Direct Labout Build - Floor Insulation & Screed 175mm

B

Birroc

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Our engineer specified 100mm insulation and 75mm screed in our 2 storey build. Is 100mm insulation in the floor overkill ? I was thinking of making it 50mm which would give me some more floor-to-ceiling height and save me money on insulation that I could use better in the attic/roof.

Also for the second floor (above hollowcore), what depth of screed is normal and should i put insulation on the second floor too ?

any advice appreciated.
 
Thicknesses of insulation are meaningless unless the actual insulation type is specified, i.e. are we talking about polystyrene (expanded/ extruded) polyisocyanurate, polyurethane etc. In the current climate (pardon the pun) of rising oil prices etc I don't think there is any such thing as "overkill" when it comes to insulation- you should put in the greatest amount (and best quality) of insulation you can...
 
assuming were talking about polyurethane insulation.....

1. have you UFH? if not i dont see the advantage of that construction make up
2. if UFH is installed the new regs (2007) require a u value of 0.15... 100mm MIGHT barely make this.... 120mm (2 x 60) would be better.
3. If you are only at this stage then the extra insulation thickness shouldnt affect your floor to ceiling heights, alter accordingly.
4. are you putting UFH on first floor?
 
100mm kingspan went in our floor, 100mm kingspan in the roof and putting insulated plasterboard on the inside of the external walls too. i think we put 60mm kspan in the walls.
 
syd, how much should we put in the roof ? we haven't started the insulation on it yet as husband is going to do it during August when we are on hols to Ireland. he is a carpenter so no prob with cutting the shapes etc. I have just now asked him about the roof insulation and said it is 100mm on the inside of roof and then covered with 25mm insulated plasterboard. I should mention maybe that our house is a 3 storey i.e. 2 proper staircases as we have put two bedrooms and shared bathroom in the roof space with 3 velux windows on the back of house, 2 dormer windows on front of house and a window in each of the gables so lots of light.
please advise if you think this is still not a high level of insulation for the roof? thanks
 

Thanks all.
The plans call for 100mm EPS insulation. No, there is no UFH anywhere.

The distance from raft floor to bottom of ceiling batten is 2.6m - if I add 175mm, I will be down to 2.425, I would prefer closer to 2.5m
 
birroc,

Use PU or PIR insulation instead of EPS... much better performance (this is typically Kingspan or Xtratherm)
If theres no UFH then 100mm PU is fine.... i didnt know about the raft, the construction makes sense now.
This should solve your height issue as well..... is the ceiling installed already?? if not id be trying to steal another 100mm from somewhere... 2.5 before floor and ceiling is small enough.... especially with hung light fittings....
 

I am not sure I understand Syd. The battens for the ceilings are in place. If I use 100mm insulation (whichever type) and 75mm screed, my floor-to-ceiling will be about 2.425m

The only saving I can make is to reduce the screed or reduce insulation to 50mm.
 
You could consider using a thin screed product such as easyscreed...
[broken link removed]

my fear would be.... as it stands you can have a f-c height of 2.425... screed to underside of batten.
if you float a timber floor it will probably take up 25mm
the minimum plasterboard with a skim finish is about 10mm

this beings your f-c to approx 2.39.... if you hang a pendant light from that it will be very low....
 


Don't agree with that at all - besides, which do you mean by EPS -Expanded or Extruded ? There's a world of a difference..........I have extruded everywhere, and my advice is at least 100mm. With UFH I'd have 150 if poss.

Lorna - If you have a cut roof/trusses, then fill the rafter bar the ventilation space under the felt. Whether this gives you 100/125/150 I don't know, without knowing your rafter size. Then, used and insulated plasterboard over that again - with a min of 25mm insulated backing - and if you can, 50mm. You can never have too much insulation under a roof.

One advantage of low ceilings..........there very easy rooms to heat !!
 

what do you not agree with??

.. that PU or PIR insulation is better performing than EPS..???

they are.

Birroc stated that EPS was specified. Of course it makes a lot more sense to incorporate the same thickness of PU or PIR.
Typically:
Extruded polystyrene, Thermal Conductivity 0.03 - 0.034
Polyisocyranuate, Thermal Conductivity 0.022 - 0.023
 
I don't agree that it's much better. And that's when the insulation is new. PU and PIR decay over time, and their u-value changes over a period. This is due to the blowing agent used in their manufacture.

EPS on the other hand, has an effective blowing agent of air, and so does not decay thermally over time.

As for the u-values for floors, I did a quick calc on a 100m2 slab, 14 x 7.15m in size, 4 sides exposed with a 300mm wall, using:
70mm screed
on 100mm insulation
on 200mm conc slab
on gravel.

Difference in u-values between a 0.24 and 0.29 insulation (declared value of EPS Floormate), is 0.17 vs 0.19. That margin is not enough to call it 'much better', and again, it's a caveat based on the 'as new' condition of the insulation. What it'll be down the road, is anyone's guess.
 
The 0.023 TC value of PU or PIR insulation is actually a value that includes air diffusion over time, its not an 'as new' value, according to the manufacturers It i stested in accordance with the 90/90 principes of European Standard EN 13165: 2001.

They claim the from factory TC value is closer to 0.017-0.018

Whilst 0.17 to 0.19 may not be considered much better, with the ever increasing and tightening of energy conservation regulations, EPS and XPS are being used in less frequency because of their lesser performance.

When trying to achieve BERs in the area of B1 or A3 every 0.01 of a u value is precious.

Polystyrenes still have many pluses over PU or PIR, especially their recyclable nature, but on performance they do fall short.
 
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