UKH

Hello helpful builder type people! 

We have retrofitted wet UFH throughout the living area of our house (low profile system onto suspended wooden floors.) It's working brilliantly, very happy.

So now we need to sort the entrance hall, which is on a lower level and has a concrete floor. We are planning to use the same system, but are unsure what to do about insulation. On the suspended floors, there's wool insulation under it, hung in wire netting. For the concrete floor, do we need to insulate under our heating or not? Part of me thinks maybe best to just lay it straight down and then we have a big mass of concrete which stays warm for longer. However there is also the argument that we are just going to lose heat this way as it heats up the ground underneath and then we lose it. 

So, insulation or not? And if we do, any suggestions on what to use?

Thanks!

We're considering low profile underfloor heating (wet) in our new bungalow. How disruptive was the laying? The Mrs isn't too keen on the disruption. We're going solar/air source heat pump and insulating the hell out of the place - but floor (suspended timber joists) is a big unknown.

We were living in the house as we were doing it, fitting it ourselves, and both working and dealing with 2 crazy dogs! So, it was highly disruptive and felt like it went on for ages! BUT, I don't regret it at all. I hated the process, but I love that we have it now and it wouldn't put me off doing it again. 

We also got heat pump and extra insulation. Getting solar panels once we have fixed the roof

I used 50mm routed XPS panels with 100mm spacing and 16mm pipe on a concrete/screeded beam and block (I think) floor with no other insulation, with engineered oak floated above it. It works, but is slow to respond and doesn't have much thermal inertia so you can tell an hour or so after its gone off. 

Hmm, I don't mind it being slow to heat up, but I was hoping it would have good thermal intertia. Do you know what is under your beam and block floor? Is it likely to be bedrock or soil? I don't know how much difference either of those would make but just wondering how similar it is to ours. I think ours is probably a straight concrete pour onto bedrock, but it's a bit hard to tell!

Actually, those panels are insulated, aren't they? So the heat might not be going down into your concrete floor through them? We have just plastic trays which we have been laying the pipes in and then infilling with screed, so no insulation as part of the system at all. 

A modern beam and block floor will have a ventilated void beneath, typical regs 400mm clearance to inert / treated subsoil/ hardcore.

An older b+b floor may just have a void otherwise it would have been cheaper to just laid a concrete floor.

Older concrete floors might be laid straight onto bedrock or hopefully consolidated ground with or without a dpm. Dpm is typically black visqueen sheet lapped up at the edges then cut off after concrete sets, worth having a look, may have to remove some skirting. 

Drilling a hole could provide answers but would  damage any dpm if its there. Worth getting/ doing a damp test on the concrete floor prior to any ufh work.

On the solar panels, you presumably saw Rob Ward's post about his panels effectively being free becauae of needing less slates  for his roof repairs.

https://www.theunderfloorheatingstore.com/products/xp-pro-insulation-board

Something like this, you can get thicker ones and some with channels in for wet systems piping, then put laminate over. You can get away with just a 20-30mm floor height increase, but obviously more means better insulation. 

Note. I'd seal the floor or dpm first. 

There would be no space for a void under this floor, it's almost certainly straight onto bedrock. There is damp in a couple of patches of wall, and we can't get anyone to turn up and look at it! We have tried endlessly! However, no sign of damp floor.

The roof is currently metal and really needs to be replaced with rubber as it's too flat for metal. We can't get anyone for that either, so likely doing that ourselves too. 

Seal with what? We usually prime all of the floors with diluted SBR before we lay it, usually a couple of coats. Is that sealed enough or do we maybe need something different?

I've no idea if this is a good example or not  as I know fek all about such things... we just got underfloor heating on a concrete floor the plumber poured some sort of self leveling compound on top of the concrete and layed the insulated panels that the pipes slot into directly on top. It was working brilliantly until the pump broke....

It's really hard to get a reliable answer on this one. Our house is solid wall/concrete floor almost certainly just on top of the subsoil.

Some say to dig out the floor completely and put down a couple of hundred mm of insulation, or limecrete. A big expensive job obviously. Others say a 20-30 mm low profile system will be fine insulation wise. Who's right?

As to the latter, there must be something to be said for the idea that a concrete or earth subfloor heated constantly would retain some heat with its mass? Decisions decisions..

