UFH pipes in slab under blockwork walls

[Thorfun]

20 hours ago, Thorfun said:

I'm resurrecting this thread as I have a vaguely pertinent question about it all. ?

 

despite what @Bitpipe said above I've decided to go back on my decision about UFH in the basement and I am going to run the pipes for it even if I never connect it up. I have the pipes here and I'd rather do it now than regret it later for the £500 the pipes cost.

 

now, I have a question/dilemma about the fitting of the pipes.....

 

we have between 80mm - 100mm from slab to the level threshold doors in the basement. I am going to go for concrete based liquid screed and have 200mm EPS300 under the slab.

 

my dilemma....

 

if I put 20mm EPS100 and leave 20mm for floor finishes my screed will be between 40 - 60mm thick so will save money on screed and the EPS is relatively inexpensive. This also allows me to simply staple the UFH pipes to the EPS rather than having to buy click tracks and stick them to the slab. more savings! but, if I put the 20mm EPS down will that actually help or hinder the UFH (should I ever use it)? I'm wondering if any heat that goes down through the EPS in to the slab will just sit there between the 200mm EPS under the slab and the 20mm EPS above the slab and it's a bit of a waste. or will the heat warm the slab and act like a thermal store with a gradual release through the 20mm EPS above the slab as it's the path of least resistance for it?

 

or should I pay the extra for the 60 - 80mm screed and click tracks and just use the 250mm slab as a thermal store?

 

I'm tempted to put down the 20mm EPS as it will be a lot cheaper but I'd just like to know if it could be a potential mistake or if I'm worrying about nothing again?

 

upon further research it would appear that the above dilemma about 20mm insulation is a moot point as it appears that UFH pipe staples come in 40mm or 60mm lengths. so with 16mm pipe from Wunda and 20mm EPS those staples are too long and won't hold the pipes down. so I'm going to have to use some form of click track or egg crate product.

 

even with 25mm EPS or PIR it's borderline that the 40mm staples will fit.

 

so for the next question, with the 250mm slab and between 50mm - 70mm concrete liquid screed on top will the UFH (if required) be effective at all? I presume the response time will be stupidly slow but it could be that once the slab gets up to a nice low temperature then it will stay there for quite a while due to the 200mm EPS underneath the slab?

 

the only other option is we only leave 10mm for our floor covering which will limit us to LVT in the room with the level threshold sliding door (the other rooms could have a little step up to tiles I guess although I'll need to check door heights) and we could then put 30mm insulation and 40mm - 60mm screed.

 

I really don't know which way to go.

[Thorfun]

more thinking and discussion has been done on this subject with the lovely lady of the house. we've decided that we're both happy using LVT in the basement throughout and so we'll leave 10mm floor covering. I phoned Cemfloor and they said that 40mm minimum for their product. that means I can have 30mm insulation which is enough to use staples!

 

so I think I've made a decision at last! 

 

yay for me.

 

just need to confirm with the screed installers that the plan is fine and I can crack on with it all.

[Bitpipe]

On 10/01/2022 at 16:02, Thorfun said:

I'm resurrecting this thread as I have a vaguely pertinent question about it all. ?

 

despite what @Bitpipe said above I've decided to go back on my decision about UFH in the basement and I am going to run the pipes for it even if I never connect it up. I have the pipes here and I'd rather do it now than regret it later for the £500 the pipes cost.

 

now, I have a question/dilemma about the fitting of the pipes.....

 

we have between 80mm - 100mm from slab to the level threshold doors in the basement. I am going to go for concrete based liquid screed and have 200mm EPS300 under the slab.

 

my dilemma....

 

if I put 20mm EPS100 and leave 20mm for floor finishes my screed will be between 40 - 60mm thick so will save money on screed and the EPS is relatively inexpensive. This also allows me to simply staple the UFH pipes to the EPS rather than having to buy click tracks and stick them to the slab. more savings! but, if I put the 20mm EPS down will that actually help or hinder the UFH (should I ever use it)? I'm wondering if any heat that goes down through the EPS in to the slab will just sit there between the 200mm EPS under the slab and the 20mm EPS above the slab and it's a bit of a waste. or will the heat warm the slab and act like a thermal store with a gradual release through the 20mm EPS above the slab as it's the path of least resistance for it?

 

or should I pay the extra for the 60 - 80mm screed and click tracks and just use the 250mm slab as a thermal store?

 

I'm tempted to put down the 20mm EPS as it will be a lot cheaper but I'd just like to know if it could be a potential mistake or if I'm worrying about nothing again?

 

 

Running pipes and not using is not a bad strategy if it gives you peace of mind for nominal cost. However you're seeing the dilemma that we faced.

 

Like us, you have a thick layer of load bearing EPS (we went for 300mm) under the concrete slab. I assume that the external wall insulation ties in to this so the basement is 'wrapped' externally in insulation (ours is 200mm EPS 70). This means the basement structure will warm to an ambient temperature (ours is about 19-20) and stay there year round. Remember also that the ground stays at a nominal temperature of around 6-7 degrees year round irrespective of surface temperature so it's a fairly stable system.

