How To Insulate A Flat Roof From The Inside

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Homes with flat roofs enjoy the benefit of easy repairs and cleaning. Flat roofs have up to 10° pitch (slope of the roof). That being said, this type of roof makes it easier to install solar panels and satellites. It is also more accessible and painless to install. And just like any other roof, flat roofs also require insulation. Knowing how to insulate a flat roof from the inside is a skill you can learn for a DIY insulation process.

When it comes to how to insulate a flat roof from the inside, the best time to do it is during roof construction. However, even with insulation already in place, homeowners prefer more. Adding insulation from the inside, otherwise known as cold roof, requires placing the insulation material in the middle of the joists under the roof’s surface.

Read on to learn more about how to insulate a flat room from the inside.

Understanding The Cold Roof Method

The cold roof method has been widely used in the past. However, it is not recommended nowadays, considering that it can cause condensation and may damage the roof structure in the long run.

Though you can install a ventilation system to prevent such from occurring, the cold roof method is still disadvantageous because of the labor cost and the fact that it reduces the internal space of the house. That is why experts advise using a warm roof deck as an alternative to insulating the roof from the inside.

How To Insulate A Flat Roof From The Inside

Though a cold roof is not advisable, some homeowners still prefer this kind of insulation. Homeowners do not need to spend more on scaffolding. They also do not have to think about how to access the roof exterior safely from the outside. So, how do you insulate a flat roof from the inside?

Here’s a very basic guide.

1. Choose and prepare the insulation material you want to use. The insulation thickness will depend on the material you use and its manufacturer’s specification. The insulation material should be placed between the joists. However, a ventilation gap of 50 to 60 mm is required between the roof and the insulation to allow airflow.

• Provide a ventilation opening at the part of the roof where it meets the walls or at the upstand. Do not forget to add a vapor barrier or membrane at the insulation base for your flat roofing. Before putting the plasterboard on, staple the joists.

• If the insulation is added to a flat roof of an old building, the ceiling should be taken down first. And for properties with shallow joists, use spray foam insulation as your insulation material.

Hot Roof System: Recommended By Experts

As mentioned earlier, experts do not recommend insulating a flat roof from the inside anymore. Instead, the current trend is to insulate using a hot roof system, otherwise known as a warm flat roof. This type of insulation does not lead to condensation. Instead, the insulation material is put on top of the roof structure.

A warm roof deck usually uses at least 100mm of rigid insulation placed on top of the roof joists or the vapor control layer. Then, another layer of a waterproofing system is applied above the insulation material. No ventilation is required for a hot roof system.

Frequently Asked Questions

How much does it cost to insulate a flat roof?

The cost of insulating a flat roof will depend on several factors. The type of insulation material you use, the quality of the insulation material, the size of the flat roof, and the method of insulation (cold or hot) affect the total cost.

You may also need to spend more if you choose to have the insulation installed by experts, yet you can save from labor cost if you do it by yourself (given that you have the knowledge and the skill to insulate.)

Is it a bad idea to insulate a flat roof internally?

Though cold roofs have been used widely in the past, it is not advisable now. The insulation can become saturated with water quickly, thus, reducing its effectiveness. In addition, the condensation formed can damage the supporting wood, concrete, or metal. Frost and the winter months may also accelerate the damage, and it will destroy the roof sooner rather than later.

What are the common types of flat roof insulation material?

The most common materials used for flat roof insulation are wood fiber, perlite, polystyrene, polyisocyanurate, and cellular glass. All these materials have their own pros and cons. So, if you do not know how to insulate a flat room from the inside using these materials, it is best to consult with a roofing professional for expert advice on what to use.

How do you choose the right type of flat roof insulation?
The skill on how to insulate a flat room from the inside is worthless if you do not know the type of flat roof insulation material to use. You should determine the R-value climate zone in your place first. Once you know the R-value of the insulation material you need, it will be easier for you to narrow down your choices and pick the best insulation.

Is it worth it to insulate my flat roof?

Definitely! Insulating your flat roof will help control the temperatures inside your house. Thus, making it a more comfortable place to live in, especially during winter.

What are the pros and cons of a cold roof system?

As said earlier, the primary disadvantage of the cold roof system is the formation of condensation, which can lead to the destruction of the flat roof. However, it also comes with side benefits. A cold roof system is suitable for external outbuildings and houses in hot countries or regions.