In the winter, humidity from the house's interior will get past the insulation and come in contact with the cold roof sheathing, where it will condense into water. Without a proper air-space to allow the insulation and roof to dry out, this water will collect, potentially leading to rot and mildew.
Insulation is technically a solid with a lot of air in it therefore, it is NOT an air gap. You literally must have a VOID, nothing in the air gap except air itself. So if you are installing under a roof or in a wall, you must create an air gap.
PIR Rigid Board Insulation
It's made of PIR (polyisocyanurate) and normally inserted between the rafters with a minimum of a 50mm gap between it and the roofing material.
Experts usually advise builders that you can't install fiberglass insulation directly against the underside of roof sheathing.
Where eave or cornice vents are installed, blocking, bridging and insulation shall not block the free flow of air. Not less than a 1-inch (25 mm) space shall be provided between the insulation and the roof sheathing and at the location of the vent.
Find the total airflow required.
How long is the ridge of the roof in mm? Multiply the length in mm, by the continuous airflow required. Eg – for a 10m long roof, requiring 5mm continuous airflow Do 10m x 1000 = 10,000mm long roof Then 10,000mm x 5mm = 50,000mm2 airflow.
However, you may be wondering, can insulation touch the roof? Your attic insulation should not touch the roof. You will need to place plastic or foam baffles in between the attic insulation and the roof to allow airflow and decrease the possibility of mold in your home.
The reflective side must be facing downwards when in roofs, upwards when installed underneath a floor and inwards when installed in walls. For roofs, it should be positioned on a downward angle to stop mass amounts of dust from settling on it as this can also dull its reflective properties.
As a general rule, vapour impermeable foam (any foam) on the outside of the studs should be twice as much as the fibrous insulation included in the stud bay, this is known as the 1/3 : 2/3 rule. So, if we had R2. 7 glass wool in the stud bays then we need R5. 4 foam on the outside of the studs (Total R8.
It may reduce the efficiency by as much as 30 to 50%. About the insulation touching the roof. 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".
There comes a point where too much insulation starts to have a negative effect — financially, environmentally, and in terms of the longevity of your home. So yes, it is possible to over-insulate your house.
The rule may be stated: Insulation resistance should be approximately one megohm for each 1,000 volts of operating voltage, with a minimum value of one megohm.
Doubling the thickness of insulation will double the insulation's R-value, cutting heat loss in half. Each time the insulation layer is doubled in thickness, this rule applies.
The Insulation Solution – Encapsulation and Wall Insulation
The vapor barrier should be installed facing the conditioned space (the interior living space of your home). If the insulation was installed upside down, we suggest removing it.
Insulation below the slab is more common and arguably better as the slabs help to absorb the heat, meaning overheating is less likely. The DPM is placed over a layer of sand to protect it from the sharp concrete stones (otherwise you risk puncturing the insulation).
roof insulation is no-contest. The floor wins every time. Insulating the floor is standard practice for an unfinished attic space. The exception to this rule takes place when families opt to convert an unfinished attic space into something usable or livable.
The Not So Good Things. This type of insulation also leaves gaps, which can reduce the overall effectiveness of the finished installation. The material isn't the safest either, and has been known to cause respiratory problems after extended, direct exposure.
However, if insulation is not installed properly, it can create areas where moisture can accumulate and lead to condensation. For example, if insulation is installed too close to a roof or wall, it can create a cold surface that attracts moisture and leads to condensation.
If your insulation is laid in contact with roofing felt that is impervious - condensation will run down the felt and make the insulation damp.
The two main dangers associated with too much ventilation involve roof damage and increased utility bills. If you have too much air circulating, your roof will collect moisture causing damages that will weaken spots and then cause leaking.
Most codes use the 1/300 rule for minimum residential attic ventilation recommendations. This means that for every 300 square feet of enclosed attic space, 1 square foot of ventilation is required – with half at the upper portion (exhaust vents) and half in the lower portion (intake vents).
Doubling insulation does double R-value. Due to the law of diminishing returns, doubling insulation from R-10 to R-20 will reduce energy consumption more than doubling R-20 to R-40. Attics usually have plenty of space for doubling insulation.
Yes. For example, two R-19 batts can be stacked on each other to create R-38 insulation.
The bigger the R value, the better the insulation is at slowing down the heat transfer. So R19 is better insulation than R13, and R30 is better than R19. The larger the R value, the better the insulation value.