Can I Build Over My Existing Roof?

One question which all roofing companies hear from time to time is, “Can I build over my existing roof?”

Re-roofing over an existing roof is a somewhat controversial topic and there are varying opinions about whether it is a suitable thing to do or not. The answer is very much dependent upon the condition of the existing roof.

An entire re-roofing project is a very expensive endeavour; it is worth the cost, but in many cases more affordable alternatives are adequate. Options may include repairing and patching the existing roof, or completely removing and replacing the old roof with a new one. Or you may prefer to build a new roof over the existing one, leaving it in place.

The decision to build over an existing roof may not be entirely in your hands:

  • You can’t mix roofing materials – asphalt shingles must be re-roofed with asphalt shingles. Wood and slate tiles can’t be built over.
  • Curling or warped shingles need to be removed.
  • If you have two layers of existing shingles, you’ll need to be aware that adding a third layer will result in a roof that is very heavy and may cause future damage to the home.
  • Any visible damage (mould, cracks, rotting) requires removal of the old roof.

Dykstra Knight will be able to perform a comprehensive assessment of the condition of your roof and what will be your best option regarding repair or re-roofing / replacement. Building over your old roof is a more affordable option than complete re-roofing, as long as your existing roof is suitable for such.

Pros: Roofing over your existing roof structure, when appropriate, saves time and money – up to thousands of dollars will be shaved off the overall cost of installation and labour, as well as removal and disposal of old shingles and roofing materials.

Cons: If you do re-roof over an existing roof, you need to be aware of some potential drawbacks:

  • Issues that occur in your roof will be more difficult to identify and find the source of the problem e.g. leaks, algae, moss, mould, rot
  • It costs more to remove both the new and old roof to repair damage
  • More heat will potentially become trapped in your rooftop, resulting in curling and warping
  • Your roof will be significantly heavier when built over
  • Future roof replacement will cost more, and re-roofing over an old roof as opposed to complete replacement will diminish the value of your home.

While re-roofing over an existing roof is quicker and more affordable than full roof replacement, it can only be done in certain circumstances. A full roof replacement with removal of the old roof will always provide the premium result possible.