Best floorboards for UFH - dry screedboard vs chipboard

[embra]

Hi everyone,

 

Looking for some advice on best floorboard to finish our under floor heating system that will be installed across ~70 m2 ground floor. Sketch of floor construction attached.

 

Background: The system is being installed on top of existing beam and block sub floor, constrained to limited stack height. Our property was originally built ~1990 and is located in Edinburgh, Scotland. The UFH will the thermostatically controlled, using hot water generated by air source heat pump & solar thermal panels. Our intention would be to run the system year round, trusting control system to do it’s job.

 

UFH system: https://horstad.com/product-category/ufh-floor-types/eps-overlay-concrete/

 

The options I am considering:

1)     20 mm Dry Screedboard (e.g. https://www.builderdepot.co.uk/20mm-cellecta-deckfon-screedboard-20-dry-screed-panel-1200mm-x-600mm-4ft-x-2ft)

Cost: £37.92 per m2

Thermal resistance: 0.050 m²K/W

 

2)     18 mm Chipboard (e.g. https://www.builderdepot.co.uk/18mm-p5-moisture-resistant-tongue-groove-chipboard-flooring-2400mm-x-600mm-8ft-x-2ft)

Cost: £10.71 per m2

Thermal resistance: 0.105 m²K/W

 

 

The reasons I’m considering the screed board are:

1)     Higher thermal mass, floor would retain heat for longer (and take longer to heat up, but this would be offset by continually running system, and point 2)

2)     Lower thermal resistance, spreading heat more consistently and heating up faster when UFH is active. Compared to chipboard, more heat would transfer “up” to the house rather than “down” to the ground in any given time period.

 

Potential concerns:

1)     Lower thermal resistance lowers u-value of floor, effectively losing heat faster when UFH is not active.

 

Finished flooring will be as follows:

Dining area - LVT

Kitchen – LVT (small chance of porcelain tile)

Utility – LVT (small chance of porcelain tile)

Living room - Carpet

Bathroom – Porcelain tile

Hallway – LVT

 

Interested to hear experience and advice from anyone who has installed or considered similar.

 

Thanks in advance!

[ProDave]

STOP right there.  50mm EPS is nowhere near enough insulation under UFH.  100mm absolute minimum, 150mm much better.

[JohnMo]

My summer house has 50mm grooved EPS, but also has another 150mm of EPS below it.  This is ground bearing so will only see around 6 degs below it.

 

With block and beam if it's -5 outside your floor will see -5, as it's ventilated.  Your heat pump will have to run a very high temperatures to cope with heating the house and the downward heat loss.

 

You will be spending a small fortune to run the heating, as @ProDave stop and think about this.  50mm  (in fact only 34mm below the UFH pipes) is madness.

 

Not sure I would trust the heating to look after itself, it will kick in cost you money then switch off again as soon as the sun comes out. I would be switching the heating off at some date and back on at the start of the heating season.

 

 

 

 

[Iceverge]

I would consider some PIR, or even phenolic . As much as you can fit. Then layers of OSB staggered, glued and screwed for the floor. 

 

With your proposal and carpet especially it's unfortunately unlightly you would get any heating effect at all from the UFH in colder months. 

 

Use large radiator's for the heating instead. 

 

 

Alternatively cut out the block and beam with a concrete saw and put 300mm of EPS and 100mm of fiber reinforced concrete in instead with UFH. That would work well. 

 

 

 

 

 

 

 

[embra]

@ProDave, @JohnMo, @Iceverge I share your concern about the heat loss through the beam and block / uninsulated cavity. I have opened a separate thread specifically for that topic, and would appreciate your thoughts and advice there. I've added the link below.

 

Due to constraints internally, I cannot install any greater than 50 mm insulation on top of the beam and block sub-floor. I could install e.g. 25 mm Kingspan K103 along with 25 mm grooved EPS, to increase the u-value with same stack height. 

