Can insulation touch roof membrane?

Author: Triston Gerlach  |  Last update: Saturday, July 26, 2025

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.

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.

What is the gap between insulation and roof membrane?

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

Can insulation touch a breathable membrane?

No. Tyvek® breathable roof membranes are suitable for non-ventilated pitched roof applications only. In flat roofing a Tyvek® roof membrane may only be used as a protection layer over insulation or as a separation layer between metal sheeting and a supporting deck.

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 ...

How to Insulate a Roof over rafters with BreatherQuilt, The TLX Gold Alternative

How much space should be 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.

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.

Should insulation touch roof felt?

Insulation laid so that it covers the eaves, significantly reduces ventilation to the roof. 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.

Is roof membrane breathable?

They are installed in external walls and roof structures to prevent water ingress, but their vapour-permeable quality allows moisture to escape. A breathable membrane helps with ventilation and effectively allows a building to breathe.

What is the difference between roof membrane and house wrap?

A good house wrap should allow water vapor to escape while preventing liquid water and air infiltration. Synthetic roof underlayment, however, is generally less permeable than traditional house wraps, which may lead to moisture buildup and condensation issues within the wall cavity.

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.

How tight should roof membrane be?

Never pull your roof membrane under tiles too tight

The ideal measurement of this will sit between a minimum of 10mm and a maximum 15mm. If the membrane is taught, there is risk of tearing and the water could become trapped behind the tiling batten.

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.)

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 goes between roof and insulation?

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

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.

What are the disadvantages of membrane roofing?

Cons
  • One of the biggest limitations of an otherwise possible roofing option is its high cost. ...
  • They're more susceptible to punctures or tears from falling debris or foot traffic, requiring careful handling and maintenance.

What type of insulation is used when using a membrane roof?

In a protected membrane roof, also known as an inverted roof membrane assembly (IRMA), the insulation is installed on top of the membrane. The insulation may be exposed to water, so it should have minimal water-absorption characteristics. Extruded polystyrene (XPS) is the most suitable type.

Can you walk on roof membrane?

Yes to an extent. EPDM is designed to take LIGHT foot traffic during installation and for occasional cleaning or maintenance. If you require more use than this, i.e. for a balcony, then there are additional materials that can be laid over your EPDM for a more durable solution.

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.

What is the gap between roof felt and insulation?

If the roof covering or roof membrane is a material of high moisture resistance or impermeable, then the building regulations require a 50mm wide ventilation gap beneath the roofing felt and tiles.

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.

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.

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.

How much air space is 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.

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