retrofit underfloor heating viability in 70s house

[Dave4290]

Need to replace oil boiler and am looking at ASHP (no gas area). Have heard they are not very good in old houses unless you pair with UFH so was wondering whether it is viable to retrofit UFH into a 1970s house. House has concrete base with 200mm suspended timber floor where current radiator pipes live. Cavity wall insulation, double glazing, loft insulation, but is quite drafty being an old property.

1. if I remove the suspended timber floor will 200mm be enough space to install required layers .... vapour barrier, insulation, UFH in screed
2. can i keep the radiators upstairs and link this in with the UFH downstairs
3. how long would the screed need to be left before walking on it and putting down new floor coverings

 

[cross thread]

Plenty of options for suspended floors and under floor systems if you look.yes you can have rads upstairs.

 

[Dave4290]

Thanks @cross thread I would actually like to remove the suspended floor as it has seen better days and is not ventilated. Trying to work out if 200mm is going to be enough space to install the UFH

 

[Mr Chibs]

I think you may need a bit more, from ground up, left out DPC’s as the don’t add to the height

hard core 100mm
sand blinding 25-50mm
concrete 100mm
insulation 100-150mm
screed for UFH 75mm

 

[Dave4290]

@Mr Chibs for clarification, if the house already has a concrete base do you mean I would only need the top two layers? i.e. insulation 100-150mm and screed for UFH 75mm so total 175-225mm?

hard core 100mm
sand blinding 25-50mm
concrete 100mm
insulation 100-150mm
screed for UFH 75mm

 

[Dave4290]

Using an online retrofit UFH calculator looks like I may in be the region of £135-£185 sq mt. So for a 130sq meter property i'd be looking at £17550 - £24050 ouch!

Ok might need to look at plan B - upgrading existing radiator sizes

 

[Notch7]

@Mr Chibs for clarification, if the house already has a concrete base do you mean I would only need the top two layers? i.e. insulation 100-150mm and screed for UFH 75mm so total 175-225mm?

hard core 100mm
sand blinding 25-50mm
concrete 100mm
insulation 100-150mm
screed for UFH 75mm

you would need to check what the concrete base is.

A solid concrete floor slab is constructed with compacted hardcore, sand blinding, concrete.

A concrete oversite under a suspended floor might just be a layer of concrete straight over soil - just to blind it off and stop weeds growing, vermin etc.

 

[Mr Chibs]

You can do most of the donkey work yourself… if you wanted to and have the time, it will bring the cost down.

No you don’t need two concrete layers, but as Notch has said, you might have an oversite layer, as opposed to a slab.

If the floors were in OK condition you could investigate spreader plates, but not something I have knowledge about.
Others will comment.

 

[Notch7]

3. how long would the screed need to be left before walking on it and putting down new floor coverings

conventional 65mm sand cement screed: around 70 to 100 days before tiling

mapei top cem 24 hours

 

[Mister Banks]

Is an ASHP and UFH viable in a draughty 1970’s house?

 

[Dave4290]

@Notch7 silly question but is there any easy way or tell tale signs whether its a concrete slab or concrete oversite. The suspended floor isn't made using normal floor joists but rather 3x2 wooden floating frame then chipboard (200mm gap). The property site above the ground - has four course of bricks then DPM sitting on top of at least two more rows of bricks (could be more without digging) so in total sites quite high off the surrounding ground - if that gives any indiciation


@Mr Chibs i'd happily rip out all the old suspended floor and do any donkey work but have no clue about laying pipes and screed

 

[Dave4290]

Is an ASHP and UFH viable in a draughty 1970’s house?

I guess that is my question. We are little limited as we do not have access to oil. When i say draughty its not like we have a hurricane flowing through, more it is quite a cold house despite having the usual insulation. We don't for example have condensation normally associated with this type of property, so my assumption is the ait is escaping out from the building

 

[Notch7]

@Notch7 silly question but is there any easy way or tell tale signs whether its a concrete slab or concrete oversite. The suspended floor isn't made using normal floor joists but rather 3x2 wooden floating frame then chipboard (200mm gap). The property site above the ground - has four course of bricks then DPM sitting on top of at least two more rows of bricks (could be more without digging) so in total sites quite high off the surrounding ground - if that gives any indiciation


@Mr Chibs i'd happily rip out all the old suspended floor and do any donkey work but have no clue about laying pipes and screed

is there any evidence of a DPM lapped up around the edges anywhere.

do you have air bricks

by floating do you mean the joists are sitting on a wall plate fixed around the perimeter or joists sitting on spacers on the concrete.

TBH I’m not sure of an easy way to tell - prob a pro builder will have more knowledge on this.


BTW, underfloor heating is very efficient if and only if the screed is very well insulated, which is what you are looking to do. I think current regs maybe 100mm insulation.

underfloor heating works well with ASHP as it uses a low flow temperature.

I think UFH works best with tiles as the heat transfer is very quick - not so great under carpet or timber.

 

[Dave4290]

is there any evidence of a DPM lapped up around the edges anywhere.

do you have air bricks

by floating do you mean the joists are sitting on a wall plate fixed around the perimeter or joists sitting on spacers on the concrete.

TBH I’m not sure of an easy way to tell - prob a pro builder will have more knowledge on this.


BTW, underfloor heating is very efficient if and only if the screed is very well insulated, which is what you are looking to do. I think current regs maybe 100mm insulation.

underfloor heating works well with ASHP as it uses a low flow temperature.

I think UFH works best with tiles as the heat transfer is very quick - not so great under carpet or timber.

is there any evidence of a DPM lapped up around the edges anywhere. - No nothing inside - I can see what I think is a DPM between some of the courses of brick from the outside of the property

do you have air bricks - no which is partially I wanted to do something with the floor as it currently has no ventilation

by floating do you mean the joists are sitting on a wall plate fixed around the perimeter or joists sitting on spacers on the concrete. - the 3x2 joist frame are sitting on spacers directly on the concrete