Yes, an air gap between the roof and insulation is needed, especially for traditional materials like fibreglass, mineral wool, and foil insulation.
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.
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.
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.
A layer of rigid insulation board can be added either on top of the roof's weatherproof layer or directly on top of the timber roof surface, with a new weatherproof layer on top of the insulation. This is best done when the roof covering needs replacing anyway.
A vent baffle should be installed between the insulation and the roof decking to maintain the ventilation channel.
Yes it can touch. As long as there is nothing obstructing flow from the soffits - which sounds like the baffles are.
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.
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).
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.
This should be confirmed in the membrane manufacturer's BBA certificate, though 25mm to 50mm is typical.
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.
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.
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.
(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.)
You can't simply leave a gap between your insulation and the surface and call it a day. This is where sizing comes in, and it varies depending on the material used and where it's installed. It's recommended to leave an air gap insulation of at least 25mm or 1 inch for the walls and ceilings.
Yes, you should leave an air gap between the insulation and the roof to allow proper ventilation and prevent moisture buildup. This is especially important for materials like fibreglass and mineral wool but not necessarily for spray foam insulation.
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.
Where the distance from the top of the braced wall panel to the top of the rafters or roof trusses above is between 91/4 inches (235 mm) and 151/4 inches (387 mm), blocking between rafters or roof trusses shall be provided above the braced wall panel in accordance with Figure R602.
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.
The property values indicate that an air gap with a thickness of less than 4 cm is an excellent insulator. The use of double walls with an insulating air gap led to a decrease in surface transmission coefficients from 35.63% to 47.48%, depending on the type of wall material.
As a general rule, it's always best to insulate between and above the rafters or between and under the rafters. There are a few reasons for this: There are certain U-values required by UK Building Regulations that insulation must meet, which only insulating between rafter often doesn't.
Excessively thick insulation can block most ventilation sources, reducing air quality and restricting air exchange within the loft.
Insulation is often laid in contact with the roofing felt. Where the felt is impervious any contact condensation will run down the felt and make the insulation damp.
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.