EPS u-value + PIR (Celotex) u-value = ???

[oranjeboom]

Right, evening all.

 

I have sufficient depth in my ground bearing slab build up for 260mm of insulation and need to achieve at least a u-value of 0.11w/m2k. To achieve this I was going to use a mix of PIR and EPS.

 

If I were to use the below, what overall u-value do I end up with?

100mm celotex (0.16)

160mm jablite (0.164)

 

(My P/A is 0.449)

 

 

 

Original plan was to go for 275mm EPS which would get me a u-value of 0.11, but now I've got a bit less to play with. I'd like to stick with that target u-value.

 

Head is full of petrol fumes after whackering and levelling all day so my mathematical skills are even worse than usual.

 

Another option I have would be to go for EPS100 instead of EPS70 but I have some 100mm celotex on site that I'de like to use up.

 

Thanks in advance.

[Alexphd1]

Depending on what you are building but I don't know if eps70 will carry enough load, we have a mix of eps100 & 300. Maybe I am talking rubbish but was their not something about PIR insulation soaking up water and lowering the u value? 

Edited February 19, 2017 by Alexphd1

[oranjeboom]

11 minutes ago, Alexphd1 said:

Depending on what you are building but I don't know if eps70 will carry enough load, we have a mix of eps100 & 300. Maybe I am talking rubbish but was their not something about PIR insulation soaking up water and lowering the u value? 

PIR is regularly used below slabs with the use of DPM so should be fine. I'll most likely put EPS at the bottom also. As for EPS70, I think that is fine for domestic settings. Why did you use EPS300? Do you have a 747 parked in your lounge?

 

EPS70 cert: http://www.insulationexpress.co.uk/documents/Kay-Cel Flooring Insulation BBA Certificate.pdf

[Oz07]

My understanding is double eps =pir so rough and ready you'll have 360mm eps. Work your figures on online calc based on that. Sure someone will give you a more precise answer though!

[Triassic]

7. Moisture resistance – Celotex, due to having a closed cell structure, is a hydrophobic product meaning it doesn’t absorb water. This allows the thermal performance and reliability of the product to be retained over time.

 

https://blog.celotex.co.uk/technical/10-advantages-of-pir-insulation/

[Onoff]

From the bottom up mine is:

 

Compacted <40mm hardcore

Sharp sand blind

25mm EPS

DPM

150mm PIR (100+50)

Polypipe tray with UFH

A142 mesh

100mm Concrete

Tiles

 

Calcs, values.....not a clue, all based on rule of thumb, anecdotal evidence & plagiarism!

[Ian]

There's a good free calculator here:

http://www.changeplan.co.uk/u_value_calculator.php

 

Click on the drop down menu for Element Type to show "Ground Floor  (floating)"  for the bit of the calculator you need.

 

Ian

Edited February 20, 2017 by Ian

[TerryE]

18 hours ago, oranjeboom said:

I have sufficient depth in my ground bearing slab build up for 260mm of insulation and need to achieve at least a u-value of 0.11w/m2k. To achieve this I was going to use a mix of PIR and EPS.

 

Just out of interest, why?  That is why 0.11 rather than 0.12 or 0.15 even?  Remember that the temperature under your slab stays at a pretty constant 9-12°C so the loses are a lot less than you think. -- that's if you have a hard contact slab rather than a ventilated floating block and beam construction where the air circulation under the floor can drop the temperature down to ambient.  If you have some large panelled patio doors or the like, then at a U value of ~1 or less if you are lucky -- or bi-fold doors which can often leak like sieve and screw up your air losses, these together can dwarf your delta losses on the slab.

 

My point here is that you nee to regard your house as a total system and invest where it does the most good.

[A_L]

hello,

 

@oranjeboom, assuming lambda values of 0.022W/mK for celotex and 0.038W/mK for EPS then for floor areas from 100m² to 400m² and a P/A ratio of 0.449 the U-value for your 100mm Celotex and 160mm EPS is 0.09W/m²K

[Oz07]

There you go a custom calc well done

[oranjeboom]

15 hours ago, Onoff said:

From the bottom up mine is:

 

Compacted <40mm hardcore

Sharp sand blind

25mm EPS

DPM

150mm PIR (100+50)

Polypipe tray with UFH

A142 mesh

100mm Concrete

Tiles

 

Calcs, values.....not a clue, all based on rule of thumb, anecdotal evidence & plagiarism!

