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What is a Roofing Cap Sheet?

what is a roofing cap sheet

A roofing cap sheet is a metal or plastic material that covers the top of your roof.

It protects the shingles and other materials from damage, which could lead to leaks. 

In this blog post, we will discuss how you can find out if you need a roofing cap sheet, what it does for your home, and why it’s important to have one installed.

What are the Benefits of a Roofing Cap Sheet?

A roofing cap sheet can be made out of multiple materials, but typically they are made out of metal or plastic. 

A good reason to use these types of materials is because they will not rot, warp, or break when they are exposed to the elements. 

This means that your roof will be well protected from water damage and other weather-related issues.

When Should You Consider a Roofing Cap Sheet?

If you have an older home in need of some roof repair services , it’s very likely that part of this process is having a roofing cap sheet installed. 

If you are in the process of putting a new roof on your house, then it’s very likely that part of this will be having one too.

Emphasize a flat roof with bitume

If You Need Roof Repair Services

If you have noticed leaks or other damage to your shingles, there is a good chance something has happened with your roofing cap sheet. 

This could be due to the age of your roof, or that you need a new one installed because it has worn down over time. 

If this is the case, contact us at Roof Power today to get an estimate on how much it will cost for our professionals to inspect and replace your roofing cap sheet!

If You Are Installing a New Roof

If you are in the process of putting a new roof on your home, then it’s very likely part of this will be having a roofing cap sheet installed. 

If you notice there is no “cap” on top of your shingles when looking at other homes that have recently had their roofs replaced, then your roofer should be installing one for you.

If You Are in Need of Roof Repair Services

Contact us at Roof Power today to get an estimate on how much it will cost for our professionals to inspect and replace your roofing cap sheet! 

We provide fast, professional services that are guaranteed to give you the peace of mind knowing that your roof is well protected from water damage and other weather-related issues.

Flat Roof Covering Works with Roofing Felt

Why do I need a Roofing Cap Sheet?

A cap sheet is required if you are putting additional insulation on top of the existing roof deck. 

It may also be called a modified bitumen membrane, ballast sheet or an ice and water shield.

A combination of layers to create one seamless barrier against the elements. 

The underside is covered with sealant to prevent any moisture penetration while the upper surface meets most roof coverings and is appropriate with most building codes.    

What is a cap sheet made of?

Typically modified bitumen membrane or PVC material, available in roll form or pre-cut sheets. 

Often comes with an aluminum foil laminate on one side for added strength and fire protection.

Sealing a flat roof

What is it used for?

A cap sheet is used to cover old roof decks before an additional layer of insulation is added through spray or blown-in application. 

It creates a seamless barrier between the roof deck and insulation that prevents moisture penetration into the building assembly below, which can cause problems with mold, odors, corrosion, and rot.

How is it installed?

When installing a cap sheet, adhere the bottom side to the sub-deck so that the adhesive properties activate properly. 

There will be a strip of roofing felt underlayment at the perimeter which should overlap onto your roof for added protection against water damage.

Once that’s in place you will install the cap sheet to cover the sub-deck. 

The upper side of the membrane is covered with sealant which should also overlap onto your roof decking for added protection.

Once this process has been completed you will lay down additional insulation on top of the newly installed membrane, spray water-resistive barrier (WRB) over that and then install your finished shingle or metal roof.

How do I maintain my cap sheet?

A clear coat of mineral-based, water-based, or solvent based sealer should be applied at least once a year to the upper side of the membrane. 

This will help protect it from UV rays that can cause the cap sheet to lose its elasticity and shrink. 

Also, be sure to stay off the roof surface unless absolutely necessary as you don’t want to puncture or tear the cap sheet.

Conversely, if you’re planning on re-roofing your home in the near future and think your existing cap sheet may still have some life left in it there are a few steps you can take.

  • First, you’ll want to make sure the upper side of the cap sheet is clean and free of debris before applying any sealant or coating.
    • Next, if the upper side isn’t smooth it’s best to lightly scarify (use a weed torch or grinder) that surface in order to give the new coat something to adhere to.
  • Finally, you’ll need to follow the same cleaning and coating procedures for this new layer of cap sheet that you used on the previous surface with one crucial difference; when installing the new layer be sure that its sealant overlaps onto the old layer in order to prevent moisture penetration between them.

When is it time to replace my roofing cap sheet?

The typical lifespan of a roofing cap sheet is around 15 years. 

As previously mentioned, re-coating your existing membrane more often will help it last longer but sooner or later you may need to install a new layer.

Repairing or replacing your roof’s cap sheet is more expensive than repairing the rest of your roof deck but it’s a crucial component to keeping the structure free from water damage. 

If you’ve noticed any leaks or dampness in your attic space during or after a storm then you should have a professional take a look at your cap sheet and insulation.

Flat Roof Covering Repair Works

What else should I know?

If you’re just adding a layer of additional insulation to the sub-deck the cap sheet may be your only barrier against moisture penetration.

However, if you’re applying spray or blown-in insulation to your roof deck then you’ll need an additional layer of WRB over that to prevent any moisture from bleeding through.

Finally, it’s best practice to install a new layer of cap sheet over your entire roof deck when re-roofing to ensure a seamless barrier between your insulation and any future WRB.