Garage Roof Insulation

Garage Roof Insulation – If you have a room directly above the garage, handling the heating or air conditioning – depending on the weather and location – becomes a huge challenge and needs special care. Let’s take a look at some of the major reasons why garage roof insulation is important.


    1. Greater exposed area

The first and probably the biggest problem with a garage is the increased surface area that is exposed to outside temperatures.

For example, your dining room may be surrounded by other room walls on three sides with just one wall exposed to the outside, whereas a room above the garage is exposed to the outside air through the garage floor, three walls and a ceiling.

This means that if your garage is not sufficiently insulated, there will be huge conductive heat losses. Even if you have insulation installed, if it is not properly done there will still be heat loss.

For example, if you have roof rafters in your attic that are not insulated adequately, money is literally leaking out in terms of lost heat and increased energy bills.

    1. Air leakage

With a room over a garage, the chances of air leakage are higher due to the nature of the construction, so you need to ensure the proper tightening of band joists, duct soffits in garage ceilings, knee walls, block/drywall joints in garages, lolly columns and other penetrations of the garage ceiling.

    1. HVAC issues

Heating a room above a garage ceiling can often cause problems even for experienced HVAC installers unless the garage ceiling is properly insulated.

Since the duct that connects this room with the garage is usually the longest in the house and it passes through the colder space between the garage ceiling and room floor, the heat delivered to the room is reduced.

The central heating system may detect that the air in the main body of the house is warm enough and make the thermostat turn the furnace off.

Since the room above the garage is colder than the rest of the house it will never achieve optimum temperature, unless of course the heat loss through the garage ceiling is dealt with through proper insulation.

  1. The nature of garage construction

Garages, more often than not, are not constructed with the same attention to detail as the rest of the house, so they often end up having no airtight drywall setup.

This means that outside air can affect the temperature of the garage and the room above or beside it. Furthermore, the concrete slabs on which garages are built are usually not insulated, or if they are the insulation is inadequate.

Also, most garage doors are very hard to effectively insulate, which adds to the overall problem of heat loss due to contact with outside air.


Things to Consider Before You Start Your Garage Roof Insulation Project

Once you have decided to insulate your garage roof, there are various things to consider, pitfalls to avoid and best practices to follow to get the job done perfectly. Let’s take a look at how to perform a garage ceiling insulation effectively.

Types of garage roof – Pitched or Flat

Roof construction in different parts of the world is done differently. Before doing anything else, take into consideration the type of roof your garage has and plan out your insulation accordingly.

If it is a pitched roof or if you plan to build a room above the garage with a pitched roof in the future, the requirements will be different than if you are dealing with a flat roof with less than 10 degrees of pitch.

For a flat roof, you will need to check for waterproofing as well and make sure the existing roof structure is not damaged, as the requirements for insulation will be different if there is damage.

Types of garage roof – Warm or Cold

There are two different methods of insulating a roof that vary on the basis of roof structure. In a warm roof structure, the insulation is placed ‘above’ or ‘above and between’ rafters in order to avoid heat loss and energy transfer.

In the case of a cold roof structure, the insulation is placed ‘between’ or ‘between and under’ the rafters or at ceiling joist level and the roof is ventilated by leaving a 50mm gap above the insulation which vents air to the outside.

Safety precautions and mistakes to avoid during garage roof insulation

Following the necessary safety precautions while installing garage roof insulation is essential in order to avoid any potential accidents.

  • If you are taking a DIY approach, be sure to plan out everything in detail beforehand. From materials to tools and measurements, stay on top of everything to avoid any surprises during installation.
  • Use safety gloves to protect your hands.
  • Wear a face mask or respirator to avoid inhaling any dust particles that can be harmful to the lungs.
  • Instead of using a tall A-frame ladder to perform the entire insulation process, use scaffolding which is much more stable and thus a safer option.
  • Don’t forget to add a vapor retarder to your garage roof insulation installation. This helps prevent garage floor condensation and water logging on the sheathing and wood trusses.
  • Make sure that the materials you buy for your insulation are in compliance with the local construction rules and regulations and follow the fire codes.
  • Thoroughly read the material specifications provided by the manufacturer and follow the recommended steps on how to use the materials for a successful installation.

Garage Roof Insulation Guide

Insulating and air sealing a garage typically costs less than a few hundred dollars and can be easily accomplished as a DIY weekend project. Before you get started, however, you will need to determine whether you have a flat or cathedral-style garage roof.

If you have a flat garage roof and an attic above, you can install the garage insulation from below using a standard ladder.

However, if you have a cathedral-style garage roof, you will need ascaffolding to get into the upper areas of the roof. In either case, you will need to follow the general steps below to insulate your garage roof.

  1. Carefully study the roof for any electrical outlets or any other objects, such as lighting. As a general rule of thumb, you are going to have provide airflow around these objects in order to prevent the risk of a fire or electrical hazard. That means you will have to carefully cut out areas of the fiberglass bats for your roof’s specific configuration. There should be three inches of ventilation around a light fixture and one inch of ventilation around a heat source.
  2. Buy fiberglass bats that match the configuration of your roof. If there are wooden trusses or frames in the roof, you should buy fiberglass bats that will fit snugly (known as “friction-fitting”).
  3. If you have a cathedral-style roof, you will also need to buy attic baffles, also known as channel vents and vent chutes, in order to direct airflow through the attic. These attic baffles need to fit the overall configuration of your sloping roof and provide space between the wood and the fiberglass insulation.
  4. If you have a cathedral-style roof, you’ll want to install the fiberglass bats from the top, into the roof, all while standing on your scaffolding. If you have a flat-style roof, you’ll install the fiberglass bats from the bottom while standing on your ladder.
  5. If you live in a cold climate, you will need to install a vapor retarder over the fiberglass filling. This vapor retarder – essentially a plastic sheet – keeps water from entering the insulation and causing mildew or other problems.
  6. Make sure that there are no extra holes or spaces in the ceiling covering or garage roof. If you find them, you can either use caulking to fill holes in the roof or cut out and insert pieces of fiberglass bat in a process known as “loose-filling.”

When you’re done, you’ll have a garage that efficiently traps heat and minimizes heat loss. You will have the right type of ventilation to ensure proper airflow, and the right type of protection to prevent mildew or condensation buildup.

Just remember – insulating a garage roof takes a bit more effort and planning than insulating a garage wall, but the extra effort is worth it!

Last update on 2023-07-04 / Affiliate links / Images from Amazon Product Advertising API

Founder & Editor

Hi, I’m Jim. I was a roofing constructor for 20 years, before deciding to start and gather the best content about roofing. I love woodworking and construction and it was only natural for me to start this passion project of mine. Thank you for visitng.