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Warm or cold? You may hear the terms “warm roof” and “cold roof” in conversations with roofers and contractors talking about improving the efficiency of your roof. You are confused by the terms and don’t know which you have or would want in a new construction. Read on to get a nailed-down clarification.

There are some major differences between the warm roof and cold roof options. The primary difference is in the configuration of where insulation is placed, but other differences include the construction cost and the cost of energy over the long term.

What’s the Difference In How Each Is Built?

Cold roof construction has been the standard for decades. A cold roof is where insulation is placed below the roof rafters. 

That keeps the living space warm but allows space above the ceiling to remain cooler. 

Warm roof construction is a fairly new concept but is catching on in the construction world because of its energy efficiency. However, it is mostly used in flat roof construction rather than sloped roof buildings because of its expense and the difficulty in adapting it to a sloped roof residence. 

This method is when rigid insulation is put on top of the roof rafters. A warm roof design makes the upper portion of the space as warm as the living areas. 

Which Method Is Preferred?

Anyone in construction will tell you that a warm roof has many benefits that don’t exist in a cold roof. The primary benefit is it reduces heating costs and saves money over time. 

Another benefit over cold roof construction is a warm roof doesn’t need to be ventilated. After all, the warm air is being kept below the roof so there isn’t space for condensation to occur. 

Cold Roofs

In cold roof construction, the warm air of the living space rises and meets the cooler air of the roof space above the rafters. That causes condensation and those who install a cold roof should also install ventilation to reduce the moisture. 

Two disadvantages exist in warm roofs over cold roofs. 

  • The cost of installing a warm roof is excessive.
  • The weight must be figured into the architecture or it won’t work. 

Warm Roofs

A warm roof has a lot of additional weight because of the type and amount of insulation used. An architect must consider that when designed the building because the design must include extra support. 

That is one reason a residential sloped roof doesn’t work for warm roof construction, at least if it is already built. A sloped roof built to cold roof standards doesn’t have the extra strength in it to handle the additional weight of insulation used in a warm roof. It would need roof trusses that are stronger than what is in it now. 

When Should I Consider My Roof Options?

The best time to consider which roof to go with is during construction. That is when extra materials are added to support the weight if you choose to go with a warm roof. 

Those who already have a home won’t have much of a choice in a cold or warm roof option because you must go with however the house was built.

However, it is good to know how the type of roof construction in your home is going to be in terms of moisture and energy. You can make changes to improve both even if you have a cold roof construction. 

How to Work With a Cold Roof Construction

The first thing to do is make sure you have proper ventilation in the roof to offset the moisture. Moisture can create mould and mildew so it should be avoided. 

A roof space that has poor ventilation can be remedied.

You will need to talk to a roofer or contractor about how to do that without a lot of additional costs. 

Make Sure You Have Good Insulation

It may surprise some homeowners how little insulation is in the attic space. They never looked up there in all the years they’ve lived in the house, except maybe to take down a box or two of holiday decor. 

Builders know this and sometimes skimp on attic insulation, putting just enough in to pass inspection.

Look at yours and see if you need more. It doesn’t hurt to cover the top portion of the house under the rafters with good, thicker insulation to save on energy costs both summer and winter. 

What Are My Insulation Options?

There are three main types of insulation available:

  • Cotton
  • Mineral Wool
  • Fiberglass

Anyone in construction is going to advise you to go with fibreglass. It is the right material that will work perfectly in tight spots around pipes, wiring, or awkward framing. It is blown in rather than laid in.

Because it is blown in, it is faster and easier to work with for those who know what they are doing. 
Fibreglass insulation is more expensive than any other option.

Those looking to economize can go with rolling out paper-faced insulation. You can lay it between joists to better insulate your house. 

However, if you want the more ‘green’ insulation you can opt-in for something like:

  • Sheeps Wool
  • Hemp wool

What Is the Cost?

The cost of the varying insulation types depends on where you buy it from, your attic’s square footage, and what your installer is charging you as their fee. 

Attic insulation costs typically run between €1,500 and €5,000 depending on the thickness, size and type of insulation.

However, a well-insulated attic can cut 10 to 50 per cent off your heating bill, according to the Department of Energy.

Can I Do It Myself?

You can install insulation in the attic yourself. It is simple and cost-effective.

Your choices are slightly more limited, depending on how comfortable you feel using a blower.

To install fibreglass or mineral wool you will need gloves, a mask and you will also need to wear a long-sleeved shirt and pants.

To install hemp or sheep wool you don’t require any protective gear.

The first place to start is with the flooring that is usually up in most attics. That will need to be ripped up so you can fully insulate underneath. The flooring can’t go back in either because there will be too much insulation. Your off-season boxes of items will need to find a new home. 

Choices of Insulation

You have two insulation choices in either loose-fill or batting. Loose-fill comes in bags. You can rent a special machine to blow it in place or you can pour it into place and manually spread it.

You must be warned that is labour-intensive. It also isn’t as effective. 

Loose-fill comes in many types including fibreglass, cellulose, or mineral wool.

Fibreglass is recycled sand and glass spun into fibres. It’s lightweight and settles well. Cellulose, made from recycled paper, is widely used but it can get mouldy if it is exposed to moisture. It has fire and insect resistance. 

Mineral wool, made from rock or slag fibres, has a natural fire resistance but is pricier than other loose-fill products.

Batts is the insulation that comes in sheets like the image below.

It has different thicknesses and widths and can come with a facing, usually made of paper or foil, that works well as a barrier against vapour. This option is best if you have standard joist spacing and a large space to work with without obstructions.

Batts also come in fibreglass, cellulose, and mineral wool but they also come in cotton.

Cotton batts are made from recycled denim. It does a great job of blocking airflow and sound but it is more expensive than other choices. 

Putting in Your Insulation

You can put in your new insulation over the old. With the batts, you will need to measure and cut to lay them between the joists. 

The loose fill works well around electrical areas but you may need some professional help to properly insulation around those areas.

Other Things to Consider

One consideration for choosing the right insulation is whether your area has recommendations or requirements for specific types of insulation.

There are some recommended “R-values” you may need to follow. An R-value is how resistance to heat flow is measured. Higher values mean better effectiveness. You will also need to seal any gaps where drafts can enter. 

The attic floor is the most important part of the home for insulation but you should also consider insulating the attic walls as well. It will cost more to insulate the walls but then you know the whole space is completely energy efficient.


Taking a look at your roof and attic space with fresh eyes will lead to improvements that will not only keep you warm in winter and cool in summer but will also maximize your energy savings.

Just because the insulation is hidden doesn’t mean it isn’t important!