How much air space is between insulation and roof?

Author: Vivienne Keeling  |  Last update: Sunday, June 29, 2025

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 there be an air gap between insulation and roof?

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.

What is the ventilation gap for roof insulation?

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.

What is the minimum air gap between roof and insulation?

An air gap will need to be 50mm wide, and the best way to ensure this is to attach timber battens of a 50mm width within your roof, which you can then place the insulation boards against. Use tantalised roofing battens of 50mm. These should be attached to the roof joists using a screwdriver or a nail gun.

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.

The Best Home Insulation Diy

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.

What goes between roof and insulation?

A vent baffle should be installed between the insulation and the roof decking to maintain the ventilation channel.

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.

What is the minimum air gap for insulation?

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.

What is the roof ventilation rule?

A universally accepted guideline for roof ventilation is the 1/150 ventilation rule. According to this rule, a roof must have ventilation that is at least one square foot for every 150 square feet of attic or crawl space. A minimum of 13.3 square feet of ventilation is needed for a 2,000-square-foot attic.

Does roof insulation need ventilation?

But it's not the only important player that helps keep you comfortable throughout the changing seasons. In addition to having proper roofing insulation, your attic space must also have an effective roof ventilation system that maintains a flow of ambient air throughout.

What is the R value of 1 2 air gap?

In our example, the ½” airspace bounded on all sides by building materials has an R-value of 0.90. For ideal airspaces of less than ½- inch thickness, or otherwise not complying with ideal airspace conditions, there are two options to determine airspace R-value.

Can you have too much roof ventilation?

Common Over-Ventilation Problems

Too much ventilation can work against the airflow of your attic because having too many vents can cause them to start to work against each other. If the wrong types of vents are installed, these can also work against each other in a way that moisture or frost can regrettably develop.

How close can insulation be to the 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.

What is the gap for roof ventilation?

Ideally you want about 3 to 6 inches of space at the top and 3 to 6 inches of space at the bottom.

What is the ventilation gap between roofing membrane and insulation?

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

How much air space 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.

What is the standard air gap?

The required air gap shall be not less than twice the diameter of the effective opening of the outlet and not less than the values specified in Table P2902. 3. 1. For SI: 1 inch = 25.4 mm.

What is a typical air gap?

What is an Air Gap and Why is it Important? In plumbing, an air gap is a vertical space (usually one inch or more) between the end of a pipe or faucet and the top of a nearby basin or sink. It creates a separation between the water supply and potentially contaminated water in a sink or other plumbing fixture.

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.

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.

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.)

Is exterior insulation worth it?

Exterior insulation has advantages. First of all, it substantially increases the true R-value of walls at a fairly low cost. For example, adding one inch of R-5 exterior insulation raises the real R-value of a 2x4 wall with R-12 cavity insulation from just R-10.7 to R-16.

What is the R-value for roof insulation?

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.

How much of a difference does roof insulation make?

Roof and ceiling insulation. Installing roof and ceiling insulation can save up to 45% (or more) on heating and cooling costs.

Previous article
Does Tide really clean in cold water?
Next article
What is the formula for a fire extinguisher?