So, a couple of interesting little quirks we have discovered. First, and most pressing is that the groundfloor is not actually a suspended timber floor, but instead it is a floating floor on a concrete slab. with 45mm of polystyrene acting as the structural support and insulation with a chipboard floor floating on it.
Overall this gave the original construction a U value of just 0.45W/m2K.
Now, for those of you who don’t know what U values are here is a quick explanation:
To put it simply, U-Value is the measure of the rate of heat loss through a material. Thus in all aspects of home design one should strive for the lowest U-Values possible because the lower the U-value – the less heat that is needlessly escaping. So for example single glazed windows have a typical U-value of 5.6 while double glazed windows have a typical U-value of 2.8.
The calculation of U-values can be rather complex – it is measured as the amount of heat lost through a one square meter of the material for every degree difference in temperature either side of the material. It is indicated in units of Watts per Meter Squared per Degree Kelvin or W/m2K. Note that Kelvin is used as the scale of temperature difference, but this is numerically equal to oC. So for example, one square meter of a standard single glazed window will transmit about 5.6 watts of energy for each degree difference either side of the window or a U-Value of 5.6. A double glazed window will be significantly better with a U-value of 2.8 i.e. only transmitting 2.8 watts of energy in similar conditions.
Ok – so to put it into context a little, the Building Regulations 2010 Part L1A for new floors set the U value that must be achieved at 0.22W/m2K – quite difference from where it is currently.
Also – this has a knock on effect on the type of underfloor heating – as there are no existing floor joists do we go for a floating floor system? Do we go ahead and remove what we have already? It seems almost ridiculous to pull up 80m2 of chipboard and polystyrene and send it to be recycled if it can remain where it is and we simply build above it?
Well with some careful thought and further investigation, also taking into account the height of door lintels (if we raise the floor what effect does this have on door openings?), the need for drainage, and so a certain amount of “drop” for waste water to run away from the proposed wetrooms, we have made a decision – to retain the existing floor laying new 50mm x 50mm timbers with added insulation between (an additional 30mm of celotex) then the UF system (17mm deep) then the new floor finish (still to be decided). I am still to work out the final U value – but this will definitely be a significant improvement – I’ll put all the U values and details on this blog at a later date.
We also calculate that this will save transporting 3.52 cubic meters of polystyrene and 2 cubic meters of chipboard to be recycled – basically another luton lorry load saved! This will also remove the need for days of labour (saving costs) and allow us to move on quickly on this job which has such a tight schedule.
Enough for today, more soon.