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Author Topic: Floor Insulation.... Unlimited Space..... UFH  (Read 4405 times)
Bikerzz
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« on: November 17, 2019, 09:24:16 AM »

Ladies and Gents you are going to be happy, the builder came to look at my project again and said the timber suspended floor I have he is going to chop out and put the wall Im removing in it in layers, paddy whacking and will do a solid concrete base as makes sense. Which means I can put a HUGE amount of Insulation in before the liquid UFH goes in.
The rest of the house will be block and beam with 50-80mm insulation and 50mm liquid screed.

So what do I do on the new solid concrete floor?
2 layers of XPS 200mm to make 400mm?
Do I keep it at 50mm Liquid screed?
This part of house is the living room and kitchen in the middle part of the house (it had a 3 sided extension in 1994) hence some timber and some block and beam.
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TT
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« Reply #1 on: November 17, 2019, 10:00:04 AM »

Remember the perimeter detail with regards to dpm lapping and insulation
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Countrypaul
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« Reply #2 on: November 17, 2019, 11:07:30 AM »

If you have that much space, why don't you just put block and beam in the same as the rest of the floor? - in our case that we did that and didn't need concrete beneath just a simple trench fill foundation for the new walls.

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A.L.
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« Reply #3 on: November 17, 2019, 04:18:38 PM »

hello,

Which means I can put a HUGE amount of Insulation in before the liquid UFH goes in.

you don't give any details for your extension, but as an example for a 5x6m extension with xps(thermal conductivity 0.027) U values are 200m/0.11, 300mm/0.08, 400mm/0.06. So unless the xps is cheaper than what ever else would go there don't overdo it  whistlie
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Bikerzz
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« Reply #4 on: November 17, 2019, 06:29:25 PM »

Because Block and beam would cost far more and I am removing a 4.5m wall so can use that as hardcore. To buy beams and blocks I would imagine would cost more than some concrete and Ive saving skip space by chucking my wall thats coming out in the void. Its what the builder suggested.

The extension is block and beam which I will only get 50-80mm of Insulation in.
Sorry I meant EPS, yes its well over doing in compared to rest, but I will spend most of my time in living room and kitchen, Its in middle of house so only 7m of it boundary an external wall.
So it needs about 24 sheets:

Jablite EPS100 at 150mm 780 Which is 0.036w/mk
The 50mm Kingspan K103 is 0.018w/mk

What thickness at 0.036w/mk do I need to match or beat 50mm at 0.018? Iv been google for an hour for U to R calculators and I just cant grasp it, is it double as it looks? So 100mm equals it?

Its approx 3m into hallway is timber suspended

https://imgur.com/SZpOtiw
« Last Edit: November 17, 2019, 08:01:57 PM by Bikerzz » Logged

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A.L.
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« Reply #5 on: November 17, 2019, 08:26:30 PM »

hello again,

What thickness at 0.036w/mk do I need to match or beat 50mm at 0.018? Iv been google for an hour for U to R calculators and I just cant grasp it, is it double as it looks? So 100mm equals it?

Yes 100mm of 0.036 has the same thermal resistance as 50mm of 0.018
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biff
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« Reply #6 on: November 17, 2019, 08:35:37 PM »

Hi Bikerzz,
           I think that your builders idea is a good one. May I suggest that you insert either black or orange 4 inch soil pipe  from front to back at air  brick level possibly T, ing in the middle to continue the air flow. These pipes can later be used to carry cables  or water pipes. By T, ing off you can cover all your bets for anything that needs access later. .
It is also very important to have the DPC membrane upstanding 150 . You can stick it to the wall  behind the skirt. Check to see what the Radon gas reading is for your area and if it is high, then either join the floor membranes to the wall DPCs with a suitable sealer that can be trowlled on to the wall behind the skirt.  If the Radon gas readings are high, you will probably  find a connection sump or just well vented access to the outside under the other floors.
            Have fun
       Biff
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Fintray
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« Reply #7 on: November 17, 2019, 08:49:51 PM »

Example U values from the Jablite BBA certificate:



* Jabfloor.jpg (166.21 KB, 1150x772 - viewed 401 times.)
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Bikerzz
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« Reply #8 on: November 18, 2019, 07:57:00 AM »

Hi Bikerzz,
           I think that your builders idea is a good one. May I suggest that you insert either black or orange 4 inch soil pipe  from front to back at air  brick level possibly T, ing in the middle to continue the air flow.