 

Setting aside the concern on heat loss into the beam and block / cavity for one moment, do you have any opinions on the floorboard specification for this UFH arrangement?

 

 

 

 

[Adsibob]

1 hour ago, embra said:

Setting aside the concern on heat loss into the beam and block / cavity for one moment, do you have any opinions on the floorboard specification for this UFH arrangement?

Pointless question of the day. A bit like asking: ignoring the temperature issue, can humans walk on the sun?

[Jilly]

2 hours ago, embra said:

@ProDave, @JohnMo, @Iceverge I share your concern about the heat loss through the beam and block / uninsulated cavity. I have opened a separate thread specifically for that topic, and would appreciate your thoughts and advice there. I've added the link below.

 

Due to constraints internally, I cannot install any greater than 50 mm insulation on top of the beam and block sub-floor. I could install e.g. 25 mm Kingspan K103 along with 25 mm grooved EPS, to increase the u-value with same stack height. 

 

Setting aside the concern on heat loss into the beam and block / cavity for one moment, do you have any opinions on the floorboard specification for this UFH arrangement?

 

 

 

 

Yep, don't do it.

Edited April 9, 2023 by Jilly

[Temp]

7 hours ago, embra said:

UFH system: https://horstad.com/product-category/ufh-floor-types/eps-overlay-concrete/

 

 

We have a system that is similar but we put it on top of an extra layer of insulation making 80mm in total. On top of that we have 21mm Engineered Oak. Works OK but only if we have a flow temperature of 50-55C. Would be no good for an ASHP system.

 

I can't imagine what 18mm chipboard and carpet would be like on top of this system. We only have carpet in areas with ufh in screed. 

 

If building again I would fit even more insulation under the UFH.  

 

 

Edited April 9, 2023 by Temp

[embra]

8 minutes ago, Temp said:

 

We have a system that is similar but we put it on top of an extra layer of insulation making 80mm in total. On top of that we have 21mm Engineered Oak. Works OK but only if we have a flow temperature of 50-55C. Would be no good for an ASHP system.

 

I can't imagine what 18mm chipboard and carpet would be like on top of this system. We only have carpet in areas with ufh in screed. 

 

If building again I would fit even more insulation under the UFH.  

 

 

Thanks for the insight, do you mind sharing the build up of your system? Is the engineered oak laid directly on top of the insulation board and UFH pipes?

 

You've summarised the reasons why I'm thinking that a dry screed board may be a better option, since it offers a lower thermal resistance.

[Temp]

25 minutes ago, embra said:

Thanks for the insight, do you mind sharing the build up of your system? Is the engineered oak laid directly on top of the insulation board and UFH pipes?

 

You've summarised the reasons why I'm thinking that a dry screed board may be a better option, since it offers a lower thermal resistance.

 

We fixed down 80mm deep battens to our B&B floor. Then between theses battens we fitted insulation and the UFH in its foiled insulation which also totalled 80mm deep. Then the Engineered Oak was secret nailed and glued to the battens. Use lots of glue in the T&G.

 

,I believe wood flooring should be at least 18mm thick to meet building regs. We went for a 21mm thick 200mm wide board.

 

PS In the past I have heard of problems with thin chipboard over regular EPS without battens. Under load the boards bend and compress the EPS eventually leading to the EPS crumbling. Some manufacturers recommend battens in high traffic areas like doorways.  Not sure how real this problem is these days. 

[embra]

7 hours ago, Temp said:

 

We fixed down 80mm deep battens to our B&B floor. Then between theses battens we fitted insulation and the UFH in its foiled insulation which also totalled 80mm deep. Then the Engineered Oak was secret nailed and glued to the battens. Use lots of glue in the T&G.

 

,I believe wood flooring should be at least 18mm thick to meet building regs. We went for a 21mm thick 200mm wide board.

 

PS In the past I have heard of problems with thin chipboard over regular EPS without battens. Under load the boards bend and compress the EPS eventually leading to the EPS crumbling. Some manufacturers recommend battens in high traffic areas like doorways.  Not sure how real this problem is these days. 