 

So all that said, if you add a heated layer to the surface of the basement slab then you either need to isolate it from the rest of the slab (to avoid the storage heater effect) or go for the opposite approach.

 

Another 'peace of mind strategy' that you may consider is to put isolated electrical spurs in the walls to allow for small space heaters in future (what we did for our bedrooms, never used after 6 years). Or lay 150w UFH wire in the area if you're worried about cold ceramic tiles underfoot (what we did in our bathrooms, although that would have been unwarranted in basement as our bare slab is comfortable underfoot, we then laid Karndean over it).

 

Or even just plug in an air fans if the basement ever feels cool and it will warm up very quickly. 

 

 

Regarding traditional screed, we did not use any. The cast floor was tamped flat (not perfectly) and the flooring guy used a self levelling compound ranging from 10mm max to 2-3 mm min to give a stable surface to work with. Why don't you do this, save on screed and have slightly taller rooms?

 

Our basement contains two fridges in the hallway plus TVs and other gadgets in the den rooms. The gym has an occasionally used running machine. All are perfectly comfortable temp. The plant room has the MVHR, gas boiler and UVC so they also contribite heat into the envelope.

 

Just keep in mind that however you do it, any additional heat you introduce into the basement will propagate into the upper structure so may make the house much warmer than intended.

 

It is very easy to overheat a passive standard house, even in winter. We had one additional family down for Christmas and were opening windows to get some cooler air in after making the xmas dinner.

 

 

[Thorfun]

 

1 hour ago, Bitpipe said:

Regarding traditional screed, we did not use any. The cast floor was tamped flat (not perfectly) and the flooring guy used a self levelling compound ranging from 10mm max to 2-3 mm min to give a stable surface to work with. Why don't you do this, save on screed and have slightly taller rooms?

our ceilings are already 3m in the basement, not sure we need extra ceiling height! also, I'm working to a level to give us a level threshold to the sliding door out to the sunken courtyard. so that is between 80mm - 100mm from the slab (our slab pour is pretty bad). so the extra cost for the extra screed will be more than putting down EPS to bring the height up.

 

I fully understand your argument and I know you're right about not needing heating but I just can't convince myself. like you say 'a small price to pay for peace of mind'. I doubt we'll ever use it but I've already paid for the pipes so that money is gone and forgotten about so I think it's a no brainer for me to just install the pipework and then just leave it disconnected. I'm pretty sure it'll actually save me money by putting the EPS and UFH pipes down when factoring in the extra screed cost.

 

1 hour ago, Bitpipe said:

Another 'peace of mind strategy' that you may consider is to put isolated electrical spurs in the walls to allow for small space heaters in future (what we did for our bedrooms, never used after 6 years). Or lay 150w UFH wire in the area if you're worried about cold ceramic tiles underfoot (what we did in our bathrooms, although that would have been unwarranted in basement as our bare slab is comfortable underfoot, we then laid Karndean over it).

 

Or even just plug in an air fans if the basement ever feels cool and it will warm up very quickly. 

 

I had another mild panic moment about heating on the first floor even though I'd already decided we didn't need it (I guess I have too much time sitting at my desk for the day job while thinking about the build!) and was thinking about putting in low profile UFH throughout upstairs but after discussing it with the wife she gave me a metaphorical slap around the face to bring me to my senses and we're back doing what we originally agreed with the electric UFH and towel rails in the en-suites and we are going to first fix for air conditioning at least (probably 2nd fix it now as well) and so we can use that for supplementary heating if required. but for the basement I think I'll just stick with the UFH for now. I might still put isolated spurs for electrical heaters but tbh I doubt it as I really don't think it'll be necessary. 

 

 

[Thorfun]

21 hours ago, Thorfun said:

I phoned Cemfloor and they said that 40mm minimum for their product. that means I can have 30mm insulation which is enough to use staples!

sadly this information wasn't correct. a 30mm cover for UFH pipes is required. it 'can' go to 25mm at a push though. but with 16mm pipes and 30mm cover we're looking at 46mm minimum screed.

 

so the final decision is leaving 10mm for LVT flooring with 25mm EPS100 gives us a screed of between 45mm - 65mm.

[Bitpipe]

3 hours ago, Thorfun said:

 

our ceilings are already 3m in the basement, not sure we need extra ceiling height! also, I'm working to a level to give us a level threshold to the sliding door out to the sunken courtyard. so that is between 80mm - 100mm from the slab (our slab pour is pretty bad). so the extra cost for the extra screed will be more than putting down EPS to bring the height up.

 

I fully understand your argument and I know you're right about not needing heating but I just can't convince myself. like you say 'a small price to pay for peace of mind'. I doubt we'll ever use it but I've already paid for the pipes so that money is gone and forgotten about so I think it's a no brainer for me to just install the pipework and then just leave it disconnected. I'm pretty sure it'll actually save me money by putting the EPS and UFH pipes down when factoring in the extra screed cost.

