Should you insulate the inside of your roof?

Author: Elliott Davis  |  Last update: Tuesday, June 16, 2026

A properly sealed attic or well-installed insulation in a roof is much more efficient in terms of energy. A roof is a very large surface area, and can easily lose heat during the winter if not properly insulated. Roof insulation will also make your air conditioning significantly more effective in the hot summer months.

Can you insulate the underside of 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 to insulate a roof inside?

To insulate an existing flat roof from the inside, first, inspect the loft for any damage that may need repair. Next, install a vapour barrier to prevent moisture build up. Then, measure and fit the insulation material between the loft joists, starting at the eaves and leaving a 25mm gap for ventilation.

Is it better to insulate the roof or the ceiling?

The answer to these issues may be adding insulation, but that still leaves the question of where to apply additional thermal protection to see the most benefit. While both ceiling and roof insulation will increase your home's resistance to outside temperatures, insulating the ceiling should be your priority.

Is it worth insulating internal ceilings?

Yes, insulating internal ceilings is worth it as it enhances energy efficiency by reducing heat transfer between floors, and improves soundproofing, creating quieter living spaces. Additionally, it can contribute to overall comfort and potentially lower energy bills.

How to Prevent Damp in a Flat Roof

Do you need to insulate interior ceilings?

Insulation keeps your home from losing and gaining excess heat, and one of the places it matters most is in your ceiling. Many homes in Canada lack adequate insulation, costing homeowners more money on energy bills to keep their houses warmer in the winter and cooler in the summer.

Is internal insulation a good idea?

Internal insulation is one of the most effective ways to make your home more thermally efficient, mostly because of how much heat is lost through your walls. Increasing your thermal efficiency brings other benefits, such as reducing your carbon footprint and lowering the cost of your energy bills.

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.

Is it better to insulate the roof from inside or outside?

Breathable external roof insulation, therefore, provides greater levels of security against moisture accumulation over the life time of the building. Living spaces in attics can be too cold in winter and too hot in summer.

Should there be insulation in the roof?

For optimal energy efficiency, your home should be properly insulated from the roof down to its foundation. The illustration above shows all the areas of the home where there should be insulation.

Can you over insulate 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.

Do you need an air gap between roof and insulation?

Yes, an air gap between the roof and insulation is needed, especially for traditional materials like fibreglass, mineral wool, and foil insulation.

Can you insulate a ceiling from the inside?

Yes, you can insulate your ceiling from the inside. This approach is particularly convenient when access to the loft or attic is challenging. .

Is it okay to insulate roof rafters from the inside?

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 do I stop condensation on the underside of my roof?

We can try to prevent water vapour from reaching the roof space as much as possible by opening windows, installing window ventilation systems and changing our living habits. A well-sealed ceiling will minimise air leakage through to the roof space.

What to put on the underside of a roof?

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.

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 I insulate my roof from inside?

Use the right method to insulate a roof from the inside

For example, insulation board and mineral wool must only be installed after any holes or tears in the vapour barrier have been sealed to prevent air from getting in. Then, at least two layers of insulation must be installed to reach the recommended R-value.

Is it better to insulate inside or outside?

External insulation maintains internal space, reduces thermal bridging, and improves thermal performance. However, it entails greater initial investment and external cosmetic considerations. Internal insulation is more cost-effective and enhances the comfort of a living space.

Is it possible to have too much insulation in your attic?

Too much of anything is bad, including too much insulation in an attic. Over insulating your house and tightly sealing it too much creates a vapor barrier and forces moisture to settle on fixtures inside your home (hello, water damage!).

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.

What is the most important place to insulate a house?

The Most Important Areas of Your Home To Insulate
  1. Attic Insulation: While being on the first floor of a house, you probably wouldn't directly feel it if cool air was rushing in during the winter. ...
  2. Wall Insulation: This one probably makes the most sense out of all of them! ...
  3. Floor Insulation:

Do you insulate internal walls NZ?

There are several locations where insulation is recommended to be installed in new homes including: External walls. Internal walls, including between the house and any attached buildings such as a garage. Between storeys in a double storey home.

What is the downside of insulation?

Irritation to skin and respiratory system

Wall insulation solutions like Rockwool are made of ultra-fine fibres. While thermally efficient, they can cause skin and respiratory irritation.

What is room in roof insulation?

Installing room in roof insulation involves insulation boarding being fitted in between the rafters underneath the existing plasterboard walls. Room in roof insulation works by trapping heat within your home to create a blanket effect.

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