DOES INSULATING FROM THE INSIDE MAKE SENSE?*
Insulating a house is essential to pay lower bills and enjoy consistent temperatures throughout the year. However, not everyone can install external insulation due to either the age of the house or general restrictions made by the Council. This raises the question of how to insulate a house from the inside and whether it makes sense at all.
In this blog post, we will delve into the topic and address common questions surrounding interior insulation. We will also explore various methods, including affordable options and suitable insulation materials for interior walls.
IN WHAT CIRCUMSTANCES CAN'T A BUILDING BE INSULATED EXTERNALLY?
There are several reasons why it may not be possible to install external insulation on a house. One of them is the involvement of a historic preservation officer. When a building falls under their jurisdiction, it will never be possible to insulate it from the outside.
Another example could be urban planning regulations in certain parts of the country. There are places where specific rules dictate the colour or dimensions of external walls or even the materials used in their construction, which may hinder the use of External Wall Insulation (EWI). Local planning and zoning regulations can dictate the appearance, materials, and design of buildings in specific areas.
Moreover, some buildings may have structural limitations that make external insulation impractical or infeasible. This can be due to the design, construction, or condition of the building, such as the presence of delicate features or insufficient load-bearing capacity to support external insulation.
Buildings with limited access or complicated architectural features may make it difficult to install external insulation. In cases where reaching the outer walls is challenging or poses safety risks, alternative insulation methods may need to be considered.
CAN YOU INSULATE A ROOM FROM THE INSIDE?
Yes, of course. If it is not possible to insulate the building from the outside, the option of insulating the walls from the inside remains. However, certain conditions need to be met, and the appropriate materials need to be used.
When deciding to insulate the walls from the inside, the dew point will shift towards the warmer side. In other words, the dew point will progress inward into the walls. Therefore, it is necessary to maintain a proper distance between the internal insulation and the masonry walls, typically achieved by using 50mm metal or timber studs.
Additionally, an appropriate vapour barrier should be installed to prevent the penetration of moisture into the external walls. It is also important to ensure proper ventilation by installing a ventilation unit in the room. Insulating the walls from the inside creates a sort of thermos effect, so good ventilation is necessary. This requires an additional airflow of approximately 50 m3/h.
Furthermore, it is advisable to use water-resistant materials such as insulated plasterboard. By following these general guidelines, it is possible to insulate a room from the inside. However, one should be aware that this may reduce the usable space within the room. Each 125mm of wall insulation will take away approximately 1 square metre of the room. This is significant considering the limited space available in homes in the UK.
IS IT BETTER TO INSULATE INSIDE OR OUTSIDE?
To answer this question accurately, we need to recall the principles of physics that we learned back in school. It relates to the first law of thermodynamics, which states that in a closed thermodynamic system, heat energy can be transferred between different bodies or areas with different temperatures, but the total amount of heat energy in the system remains constant. In practice, this means that heat flows from an area of higher temperature to an area of lower temperature until thermal equilibrium is reached.
Applying this principle, we can deduce that insulating the walls from the inside will have the opposite effect. As we know, the dew point - in the case of water vapour in the air - is the temperature at which the water vapour contained in the air reaches saturation due to cooling, and below this temperature, it becomes supersaturated and condenses or sublimates. By insulating the walls from the inside, we physically shift the dew point inward towards the building. In other words, the ‘warm cushion’ is further away from the cold. Following this principle, it can be inferred that it is always better to insulate the house from the outside. In this case, the dew point is shifted to the external part of the masonry wall, and it does not adversely affect the structure and temperature of our home. By insulating from the outside, we also create a protective layer that shields our home from the cold.
EXAMPLE
As an example, let's consider a situation where we feel cold and have the option of either drinking a hot tea or wearing warmer clothes. Leaving aside the fact that the British will always choose tea :), it is always better to wear warmer clothes and insulate our body from direct contact with the cold. By choosing to drink tea, our body would still remain cold, and we would only feel a slight warmth from the inside. In a short time, the heat from the tea would be lost in an attempt to warm our body, and we would return to the starting point, where we feel very cold again.