 

 

I had another mild panic moment about heating on the first floor even though I'd already decided we didn't need it (I guess I have too much time sitting at my desk for the day job while thinking about the build!) and was thinking about putting in low profile UFH throughout upstairs but after discussing it with the wife she gave me a metaphorical slap around the face to bring me to my senses and we're back doing what we originally agreed with the electric UFH and towel rails in the en-suites and we are going to first fix for air conditioning at least (probably 2nd fix it now as well) and so we can use that for supplementary heating if required. but for the basement I think I'll just stick with the UFH for now. I might still put isolated spurs for electrical heaters but tbh I doubt it as I really don't think it'll be necessary. 

 

 

 

If the UFH pipe is already purchased and you need screed anyway to make up the levels then your approach makes perfect sense, especially if you can use a bit of EPS to save some screed!

 

I think you'll be amazed at how little you will need to heat your house but, having built at the same time of year, understand how hard that is to realise until you're in.

 

Good to see you're giving the same attention to cooling as you're giving to heating as guarantee that will be your number one comfort issue.

 

One of my regrets is not making provision for air con.

 

I just spent £1000 at Ikea on their wireless battery operated blinds which by pure luck are exactly the right length such that three perfectly cover the large west facing sliders on the ground floor. All connected to their smart hub so controllable by Alexa - will make a big difference in summer as the afternoon sun can significantly overheat the GF. We have cheap linen panels for now which help a little but the blinds should be much more effective.

 

Now, crack on to your next dilemma

 

 

 

[saveasteading]

2 minutes ago, Bitpipe said:

will make a big difference in summer

 

I can't get my head round the effect of internal blinds and curtains.  The sun has already come through the glass and is in the room, and  heats up the blinds which then warm the room.

But I know it works to some extent....perhaps it slows the effect long enough to spread the heat into the evening.

 

External blinds on the other hand keep all the heat outside.

[Thorfun]

8 minutes ago, Bitpipe said:

I just spent £1000 at Ikea on their wireless battery operated blinds

we're going for external blinds built into a pocket in the timber frame so they're hidden from view. many threads on here about overheating allowed me to plan for this in advance.

 

8 minutes ago, Bitpipe said:

Now, crack on to your next dilemma

there are many!

 

[Bitpipe]

54 minutes ago, saveasteading said:

 

I can't get my head round the effect of internal blinds and curtains.  The sun has already come through the glass and is in the room, and  heats up the blinds which then warm the room.

But I know it works to some extent....perhaps it slows the effect long enough to spread the heat into the evening.

 

External blinds on the other hand keep all the heat outside.

 

Agree, we have external blinds on east and south windows (on roof also) - super effective.

 

I expect internal blinds limit the volume of air that can be heated and also stops the sun warming the floor and other objects.

 

Anyway, works

 

[Steve247]

On 14/05/2021 at 12:25, Thorfun said:

@joe90 and @PeterW I've taken another look and lifting up the top mat is never going to happen. here's a couple of photos of the mesh and chairs.

 

 

 

if you both think it'll be a complete nightmare to run the UFH pipe as per the Wunda plan...

then I think we're leaning towards just scrapping the UFH in the basement. I know that @Bitpipe doesn't have heating in his basement and says it's a comfortable temperature all year round so it is a possibility just to scrap it.

 

I guess this is a dilemma all first time self-builders go through as I have never lived in a well insulated and air tight house so trying to get my head around the concept of not needing heating is a challenge! 

 

 

I have a 200m2 basement with big cinema, gym, games room and plant room. All has underfloor heating but it’s never been used. The MVHR provides supplemental heating and its always around 22 degrees. My walls are insulated 150mm think but nothing under the slab to allow any ground heat to transfer into the bst slab. 

[Conor]

I contemplated using 50mm EPS boards on our first floor before the UFH and screed. The staples pull out easily and the EPS falls apart. 25mm will be a nightmare to work with. I'd just stick clip rails to the slab and screed straight over with 50mm liquid. Keep it simple. If you do use the EPS, use the self adhesive slip rails instead of staples (tho you'll still need staples at bends and through the ends of the rails as they will be only stuck to the polythene).

[Thorfun]

1 hour ago, Conor said:

I contemplated using 50mm EPS boards on our first floor before the UFH and screed. The staples pull out easily and the EPS falls apart. 25mm will be a nightmare to work with. I'd just stick clip rails to the slab and screed straight over with 50mm liquid. Keep it simple. If you do use the EPS, use the self adhesive slip rails instead of staples (tho you'll still need staples at bends and through the ends of the rails as they will be only stuck to the polythene).

I had read that EPS was a nightmare with ufh staples. so I decided to go with 25mm PIR in the end. still worked out cheaper than having that space done in liquid screed and using click-strips or the like. I'm hoping that the ufh staples will hold fine in 25mm PIR!