Can insulation touch roof sheeting?

Author: Dr. Elouise Balistreri DDS  |  Last update: Friday, May 2, 2025

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 you put insulation against roof sheathing?

The roof assembly can be vented or unvented; insulation can be installed above the roof sheathing, between the rafters, under the rafters, or in a combination of these different locations.

Do you need to leave a gap between roof and 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.

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.

How much space between insulation and roof sheathing?

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.

Garden room roof insulation detail

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.

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 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.

Can fiberglass insulation touch roof sheathing?

Most building codes (including the International Residential Code) allow just one exception to these rules: in Climate Zones 2B and 3B, you can install fiberglass insulation against the underside of your roof sheathing without a ventilation channel or rigid foam above the sheathing — but only if you install tile ...

Can insulation touch roofing felt?

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.

What goes between roof and insulation?

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

What is the minimum air gap between insulation and roof?

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.

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 I lay plywood over insulation?

Can I put plywood over insulation in the attic? Yes you can install plywood subflooring directly over the floor joists and insulation on your floor. You need to install rigid insulation boards on top of the attic flooring joists and then install plywood over the top.

Should you insulate the underside of your 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.

Does sheathing help with insulation?

Sheathing is commonly added to floors, ceilings and exterior walls. There are 2 types of sheathing, one adding structural strength to the framing-known as Structural Sheathing, and Non-Structural Sheathing, used for insulation.

Can you put insulation directly against 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.

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.)

How thick should insulation be in a roof?

In general, 50-130mm of insulation is commonly used for wall insulation.To achieve the required U-Value of 0.17 W/m2K, 125mm of PIR insulation board should be used. 150-200mm of insulation is often used for roofs to achieve the recommended U-Value of 0.16 W/m2K.

Does roof insulation need to be faced?

Remember: When installing during cold climates, the vapor barrier should face the home's interior. Conversely, the vapor barrier should face the house's exterior during hot weather climates.

Can insulation touch sarking?

Sarking is a great way to protect your roof from the elements. It helps insulate against the heat and cold and prevents moisture from entering your attic space. Plus, sarking can be installed on top of existing insulation if needed!

Can insulation touch roof membrane?

You definitely don't want any insulation to touch the roof membrane as it'll pull water inside. Netting shouldn't be necessary - if the insulation doesn't touch when it is installed it'll only settle in time and won't touch later.

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.

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.

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