In general, either batt or rolled insulation or blown
The answer is yes, you can put new insulation over old. But there are some circumstances that would require insulation removal first, such as in the case of contaminated insulation from pests, water or smoke. Moisture is the biggest culprit, as it can lead to mold and mildew, as well as ceiling and roof rafter rot.
If your loft is not used for storage purposes, doubling the insulation layers is highly recommended. By doubling the insulation layers in your loft, you increase its R-value, which in turn reduces its U-value (lower U-value is better).
You should install two layers of insulation in your attic; wood joists must be covered to allow the air to move. The first layer will sit between the joists, and the second layer will run perpendicular over the joists. The first layer should have the facing against the drywall to act as a vapor barrier.
The good news is that there's no need to remove any existing loft floor insulation. Just add one or more new layers on top of it to reach the recommended amount.
Thicker is better
The thermal barrier of a home should consist of a continuous layer of insulation on all sides—including the lowest floor, the exterior walls, and the ceiling or roof. Doubling the thickness of insulation will double the insulation's R-value, cutting heat loss in half.
Absolutely! By reducing the amount of energy needed to heat your home, loft insulation also reduces carbon emissions.
In many cases you can add new insulation on top of old insulation, unless the old insulation is wet, mouldy, or vermiculite. If the old insulation is dry but appears to have previously been wet, you should look for the cause and repair the problem.
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.
Roof insulation batts can be added in more than one layer. Adding a double layer of roof insulation negates the effects of thermal bridging and seals any gaps that may be present in the first layer.
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.
It is possible to over-insulate your house so much that it can't breathe. The whole point of home insulation is to tightly seal your home's interior. But if it becomes too tightly sealed with too many layers of insulation, moisture can get trapped inside those layers.
Can Loft Insulation Be Too Thick? Although it can be tempting to believe more is always better, exceeding recommended loft insulation thicknesses can actually have a number of negative consequences. The most common of these is poor ventilation, which can lead to issues such as damp, condensation, and mould.
Do I Have To Remove Old Insulation? Unless your insulation is wet, moldy or infested with pests, you don't need to remove it before adding insulation on top of it. ENERGY STAR® recommends that you inspect your insulation for signs of mold, mildew, moisture and pest infiltration before making this determination.
The higher the R-Value, the better the thermal performance of the insulation. The recommended level for most attics is to insulate to R-38 or about 10 to 14 inches, depending on insulation type.
According to Home Energy Scotland, an uninsulated home loses a quarter of heat through the roof. And even if you already have some insulation in place, topping up your loft insulation can make a big difference.
To reach the recommended loft insulation depth of between 270-300mm, a second layer can be added. Simply unwrap the insulation and lay at 90-degrees to the first layer and ceiling joists.
We'd recommend everything in moderation. While some people argue that an over-insulated house could cause damp, mould and other issues. Typically, upping your loft insulation from 270 mm to 400 mm isn't really going to make a big difference, and so it's probably worth sticking with the lesser amount.
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.
The first layer is laid between the joists – the horizontal beams that make up the floor of the loft – then another layer is laid at right angles to cover the joists and make the insulation up to the required depth.
While both types provide insulation, R30 is the better option for maximizing energy savings in areas where heat loss or gain is a major concern. For example, R19 may suffice for interior walls, but R30 is more appropriate for exterior-facing attics or floors.
If you are not planning to put in an attic floor, a second layer of insulation may be laid at 90º to the first layer. Do not lay in a second moisture barrier, as moisture could potentially be trapped between the two layers. This second layer of insulation will make it easier to obtain the recommended R-value.
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.
On average, you can save up to 20% on your home's heating and cooling costs or up to 10% on its total energy costs by adding insulation to attics, floors, crawl spaces, and accessible basement rim joists, and by reducing unwanted air leaks all around your house.