HOW EFFECTIVE IS INTERNAL INSULATION?
If you're still unsure whether to choose internal insulation and are seeking an answer to how effective it is, you need to know that it depends on several factors. The first factor is the thickness of the insulation. By following the guidelines set by building regulations and using materials like Kingspan K118, you would be required to use a minimum thickness of insulated plasterboard of around 62.5mm. This thickness should provide you with a U-value of 0.28W/m2K. Only then can you say that internal insulation will be effective and serve its purpose.
Next, you need to consider the conditions under which it is installed. Water is a major enemy of insulation. Therefore, it is important to maintain a minimum distance from the masonry wall, typically around 50mm. Only then can you ensure that internal insulation will be effective.
Furthermore, if you use inappropriate materials for insulating the exterior wall, it is almost certain that it will be ineffective and fail to achieve its goals. It is very rare to use materials like glass wool for internal wall insulation. Its thin layer would result in almost 100% inefficiency, making insulation from the inside impractical.
In conclusion, internal insulation is effective if you adhere to the guidelines mentioned above. Only then can you talk about reducing heat loss by approximately 30% compared to not insulating the room.
WHAT HAPPENS IF YOU DON'T INSULATE WALLS?
If you don't insulate your walls, several consequences can occur. Let's consider an example:
Imagine you have a house with uninsulated walls in a region where winters are cold. Without insulation, heat from the interior of your home will easily escape through the walls, leading to heat loss. This means that you will need to continuously use your heating system to compensate for the lost heat, resulting in higher energy consumption and increased heating costs.
Additionally, uninsulated walls can create cold spots within your home. These cold spots can make certain areas uncomfortable, especially those in close proximity to the outer walls. You may notice that these areas feel chilly and are difficult to heat effectively.
Furthermore, uninsulated walls can allow moisture to penetrate your home. Moisture from the exterior or interior can seep through the walls, leading to dampness, condensation, and potentially mould growth. This can not only damage the structural integrity of your walls but also pose health risks to you and your family.
In terms of acoustic insulation, uninsulated walls offer poor soundproofing. Noise from outside can easily penetrate into your living spaces, causing disturbances and reducing your overall comfort.
METHODS AND MATERIALS FOR INTERNAL WALL INSULATION
How to Insulate a Cold Wall from the Inside
To insulate a cold wall from the inside, follow these steps:
Identify the areas with cold spots on the wall. Determine the thickness of insulation you can use, considering factors such as space availability and clearance around doors and windows. Remove any loose parts of the old plaster, especially in areas where signs of mould were visible, such as room corners or upper sections. Use metal or timber studs to create a framework that provides structural support and maintains a minimum distance of around 50mm from the masonry wall. Attach insulated plasterboard to the constructed framework, using screws, and finish the joints and edges with plaster or jointing tape. Another option is to use Low-E reflective foil insulation, which reflects cold rather than absorbing it. Keep in mind to maintain a minimum distance of 20mm between the foil and the wall. The most expensive method is to use PIR boards from brands like Celotex, Xtratherm, or Recticel. This method requires building an additional framework, attaching the PIR boards, followed by a layer of plasterboard and decorative finishing. Consider the cost comparison between different insulation methods to determine the most suitable option for your situation.
Cheapest Way to Insulate Internal Walls
The most cost-effective method of insulating walls from the inside is currently the use of insulated plasterboard, which can be installed either by the dot and dab method or using mechanical fixings. Below, we present a price comparison. We have already discussed this in another article, which you can find here.
COMPARISON EXAMPLE
The UK average day rate for a carpenter or joiner is £180.
Each room will take around 7 days to build a stud wall and fit insulation. That give us figure of £1260 for the labour cost itself. Compering to insulated plasterboard that is almost 4 times more.
When insulating walls with insulated plasterboard carpenter will be able to dot and dab boards within 2 days. That is total of £360. You save £900. Not bad, isn't it?
Standard Stud Wall Insulation Material Costs
When buying both constituent parts, timber battens and insulation, you pay either per m2 or lm. For instance 6m x 2.6m wall will require 19no 8'x4' timber battens to build a stud wall.
