UFH pipes in slab under blockwork walls

[Thorfun]

Hi all,

 

I am hoping that the rebar will be in place for the slab pour next week and so I will have this weekend to lay the ufh pipes in the basement. Wunda have designed it so that all the pipes go through the doorways but as our walls in the basement will be blockwork and there shouldn't be any penetrations/nailing in the slab do I have to stick with running pipes through doorways?

 

Basically, is it ok to run UFH pipes in the insulated slab underneath blockwork walls?

[Thorfun]

anyone have an opinion on this before I make the assumption that it's fine to do this? I've just been told by the SE that I have to attach my pipes to the underside of the top mat of rebar as there's not enough space above the top mat to do so (it would leave only 14mm between top of pipe to top of slab) and so anything I can do to make threading the pipe through the top mat easier the better!

[joe90]

Rather than route pipes through crowded doorways I drilled holes through block walls, lined with slightly bigger pipe 300mm long. I don’t see the point In all pipes being through doorways, no point loading will be on the pipes.

[PeterW]

No issues but you won’t be able to thread pipe under the mesh. You will have to lay the bottom mesh and the chairs, lay the pipes then lay the top  mesh and cable tie the pipe up to the top. 

[willbish]

It's exactly what I did. 

Insulated raft foundation will be one heating zone, so no point piping the UFH loops to exactly match the rooms above. 

[Thorfun]

1 hour ago, PeterW said:

No issues but you won’t be able to thread pipe under the mesh. You will have to lay the bottom mesh and the chairs, lay the pipes then lay the top  mesh and cable tie the pipe up to the top. 

it's too late for that @PeterW. top mesh has already been laid so it'll be a case of threading pipe under the top mesh or just forgoing UFH in the basement altogether! I'm aware it'll be very time consuming but it's the only option I have now.

[joe90]

28 minutes ago, Thorfun said:

but it's the only option I have now.

Having laid UFH pipes I don’t think it would be possible to thread pipes as you want. How difficult would it be to take that top mesh up then put it down again? (I recon faster and easier than trying to thread UFH pipe under it ?)

[Thorfun]

2 minutes ago, joe90 said:

Having laid UFH pipes I don’t think it would be possible to thread pipes as you want. How difficult would it be to take that top mesh up then put it down again? (I recon faster and easier than trying to thread UFH pipe under it ?)

I'm pretty sure the basement guys have already tied all the steels together so would be a nightmare to undo it all and then re-tie it. (I'll just pop out and take a look)

 

bugger. 

Edited May 14, 2021 by Thorfun

[Thorfun]

@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! 

 

 

[willbish]

It's not just the heating but also the potential future cooling if connecting to ASHP.

 

I was also tight for space when fitting the UFH pipes on top of the top layer of mesh but managed it.

 

Might be worth measuring what height you have available now above the mesh.

 

Perhaps using 12mm pipe might help...a tiny bit.

 

 

 

[Bitpipe]

46 minutes ago, Thorfun said:

 

 

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! 

 

 

 

Chill  Can you get a refund on the UFH kit you bought?

 

I had the same dilemma and at one point of the build even considered retrofitting electric mat heating, but glad I didn't. Since we moved in our basement has never, ever been cold and has never overheated - always a comfortable 20^oC year round. To be honest the ground floor heating rarely comes on either.

 

Try addding up all the watts that your basement electrical kit will generate (especially in rooms like cinema, gym, music, comms & plant room etc) and that's probably more than enough heating input before you add humans to the mix. Remember that your exterior is a consistent 12 degrees or thereabouts so do some thermal modelling based on that.

 

For peace of mind, you can get your electrician to make provision for a few panel heaters (i.e. just fused spurs) or just 13A sockets and add those later as a worst case measure (you won't need them). If you're tiling the WC floor, plan a 150W electric heating mat under the tiles.

 

You don't seem to have much in the way of natural light in there though - no light wells at all or just not reflected in that drawing?

