Can I Install a New Roof Over an Existing One?

At Slate Roof Professionals we get many inquiries about installing a new roof. More specifically, customers ask, “Can I install a new roof over an existing one?”

The answer is, it depends on several factors, including your existing roof’s materials and its condition.

We know that roofing projects are a major home investment, but putting new shingles over old ones is often a penny-wise, pound-foolish solution.

In general, you can only install new asphalt roofing over existing asphalt shingles . . . if the existing roof shingles are in good condition and if those existing shingles meet what’s called re-roof conditions. And you can’t mix roofing materials, like installing new asphalt shingles over wood or slate roofing (or vice versa).

What Is Re-Roofing?
A totally new roof will be more sustainable, energy-efficient, secure, and cost-effective in the long run. In some cases, however, re-roofing may be preferable or an accepted option if certain conditions are met. Re-roofing (adding a new layer over the existing roof) is only possible (with positive results) if:

  • The shingles are asphalt only (no tile, slate, metal, or wood – which require different roofing strategies).
  • Your shingles are shedding granules or are worn out (due to age, debris, or weather conditions) but there are no leaks.
  • The shingles lay flat, and are not curling.
  • No shingles are missing.
  • The underlayment and sheathing board are in good condition, even if the roof has reached the end of its lifespan.
  • You want to change the roof’s color (and the existing shingles are in decent condition).
  • You only have one layer of roofing already. Most building codes only allow two layers of roof max, to avoid weight strain on the structure.

Before you proceed with a re-roofing project, you should have a thorough roof inspection to determine if your roof is a good candidate for this solution. The inspector may advise you to rip off what’s there and do a new installation instead.

Pros and Cons of Installing a New Roof Over an Existing One

Stripping the existing shingles and completely replacing them with new roofing material is generally the best route to take. However, if your roof meets the criteria noted above, there are some pros to installing new asphalt shingles over old ones.

Pros of re-roofing

The project will cost less and go more quickly because the roofer doesn’t have to spend the time and manpower to tear off the existing roof. It is also more convenient than a full roof replacement as there is less prep time and cleanup, as there is nothing to dispose of.

Adding a new layer of asphalt shingles provides extra protection against the elements as well as additional home insulation and a second moisture barrier.

Cons of installing a new roof over an existing one

Re-roofing may be a quick fix but installing a new roof will provide long-term sustainability and remain problem-free for many years.

Placing new shingles atop old presents some serious downsides:

  • When new shingles are laid over bumpy surfaces or gap-filled foundations, it is difficult to secure the new top layer, and the defects underneath can show through.
  • An added layer makes it hard to get an accurate assessment of your existing roof’s condition, as there could be damage to the plywood decking underneath that is not visible.
  • No water or ice leak barriers – especially important in northern NJ and the NY metro area where we work, these components are essential safeguards against ice leaking under old shingles.
  • Roofing is heavy. Depending on the size and age of your home, the added weight strain of another layer of shingles may prove to be too much. This is exacerbated when we get heavy snows in the winter . . . and can lead to problems such as cracks in your interior walls or worse.
  • Warranty violations – the manufacturer may only honor its warranty when the shingles are installed as a new roof as opposed to over an existing layer. Check the warranty before re-roofing your home!
  • Your local building department may not approve re-roofing, so check the guidelines and get a permit, if needed, before starting this project.
  • Although the new layer of shingles will look good for a while (before those defects underneath start to show), re-roofing may affect your home’s value when you go to sell it. Buyers will need to know they’ll be tearing off multiple layers in the future.


New roof installations by Slate Roof Professionals

As you see, installing a new roof over an existing one may not be the best path to take for your home. The roofing experts of Slate Roof Professionals will inspect your existing roof and provide a recommendation based on its condition, material, and your goals. We install top-quality roofing materials of all types—slate, tile, metal, wood, and asphalt—on homes throughout northern NJ and Westchester County, NY. Contact our office for a consultation at (973) 857-7300 to discuss your roofing needs.