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Posted (edited)

I'm going to be putting UFH pipework on the top of 100mm Celotex insulation between joists, joists are at 400mm centres, how many runs of pipework would I need down each joist run? Length of each run is approx 5.3m.

Edited by Toppers

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give your drawing to wunda and they'll design it for you

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Depending on pipe size and output, most UFH is designed at pipe centres of between 125 and 200. Logically it would seem that you need 2 pipe runs between each pair of joists otherwise they'd be at 400 centres.

 

As @Simplysimon says, send a floor plan to Wunda, they're very good.

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1 hour ago, Toppers said:

I'm going to be putting UFH pipework on the top of 100mm Celotex insulation between joists, joists are at 400mm centres, how many runs of pipework would I need down each joist run? Length of each run is approx 5.3m.

I am going to do the exact same thing in about 3-5weeks. 

 

Have you thought about additional support for the Celotex so that when you do the biscuit mix screed the Celotex is well supported? I am thinking of setting the joists and then nailing roofing battens to the underside of the joists to create a grid to help support it all. Most details only show a support batten but I am not convinced by this being enough. The mix is not very strong either so although it should then self support across the battens if it cracked at the centre the weight would then forever be pushing down on the middle of the PIR which would cause it to bow.

 

 

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31 minutes ago, Carrerahill said:

I am going to do the exact same thing in about 3-5weeks. 

 

Have you thought about additional support for the Celotex so that when you do the biscuit mix screed the Celotex is well supported? I am thinking of setting the joists and then nailing roofing battens to the underside of the joists to create a grid to help support it all. Most details only show a support batten but I am not convinced by this being enough. The mix is not very strong either so although it should then self support across the battens if it cracked at the centre the weight would then forever be pushing down on the middle of the PIR which would cause it to bow.

 

 

 

Yes I was going to do a similar thing with slate lathe and some 1 x 1 timber to let the insulation sit 25mm below the top of the joist.

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Posted (edited)
5 minutes ago, Toppers said:

 

Yes I was going to do a similar thing with slate lathe and some 1 x 1 timber to let the insulation sit 25mm below the top of the joist.

When are you doing yours?

Are your joists only 5x2? Note, if so you will only get 20mm above 100mm PIR as 5x2's are 120x45/47. So your PIR will sit level with bottom of the joist? Or do you mean 1x1 level with the bottom and the PIR sits on that so it's about 25mm up and 20mm from the top?

 

 

Edited by Carrerahill

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5 minutes ago, Carrerahill said:

When are you doing yours?

Are your joists only 5x2? Note, if so you will only get 20mm above 100mm PIR as 5x2's are 150x45/47. SO your PIR will sit level with bottom of the joist? Or do you mean 1x1 level with the bottom and the PIR sits on that so it's about 25mm up and 20mm from the top?

 

 

 

I'm using 6 x 2 joists which finish about 147mm, I've had some timber machined up to 22 x 22mm to give me 25mm at  the top, I'll be using 16mm pipework. I'm putting the joists in over the next few days then the insulation to follow after the building inspector has been.

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2 hours ago, Toppers said:

I'm going to be putting UFH pipework on the top of 100mm Celotex insulation between joists, joists are at 400mm centres, how many runs of pipework would I need down each joist run? Length of each run is approx 5.3m.

I think a lot more detail is needed.

 

Will this be the Celotex with the grooves in for the pipes to fit flush? or will it be as someone else suggested be covered with a biscuit mix?

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1 minute ago, ProDave said:

I think a lot more detail is needed.

 

Will this be the Celotex with the grooves in for the pipes to fit flush? or will it be as someone else suggested be covered with a biscuit mix?

 

I going to use standard 100mm Celotex and the 8:1 biscuit mix.

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1 minute ago, Toppers said:

 

I going to use standard 100mm Celotex and the 8:1 biscuit mix.

Okay as someone who did this (a little different) I wanted to be clear that you are putting battens along the top of the joists to support the floor, with the biscuot mix filling in between as a heat spreader, but not supporting the floor.

 

This solves the problem of how the UFH pipes cross the joists, you leave a small gap in the battons.  and it means you don't need much support for the celotex.

 

I take it the joists have been specified taking into account the extra dead load they have to support.

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Posted (edited)
4 minutes ago, ProDave said:

Okay as someone who did this (a little different) I wanted to be clear that you are putting battens along the top of the joists to support the floor, with the biscuot mix filling in between as a heat spreader, but not supporting the floor.

 

This solves the problem of how the UFH pipes cross the joists, you leave a small gap in the battons.  and it means you don't need much support for the celotex.

 

I take it the joists have been specified taking into account the extra dead load they have to support.

 

No I was going to leave the Celotex 25mm below the top of the joist and infill that with the biscuit mix. I assume this is the same difference.

Edited by Toppers

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22 minutes ago, Toppers said:

 

I'm using 6 x 2 joists which finish about 147mm, I've had some timber machined up to 22 x 22mm to give me 25mm at  the top, I'll be using 16mm pipework. I'm putting the joists in over the next few days then the insulation to follow after the building inspector has been.

Ah got you.

