Rigid
Our Conclusion. We recommend spray foam insulation because of its relatively simple installation process, high R-value, and applicability to different climate regions.
The best solution, by far, would be to install a thick layer of rigid foam insulation above the roof sheathing, followed by a second layer of roof sheathing and new roofing. Not cheap, but effective.
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.
Some common types of insulation used for roof rafters include fiberglass batts or blanket insulation, cellulose, and spray foam. Fiberglass batts are one of the most affordable options and offer decent resistance to heat flow with an R-value between 3.2 and 4.3 per inch, depending on where they are being installed.
Foil insulation
Single or multi-layer rafter insulation foil is an aluminium-based membrane that is both affordable and easy to install onto roof rafters.
In unfinished attic spaces, insulate between and over the floor joists to seal off living spaces below. If the air distribution is in the attic space, then consider insulating the rafters to move the distribution into the conditioned space.
Fibreglass: This is the best roof insulation material for the budget-conscious. It is affordable and will cost around £10 per m2. Its lightweight batts or rolls are ideal for roof rafter insulation and can be cut to fit between the rafters.
When the choice is made to insulate along the underside of the roof deck, spray foams have advantages over other insulation types because of the ability of spray foams to effectively air seal complex assemblies.
Yes, an air gap between the roof and insulation is needed, especially for traditional materials like fibreglass, mineral wool, and foil insulation.
(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.)
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).
Rubberized Asphalt Underlayment
It is made by combining asphalt with rubber polymers, which not only ensures waterproofing but also offers self-sealing properties around nails and fasteners. This is an important feature, especially in areas that are prone to wind-driven rain and ice dams.
Insulation helps to regulate the temperature inside the house by blocking out heat and cold during the summer and winter, respectively. It is placed against the underside of the roof deck where it can prevent heat or cold from entering the attic.
Common materials used in flat roof insulation include polyisocyanurate (PIR) boards, expanded polystyrene (EPS), extruded polystyrene (XPS), mineral wool, and spray foam. Additionally, materials such as PIR and EPS are cost-effective, contributing to the overall low cost of roof insulation for flat roofs.
Compared to fiberglass batts, mineral wool batts offers superior insulation and has about a 22-37% higher R-value per inch. For commercial settings, the higher cost of soundproofing with rockwool insulation may be offset by the thermal regulation it provides, helping to reduce heating and air conditioning bills.
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.
All Spaces Containing Fiberglass Insulation Require Ventilation. Ed, Areas (crawl spaces, attics, joists spaces etc) that contain fiberglass insulation require some sort of ventilation to help remove the moisture that will occur when warm air meets cold air and the humidity is at a certain level.
Since 2003, current building regulations recommend a depth of at least 270mm (mineral or glass wool) in the loft – use this as a starting point rather than a finishing line to see larger savings. In 1995, the recommended depth was 200mm. Prior to that it was less than 100mm.
House insulation: The most effective insulation
So having in mind that spray foam, fiberglass, and cellulose are the three mostly used insulation materials we made a comparison, and here are the results: Spray foam has by far the highest R-value, which is crucial for homes in extremely cold climates.
Insulating between roof rafters is not only okay, but it is often recommended as a way to minimise the use of headspace while maintaining comfortable indoor temperatures.
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.
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.