slab insulation

tattoo

Hi all

I've just started a self build and already the headaches are coming thick and fast. At the moment i'm confused about the slab insulation.

Surveyor has recommended 'Kingspan tf70' but says it must be thicker than 50mm. Everyone else including tradesmen say 50mm is plenty.

I would normally go with what surveyor says but getting a hold of anything over 50mm is difficult as all builders suppliers in the area only have the 50mm.

The ground floor is 119sqm. I would really appreciate any help

galwaytt

Well, 2 x 50 would work, and probably better. For a start, you would be lapping the joints.

OTH, I was once told that, once more than 1m in from the walls, the benefit of extra insulation thickness over std, is negligible. I imagine it could be so.

ardara1

Heatloss in floor is from the perimeter mainly - divide your total area by the perimeter length - let me know the ratio and I'll let you know what thickness to achieve the 0.25 in the regs - However regs are MINIMUM - I would say min 75mm Kingspan TF 70 or Xtratherm or 125mm Aerobord HD - THEN if you're putting in UF Heating increase by 30%

Most floors WILL NOT meet regs at 50mm

Mellor

Area perimeter ratio does not affect the u-value. the same build up of materials gives the same u-value no mater what the area. if you are going by elemental U-values. 0.25 is the min no matter what the area/perimeter ratio is. are you thinking of the OHL method, the whole house average is adjusted by the volume/exposed area ratio.

I would agree that regs are minimum, and go as low as you can. Get best materials available for the job.

ardara1

Mellor wrote:

Area perimeter ratio does not affect the u-value. the same build up of materials gives the same u-value no mater what the area. if you are going by elemental U-values. 0.25 is the min no matter what the area/perimeter ratio is. are you thinking of the OHL method, the whole house average is adjusted by the volume/exposed area ratio.

I would agree that regs are minimum, and go as low as you can. Get best materials available for the job.

Mellor - thats wrong - they only way of calcu

lating the U-value is by working out the Perimeter area ratio.In th eOHL method you still have to work out the U-value by using the P/A ratio - the only type of floor this doesn't apply to is when it is exposed to the under side eg car parks with apartment above.

tattoo

thanks lads for all info. the area-perimeter ratio works out at 2.6

area - 119sqm

perimeter - 45.7m

again, thanks lads

ardara1

Current Elemental regulations ask for a U-value of 0.25

50mm K Span/Xtratherm = 0.27
55mm meets 0.25

75mm = 0.21
100mm = 0.15

Passive house target ask for an average of 0.15 in the fabric

Cheers

Mellor

sorry I thought you were adjusting the value by the ratio, like in OHL. (where after the U-value is calculated, the max permitted is calculated using 0.24+019 V/A (V/A can be taken from P/A)
I misread your post and i take it from the above post you were using the (.457(2A/P)+d) formula. Thats not all of it but i cant remember the other symbol at the start.

out of curosity what conductivity did you use foe the extra therm? I have a CD I got from them that had all their product info on it, and just wondering if its up to date still.

ardara1

Mellor wrote:

sorry I thought you were adjusting the value by the ratio, like in OHL. (where after the U-value is calculated, the max permitted is calculated using 0.24+019 V/A (V/A can be taken from P/A)
I misread your post and i take it from the above post you were using the (.457(2A/P)+d) formula. Thats not all of it but i cant remember the other symbol at the start.

out of curosity what conductivity did you use foe the extra therm? I have a CD I got from them that had all their product info on it, and just wondering if its up to date still.

I used the Kingspan conductivity of 0.023 - I assume xtrathrms the same ? - I use the BRE calculator (£25) available from their web site it allows you to change the values - haven' seen the disc from xtratherm.

Mellor

ardara1 wrote:

I used the Kingspan conductivity of 0.023 - I assume xtrathrms the same ? - I use the BRE calculator (£25) available from their web site it allows you to change the values - haven' seen the disc from xtratherm.

