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Design Dilemma
ben_siegmund

Celotex or Actis Triso Sol for underfloor heating

Ben Siegmund
7 years ago

We are in the process of refurbishing our house and want to install a wet underfloor heating under a screed and porcelain tile floor.
Having taken up the existing floor we were surprised to find a solid concrete base (we were expecting suspended timber). The original idea was to take up the suspended timber and replace with block and beam, however having a solid concrete base has worked in our favour from a cost perspective.
The downside is that we now have a floor level we are more or less stuck with (to remove the existing concrete base will be expensive and possibly uncover any number of sins). The question is:
Do we put down Celotex or Triso Sol under the underfloor heating? Celotex is much more transparent in their detail (performance figures and data) and has a much lower cost; Triso Sol is a little more of an unknown with quantifiable information about its efficiency very hard to come by and it is also a fairly hefty price tag by comparison.
The dilemma comes from not wanting to lose ceiling height. In using Celotex, we will lose around 150 - 170mm, but with the Triso Sol this is halved.
If Triso Sol can come close to the performance of Celotex, I am happy as I would forgo some efficiency to maintain the ceiling height, but in the absence of any meaningful data on Triso Sol, I am sceptical about how good it really is.

Comment (1)

  • PRO
    Jo Chrobak Invent Design Create Ltd
    7 years ago
    last modified: 7 years ago

    Hi Ben,

    You have a few issues here and I would be surprised if your building control officer hasn't raised them already. The underfloor heating company and your builder also have a duty of care to inform you that what you are embarking on here needs some professional help. I will do my best to help you with the above issue, but it does worry me about what is going on in the rest of the house!

    You will need both a Celotex AND a Trisol Sol type foil backed insulation. The Celotex PIR insulation is required for your thermal envelope. You should be aiming to achieve a minimum U-value of 25 W/(m2.K)8 - as per Bart L1B of the building Regulations. But (and this is my disclaimer) without knowing what is going on in the rest of the building this may possibly be a much higher requirement (a lower U-value is a higher number). So use this as a guide only and you should call up Celotex instead of just using the online calculators, they can explain what and why you need the thicknesses you need. Don't forget that underneath the insulation you will also need a DPM - the whole floor construction needs to be considered as a system - Celotex can help you with this to a point as their calculations will give you the required minimum buildup (but this buildup still needs checking off by building control to ensure that for example if you are in a RADON gas area that the inside of your property will be a healthy and safe place to inhabit). If you are following drawings by someone - just a note that they sound a little incomplete if you feel that you can choose either insulation.

    Once you have a safe and secure thermal envelope which might entail screed or WBP ply on top of the PIR insulation as part of that, then you can consider the underfloor heating requirements, which will go on top and usually require something like a Trisol Sol as part of their own build up system so that the heat reflects into the building rather than into the ground outside (saving you money and lots of energy). The number provided by Trisol Sol are 01249 462 888. In Europe, they often build buildings by insulating on the outside of the slab, so if the slab is insulated on the outside already, you may be able to get away with just using the Trisol Sol - but there are so many variables here that I'll over complicate my answer to you if I list them here, so finding out if the slab is insulated below will affect your thermal envelope calculation.

    Underfloor heating can be simple or it can be complex (not much help for you sorry). You will need to (at a minimum and if you haven't got a pro helping you) to call the underfloor heating company and see what their buildup requirements are and whether what you have below is compatible with their system. This could take you a few minutes on the phone or a few days depending on how good the technical department is. Then you will need to ensure that your thermal build-up and your heating buildup are compatible and then you start looking around to see if the overall buildup (possibly around 200mm at this point) will be giving you a large step or a level enough threshold into the room you have designed to be viable.

    If the step is unacceptable and or your head-height is restricted by what you have created, you have to go back to your metaphoric drawing board and see where you can change the build-up. Kingspan do a product that is vacuum sealed. It is super expensive, but will lower the head-height if you are really desperate - but you will need to work out your thermal buildup again using the Kingspan system and then check again with the underfloor heating manufacturer whether these two systems are compatible (a couple more phone calls). You may have to consider a much thinner underfloor heating system too, which again will start to get more expensive and then may not reach your required heating load (Building Regulations for heating and ventilating the room etc. etc.).

    Building control are really great (in my experience) and as a minimum I would give them a call and tell them what you are doing and ask for some help. What you are creating needs to be safe (and practical) not only for you but for the future users of the building and then signed off when complete or else you may have difficulty selling your building afterwards.

    I hope I gave you some guidance to start in the right direction, but you have a few days of work ahead of you! Good luck.

    Jo

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