Considering that over 8% of heat is lost through our floors, insulting them is a must for heat loss prevention and modern sustainable living.

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Floor Insulation is adding insulation to the ground / bottom floor of a house. As we can see from the above picture at least 8%, although the SEAI note 20%, of our heat loss occurs through the floor.

Depending on the age of your home there are generally 2 types of floor.
1. Concrete Floor
2. Suspended Timber Floor
Not all renovation projects require floor works to meet the desired B2 energy rating. A B2 is recognised as the benchmark for excellent energy performance and home comfort. Floor insulation should be given serious though on a renovation project because “once it’s done, then it’s done
forever and saves money forever”.


There is a SEAI Grant available but only by using a One-Stop-Shop provider. The grant is €3,500 and generally aims to cover about 50% of the cost of Floor Insulation. However this is a very broad statement as it depends on the area of the ground floor and whether Type 1 or Type 2 insulation is required.

Always call us for a quotation as the figures greatly vary for floor insulation cost on 087 6089310


If you have an existing concrete floor the best option is to remove it. This involves heavy duty work with kango-hammers and sometimes a mini-digger. Generally 2-3 days has the floor removed. Once removed we are down to bare earth. Stone chipping's (Hardcore) are first installed followed by binding sand then a Radon barrier to protect from radon gas.

Above this we install the insulation then a plastic membrane to stop the concrete from flowing between the insulation sheets. Generally 50mm to 100mm of concrete is then poured and levelled. Hey presto a newly insulated concrete floor! It should be noted that it’s an ideal time to install underfloor heating pipes if that is the preferred heating method.



In the mock-up shown opposite during my training at the SEAI Center of Excellence the floor is painted red to reflect the radon barrier. We then installed two layers of polystyrene, each 150mm thick to give us the required U-Value of 0.25 W/m 2 K (more about this below). The upper layer of insulation must be installed at 90° to the layer below. This gives strength, greatly reduces thermal bridging and helps to ensure an even, flat floor.


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It is very important to install insulation around all the perimeter, even internal walls. This reduces thermal bridging. It must be a minimum of 50mm thick. PIR board (polyisocyanurate) is ideal for this as the same material is used on insulated plaster board. So after the concrete is poured we have the same insulation material meeting at the walls thus reducing cold spots and giving us a uniform insulation around the perimeter.


Hundreds of thousands of homes in Ireland have suspended timber floors. If your house is Georgian Style 1740-1830, Victorian Style 1830-1901 or Edwardian Style 1890-1918 then you most likely have suspended timber floors. Back in the day these were a great solution to overcome the difficulty of damp-proofing floors next to the ground. The major problem was that outside air flowed beneath the floors. Kiln dried floor boards were not in existence at the time so freshly cut timber flooring (Red Deal) was installed. This naturally shrank in the heated environment of a home leaving gaps
between the floor boards. That’s not really an issue in summer but in Spring, Winter and Autumn this air is Baltic, greatly reducing the temperature in the room and making it draftee and uncomfortable.

Thankfully we have modern day solutions to eliminate this draft and insulate the floor. It’s a bit counter-intuitive but we must maintain outside air beneath the floor to ensure the floor joists don’t rot and also to eliminate the build-up of mould and condensation. The solution to insulating a suspended timber floor is three fold:
1. Vapour Control Layer
2. Insulation
3. Airtight Membrane

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The (1.) Vapour Control Layer (VCL) is first installed over the joists. It is critically important to seal this around all the periphery to prevent cold air and moisture emanating from below. Battens are generally used to keep this taught thus providing a base for the insulation. A typical VCL is shown opposite.

Next the (2.) Insulation is installed. Earth-wool and Hemp are ideal as they are breathable so if any moisture should penetrate the floor structure over the building’s lifetime, it can dry out. Both Earth-wool and Hemp also achieve a snug fit to the floor joist which inevitably are never parallel.

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Conventional foil-faced, impervious PIR/PUR boards are a poor choice for insulation as they are not breathable and never achieve a snug fit to the joist resulting in thermal bridging and inconsistent insulation. The pictures opposite are taken form my training at the SEAI Centre of Excellence, as can be seen, they recommend Earth-wool.


Finally, an airtight (3.) Membrane covers the Insulation, Joints and VCL. Again it is critically important to seal this around the periphery. The chosen floor coving, be it Wood Floor or 18mm plywood/OSB (for Carpet and tiles) can go down. The great thing about this insulation method is that the floor
level is not changed so Doors, Skirting, Stair Risers, Fireplaces, Etc. do not need alteration works.

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It’s impossible not to lose heat through your building fabric e.g. Attic, Walls, Windows, etc. so we must think in terms of acceptable Heat Loss. The U value is a measure of heat transfer (or heat loss) through the building fabric. The lower the number, the better the insulating performance. U-values generally range from 0.1 (very little heat loss) to 1.0 (high heat loss).

And here is where the SEAI come in, they updated the Building Regulations in relation to home Energy in 2019 - Part L now includes the Energy Performance in Buildings Directive (EPBD) requirement for Nearly Zero Energy Buildings. The table below, taken from Part L, shows the u-value
that we need to achieve for floor insulation is U= 0.25 W/m 2 K

rETROFIT U-VALUES (Material change of use or alteration


We need to think of both of the type of insulation and much of it (thickness) that we need? Thankfully, U-value takes care of this too. U-Value is made up of the materials thickness and its thermal conductivity λ. It’s a legal requirement that both are clearly marked on an insulating material. Don’t worry, we are not getting into formulas – here’s what I recommend - Knauf
Earthwool Insulation 200mm. This is what we used at the SEAI centre of excellence and here’s why:

  • Knauf Earthwool Insulation @200mm depth gives a U-Value of 0.22 W/m 2 K which exceeds the Building regulation standards
  • Excellent thermal performance
  • Non-combustible A1 Euroclass Reaction to Fire classification
  • Lightweight quilt for ease of installation
  • It’s non-toxic unlike fibre-glass and Spray Foam Insulation
  • Attic Joists are generally 230mm so will take 200mm of insulation plus the battens.
  • It fits snug between the joists unlike rigid insulation which is always gappy.
  • A uniform depth of 200mm is easily achieved (ensuring we meet our 0.25 W/m 2 K target) unlike spray foam which is never a uniform thickness.


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