Over or in screed

[geoffdg]

Hi all,

I have searched and have not been able to find this question, although I am sure it will have been asked previously. The question is is it better to have the UFH in the screed or on top, like the Wunda system which is installed on the finished screed. The main advantage seems to be the quicker warm up time and I cannot see any downsides. 

 

Thanks,

Geoff

[Declan52]

If it Heats up quick it will cool down quick. 

[Mr Punter]

You also need to consider cost, speed and ease of installation and required floor finish. I had a quick look at the Wunda site and was surprised to see they showed a solution involving notching the top flange of an I joist floor, which I thought was a no-no.

[Jeremy Harris]

Is having UFH that heats up quickly a significant advantage over having a system that just maintains a steady temperature?

 

It's certainly a fair bit cheaper to just fit the UFH pipes inside a concrete floor slab, as the only additional stuff needed is the pipe and a bucket load of cable ties.

[scottishjohn]

have a relatively thinner slab if you want quick heat change

,but  as JS says it will also cool quicker

no free lunchs 

but a suspended floor will need  a different  solution

maybe a dry biscuit mix ,all depends how much height you got to play with 

I did a retro fit ufh in suspended floor 17years ago in present house -

and to keep floor height as it was  I routed all the chipboard flooring to take small bore ufh pipes  then got strength back in floor by sheathing in 8mm ply glued and screwed 

and under floor fitted with 75mm pur ,then air gap and space blanket whole of underside of floor

yes it works,  and i could do it a bit at a time while house was livable  as I was lucky enough to have 2-3ft ish under house to work in 

would i do it that way again 

NOT A chance - very slow and hard work 

should have bite the bullet  and accepted a bit less ceiling height and trimmed the doors  and built a 40mm  thick system on top- would have been done in a week 

success and failure will be dependant on attention to detail 

[Nickfromwales]

The overlay systems need a painfully accurate control system to stop over & under shoot of the set room thermostat set point. These types of floors continuously give me a headache as I get called out to installs for rental / residential tenants who just cannot get their head around UFH, and the usage patterns of.

They typically need a higher water temp to achieve what a slab would do with say 10^oC lower flow temp, so suffer from the hysteresis of the floor not being accurately responded to by the room stat or the heat source.

FWIW, I would not quote for an overlay system as its a PITA to control and an equally large PITA to get a customer / end user to understand how to use it properly.

Not a fan, sorry.

[geoffdg]

Thanks everyone, it looks like in screed wins. I will pass your comments onto my son, he was the one that suggested over screed.

 

Geoff

[Cpd]

10 hours ago, Nickfromwales said:

FWIW, I would not quote for an overlay system as its a PITA to control and an equally large PITA to get a customer / end user to understand how to use it properly.

Not a fan, sorry.

given  I have a traditional 10x5m one and a half story cottage with NO option to lay pipes in a screed (as talked about before) and a desire to run an ASHP for DHW and space heating in a bid to reduce my Electricity bills and having been pointed at the WUNDA overfloor system in the past....... (can’t find the panic button) given the small nature of the cottage, the fact that it is well insulated and very air tight with MVHR and will be occupied by holiday geusts every day of the summer (6 months) and by my lot in the winter (as I upgrade my own house next door)  would you recommend that I drop the idea of an over floor system and start to look at radiators specifically designed to run from an ASHP ?  I would have NO problem with the visual impact of radiators as the whole “decor” is to be very quirky and rustic...... 

 

I was part way through using JSH spreadsheet to provide more heating requirements but can’t load it on this iPad, but will get specifics before moving this forward, BUT I would welcome your opinions on over floor v radiators with the broad variables at this stage.  Thanks      

[Ferdinand]

13 hours ago, Nickfromwales said:

The overlay systems need a painfully accurate control system to stop over & under shoot of the set room thermostat set point. These types of floors continuously give me a headache as I get called out to installs for rental / residential tenants who just cannot get their head around UFH, and the usage patterns of.

They typically need a higher water temp to achieve what a slab would do with say 10^oC lower flow temp, so suffer from the hysteresis of the floor not being accurately responded to by the room stat or the heat source.

FWIW, I would not quote for an overlay system as its a PITA to control and an equally large PITA to get a customer / end user to understand how to use it properly.

Not a fan, sorry.

 

Is there anything which can help mitigate the downsides of an overlay system by providing a measure of buffering and persistence in the heat?

 

eg spreader plates on the top, say under the underlay which then has laminate on top?

 

Possibilities might be metal sheet, or even slate or cheap tiles or similar. Creative sourcing would be required.

 

There is no point in having something thicker than a screed, but something may be possible. Quirky, mind .. so probably strictly for self-builders.

 

Ferdinand

 

Edited February 5, 2019 by Ferdinand

[scottishjohn]

ceramic tiled floor would be a good heat sink ,which is what i used on my suspended  floor