[Bitpipe]

10 minutes ago, willbish said:

It's not just the heating but also the potential future cooling if connecting to ASHP.

 

Is yours in a basement or a regular GF?

 

The basement should not require active cooling either as solar gain will be limited or non existent - we have the largest GRP lightwells we could find (MEA's 2000mm x 800mm) one per room and while bright, they are never in direct sunlight, most of it is diffused off the interior of the lightwell.

 

 

Edited May 14, 2021 by Bitpipe

[Thorfun]

31 minutes ago, willbish said:

Might be worth measuring what height you have available now above the mesh.

 

Perhaps using 12mm pipe might help...a tiny bit.

 

we'll have between 30 - 40mm between top of mesh and top of slab. working on 30mm with the 16mm pipe it leaves only 14mm between top of pipe and top of slab. I sent this information to the structural engineers and they said that isn't enough. not sure 12mm pipe would help much tbh and, it's probably too late as the pour is on Tuesday.

[Thorfun]

34 minutes ago, Bitpipe said:

 

Chill  Can you get a refund on the UFH kit you bought?

 

I had the same dilemma and at one point of the build even considered retrofitting electric mat heating, but glad I didn't. Since we moved in our basement has never, ever been cold and has never overheated - always a comfortable 20^oC year round. To be honest the ground floor heating rarely comes on either.

 

Try addding up all the watts that your basement electrical kit will generate (especially in rooms like cinema, gym, music, comms & plant room etc) and that's probably more than enough heating input before you add humans to the mix. Remember that your exterior is a consistent 12 degrees or thereabouts so do some thermal modelling based on that.

 

For peace of mind, you can get your electrician to make provision for a few panel heaters (i.e. just fused spurs) or just 13A sockets and add those later as a worst case measure (you won't need them). If you're tiling the WC floor, plan a 150W electric heating mat under the tiles.

 

You don't seem to have much in the way of natural light in there though - no light wells at all or just not reflected in that drawing?

I probably could get a refund on the UFH pipe from Wunda but as we're going to install wet UFH on the ground floor I might as well just keep it for when that happens. 

 

when I discussed this with the wife she also said that most of the rooms in the basement are active rooms so when we're playing music or in the gym then we'll be generating heat, the cinema projector will chuck out enough heat as well and so it'll just be the games room area which will probably end up being a den for the kids and their mates so that might be the only potential area that needs heating and if there are a few of them then I'm sure it'll be fine.

 

We don't have much natural light. we were thinking of light wells but it was an expense and complication that we decided not to bother with as the activities that the rooms have been earmarked for don't really need natural light and there should be enough coming through the sunken courtyard sliding doors to make the games room area light enough for teenagers. ? 

[Thorfun]

anyway, I've made the decision now. we're not having UFH in the basement for now. we'll see how it all goes and can always add something later if at all required but we don't think it will be going on the levels of insulation we have and other member's experiences.

 

means my original Saturday plans are now back on! woo-hoo! ?

 

Edited May 14, 2021 by Thorfun

[Bitpipe]

Well done, you've saved yourself a lot of stress as laying UFH pipe is not as easy as you think, especially when you're on a deadline and doing it first time.

 

I had planned to do my alu spreader plates on GF joists and lay pipe as a DIY job over a weekend. The TF crew just stepped in and took over the pipe laying as I was too slow - they'd done it dozens of times before and did a great job. Cost me a few bacon sandwiches but that was it!

[Thorfun]

53 minutes ago, Bitpipe said:

Well done, you've saved yourself a lot of stress as laying UFH pipe is not as easy as you think, especially when you're on a deadline and doing it first time.

 

I had planned to do my alu spreader plates on GF joists and lay pipe as a DIY job over a weekend. The TF crew just stepped in and took over the pipe laying as I was too slow - they'd done it dozens of times before and did a great job. Cost me a few bacon sandwiches but that was it!

