Roof insulation is very important to reduce the temperature of your home on a sunny day. It facilitates a warm environment in both summer and winter.

Installing new insulation materials can be costly. If you have a budget constraint, then you can insulate your roof from inside your house. Hence, this work is quite tricky and needs a lot of experience.

Do not worry, if you are new to this roofing job. Through a proper guideline on how to insulate a flat roof from the inside, it can become simple and easy for you.   

So, let’s move forward and have a brief discussion about this topic.

What is roof insulation?

Roof insulation is a type of thermally moderated shell that uses a variety of protective coatings.

Roof insulation can be of various types. Much difference is seen between flat roof insulation and pitched roof insulation. Again, the procedure for insulating from inside the house is different from the outside insulation process.

Types of roof insulation

There are three basic forms of insulation: sheet, blown, and stiff. Fiberglass, polyester, viscose fiber, vermiculite, polystyrene and styrofoam are some of the materials utilized in these three forms of insulation. 

Required Tools

Some tools are always a must when implementing any type of roofing task. And when insulating a roof, these materials must be gathered.

  • Utility knife
  • Staple, crowbar
  • Roofing nails
  • Screw gun
  • Chalk
  • Reflective tape
  • Prodex 48 inch
  • Fast action

These  tools etc are very essential in insulating a roof .  

How To Insulate A Flat Roof From The Inside

How To Insulate A Flat Roof From The Inside: Step by step

If you are thinking about insulating your roof, then you can follow a couple of instructions described here. 

Step 1: Preparation

The first thing while doing any roofing job is to make a thorough inspection and if needed, get a professional consultation. Make a decision on what is best for you according to budget and the overall situation of your roof condition.

Step 2: Choose the insulation material

There are a lot of options available in the case of insulation materials such as polyisocyanurate, expanded polystyrene, extruded polystyrene, and many more.

The most popular among them is polyisocyanurate with a higher R-value and is mainly used in the existing flat roof insulation process. Extruded polystyrene is comparatively cheap and also gives a good performance.

After choosing a material that fits well with your requirements, you can proceed further. 

Step 3: Installation below the ceiling

Make sure to drape prodex (72 inches or 48 inches) or fast action or any other insulating material over the main structure or trusses. Allow them to droop over at least 2 inches while applying to the deck.

Another option is to directly install insulating materials and then apply 1”* 3” furring strips on top of them.

Step 4: Sealing 

After the installation of insulating materials, make sure to seal them properly. Secure for water leakage or damage that can cause any hazard to your roof.

Why insulation is important

Insulation helps to retain heat in cold weather, heat protection in hot weather, saves energy consumption, makes proper ventilation, and also adds a layer of protection.

It saves energy indirectly by controlling the temperature of your home to keep it moderate. In winter, an insulated roof prevents heat from escaping your home making it warm and cozy. 

On the other hand, in summer it does not allow heat to enter from outside to homes inside making it less hot. 

How much insulation is needed

How much insulation is enough to protect your home is always a burning question.

Sometimes people make the mistake of thinking that if they insulate the attic more, then their home will be properly insulated, but that is not the case. Initially, this seems to work but in the long term, this does not make much of a difference.

Scientifically, the isolation amount is directly related to the U value that depicts the temperature difference in your house.

Final Words

Do you think this article has helped you? I hope at least now you can tell the basics of how to insulate a flat roof from the inside.

However, insulating a roof from inside the house if not done properly, can create damage to your roof. So it will be better if you get an experienced person by your side while doing this job. 


As a civil engineer and roofer, I love to share the experience that I have gained through the last couple of years. In the roofing industry, practical experience is a very crucial fact that can help you a lot. Hence, I want to help you with my blog.

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