 

@Onoff Yes, I've covered your updates with interest over the past 12months or so. You should have popped round for some hardcore levelling as I read you'd been round to @PeterStarck the other day! Could have used your expertise levelling 90sqm.

 

 

4 hours ago, A_L said:

hello,

 

@oranjeboom, assuming lambda values of 0.022W/mK for celotex and 0.038W/mK for EPS then for floor areas from 100m² to 400m² and a P/A ratio of 0.449 the U-value for your 100mm Celotex and 160mm EPS is 0.09W/m²K

 @A_L Thanks! Yes, I came to the same result using the changeplan calc in the end.

 

6 hours ago, TerryE said:

 

Just out of interest, why?  That is why 0.11 rather than 0.12 or 0.15 even?  Remember that the temperature under your slab stays at a pretty constant 9-12°C so the loses are a lot less than you think. -- that's if you have a hard contact slab rather than a ventilated floating block and beam construction where the air circulation under the floor can drop the temperature down to ambient.  If you have some large panelled patio doors or the like, then at a U value of ~1 or less if you are lucky -- or bi-fold doors which can often leak like sieve and screw up your air losses, these together can dwarf your delta losses on the slab.

 

My point here is that you nee to regard your house as a total system and invest where it does the most good.

 

@TerryE - Good question! For some things you can aim/hope what you have done is correct. Nothing too scientific. Cross your fingers and hope for the best. That's almost the stance I took when I started looking at UFH in the old part of this house. I almost got schmoozed into going to a retrofit UFH system by a well known UK UFH company until I started looking into the science/facts a bit more. UFH with 20mm of EPS powered by an ASHP just isn't going to work. So I bit the bullet and dug up the old slab (plus an actual WW2 bullet) down to approx 500mm. U-value of 0.11 as it's better than BuildRegs...(well that ain't hard is it!!) and I noted that was the magic value that appeared to work for someone else on this forum.

 

So I've spent the £ on areas where it's going to matter on this retro/extension: slab insulation, EWI, 3G passivhaus windows and discarded other stuff like ASHP, leaky bi-folds,and fancy-looking log burners that are supposedly 99% efficient and very environmentally friendly.

9 hours ago, Ian said:

There's a good free calculator here:

http://www.changeplan.co.uk/u_value_calculator.php

 

Click on the drop down menu for Element Type to show "Ground Floor  (floating)"  for the bit of the calculator you need.

 

Ian

@Ian Thanks Ian - I did come across this last night but got a bit bamboozled until I had a better look this evening. Quite simple in the end - amazing what fumes do to your head!

 

Edited February 20, 2017 by oranjeboom
Pic for onoff

[TerryE]

@oranjeboom, my main concern about that extra 0.02 on the slab U value is that it might entail you having to raise your FFL by 100mm or whatever, so you might loose 10cm of room height, say, for two shades of bugger all difference on your actual heating bills.   How you achieve your airtighness (for example) is going to be far more significant in your overall heat balance.

[oranjeboom]

Thanks Terry. I have my datum set by the extensions and managed to retain the original FFL in the old part of the house. One of the very reasons to dig out 500mm in the old house as I didn't want to re-create door lintels and lose ceiling height. As for air tightness, that is indeed going to be an issue with a renovation - awaiting my rolls from ProDave 

It's going to take more than a few rolls and MHVR of course...

[CC45]

On our timber framed 240m2 build I've used 20 rolls so far, with prob another 5 to go plus window tape - 8 rolls (only 25m per roll) to be stuck down yet.

 

You use a lot more than you think.  Wish we'd built a square box now!

[TerryE]

Our TF manufacturer used a special to purpose air-tight OSB for the internal membrane and went to great lengths to address the vulnerabilities around the ends of joists, etc., and also contracted a guaranteed level of airtightness.  Many of the high-end window installers (we used ecoHaus Internorm SW) make a particular emphasis of their installs being airtight as well.  So it's a lot easier getting the airtightness sorted when the build technique is optimised for air tightness in the first place.

 

Unfortunately, this isn't always possible, especially in the case of an upgrade to an existing property.

 

[Onoff]

8 hours ago, oranjeboom said:

 

@Onoff Yes, I've covered your updates with interest over the past 12months or so. You should have popped round for some hardcore levelling as I read you'd been round to @PeterStarck the other day! Could have used your expertise levelling 90sqm.

