All in all, insulating your eaves is a necessary step if you want to achieve full thermal efficiency in your home, but it's highly recommended to work with a professional installer who can ensure sufficient space is created for ventilation.
For optimal energy efficiency, your home should be properly insulated from the roof down to its foundation.
The most common mistake homeowners make when installing insulation is to block the flow of air at the eaves. NEVER COVER ATTIC SOFFIT VENTS WITH INSULATION — use rafter vents and soffit vents to maintain airflow.
Sealing the eaves in cold climates can help prevent the water from seeping through roof shingles and underlayment. Sealing the eaves should be done in Climate Zone 5 and higher. It is accomplished using a self-sealing bituminous membrane with a peel-and-stick adhesive backing or a similar product.
Never place insulation close to water heaters, oil burners or anything hot. The backing is especially flammable and will be a major fire hazard for your home.
One of the less obvious but crucial benefits of insulating attic roof rafters is moisture control. Insulation helps prevent condensation, which can lead to mold and mildew. Mold is not only damaging to your home but also a health hazard.
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.
Ventilation at the Eaves
Roof voids must be ventilated in order to stop warm air condensing on cold surfaces. Condensation encourages rot and mould growth. The air gap dimensions shown on the drawings are the minimum widths required for clear continuous ventilation air paths at the eaves.
It increases the energy efficiency of the building. This is because a roof without eaves significantly reduces the risk of leaks. These are the main cause of heat escaping outside the property, leading to higher electricity bills. It exposes the windows, thereby increasing the sun's input.
The unintended consequence of your recently installed roof vents is that your house got colder. In the winter months, warm attic air is vented to the outside through the ridge vents and is replaced by colder outside air sucked in through the soffit vents. In essence there is a mini jet stream in the attic.
Check for damage or cracks
Inspect your fascias and soffits to look for gaps, cracks, or other damage indicators. These cracks could let water leak in and cause rotting or decomposition. Addressing any problems as soon as you become aware of them is critical.
Regular Soffits (Non-Vented)
These soffits do not have any openings or vents and therefore do not allow any airflow through the attic. Non-vented soffits are typically used for aesthetic purposes and are not recommended for homes as they can cause moisture buildup and mold growth.
Cold outside temperatures often lead to condensation on the inside of your roof if not insulated well. Ice dam formation on your roof might also lead to water infiltration between your slates. Proper insulation prevents moisture damage to your roof structure.
Insulation beneath the floors of your home and along foundation walls can help improve energy efficiency and preserve your home's air quality. Without insulation, both warm and cool air can escape through the floors and cause your home energy systems to work harder to keep a stable indoor temperature.
The air temperature will be hotter on your roof than it is on the ground. And that's not just because you're in direct sun or without shade.
If a building has a well sealed ceiling* then 3mm eaves ventilation is required. If a building has a normal ceiling then 7mm eaves ventilation is required. In practice, a commercially available 10mm eaves ventilation system would normally be used.
We recommend that one vent be installed for every 90m2 of roof space. It is also important to remember to allow the air to be replaced from somewhere, and so we recommend 4 eave vents per roof vent, and ideally one internal ceiling grille, to allow any hot trapped air to escape from inside your home.
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.
Also, when laying down additional insulation, work from the perimeter toward the attic opening. Never lay insulation over recessed light fixtures or soffit vents. Keep all insulation at least 3 inches away from recessed "can" lights, unless they are rated IC (Insulated Ceiling).
Rigid foam is the best insulation for rim joists. We chose 2-in. -thick (R-10) “extruded polystyrene.” Don't use “expanded polystyrene,” which is a less effective air and moisture barrier.
If you go with a hybrid assembly, Kohta recommends using fibrous insulation on the underside. You could use open-cell spray foam there, but cellulose or fiberglass would be much less expensive and do the job just as well when installed properly.
Yes, an air gap between the roof and insulation is needed, especially for traditional materials like fibreglass, mineral wool, and foil insulation.
So if you are insulating a pitched roof, we would recommend having insulation either above or below the rafters.