The disc is good. has a large list of values. I think 0.023 is the lowest for rigid insulation. so no improvement in the last few years. kingspan might have a new insulation that has a 0.022 value now, but i could be mistaken, it could be .023

tattoo

cheers lads for all advice.

have decided to go with kingspan tf70, 60mm. will give me a U value of .22

thermal conductivity - .023

seeing as this is early days in build i think i'll be back on soon for your expertise:)

ollie30

rep from springvale(aerobord) told me springvale platinum floorshield 100mm approx .20w/m2k- 125mm 0.17 you would need to verify with their tech dep but thats what he told me at a show

ardara1

tattoo wrote:

cheers lads for all advice.

have decided to go with kingspan tf70, 60mm. will give me a U value of .22

thermal conductivity - .023

seeing as this is early days in build i think i'll be back on soon for your expertise:)

The calcs I gave previously were correct using your p/a - 60mm of KS will not achieve 0.22 BUT 0.24 - make sure you get what you've been told - 60mm JUST meets current regulations.

Mellor

[quote-tattoo]cheers lads for all advice.

have decided to go with kingspan tf70, 60mm. will give me a U value of .22

thermal conductivity - .023

seeing as this is early days in build i think i'll be back on soon for your expertise [/quote]


it probably gives a .22 values in a standard shaped house, there are probably BS's for how manufacturers supply this infoe to insure they are all on same page.
i'd reccomment more insulation, at least 75mm

ardara1

Mellor wrote:

it probably gives a .23 values in a standard shaped house, there are probably BS's for how manufacturers supply this infoe to insure they are all on same page.
i'd reccomment more insulation, at least 75mm

Hi Mellor -

It gives a value of 0.24 - the standards you're looking are 13370 and 6946 BS & IS EN.

If you're working off the same P & A the answer should be the same - I've checked it on 3 different types of software - your lambda value for ground may differ slightly ? - If you are in volved in energy assessment getting the U-value calc correct is pretty much critical - what software do you use?

Mellor

ardara1 wrote:

Hi Mellor -

It gives a value of 0.24 - the standards you're looking are 13370 and 6946 BS & IS EN.

If you're working off the same P & A the answer should be the same - I've checked it on 3 different types of software - your lambda value for ground may differ slightly ? - If you are in volved in energy assessment getting the U-value calc correct is pretty much critical - what software do you use?

sorry, that was a mistype i my behalf.
i was suppose to write "it probably gives a .22 values in a standard shaped house". in response to tattoo

have decided to go with kingspan tf70, 60mm. will give me a U value of .22

i wasn't too clear, but i meant that the u value the manufacturers give on website is probably based on a specfic house shape and P/A ratio, probably the best case scenerio. so that they are all on level standing when comparing.
i wasn't talking about the .24 you posted,
it gives .24 in my software, small pfogram from xtratherm. only does u values not full energy calc.
sorry if i had you confused.

one intersting point i thought of when you mention lamda values. if the value for the site is unknown, a value of 2 is taken in ireland (irish regs)
in the UK, they take 1.5 as standard (afaik). that is why on international sites (xtratherm) they often quote set insulation thickness at two u-values.

ardara1

Mellor wrote:

s
it gives .24 in my software, small pfogram from xtratherm. only does u values not full energy calc. sorry if i had you confused.

If yhe answer using the same P & A was 0.24 the software is wrong - if you're using it to do assessment - the BER is wrong - i'd bring it up with them

Mellor

ardara1 wrote:

It gives a value of 0.24 - the standards you're looking are 13370 and 6946 BS & IS EN.

If you're working off the same P & A the answer should be the same - I've checked it on 3 different types of software - your lambda value for ground may differ slightly ? - If you are in volved in energy assessment getting the U-value calc correct is pretty much critical - what software do you use?

If yhe answer using the same P & A was 0.24 the software is wrong - if you're using it to do assessment - the BER is wrong - i'd bring it up with them

Mellor wrote:

it gives .24 in my software, small pfogram from xtratherm. only does u values not full energy calc.
sorry if i had you confused.

I think yo may have mis-read my post. I got the same answer as you.

ardara1

Mellor wrote:

I think yo may have mis-read my post. I got the same answer as you.

Sorry Mellor - you're right.

Mellor

anyway the moral of the post is,
put in more its always better in a house.