Cheers Biff. Not sure if you looked the image, but I dont think I need to do that as there is still airflow all the way around my "new slab bit"
Thanks Fintray I think 200mm of the Jablite 100 will be higher than rest of house so prob just do that.
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Bikerzz
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« Reply #9 on: December 14, 2019, 09:02:28 AM »

Oki so builder was around having another look and I spoke to him about this.

He said build base up, then 200mm Polystyrene (or whatever), then 4" concrete base, then put pipes on that with the liquid screed. He said more thermal mass in there then and a better base. Would you all agree? If so which insulation and how much can I get in with the concrete going ontop? Still 200mm polystyrene stuff? I presume I need a 2 DPMs both around insulation like this too?
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marshman
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« Reply #10 on: December 14, 2019, 01:32:31 PM »

Oki so builder was around having another look and I spoke to him about this.

He said build base up, then 200mm Polystyrene (or whatever), then 4" concrete base, then put pipes on that with the liquid screed. He said more thermal mass in there then and a better base. Would you all agree? If so which insulation and how much can I get in with the concrete going ontop? Still 200mm polystyrene stuff? I presume I need a 2 DPMs both around insulation like this too?

2 comments (based on personal experience and living with UFH for over 30 years).

1. 200mm of polystyrene seems overkill to me. I know with insulation the more the better but it reaches a point when the gains are almost too small to measure. My current house - renovated old farmhouse with parts dating back to the late 1600's - has "only" 50mm of polystyrene ON TOP of the concrete oversite (base) covered with 1" pitch pine floorboards and then carpet. My previous house, a self build, had 2 layers of 2L2 (foil covered bubble wrap!) ON TOP OF concrete oversite with UFH pipes in a 50mm screed.

2.  The response time of the pipes in screed was slow, under floorboards it is quicker but not fast by any standards. With the best part of 150mm of concrete to heat I would worry your system will be very, very slow to respond. Yes you will have thermal mass, but I think it is in the wrong place. Just my opinion! My current hoouse has all the thermal mass in the walls and large central chimney/inglenook fireplace.

Both places are/were stupidly cheap to heat, first place had a condensing gas boiler (in the late 1980's) and my current place a GSHP.

Roger
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splyn
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« Reply #11 on: December 14, 2019, 06:44:51 PM »

1. 200mm of polystyrene seems overkill to me. I know with insulation the more the better but it reaches a point when the gains are almost too small to measure.

[EDIT] The calculation below isn't reasonable because it's mixing average seasonal temperature with a 45C floor temperature needed at maximum design load for, say -1C outside temp. The average seasonal floor temperature required would be 20 + (45-20)/(20-(-1)) x (20-7) = 35.5C. The point still stands  however -the ground losses will be more than double those of an unheated floor so better insulation is warranted.

Personally I'd go for more or use better insulation. With an unheated floor the surface temperature might be around 17C; if the average outside temperature during the heating season is, say 7C, the temperature difference is 10C. With a heated floor at 45C the average difference is 38C meaning the losses are nearly 4 times as much! (And the carpet/underlay insulation doesn't help in this case).

 You can get some pretty good deals on Kingspan/Celotex etc. seconds which would be fine for floor use - you should be able to get 300mm polyurethane for less than 500. The law of diminishing returns applies though - the losses through the edge of the slab through the wall will become a bigger proportion of the total losses as the underslab insulation thickness increases. I'd suggest playing with the free heat flow modelling software THERM (easily found with Google) - it's quite surprising how big a problem thermal bridging effects can dominate losses when you you are trying to achieve U values of 0.2 or better. The interface is a bit clunky and frustrating until you get used to it but there are some video tutorials.