I'll save my UFH pipe laying for the ground floor when I will have lots of time. 

 

thanks all for the advice and I'm 99.99999999% sure we've made the right decision. ?

 

[Conor]

23 hours ago, Thorfun said:

anyone have an opinion on this before I make the assumption that it's fine to do this? I've just been told by the SE that I have to attach my pipes to the underside of the top mat of rebar as there's not enough space above the top mat to do so (it would leave only 14mm between top of pipe to top of slab) and so anything I can do to make threading the pipe through the top mat easier the better!

Stick a strip of 25mm Eps all around your formwork and increase the concrete thickness so you have enough cover over the pipes (min 40mm) on top of the mesh. I don't think a slightly thicker slab will be an issue, unless you have really strict ridge height limitations....

 

Even though we're not watertight yet, our basement is significantly cooler than the rest of the building. Most of our UFH will be in the basement.

Edited May 15, 2021 by Conor

[Conor]

11 hours ago, Thorfun said:

 

 

thanks all for the advice and I'm 99.99999999% sure we've made the right decision. ?

 

 

That 0.00000001% will niggle you at you for ever ?

[joe90]

18 hours ago, Thorfun said:

most of the rooms in the basement are active rooms so when we're playing music or in the gym then we'll be generating heat, the cinema projector will chuck out enough heat as well

Quite, my not putting heating in upstairs was a “leap of faith” and occasionally during very cold weather it requires a little heat from a portable heater, but on the whole still not worth the effort or cost. (Especially in your case @Thorfun with the mesh  already down).

[Thorfun]

1 hour ago, Conor said:

Stick a strip of 25mm Eps all around your formwork and increase the concrete thickness so you have enough cover over the pipes (min 40mm) on top of the mesh. I don't think a slightly thicker slab will be an issue, unless you have really strict ridge height limitations....

 

Even though we're not watertight yet, our basement is significantly cooler than the rest of the building. Most of our UFH will be in the basement.

it's an interesting idea but with the pour on Tuesday it's all a little late in the day!  I'm happy with our choice and there are always low level ufh options later down the line if required. especially as we won't be fitting out the basement for a couple of years due to budget constraints so we'll have time to live in the house and can then decide the best course of action.

[Bitpipe]

1 hour ago, Conor said:

Even though we're not watertight yet, our basement is significantly cooler than the rest of the building. Most of our UFH will be in the basement.

 

As was mine, however once the rest of the house was watertight, insulated and occupied the basement reached its current temp and has never wavered over 5 years.

 

I'd worry that when your ground floor needs heat, you need to warm it up via the basement which may make it uncomfortably warm.

 

 

[Conor]

31 minutes ago, Bitpipe said:

 

As was mine, however once the rest of the house was watertight, insulated and occupied the basement reached its current temp and has never wavered over 5 years.

 

I'd worry that when your ground floor needs heat, you need to warm it up via the basement which may make it uncomfortably warm.

 

 

We'll have three zones, one for each floor. Just going light on the UFH on the middle floor. Going by how relatively cheap UFH pipes are, I might just go full on UFH for the middle floor.

[Bitpipe]

3 hours ago, Conor said:

We'll have three zones, one for each floor. Just going light on the UFH on the middle floor. Going by how relatively cheap UFH pipes are, I might just go full on UFH for the middle floor.

 

When you say middle, do you mean ground floor?

 

That's the only floor that has UFH in our house so basement is constant temp and needs no additional heat injected (appliances, people etc generate enough). GF UFH comes on a few times over the winter and second and attic floors have no heating apart from in the bathrooms (electric 150W under tile mats + wet towel rads). Rooms in roof are always warm due to solar gain from the roof and velux, even though there are binds etc.

 

I've noticed that if I go into the spare bedroom on 1st floor it feels cooler as its never occupied but within 15 mins it's as warm as the other bedrooms.

[Thorfun]

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?