It is best to have a gap between loft boards and insulation to ensure its effectiveness. It is also best to use the right materials, although this can affect the cost.
If using rigid insulation boards to insulate your loft there must be a gap between the roof covering and the insulation to allow air to circulate. This prevents any build-up of warm air that could lead to condensation. For this reason, a minimum gap of 50 mm must be left between the two to prevent it occurring.
You don't need a gap between the boards and insulation, just make sure you don't compress the insulation, but you do need a gap in the corner where the roof comes down to allow airflow from the soffits into the loft.
It's important to leave a ventilated air gap between the insulation and the boards to prevent condensation on the underside of the boards. Make sure you don't squash the mineral wool when you fit the boards on top, as this will reduce its insulation value.
Building scientists recommend, and building codes require, that the insulation installed between the rafters must be in direct contact with the underside of the roof sheathing. An air gap between the sheathing and the fluffy insulation (or the spray foam insulation) is not permitted.
In roofs, the air gap should be larger, typically around 50mm (2 inches), to allow for proper ventilation and prevent condensation. It's important to note that some insulation materials, such as spray foam, do not require an air gap.
If the insulation is installed properly, there should be a 2" air space above the insulation to the sheathing. In all practical purposes, this is should be easy to do if the rafters are 10" deep and the insulation is only 8". If that is the case, the random touching of the insulation buckling up will not matter.
Should I remove old loft insulation before laying new? Older insulation material will typically need to be removed before adding new insulation. However, in some cases the material may be in good condition, meaning you can simply top up the existing insulation material for a fraction of the cost of a full replacement.
One way that excessive loft insulation can cause dampness is by blocking ventilation. Proper ventilation is necessary to allow moisture to escape from the building. If insulation is installed too thickly or packed too tightly into the loft, it can block air flow and prevent moisture from escaping.
Does Insulation Count as an Air Space? Typically we suggest you have an air gap between 1/2″ and 3/4″ for the radiant barrier to work. Air gaps larger than this work well too – they promote ventilation on the foil and help keep the air dry and the air temps lower.
Boards for loft flooring can be installed on top of insulation using plywood, wood, or plastics. Installing loft flooring and boarding over insulation helps save space, prevent heat loss, and increase home value. Adequate loft insulation can also help reduce CO2 emissions by 125kg annually.
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.
Yes, an air gap between the roof and insulation is needed, especially for traditional materials like fibreglass, mineral wool, and foil insulation.
According to regulations, loft insulation depth must be at least 270mm, which is usually higher than most loft floor joists. So when you try and board directly onto these joists, you're going to end up squashing the insulation down, which in turn means your insulation won't pass a building control inspection.
Squashing Reduces Thermal Performance: Compressing insulation can decrease its ability to trap air and prevent heat from escaping. Studies have shown that squashing insulation from 270mm down to 100mm will reduce its performance by over 50% significantly affecting your home's energy efficiency.
Lay out insulation rolls close together to prevent any gaps in your attic insulation. Go right to the edges of the loft space with your insulation to maximise its efficiency.
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.
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.
Loft insulation usually lasts 40 years or more if properly maintained and pays for itself many times over its lifespan. However, this greatly depends on how well it was installed and the type of material used.
Because it is applied so thickly, it cannot settle. The insulation works by preventing heat transfers through millions of tiny air pockets. As long as the insulation stays fluffy and thick, you maintain the high R-value you paid for.
However, insulation can start falling from fiberglass batts after 15 to 20 years, so if your insulation was installed in batts well over a decade ago, it might be time for an inspection or a home energy audit.
(Source: NRCA.) In the event you are erecting a “cold building” (such as a refrigeration building) that stays at 32 F (0 C) degrees or less inside, you will need a vapour barrier on the outside of the insultation to prevent warm exterior air from entering and potentially damaging the roof's insulation. (Source: NRCA.)
A vent baffle should be installed between the insulation and the roof decking to maintain the ventilation channel.
To maintain airflow, leave a space of 38 to 50 mm (1 1/2 to 2 in.) between the top of the insulation and the underside of the roof sheathing.