Quote
2.  The response time of the pipes in screed was slow, under floorboards it is quicker but not fast by any standards. With the best part of 150mm of concrete to heat I would worry your system will be very, very slow to respond. Yes you will have thermal mass, but I think it is in the wrong place. Just my opinion! My current hoouse has all the thermal mass in the walls and large central chimney/inglenook fireplace.

I agree - 200mm of concrete and screed will take forever to heat up and cool down - 36m^2 would take about 120kWh of heat to raise by 25C. The floor would be perpetually too hot or too cold when the outside temperature changes. I went for a more expensive Gyvlon screed to minimise the screed thickness to 40mm to get the thermal mass as low as possible, but even that means more thermal mass than I would have liked.

However, 40mmm is the minimum thickness so getting the insulation level right is critical and a lot of careful work if you need to match an existing floor height. I used a layer of sand over the concrete subfloor to level it and get the right for the insulation I used. Also bear in mind that insulation has a few mm of tolerance on its thickness so measure it if you intend to minimise the screed thickness.
« Last Edit: December 15, 2019, 06:45:37 AM by splyn » Logged
marshman
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« Reply #12 on: December 15, 2019, 01:17:29 AM »

1. 200mm of polystyrene seems overkill to me. I know with insulation the more the better but it reaches a point when the gains are almost too small to measure.

Personally I'd go for more or use better insulation. With an unheated floor the surface temperature might be around 17C; if the average outside temperature during the heating season is, say 7C, the temperature difference is 10C. With a heated floor at 45C the average difference is 38C meaning the losses are nearly 4 times as much! (And the carpet/underlay insulation doesn't help in this case).

 

But the floor temp would/should never be anything like 45 deg C.  The point I was making was I have much less insulation, yet both houses were very efficicient indicating minimal heatloss through the floor. 

Roger
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splyn
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« Reply #13 on: December 15, 2019, 07:32:02 AM »

1. 200mm of polystyrene seems overkill to me. I know with insulation the more the better but it reaches a point when the gains are almost too small to measure.

Personally I'd go for more or use better insulation. With an unheated floor the surface temperature might be around 17C; if the average outside temperature during the heating season is, say 7C, the temperature difference is 10C. With a heated floor at 45C the average difference is 38C meaning the losses are nearly 4 times as much! (And the carpet/underlay insulation doesn't help in this case).

But the floor temp would/should never be anything like 45 deg C. 

The floor surface temperature would typically be between 25C and 29C depending on the output required,  but the screed temperature next to the insulation will be rather higher due to the thermal resistance of the screed and the floor covering. It won't be far off the mean water temperature which could be as high as 55C in some designs.

You did however make me revisit my original post and I realised that I had much overstated the losses which I have edited.

Quote
The point I was making was I have much less insulation, yet both houses were very efficicient indicating minimal heatloss through the floor.

Good point; it's easy to overlook that the absolute losses are small at these levels of insulation such that money may be better spent elsewhere. For a floor with a mean water temperature of 45C outputting 75W/m^2, the loss at -1C is only 6.9W/m^2 for a U value of 0.15, or 9%. Over most of the heating season the losses are much less so you'd never get your money back by doubling the insulation.

It does beg the question though why recommended U values for floors and ceilings are 0.11 for new builds but don't require better floor values for underfloor heating (at least I don't think they do). Perhaps 0.11 is simply a practical and economic limit.
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« Reply #14 on: December 15, 2019, 10:23:05 AM »

I am "suspicious" of the assumed ground temperatures using in heatloss calculations for the floor. Just because the average outside temperature is for example 6 deg C, doesn't mean the relevant ground temperature is 6 deg C, may be very late in the heating season but not all the time. At a depth of 1.5m the ground temp at my place is currently a fairly constant 12 deg C at my house, though the average outside temp has been regularly down to 6 deg C.  A properly designed UFH system will run constantly at low temperatures - ave water temp of < 30 deg C - mine is <25 deg C. So my practical experience and my gut feeling says ground insulation is often overdone and the money would be better spent elsewhere (draught proofing and MHRV).

Roger
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