 

Could you post progress pics please and let us know how you get on?

 

Please note my edit in my post, I hit 5 rather than 2 - 120*145mm for a 5x2 - ish.

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Posted (edited)

This is what I have been advised to do but without the OSB directly above the Celotex. - but I think I will run the battens under the joists and let the PIR sit lower, I also suspect this will be stronger (I will need to get good fixings and use plenty support).

 

ufh2.gif.516f5c946bf43e8fed63ef1871b2d129.gif

Edited by Carrerahill

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4 minutes ago, Toppers said:

 

No I was going to leave the Celotex 25mm below the top of the joist and infill that with the biscuit mix. I assume this is the same difference.

This is how I am doing it - but I could do it as per prodave as I could just remove a 19mm piece of the plate the joists sit on and use 19x38mm battens over the top - hmm!

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4 minutes ago, Toppers said:

 

No I was going to leave the Celotex 25mm below the top of the joist and infill that with the biscuit mix. I assume this is the same difference.

Your proposed idea gives you one MAJOR problem.  How will the UFH pipes cross over a joist, which they will to at one end, crossing over every joist.

 

You cannot notch a posi joist.

 

I did it this way on a very small section of floor under the bathroom, and I threaded the pipe between the top and bottom chord at one end, but it was VERY hard work with only a short run of pipe to keep threading through.  If you are going to be doing anything like a normal sized room, you could be having many tens of metres of UFH pipe and threading it through again and again is going to be somewhere between extremely hard, and impossible.

 

Battens along the top with a small gap at one end for the pipes to pass solve all this.  Set the celotex level with the top of the joists.

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1 minute ago, Toppers said:

I was going for this method:

dry-biscuit.jpg

See my post above. At the other end of the run, the pipe must cross over EVERY joist.  

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1 minute ago, ProDave said:

Your proposed idea gives you one MAJOR problem.  How will the UFH pipes cross over a joist, which they will to at one end, crossing over every joist.

 

You cannot notch a posi joist.

 

I did it this way on a very small section of floor under the bathroom, and I threaded the pipe between the top and bottom chord at one end, but it was VERY hard work with only a short run of pipe to keep threading through.  If you are going to be doing anything like a normal sized room, you could be having many tens of metres of UFH pipe and threading it through again and again is going to be somewhere between extremely hard, and impossible.

 

Battens along the top with a small gap at one end for the pipes to pass solve all this.  Set the celotex level with the top of the joists.

 

Mine are C24 joists so I don't mind chiselling a notch out for the pipework to cross.

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Posted (edited)

 I would do this

joist with insulation between up to top of joists ,then plywood then fit all UFH piping then fit battons between pip[ing ,then fill with biscuit mix ,then fix top floor to that 

this  way no load on insulation at all 

Edited by scottishjohn
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Just now, Toppers said:

 

Mine are C24 joists so I don't mind chiselling a notch out for the pipework to cross.

That's fine, you can notch them, just check you put the notches in the prescribed zones.

 

I must have got confused with another thread and thought you had posi josts, sorry for the confusion.

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4 minutes ago, ProDave said:

Your proposed idea gives you one MAJOR problem.  How will the UFH pipes cross over a joist, which they will to at one end, crossing over every joist.

 

You cannot notch a posi joist.

 

I did it this way on a very small section of floor under the bathroom, and I threaded the pipe between the top and bottom chord at one end, but it was VERY hard work with only a short run of pipe to keep threading through.  If you are going to be doing anything like a normal sized room, you could be having many tens of metres of UFH pipe and threading it through again and again is going to be somewhere between extremely hard, and impossible.

 

Battens along the top with a small gap at one end for the pipes to pass solve all this.  Set the celotex level with the top of the joists.

I think I am going to lower my joists 19mm and batten out on top now.

 

I do have a clear run home down one side the way the perimeter of the floor works out (joist change direction) but I prefer the idea of running them as I want and NOT in the confines of the joists. Good call! I have not been shown this detail before and it makes perfect sense!

 

Glad I didn't nail in all my joists a couple of weekends ago!

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Posted (edited)
2 minutes ago, scottishjohn said:

 I would do this

joist with insulation between up to top of joists ,then plywood then fit all UFH piping then fit battons between pip[ing ,then fill with biscuit mix ,then fix top floor to that 

this  way no load on insulation at all 

depth of biscuit mix?

 

direct tile onto this?

 

Edited by Carrerahill

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Posted (edited)
3 minutes ago, Carrerahill said:

depth of biscuit mix?

 

direct tile onto this?

 

If tiles --then 6mm ply on biscuit mix +tile onto that ?

it s what idid in my own floor 15 years ago with 450x450 tiles --all still there

just make sure there is no flex in joists !!

Edited by scottishjohn

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only difference was mine had  chipboard floor ,as it was a retro fit , maybe thats easier way 

 

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Posted (edited)
4 minutes ago, scottishjohn said:

only difference was mine had  chipboard floor ,as it was a retro fit , maybe thats easier way 

 

All this talk makes me wonder if I should just backfill the lot and screed over.

 

Edited by Carrerahill

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