Ok, let’s start here; the aim is to have a warm, cozy house with warm water underfloor heating (UFH), no radiators, and this all with reasonable running costs and emits no more CO2 than it has to. Number one concern for many; floor insulation?! Let’s talk insulation!
Before explaining the various floor constructions and the impact of floor insulation, it is important to have the right understanding of the (total) heat loss of your home. Heat loss can be split up into 5 separate areas; walls (35%), roof (25%), doors/draughts (15%), floor (15%) and windows (10%). This share-out is partly logically explainable because heat rises and therefore heat loss through roofs and walls are more stringent than those through floors.
The next step is to consider the possibilities of applying insulation. Insulating your loft is perhaps the easiest of all the energy-saving home improvements and it’s also within the capability of most DIYers. Walls, windows are the next elements to examine. There are great solutions on the market as double/triple glazing (also noise reduction) and solid or cavity wall insulation products which can be applied either by a DIYer or a specialist. Fourthly; the floor insulation. This might be the trickiest of all because of (a) no space under the floor construction or (b) a significant floor build-up which is not possible or practical. Moreover, the ground floor beneath a house is generally warmer than the air around it and therefore it would be further down on your list of priorities.
‘The temperature difference between an internal space to ground is significantly smaller than the temperature difference between the internal space to outside air. In general, recent research (George, Geens & Graham, BFF, Spring 2006) has shown that solid ground floor insulation as an addition to well-insulated walls and roof, contributes very little to the building’s overall thermal performance. The designer should balance the extra benefit(s) attached to installing a new slab with the cost, marginal carbon gains and pragmatics involved’
After all, now time to explain some various floor constructions and the evolution of concrete floors. Concrete floors where not unknown in the 1930s but they became more common in the 1950s. The floor is basically a bed of concrete supported by the ground directly beneath it and quite independent from the surrounding walls.
A typical floor from the 1950s might comprise a layer of hardcore (stone or brick), a 100/125 [mm] concrete slab and the floor finish. This is often timber or thermoplastic tiles in bitumen adhesive. From the mid-1960s to the mid-1990s a typical concrete floor comprised a layer of hardcore, a polythene damp proof membrane and a floor screed. Since the mid-1990s the Building Regulations have required insulation in ground floors, a concrete floor can be termed ‘cold’, i.e. concrete placed below the insulation or ‘warm’ i.e. the concrete above the insulation.
There are three general types of ground floor construction;
• (a) Solid floor; hardcore base with sand blinding, with a layer of concrete over that. To ensure a level finish to the floor, a layer of screed is added over the top of the concrete, which consists of sand and cement.
• (b) Suspended Timber floor; The ground should have a layer of concrete poured across with ventilated gaps between the underside of the timbers and the concrete. The timber floor joists are normally laid across the shortest span from wall to wall with a gap underneath. Insulation can be placed between the joists, by taking up the flooring
• (c) Suspended concrete floor; This construction is like the timber floor, but uses pre-cast concrete planks or beams with concrete blocks laid between the beams.
Of course, an insulated floor construction is more efficient then an uninsulated floor and will reduces heat-loss. This will have a positive influence on your energy usage. A break-down in costs, examine practicality and potential pay-back time might be helpful by making your decision to invest or not to invest in the floor construction;
1. The cheapest option is to retrofit insulation on top of a solid concrete floor, this will obviously
have a significant impact on floor height build-up and may interfere with doors, steps or ceiling
height. In the 1990s 50 [mm] was considered as a sufficient insulation thickness, but now is 70
[mm] considered as minimum. Add 60 [mm] of screed and a floor covering and the level rises by
close to 150 [mm]. Recommended floor insulation is a layer of 70 [mm] Polyurethane insulation.
Polyurethane outperforms Polystyrene and has a greater density. 2. To retrofit insulation under the solid floor; it is only worth digging out the floor if you’re undertaking
a major renovation. Set off against the cost – pay-back time - and the energy saving is an
motive. Figures state that insulating under the floor on the ground floor will save about
40GBP - 70GBP a year on energy costs. For many, these figures are not worth it to improve floor
constructions, because the investment can be way more effective in another area of the house.
3. Finally, if you are adding extra insulation to your floors, the work will need to comply with the relevant Building Regulations, it is your responsibility to comply. In England and Wales the floor should achieve a U-value of 0.25W/m2k or less. The U-value is a measure of how quickly heat will travel through the floor. To achieve this standard, you will normally need at least 70 [mm] of highperformance foam insulation. If you are replacing at least half of a floor, then you must insulate to these standards.
In summary; Houses build before the mid-1990s did not require floor insulation to comply with the Building Regulations. Solid floors became more popular after the 1950s and they are in various configurations, biggest difference; with or without a sand-cement screed on top. It is wiser to apply insulation materials into roof, walls and doors, before investing in the floor construction. After all, still considering improving floor insulation, there are two ways of doing it; on top or underneath. Take in mind; (a) on top: causes a significant floor build-up or (b) underneath: expensive and very messy.
Advice, because the heat loss through the floor counts for a relatively small share of the total loss we recommend focus on the elements which are more cost effective (same investment greater result) as roof and walls. Taking in mind that that actual savings on energy are averagely around 55 pound a year, investing in floor constructions is not attractive considering the pay-back time. Moreover, replacing your radiators with a UFH system counts for a significant saving on its own. Finally, all together we recommend improving insulation fabrics within reason and switch from traditional heating (radiators) to a low-temperature warm water UFH system. In our opinion the best of both worlds!
JK’s in-ground UFH system is a retro-fit warm water underfloor heating system which can be installed into all solid floor constructions without any floor build-up. If case of floor constructin (a) Solid floor or (c) Suspended concrete floor; JK’s system can be cut directly into the floor consturction. In case of (b) Suspended Timber floor, a gypsum-fibre board need to be applied on top and JK’s system will be cut into these plain floor boards. Contact us for more information.