Floor Insulation
Save Up to 15% on your energy bills from the air that is coming up through your floorboards
Considering that up to 15% of heat is lost through our floors, insulting them is a must for heat loss prevention and modern sustainable living.
Modern Insulation for Historic Homes
At RH Insulation, we effectively insulate your suspended timber floors while maintaining proper ventilation. This prevents moisture buildup and preserves the integrity of your home.
Vapour Control Layer
Blocks moisture from rising into your home.
High-Performance Insulation
Minimizes heat loss by insulating between floor joists.
Airtight Membrane
Keeps warmth in and cold out while maintaining natural ventilation.
What is Floor Insulation?
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”.
1. CONCRETE FLOOR
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.
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.
2. SUSPENDED TIMBER FLOOR
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
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.
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.
A BIT ON FLOOR INSULATION U-VALUE
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
A BIT ON FLOOR INSULATION U-VALUE
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 300mm. This is what we used at the SEAI centre of excellence and here’s why:
- Knauf Earthwool Insulation @300mm 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 300mm of insulation plus the battens.
- It fits snug between the joists unlike rigid insulation which is always gappy.
- A uniform depth of 300mm 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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Frequently asked questions
Underfloor insulation is installed beneath the floor of a property to reduce heat loss through suspended timber floors. It helps create a warmer home by improving thermal performance and reducing drafts coming up through floorboards.
A suspended floor is a floor structure where timber floorboards are supported by joists above a ventilated void. Many older homes throughout Dublin and Ireland have suspended timber floors, particularly period and traditional properties.
An uninsulated floor can account for around 10% to 20% of a home’s heat loss. Insulating a suspended floor can help reduce this heat loss and improve overall comfort throughout the property.
Yes. Underfloor insulation is one of the most effective ways to improve comfort in homes with suspended timber floors. Many homeowners notice warmer floors, fewer drafts, and reduced heating requirements after installation.
Insulation is fitted between the floor joists beneath the floorboards. This creates a thermal barrier that helps prevent heat escaping through the floor while still allowing necessary ventilation beneath the property.
Yes. One of the main benefits of underfloor insulation is reducing cold drafts that often come through gaps in floorboards. Many homeowners notice a significant improvement in comfort after installation.
Underfloor insulation is particularly beneficial in:
- Victorian homes
- Edwardian homes
- Older terraced houses
- Semi-detached properties
- Period properties with suspended timber floors
Many older Dublin homes were built before modern insulation standards and can benefit significantly from floor insulation upgrades.
The cost depends on factors such as:
- Floor area
- Accessibility beneath the floor
- Type of insulation used
- Property layout
A survey is usually required to provide an accurate quotation.
Most underfloor insulation projects can be completed within one to three days, depending on the size of the property and access requirements.
By reducing heat loss through the floor, underfloor insulation can help improve energy efficiency and reduce heating demand. The amount saved varies depending on the property and existing insulation levels.
Yes. Many homeowners report that their floors feel noticeably warmer underfoot after installation, especially during the colder months.
Yes. Improving floor insulation can contribute towards a better Building Energy Rating (BER) by helping improve the overall energy efficiency of the property.
While its primary purpose is thermal insulation, some insulation materials can also help reduce sound transmission between rooms and limit external noise entering through the floor structure.
Yes. Proper ventilation is essential to prevent moisture build-up and protect the timber structure. Professional installation ensures insulation is fitted without blocking required airflow.
No. When installed correctly, underfloor insulation should not cause damp issues. Maintaining adequate ventilation beneath the floor is a key part of the installation process.
Yes. Rooms that feel cold despite adequate heating may be losing heat through uninsulated floors. Underfloor insulation can help improve temperature consistency throughout the home.
Several insulation products can be used depending on the property, including:
- Mineral wool insulation
- Rigid insulation boards
- High-performance breathable insulation materials
The most suitable option depends on the construction of the property.
In many cases, access is required beneath the floor to install insulation between the joists. The installation method depends on the construction and accessibility of the property.
Yes. Most installations can be carried out while homeowners remain in the property. A survey will determine the most practical installation method.
When professionally installed, underfloor insulation can last for decades and continue providing thermal benefits throughout the life of the property.
Common signs include:
- Cold floors
- Drafts coming through floorboards
- High heating bills
- Cold ground-floor rooms
- Uneven temperatures throughout the house
Underfloor insulation is most suitable for homes with suspended timber floors. Homes with solid concrete floors may require a different insulation solution.
Yes. Many homeowners choose to improve attic, wall, and floor insulation together to maximise energy efficiency and comfort throughout the property.
Improving energy efficiency can make a property more attractive to potential buyers. Better insulation, improved comfort, and lower running costs are all positive selling points.
RH Insulation specialises in helping Dublin homeowners improve energy efficiency and comfort through professional insulation solutions. Our experienced team can assess your property, recommend the most suitable insulation approach, and ensure the work is completed to a high standard while maintaining proper ventilation and protecting the structure of your home.