[Date: 15.06.2023]
According to "BuildingDepot.com" current price list, that give us a cost of £255.36 for timber itself. Box of 200 Screws needed for a job will add another £68.96 to our basket. Now we need insulation. To fill and cover 15.6m2 you will need 2 Acoustic insulation rolls. Again, that is extra £159.38. To cover 2.6m x 6m wall with plasterboard you will need 6 wallboards £47.16.
Standard method ( stud wall + 100mm acoustic roll + screws + wallboard ).
£ 255.36 + £68.96 + £159.38 + £47.16 = £530.86
Insulated Plasterboard Costs
Accordingly you will need 6 boards to cover 15.6m2. That give us a figure of £312.36 ( £52.06 per board ) plus 3 bags of plasterboard adhesive £29.73.
Insulated plasterboard ( 50mm PIR bonded to plasterboard + wallboard adhesive ).
£312.36 + £29.73 = £342.09
Let's bring those figures close together
£530.86 - £342.09 = £188.77
£188.77 ( product savings ) + £900 ( labour savings) = £1049.77
£1049.77 figure is based on 15.6m2.
The costs given here are given in good faith as an indicative guide only and should be used with understanding.
Insulationgo Limited cannot accept any liability for any budget produced using these figures.
Please note, you should always seek professional advice in producing a budget for any internal wall insulation project.
Best Insulation for Interior Walls
The most commonly chosen material for insulating interior walls by builders is insulated plasterboard such as Xtratherm (Unilin) XT/TL or Kingspan K118, whether it is for the dot and dab method or mechanically fixed. Another slightly more expensive option is the use of Celotex, Unilin, or Recticel boards. Their main advantage is that they have aluminium foil on both sides, which can serve as a vapour control membrane. Less frequently, cold-reflective foils like Low-e are used due to the difficulty associated with their decorative finish.
Thin Internal Wall Insulation
The thinnest material available on the UK market for insulating internal walls is a 15mm thick product from Unilin company with dimensions of 2400mm x 1200mm. However, it is only used in specific situations where thicker insulation is not feasible. Nonetheless, this product remains very popular, as evidenced by its production volume. It is frequently purchased for applications such as insulating walls in camper vans, refrigerated units, and more. Thinner insulation options, such as Low-E foils, are also used. However, they operate on a different principle. We have already discussed this in another article on how to insulate a camper van with reflective foil, which you can find here.
Breathable Internal Insulation for Solid Walls
If for any reason it is necessary to use breathable internal insulation for solid walls, it is advisable to consider products with open-cell structures such as Rockwool mineral wool. This type of insulation is made from natural materials and allows for approximately 90% airflow through its structure, while providing excellent sound insulation properties. By using such insulation, you can expect a reduction in noise levels of around 40 dB, which is comparable to the level of a normal conversation. This means that theoretically you should not be able to hear a conversation happening on the other side of the wall.
Here are some examples of breathable products that can be used for interior wall insulation:
CONCLUSION
In conclusion, does insulating from the inside make sense? The answer depends on several factors. If there is no option for external insulation, insulating from the inside can be a viable solution, provided that the appropriate thickness of insulation materials is used and the guidelines set by building regulations are followed. By insulating internally, it is possible to improve the thermal performance of a building and increase energy efficiency. However, it is important to note that internal insulation can have some drawbacks, such as reducing the usable floor space and potentially causing moisture-related issues if not properly installed or ventilated. Therefore, careful consideration and adherence to regulations are crucial when deciding to insulate from the inside.
Related articles:
HOW TO INSTALL INSULATED PLASTERBOARD?
INSULATION BUILDING REGULATIONS IN THE UK: A COMPREHENSIVE GUIDE
A COMPREHENSIVE GUIDE TO INSULATED PLASTERBOARD FOR CEILING INSULATION
INSULATED PLASTERBOARD: FINDING THE SWEET SPOT FOR OPTIMAL THICKNESS
MANAGING MOISTURE: DO YOU NEED A VAPOUR BARRIER WITH INSULATED PLASTERBOARD?
FOIL INSULATION: TO GAP OR NOT TO GAP? THAT IS THE QUESTION!
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