A tiny bit of insulation is better than none. 400mm would be a gold standard ie. passivhus, for retro fitting it's a question of cost and convenience.

https://www.screwfix.com/p/cementone-aquaprufe-flexible-damp-proofer-waterp...

Or similar 

https://www.resinfloorcoatingsuk.com/shop/rfc-epoxy-damp-proof-membrane/

There are specifications for this. We did it on our property:

• Remove old concrete floor.
• Dig down to the centre of the earth.
• MOT type sub base. 100ml?
• Blinding sand.
• DPM.
• 100ml concrete.
• 100ml rigid PIR insulation.
• More dpm.
• UFH pipes.
• Screed.

We cheated with only 75 ml of concrete. Was it worth it? YES! However this was in the main kitchen dining area and part of a renovation/new kitchen. In an entrance hall I don't think I'd bother, unless its a large area.

Thanks. I'm considering diy.  What you describe is kind of what I expected. The dog's a lodger so can stay elsewhere...

Absolutely no way are we digging it out!! It's the lower floor, almost basement, entrance and storage area with stairs up to our living area. We want it to feel comfortable and homely, but no one will be hanging around there for long, so no need for it to be super warm. The heat does rise to the rest of the house though, it's really noticeable even if we just have the wee electric heater on in there, so definitely worth doing the way we have everywhere else

If we could have afforded it, the much better way to do it would be hire someone to do it for you and rent an Airbnb for a few weeks while they do it! 

The biggest PITA, is that you can't really fully complete one room before moving on to the next. Well, not if you want a plumber to connect and pressure test it, which did seem worth doing. 

We emptied a room. Fixed any uneven bits of floor and cleaned it all. 2 coats of primer and then screwed our panels down (ours aren't the insulated ones with grooves, ours are just plastic sheets with clips for the pipes). Then laid the pipes (there was more technique to this than I had anticipated!). At that stage we would have to put down dust sheets and ply boards as a temporary floor while we moved onto the next room. Once we had done half of the house, we got the plumber in to connect those and then we could screed the rooms we had done. Then we did the same process with the other half of the house. So each room was emptied and refilled at least twice in the process. 

Horrible job, great result 🙂

Two points:

- think you mean 'mm' not 'ml' !

- why have 2 layers of dpm? You only need one, and whose position is probably best determined by the interface with your dpc level in the external walls. 

The house is built on a 30ish degree slope, so one end is basically ground level/partially underground, the far end is nearly a storey up so a massive void! There is DPM throughout, no damp issues. The void is unventilated. I've been meaning to get a look inside it, I have a feeling it'll be chock full of building site rubble as our houses were built last on the street! 

My problem with the concept of trying to use an uninsulated slab for thermal inertia is that heat doesn't rise in solids, it just flows along temperature gradients. Above the floor you'll always have a temperature that's higher than the slab and ultimately the void/ground below, so you'll have more heat going down most of the time. If you've been installing on upper floors(?), you're heating air that's still in your house which will mainly convect back to the floor at some point, and the screed on the top so I can see that performing well.

My system spends a few hours running at 4am at a 45ish°C flow to get up to temp (from 15->20°c) for 7am, then cycles on once or twice an hour during the day. I need to add a buffer tank to minimise the short boiler cycles but it's very low on the list of priorities, probably will happen alongside a heat pump. What we can't do is heat the room up in the morning and have it remain warm all day. Highest gas use in a day over the winter was just over 100kWh, average was around 55, so still pretty good to keep the whole house above 20 upstairs and in the office, and 18/16 in the bedrooms. 

I used Artidex NA to level over old bitumenous tile goo (no primer needed for basically anything), then laid the insulation boards using spray glue and foil taping the joints. No extra dpming, but it was dry anyway. I did a mediocre job levelling, next time I'd probably have some flexible tile adhesive handy to shore up panels that didn't sit flat.

You can lay on top of a concrete floor.  We converted our garage into a room and got an underfloor heating kit.  It comprised of slot together insulation panels with pipe grooves in them (like a giant jig-saw).  We laid the panels on the floor, slotted the pipes in, attached everything to the manifold (plumber did that but), filled with water, checked no leaks then laid our engineered wood flooring on top.  It’s been there 12 years now and works great.

One DPM on the blinding sand before the concrete and then one on top of the insulation before the UFH pipes and screed. This is for a wet screed. No DPM and it would potentially escape down through the rigid insulation.

Yeah, fair point if for a wet screed.