 

 

 

I totally forgot you were down that way! Dug by hand have you? Gives a certain satisfaction I found and cheaper than the gym!

 

The photo is on the lines of what I'll do when I knock through the lounge / diner. I want level ceiling, floors and walls running through and at the mo absolutely nothing's in line/level from one room to the other.

 

A scary thought I had.....if you remove a concrete floor (s) like we have then DID the original concrete floor provide a certain lateral "stiction" holding the walls in place? It's not like traditional houses have ring beams. 

 

Be interested how you go about the EWI assuming you've traditional footings that "step out" from the external wall line.

Edited February 21, 2017 by Onoff
"Be interested...

[Jeremy Harris]

15 hours ago, TerryE said:

 

Just out of interest, why?  That is why 0.11 rather than 0.12 or 0.15 even?  Remember that the temperature under your slab stays at a pretty constant 9-12°C so the loses are a lot less than you think. -- that's if you have a hard contact slab rather than a ventilated floating block and beam construction where the air circulation under the floor can drop the temperature down to ambient.  If you have some large panelled patio doors or the like, then at a U value of ~1 or less if you are lucky -- or bi-fold doors which can often leak like sieve and screw up your air losses, these together can dwarf your delta losses on the slab.

 

My point here is that you nee to regard your house as a total system and invest where it does the most good.

 

Worth remembering that this is UFH going down in a refurb that, with the best will in the world, is not going to be close to PH levels!  This means the slab heat loss could be significant during the heating season, because the UFH is going to have to run warmer than yours or mine, Terry, in order to give enough heat output.  That may well push up the delta T between the slab and the ground to levels that are not dissimilar to the inside air and outside air.

 

Investing in good insulation under UFH, especially in a refurb, is going to be money well spent in my view.

Edited February 21, 2017 by JSHarris

[Nickfromwales]

On 20/02/2017 at 18:30, A_L said:

hello,

 

@oranjeboom, assuming lambda values of 0.022W/mK for celotex and 0.038W/mK for EPS then for floor areas from 100m² to 400m² and a P/A ratio of 0.449 the U-value for your 100mm Celotex and 160mm EPS is 0.09W/m²K

Hi @A_L. 

Thanks for the input . 

Can you give us a brief in the 'introduce yourself' section please ? . 

Many thanks ?. 

[oranjeboom]

On 2/21/2017 at 06:19, Onoff said:

 

I totally forgot you were down that way! Dug by hand have you? Gives a certain satisfaction I found and cheaper than the gym!

 

 

Cheaper than the gym, but you should see the chiropractor's bills!!

 

On 2/21/2017 at 06:19, Onoff said:

A scary thought I had.....if you remove a concrete floor (s) like we have then DID the original concrete floor provide a certain lateral "stiction" holding the walls in place? It's not like traditional houses have ring beams. 

 

Be interested how you go about the EWI assuming you've traditional footings that "step out" from the external wall line.

 

Walls have all held in place - no movement that I can tell. They do all go down to the traditional footings that I have. Only problem I had was where the old WC room had one wall sitting on the slab only - not any footings at all. So have decided to leave that small room as is. It was only going to be a cloakroom for boots, jackets etc and possibly a manifold for UFH (which I will have to have elsewhere now). Perhaps a wine room now that it will not have UFH and also a lower temp than anywhere else in house!

 

As for EWI, yes EPS all the way down to the top of the footings (still have to decide whether I leave a gap along the DPC) and how I protect the EPS below ground from future gardening spades and possibly rats/mice. I'll probably create a french drain of some kind and then also use pavers BGL. Most likely be an autumn job so time to think about that one.

 

On 2/21/2017 at 08:22, JSHarris said:

Investing in good insulation under UFH, especially in a refurb, is going to be money well spent in my view.

 

Yes, long term best bet. Don't want to be in a position whereby they wife starts plugging in electric fan heaters as the place is leaking heat. Spend big now to save £££ in future years. Shame the price of insulation is creeping up over the past 12months...and more price rises to come I see.

[PeterW]

2 hours ago, oranjeboom said:

Shame the price of insulation is creeping up over the past 12months...and more price rises to come

 

I thought that and I've just gone down the route of ordering PiR from Seconds and Co as they had an offer on - £24 for 123/128mm which is 20% better than any of the merchants or online guys could do and it's cosmetic seconds only. May well put 50mm of EPS under it too instead of sand blinding as its cheap as chips ...