Should there be space between insulation and roof?

Author: Dr. Kathryn Okuneva  |  Last update: Friday, July 4, 2025

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.

Should there be an air gap between insulation and roof?

When it comes to insulation, it's generally recommended to leave a gap between the insulation material and any other surfaces, such as walls, ceilings, or roofs. This gap provides ventilation and prevents moisture buildup, which can lead to mould and other problems.

What is the clearance between insulation and roof?

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.

How much space do you need between insulation and roof?

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.

Should insulation be against the roof?

For optimal energy efficiency, your home should be properly insulated from the roof down to its foundation.

The the wrong and the right way to insulate a loft .

Can insulation touch the roof?

Yes it can touch. As long as there is nothing obstructing flow from the soffits - which sounds like the baffles are.

Where should you not put insulation?

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.

Can you put too much insulation in a 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.

What is the gap between roofing membrane and insulation?

This should be confirmed in the membrane manufacturer's BBA certificate, though 25mm to 50mm is typical.

Is 2 inches of insulation enough?

The recommended thickness for attics is typically 12-16 inches. Spray foam insulation: As discussed earlier, the recommended spray foam insulation thickness can vary depending on factors like climate and location. For attics, a thickness of 2-4 inches is usually sufficient.

Is it okay to put insulation between roof rafters?

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).

How much insulation should be in a roof?

An uninsulated flat roof has a U-Value of around 1.5 W/m2K. When insulating one, you're aiming for a value of 0.25 W/m2K or less. To achieve this, you should insulate your flat roof with insulation boards totalling around 150mm thickness.

Where is the best location for roof insulation?

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.

Does roof insulation need vapor barrier?

(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.)

Are air gaps good for insulation?

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.

How much clearance is needed between the bottom of the roof sheathing and the insulation for a cornice vent?

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.

How much space between insulation and roof?

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.

Can you put insulation directly against a roof?

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.

Do I need to leave a gap for roof insulation?

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.

Can insulation touch roof sheeting?

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.

Can your R-value be too high?

The optimal R-value for most homes is 30, but you can go as high as 38 if you live in a tropical climate. Anything higher than 38 indicates an over-insulated space. While you might think that too much insulation can't be bad, there are some significant consequences to consider.

What is the life expectancy of roof insulation?

As a general rule, insulation should be replaced or retrofitted every 15 to 20 years. However, it may need replacing or retrofitting sooner depending on the type of insulation installed, the R rating of the original insulation, compression and movement over time, and whether any damage has occurred.

Should I insulate the underside of my roof?

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.

Can you install insulation wrong?

Besides safety concerns, installation inexperience can result in insulation mistakes that can affect both the quality of your insulation and installation. Improper placement can leave gaps and cause energy loss, lessening the insulation's lifespan.

What ruins insulation?

Moisture damage

This can occur due to leaks in the roof or foundation, inadequate ventilation, or high humidity levels inside a building. Moisture can cause the insulation material to become compressed and lose its effectiveness, leading to increased energy consumption and potential mold growth.

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