.32 kB · 4 downloads

hi @A_L. I've read through the document but I'm a little stumped.

 

"Walls which are beneath ground level should be entered as normal into the U-value calculator module of the program, but you will then need to use the total resistance of the wall calculated by the program (which can be viewed in the ground floor data entry screen) and the known depth beneath ground level to get the adjusted U-value from the following table. You should then enter this figure directly into the program."

 

I get this but according to the changeplan calculator the total resistance is 6.935 m2K/W, right?

 

 

but the table in the document doesn't go to those levels!

 

a maximum Thermal resistance of 2.5m2K/W unless I'm completely reading it wrong. Also, my basement ceilings are 2.9m high and there isn't a 3.0m column in the table either.

 

am I reading this all wrong?

 

 

[A_L]

@Thorfun ,

 

as it says in the document -

 

Quote

If the resistance is higher than that stated in the above table, you should extrapolate the figures.

 

I have given it a go - I should add that I never had to do a basement when I was actively doing SAP!

 

If we look at the table we can see that the change in U-values is rapidly declining with depth, particularly at higher R values, therefore I think you can ignore not having values for your depth and use those for 2.5m

 

The first plot shows the U values in the 2.5m column plotted against 'raw' R values in the 1st column. I think it would be difficult to give an accurate U value for a 'raw' R value of 7 from this 

 

In the second plot I have calculated R values from the U values in the 2.5m column and plotted these against the 'raw' R values in the first column. Assuming this is a straight line (y=mx + c) then a 'raw' R of seven converts to about 11.61 or a corrected U value of about 0.09

 

Edited November 25, 2020 by A_L
Remove empty space

[Thorfun]

1 hour ago, A_L said:

as it says in the document -

whoops! missed that bit, sorry. ?

 

2 hours ago, A_L said:

In the second plot I have calculated R values from the U values in the 2.5m column and plotted these against the 'raw' R values in the first column. Assuming this is a straight line (y=mx + c) then a 'raw' R of seven converts to about 11.61 or a corrected U value of about 0.09

 

thank you so much for this. it is so incredibly useful and would seem that if the extrapolation is correct that the 200mm of EPS should easily be enough.

[Thorfun]

just wanted to say a big thank you to @A_L for his assistance on this one. with his direction I have extrapolated the table as he suggested and plotted a trendline in Excel and using that I have been able to easily see the difference that different thickness and type of EPS makes to the basement walls.

 

I've come to the conclusion that 200mm EPS 70 outside the basement walls will yield a U-value of 0.095W/m2K and the basement floor with 200mm EPS300 a U-value of 0.09W/m2K, when adding in the effect of the soil, which easily hit our required targets.

 

I've really enjoyed the journey this research has taken me on.

 

this forum is brilliant. long may it continue.