There are multiple reasons you may consider reroofing your house. Your old roof could have interior damage or leaks that pose a serious liability. Perhaps you have realised that you will spend more on roof repairs than on a new roof. You might also want to make some additions to your home, but you are concerned about the integrity of your roof structure. Whatever reason you have to reroof your house, one aspect ultimately matters: whether to tear off the existing roof first or simply have the new roof installed over the old roof (overlay). An overlay may be a cheaper option but could cost you a lot more down the line and here's how.

Reduced Impact Resistance

When new shingles are installed over the already existing shingles, they tend to be less resistant to impact. This is because the new shingles won't be as well-supported as they otherwise would be when installed on a sound roof deck. If you live in an area that is prone to hailstorms, your new roof may not be able to hold up to such conditions over time.

Unnoticed Problems

The quality of your roof depends on the roof structure. This includes components such as the decking. Your roof could be having problems such as leaks that don't show through your ceiling. Dry rot, sagging boards and trusses, mould or algae are also other problems that could go unidentified if you decide to add new roof shingles over your old roof. What this means is that by choosing an overlay, you would be letting all the potential problems in your old roof get worse. Eventually, you will spend a lot of money because you won't only be dealing with major repairs, but you would have to go through your new roof layer to fix the problem and this could be complex.

Premature Deterioration of the Shingles

Your new roof shingles may not last as long as would be expected if you install them over your old roof. This is because with the added layer of roof shingles, your roof will trap more heat than it would with a single layer. Your roof shingles can be damaged by too much heat. They will start deteriorating and looking curled, which means the roof may not survive to the end of its product life. Eventually, you will have to plan for a new roof again and since most building regulations don't permit additional roof layers, your only solution would be to tear off the roof.