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.
You can insulate but you need to leave a gap between your insulation and the roof to allow the air the circulate. If you don't, your shingles will become very hot in the summer and they will prematurely get broken.
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.
Remember that a two-inch breathing space between the insulation and the roof sheathing must be included to allow for ventilation. If I leave room, it's hard to fit more than R-13 without going to rigid foam board.
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.
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.
Insulation that touches the rafters provides better coverage and reduces the risk of heat loss. By creating a tight seal between the loft insulation and the roof, energy efficiency is improved, resulting in lower energy consumption and reduced utility bills.
You can put all the insulation on top of the roof deck, all the insulation on the underside of the roof deck, or some on top and some below. You can put it all below the roof deck but use two different kinds. Your insulated roof can be a cathedral ceiling or it can be above a conditioned attic.
A vent baffle should be installed between the insulation and the roof decking to maintain the ventilation channel.
(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.)
This should be confirmed in the membrane manufacturer's BBA certificate, though 25mm to 50mm is typical.
Yes, too much loft insulation can cause dampness in some situations. Loft insulation works by trapping warm air inside a building, preventing it from escaping through the roof. This helps to keep the interior of the building warmer in cold weather, reducing the need for heating and saving energy.
The general advice we give is that you should always insulate between and above the rafters (warm roof) or between and under the rafters (cold roof).
Where eave or cornice vents are installed, insulation shall not block the free flow of air. A minimum of a 1-inch (25 mm) space shall be provided between the insulation and the roof sheathing and at the location of the vent.
The most common thickness of insulation between rafters is 170mm, and there is a general rule that thicker insulation is installed first, followed by a thinner layer of 100mm that can be installed perpendicular to the rafters to fill in any remaining gaps.
Overall, the second layer of insulation plays a crucial role in improving insulation performance, reducing heat loss, and maintaining a comfortable and energy-efficient living space.
Should you leave a gap between the insulation and the roof? Yes, you should leave an air gap between the insulation and the roof to allow proper ventilation and prevent moisture buildup.
Still, certified attic specialists may also use them during a major remodeling project. In open-cell spray foam installations, the typical R-value ranges from 3.5 to 3.6; in closed-cell spray foam installations, the average ranges from 6.0 to 6.5.
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.
Do you have any plans for furnishing/fitting out your attic in the future? Then you could simply insulate the pitched roof. But the best solution is actually to insulate both the attic floor and the underside of the roof.
Best roof insulation for roof rafters
Place insulation material between or over the sloped structural beams (rafters) to insulate the roof. Creating a thermal barrier, roof rafter insulation keeps interiors warm in winter and cool in summer, benefiting living spaces.
Excessively thick insulation can block most ventilation sources, reducing air quality and restricting air exchange within the loft.
No air space means no thermal value. The reflective side must be facing downwards when in roofs, upwards when installed underneath a floor and inwards when installed in walls.
Uncovering the risks: foam roof insulation
One of the most frequently underestimated dangers is the potential fire risk associated with foam insulation materials. Foam insulation is highly flammable and can ignite at relatively low temperatures, posing a significant threat to the safety of your home and loved ones.