In a word, yes you can install a metal roof over an existing shingle roof but there are a number of things which need to be considered.

Rooftop Preparation

For starters, you need to check with the local authority planning department to make sure there are no rules are regulations covering the project.  Most of the time, it will be okay, but it is better to ask first than to run into complications after the project has been completed.

There may be some considerations that they stipulate.  For example, they may want to ensure that the plywood under the existing shingle roof is in good shape with no soft spots. This is to ensure the screws from the metal roofing will have something solid to attach or ‘bite’ into.

Another thing the local planning department will consider is if having more than one roofing material in place at the same time is a risk to the house structure.  The original idea behind this was that a normal house structure wasn’t strong enough to support more than one roofing material – slate with concrete on top or shingles covered by clay tiles for example.  Metal roofing is extremely lightweight and therefore the consideration is often not applicable – but you may have to go through the specifications with the planning department so it’s always good to be prepared.

How does it work?

Once you know it can be done and you are permitted to do it under the building regulations, then the question turns to the technical sideof how it works.  There are two ways to install a metal roof over shingles:

• One – run a new underlayment over the existing shingle roof
• Two – install a metal roof over a shingle roof with the use of purlins or battens

With the first system, there are a couple of main benefits. For starters, the new underlayment will be a secondline of defense should any water somehow get under the metal roof.  And secondly, it would be a buffer between the shingles and the new metal roof.  This is notable because shingle roof is granulated much like sandpaper while metal roof tiles can expand and contract with weather changes.  Over time, without a buffer, the shingles could wear away at the rear of the metal tiles.

With the second system, the purlins are either nailed or screwed into the roof deck – this willdepend on how the metal roof is manufactured.  The metal is then installed to the purlins.  This creates a flatter surface to install the metal panels and combats the irregularities of the shingle.  Most experts recommend at least ¾ inch purlin and ½ inch plywood to ensure the roof system is very strong.

Finding a solution

When installing a metal roof over an existing roof, you might want professional advice.

Metrotile specialise in lightweight roof tileswhich are perfect for a host of projects. To find out more or to request a free quotationplease get in touch with Metrotile by calling us on 01249 658 514. Alternatively, you canfill out our contact formfor a quick response.