How To Insulate Vaulted Ceiling Between Rafters

Any homeowner knows that the secret to a warm, comfortable house is good insulation. However, if you own a house with a vaulted or cathedral ceiling, effectively insulating it is easier said than done.

This open style of roof looks great, but they are notorious for running up electricity bills.

The reason for this is that, as we all know, heat rises and unlike conventional ceilings, vaulted ones are much better at letting it escape. All is not lost though, with a little bit of time and the right tools, you can easily install insulation between the rafters to prevent heat loss.

In this guide, we will take you through the necessary steps to insulate your vaulted ceiling.

Things To Consider Before You Start Work

Before you start you will need to decide what kind of insulation you want to use. In this guide, we will be covering how to install fiberglass batts between the rafters of your vaulted ceiling, but there are other options available.

Cellulose or spray foam insulation can both be applied in this type of roof, but they can be a little more complex and may require a professional to be properly installed.

Before you buy your batts you should measure how deep your rafters are to know what thickness of insulation you will need. It is vital to leave at least 1 inch of space between the batt and the roof deck so air can flow.

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Because of this you may need slightly thinner batts than you would use for attic spaces or walls. In this guide we’ll be recommending faced batts which have a special outer layer for acting as a moisture barriers.

You should also measure how deep your rafters are, how far apart they are, and the distance from the rafters to the wall’s top plate and the apex of your roof.

This will give you an idea of how much fiberglass you will need to cover the area. While you are doing this, mark the position of any lighting fixtures, chimney flues or other obstructions, especially those that can get hot.

Finally, you should check the U.S Department of Energy website to see the recommended R-value is for your area. The R-value is how well a particular type of insulation blockers heat from escaping and you will want to know which one is appropriate for your house before you buy anything.

What Tools Will You Need?

The following tools will be essential for installing your insulation:

  • A ladder, scaffolding, or stilts for reaching high places
  • A utility knife
  • A staple gun
  • Baffles
  • Safety gear: protective gloves, long sleeves, pants, and a ventilator mask.
  • Safety helmet if you are climbing high heights.

How To Install The Insulation

Now that we have all the necessary equipment, we’re ready to start insulating your vaulted ceiling. First, check to make sure your roof is properly ventilated. If not, this could lead to problems with rot later on.

Check for a ridge vent in the apex of your roof, and also look for eave vents where the roof meets the wall’s top plate. Always leave these vents clear and unobstructed while you are insulating.

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Having done this start cutting your batts using your utility knife so they are the right size to fit between your rafts. If the space that needs to be filled is very long you can use two batts placed end to end.

How To Insulate cathedral Ceiling Between Rafters

You ideally want an inch of space between the batt and the roof boards, to allow for proper ventilation.

If you can’t do this because your batts are too thick, you will need to install baffles from the top of the wall all the way up to the ridge vent at the apex.

Place the pieces of insulation in between the rafters softly, avoid compressing them as this will reduce their R-value. You want the face of the insulation (the foil or craft covering on one side), to be facing downwards so it can act as an effective moisture barrier.

When placing batts end to end, pull them close enough for the facing to overlap so there are no gaps in between them.

When placing insulation around light fixtures or anything else that can get hot, it is essential to remove the facing first. For anything with an electric charge, it is safe to just remove three inches of facing from the side that is closest to the fixture.

Craft and foil facings are highly flammable, so they should never come into contact with chimney flues or non-IC type electronics.

Faced batts have extra facing that overhang the edge of the fiberglass – these are called flanges. You should staple every 8 inches along the flange to firmly attach it to the rafter.

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Use the spare insulation from your trimming pile to fill any gaps such as difficult corners or the space around lighting fixtures and other obstructions.

Follow these steps until you have insulated the entire vaulted ceiling. Now stand back and admire your work.

Remember faced, fiberglass batts are simply one of the easiest methods for insulating your cathedral ceiling, but they aren’t the only way.

If you don’t want to use faced batts, you can easily supplement them with un-faced ones and use your own plastic moisture barrier.

The vapor barrier should always point towards the warm surface, so you can easily staple it in place after you have installed your un-faced batts.


This guide contains all the information you need to insulate your vaulted ceiling with fiberglass batts. This isn’t the only insulation you can use, but it is one of the easiest and most cost effective.

If you are unsure about what insulation will work best, or uncertain if you are doing things correctly, always consult a professional before you proceed.

Otherwise, if you are confident in your DIY abilities, then there is nothing stopping you from saving money on those heating bills today.