This is suggested to achieve a u-value of 0.16 W/m²K, the expected thermal efficiency for existing dwellings and extensions. Is 400mm loft insulation too much? 400mm of roof insulation is considered beyond what is needed to achieve the desired u-value for proper thermal efficiency.
Excessively thick insulation can block most ventilation sources, reducing air quality and restricting air exchange within the loft. It can also negatively impact air circulation, which causes respiratory problems and other related health issues.
New build properties typically use 400-500mm of loft insulation. This is achieved by using 3 layers of insulation; one base layer (100mm) lengthwise between the joists and super top-up (200mm) layers laid at right angles to the joists. To achieve maximum performance, insulate with 500mm of Space Loft Roll.
It is recommended to have at least 270mm of loft insulation material in place, especially when using insulation materials such as mineral wool or sheep wool. Increasing this thickness to 300mm may provide slightly better insulation, but 270mm is considered more than adequate for the job.
Today's topic of 'discussion' with our builders is over how they have fitted the loft insulation. They quoted on fitting 400mm of glass wool, to give no worse than 0.12 u value.
In 2024, UK loft insulation rules require a minimum insulation thickness of 270mm to meet a U-value of 0.16 W/m²K, along with proper ventilation and fire safety compliance.
One important thing to remember is that insulation should never be pushed right into the eaves because it will interfere with airflow. If you're going for a warm loft then you'll need much more insulation to be able to cover the underside of the roof along with the gable and party walls.
Absolutely! By reducing the amount of energy needed to heat your home, loft insulation also reduces carbon emissions.
Since 2003, current building regulations recommend a depth of at least 270mm (mineral or glass wool) in the loft – use this as a starting point rather than a finishing line to see larger savings. In 1995, the recommended depth was 200mm. Prior to that it was less than 100mm.
In fact, adding too much insulation to your walls can lead to problems such as poor ventilation, mould growth, and condensation. This is because thicker insulation can block airflow and trap moisture, leading to indoor air quality issues and even structural damage.
This is a unit of thermal resistance and rates the insulating properties of the material. The higher the R-value, the greater the insulation. A minimum R-value of 6.1 is recommended for loft floor insulation, but ideally it would be up to 7.0.
Easier to heat and cool: When you have quality attic insulation, more heat stays in your home through the winter, and less radiates down from your attic in the summer. This resistance to heat makes it more affordable to heat or cool your home to the temperature you're comfortable with.
Too much insulation will leave humidity and moisture to accumulate in your attic space. This can lead to mold growth on your walls and insulation. There might also be water damage to the support beams in your home's roof.
Many of us know what causes mould; when moisture is trapped in the rooms of you home. Sometimes, there is insufficient insulation in the walls, so mould grows. However, not many people realise that additional insulation isn't always the answer. In fact, too much insulation can be the secret cause of mould.
Squashing your insulation reduces its effectiveness by 50%
Numerous studies on the topic have indicated that there's a huge number of Britons who don't understand why doing this is so problematic. Mineral wool type insulation (the most common loft insulation) needs to retain its full depth in order to work effectively.
Before you decide to install new loft insulation, it's important to assess the condition of your existing insulation. If the insulation is still in good condition, it may not need to be removed. However, if it's damaged, damp, or infested with pests, it should be removed before installing new insulation.
The recommended thickness for EWI typically ranges between 60mm and 100mm, depending on the type of insulation material used, the construction of your existing walls, and the age of your home.
You'll need to start laying with a minimum gap of 25mm between the eaves and the insulation to ensure a suitable air gap. Maintain this gap along two opposite sides of the loft.
Currently, the government recommends loft insulation to be 270mm thick. Some new houses have 300mm thick insulation. So if your loft has good ventilation, this is also fine. You might lose some storage space, but you will save money!
As a general guideline, it's advisable to install double layers of thermal insulation throughout your house. Nevertheless, this may not be feasible in all areas due to space limitations. Typically, it's not practical to add two layers of insulation within the walls of your home.
In the 1980s, it was quite standard to install any thickness from 25 to 50 mm. Then, building regulations stated that homes should have as much as 100 mm of loft insulation. This gradually increased to 200 mm and now stands at 270 mm for new builds and is recommended for other properties (but not essential).
Current government recommendations are for loft insulation thickness to achieve a depth of 270mm, but some new properties are increasing their level of loft insulation to 300mm. Again, as long as the loft has adequate ventilation, this is fine. You may lose a little storage space, but you will save money!
While loft insulation is an effective way to improve energy efficiency and reduce heating costs, over-insulating can lead to several potential issues. Firstly, over-insulation can lead to poor ventilation in the attic, which can cause moisture buildup and increase the risk of mould growth.
In unfinished attic spaces, insulate between and over the floor joists to seal off living spaces below. If the air distribution is in the attic space, then consider insulating the rafters to move the distribution into the conditioned space.