1. Is it essential to have insulation below underfloor heating?
It is not essential, in fact a number of people install under-tile heating systems on un-insulated concrete floors to good effect. However good insulation levels will improve the efficiency of the system, reduce warm-up times allowing greater flexibility & more importantly reduce running costs & so will pay for itself in a relatively short period of time (typically 2-5 years)
2. There are various thicknesses of Marmox – which do you recommend?
This mainly depends on your floor height, in most renovations it is impractical to raise the floor by more than a couple of cms. 10mm Marmox is our most popular size, for renovations & refurbishments but if you are able to use a thicker board, it will further improve efficiency & lower running costs. The 50mm boards for example costs approx 60% more than the 10mm, but will provide 5 times better thermal insulation. The 50mm boards are very popular in new conservatories & extensions where they effectively replace the top screed.
3. Can Depron be used without underfloor heating?
Yes it can – Depron is recommended for use directly below both our Carbon & AHT heating mats, it is also a very popular way to insulate a cold concrete floor below carpet, wood or laminate floor even without floor heating. In fact a growing number of flooring contractors use Depron instead of traditional (& usually less efficient) underlay below carpet & wood floors.
4. Can Depron be used below tiles instead of Marmox?
Yes it can, but Depron does not have the same compressive strength as Marmox so has to be installed in a different way. Marmox is simply screwed to a wooden floor or fixed to concrete using ordinary floor tile adhesive. Depron however has to be bonded to the sub-floor with a special non-solvent based adhesive, then after laying the heating cables or mat, has to be primed before being covered with a thicker layer of latex (or flexible) levelling screed. Although it appears significantly cheaper, by the time the costs of adhesives & extra latex levelling screed are added there is usually not much of a saving to justify the extra effort involved!
5. What is the difference between using something like Celotex beneath a concrete screed & Marmox on top of the screed?
Any project subject to new building regulations (extensions or new properties) will need high levels of floor insulation even if they are being heated by other methods (radiators for example) The typical floor construction to meet these regulations & achieve the required U-values will be 40-50mm of polyeurathane foam or similar fitted directly below a 50-70mm concrete screed.
A percentage of the heat generated will be absorbed into the screed, but the insulation prevents if from being lost & instead creates a ‘thermal mass’ which will retain the heat for a period of time – the same happens with bricks & stone within the wall etc. When underfloor heating is installed on top of an insulated screed, the first initial warm-up time from cold may be a few hours, but once the concrete has absorbed the heat & its temperature raised it will become an efficient way of heating.
The digital thermostat we use allows a ‘setback’ or off temperature to be set (usually 5-10 degrees lower than the heated temperature), thus ensuring that the concrete screed is never allowed to completely lose that thermal mass.
Using the Marmox boards gives a much faster warm-up time (minutes rather than hours) & whilst a small percentage of heat will be absorbed into the concrete screed, the majority is quickly transferred to the tiles making it faster to react to day to day requirements & changes in climate. This usually means that the heating is actually on for a lesser amount of time, resulting in even lower energy consumption.