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Are you losing 33% off heat through your walls?

Considering that over 30% of heat is lost through our walls insulting them is a must for heat loss prevention and modern sustainable living



Considering that over 30% of heat is lost through our walls insulting them is a must for heat loss prevention and modern sustainable living. Insulating Internal Walls is a cost effective option which keeps the external building facade intact. The repayment is quicker than exterior insulation and it’s
generally about 50% of the cost. A lot of pre 1940 houses have red brick exteriors and even older houses may have stone exteriors or even granite. Heritage houses also fall into this category.

While Exterior insulation is pretty straight forward there are numerous factors to contend with when considering internal insulation. I’ve written a Pro’s & Con’s below but the main thing to consider is the disruption to family life. Although one room can be done at a time to minimise this.
Before deciding what type of internal insulation we require we must first understand the level of heat loss that we aim to achieve. There will always be an element of heat loss i.e. it can never be totally eliminated so what level do we need?

The centre of excellence for home energy upgrades in
Ireland is the SEAI. They recommend that a B2 Energy rating should be achieved in all homes in Ireland. That's because a B2 rated home is considered the benchmark for excellent energy performance and home comfort.
Please see my write up under Attic insulation for an explanation of Heat Loss
measurement which is called U-Value. To achieve a B2 energy rating in our homes the walls must have a U-value below 0.35 Cavity and 0.55 for other wall types.

The type of internal insulation depends on the construction of the walls of your house. Generally there are 3 distinct categories of wall construction:
1. Cavity Wall Post 1940 house normally fall into this category. To confirm lift out the white box that holds your electricity meter (its outside). If you have 2 walls with a space or “cavity” between them then you have a “Cavity Wall” structure. Generally there is 50mm of white foam in the space between the walls. The thickness of cavity walls are between 270mm and 300mm. Typical U-Value = 1.78 W/M 2 K (A cavity wall is constructed by building two walls parallel to each other, using solid blocks and leaving a gap of three to four inches between them. The walls are not bridged anywhere and this eliminates the risk of water penetration to the inner leaf)
2. Solid Walls Pre 1940’s houses normally fall into this category. The walls can be made from Concrete, Brick or Stone Construction. They range from 220mm up to 600mm (sometimes even more in older buildings!). As per above if you can lift out your Electricity box this should show the construction. Breathable plaster is used inside and outside to prevent moisture ingress. Typical U-Value = 1.5 W/M 2 K These can be the most difficult walls to work with as, particularly on older houses, they are not straight, not flat and their construction can use a variety of materials.
3. Hallow Block Walls These are also referred to as 9” Cavity Block Walls. The wall is constructed solely from blocks that are 18” long and 9” wide. Here the wall is 230mm thick. A Hallow block wall is constructed by building a single wall using these hollow blocks and placing them on top of each other in a staggered manner. Typical U-Value = 2.4 W/M 2 K By their nature, a cavity block wall is bridged every seven to nine inches. Compared to a cavity wall, there is a higher risk of dampness, and mild mould growth appearing on the inner walls. This is particularly the case with older properties Sand and cement is commonly used as an exterior plaster to keep moisture out and skimming on the inside for a smooth finish.

Now, the question must be answered – Which type of internal wall insulation (4 types) is suitable for my house?

The real answer is to contact us for a site visit on 087-6089310.


These are the most modern wall types and are the most straight forward. The cavity does not need to be pumped (Cavity Wall Insulation) as we will be
preventing the heat from getting into the walls via Internal Wall insulation.
Insulated plasterboard sheets can be secured directly to the wall via bonding or mechanical fixings (specialist screws). It is relatively straight forward and the job progresses quickly as the walls are by enlarge
straight and flat.

Insulated boards come in different thicknesses depending on the amount of insulation determined by the BER assessment. An alternative to this is to batten the wall then place semi-rigid insulation placed between the battens. The advantage of this system is that services (power and water) can be installed without the need to chase the concrete walls. It also allows the walls to be straightened if they are off-plumb. The disadvantage is that it is slower to install. The option also exist to place insulated plasterboard on the battens thus doubling the level of insulation – one layer between the
battens, the second layer on the plasterboard.

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Given the high risk of mould & condensation and the multi- media that these walls are usually made from, it is always best to build a new stud wall at least 30mm away from the existing wall. This allows the existing wall to “breath”. The term “breath” refers to the ability of stone and masonry walls to absorb moisture on days with high humidity (wet days) and then emit that moisture on days of lower humidity (dry days). In effect the moisture content of the wall is uncontrollable and varies according to the weather, which in Ireland can be 4 seasons in one day.

The fee space of 30mm between the existing wall and the new insulated wall must be vented externally so the damp air can escape otherwise it will build up behind the insulated slab eventually appearing as mould spots on the plasterboard. A continuous airtight and vapour control membrane is required to eliminate drafts on the warm side of the insulation. The studs can either be timber treated with preservative or aluminium. Bottom and top rails are
first placed and levelled before the vertical studs are fixed in place. As per above, insulation is placed between the studs and if required insulated plasterboard is fixed on top effectively doubling the insulation.

Another solution for breathable solid walls is Insulted Plaster. The rigid insulation can be made of Hemp, cork and/or wood fibre and the plaster generally is a combination of lime / hemp / Cork. It is difficult to find independent conclusive research that validates manufacturers U-Value figures. It is the oldest type of wall insulation and was used along with lime based white-wash paint. Older cottages often use this solution due to the small nature of the rooms and its authenticity.


These walls have the worst U-Value as they have a solid thermal bridge every 9” throughout. However compared to solid stone walls they do not absorb moisture in the same way therefore a batten system can be used. However the battens must be insulted from the wall (DPC Strips) and plastic fixing must be used to affix these battens to stop hermal bridging.

A vapour control layer (VCL) must be installed on the warm side of the
insulation to minimise the risk of interstitial condensation on the cold
masonry behind the insulation Particular attention is required to ensure all edges of the insulation boards are continuously sealed at floors, ceilings and jambs. All board joints must be taped and all service entry points sealed to ensure the continuity of the vapour control layer.


Pros & Cons of Insulating Internal Walls

Approx 50% of the cost External Wall insulation Inconvenience to homeowners when works are being carried out
Shorter payback period Rooms unusable during works
Ideal for buildings in conservation areas Access required to all downstairs of house as electricians will need to isolate the power and plumbs will need to drain down the heating system.
Rooms are easier to heat and stay warmer for longer after heating is switched off. Kitchens and bathrooms might not be possible to insulate internally.
Helps keep your home cool in summer There will be internal dust and noise
Acts as a sound insulator Newly insulated walls and adjacent surfaces will need to be re-decorated when the work has finished.
Rooms can be done individually Slight loss of internal floor area

Costs of Internal Wall Insulation

The cost of drying will vary hugely depending on the type of wall construction as outlined above. As a typical value a 3 bed semi-detached house is €8,000 and there is a SEAI grant of up to €3,500 (terms and conditions apply). The grants are shown in the table below.

Minimalist Bold Black Yellow Package Comparison Chart Graph-2


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