Thanks for sharing! 

 

At what centres did you place the battens? Has the floor felt solid underfoot?

 

At the moment we're planning to fit battens around the perimeter of the room, in doorways, underneath kitcehn units etc. 

[JohnMo]

I also used battens in our garden room floor buildup is as follows

 

Concrete slabs

50mm EPS 70

DPM

100mm EPS 70

70x50mm battens at 400mm centres

Centres filled with 50mm EPS UFH moulds with aluminium foil. Pipes on 125mm centres

2 layers of 9mm OSB on staggered joint lines glued to each other and screwed to battens.

Floor finish will be 10mm interlocking wooden floor.

[Temp]

4 hours ago, embra said:

Thanks for sharing! 

 

At what centres did you place the battens? Has the floor felt solid underfoot?

 

At the moment we're planning to fit battens around the perimeter of the room, in doorways, underneath kitcehn units etc. 

 

I can't quite remember the spacing but it was a match for the width of the UFH panels. Eg we fitted one batten then one ufh panel then the next batten so they were no real gaps or over tight panels.  

 

Yes feels pretty solid. 

[Iceverge]

4 hours ago, JohnMo said:

I also used battens in our garden room floor buildup is as follows

 

Concrete slabs

50mm EPS 70

DPM

100mm EPS 70

70x50mm battens at 400mm centres

Centres filled with 50mm EPS UFH moulds with aluminium foil. Pipes on 125mm centres

2 layers of 9mm OSB on staggered joint lines glued to each other and screwed to battens.

Floor finish will be 10mm interlocking wooden floor.

 

How has that worked out? Any pics?

[JohnMo]

Floor prior to OSB being installed

 

[JohnMo]

Floor with 2 layers of OSB 

[Iceverge]

Good work.

 

Couple of curious questions. How did you accommodate the pipes where they crossed the battens? 

 

Is the OSB completely floating where it's attached to the battens? 

 

How does it feel underfoot? I'm long of the opinion concrete floors are too hard but I don't want every cup on a table rattling if I walk past like a bouncy suspended floor. 

 

 

 

 

[JohnMo]

36 minutes ago, Iceverge said:

How did you accommodate the pipes where they crossed the battens? 

I stopped the battens short see image

 

36 minutes ago, Iceverge said:

Is the OSB completely floating where it's attached to the battens? 

The OSB is attached to the battens.

 

37 minutes ago, Iceverge said:

How does it feel underfoot? I'm long of the opinion concrete floors are too hard

I feels pretty solid. But there is a small bow into the middle, not sure why.  The outer perimeter of battens support the inner walls which are now plasterboarded, so there is plenty of weight there.

 

However our main house is 200mm PIR then 100mm concrete, it has a feel that is not as hard as you would think.  I fell from a couple of feet on to my bum, and could feel a slight give on the floor, it hurt but as much as I was expecting.  The concrete floor is fully floating on the insulation.

 

 

[Iceverge]

1 hour ago, JohnMo said:

But there is a small bow into the middle, not sure why. 

 Strange... Up or down? 

 

Yes we have 150mm concrete over 200mm EPS. There's "some" give but it's still too hard for my gentle tastes. 

 

[JohnMo]

bows downwards in the middle.  Will have get the long straight edge out and check it properly, nothing you notice waking on it, but noticed it with the spirit level.  May use some self levelling screed once the plasterboard is all taped. 

 

[Nickfromwales]

6 hours ago, JohnMo said:

bows downwards in the middle.  Will have get the long straight edge out and check it properly, nothing you notice waking on it, but noticed it with the spirit level.  May use some self levelling screed once the plasterboard is all taped. 

 

Use the construction one, as it has fibres so you can thin it out over wooden substrates without it giving up the ghost. Primer is a good idea also, to further aid in reducing friability, but don't let it dry before putting the SLC down