You are using an outdated browser version not supported by this website.
Click here to upgrade your browser


Membrane Overlay vs Complete Roof Replacement

It’s become apparent when specifying membrane roofing materials for existing flat roofs, stakeholders aren’t fully aware of all the options available to them. Simply replacing the existing membrane or overlaying the existing material, more often than not, can be a compliant way of re-roofing your building without the cost and hassle of destroying, rebuilding or uplifting the whole roof assembly.

To be clear, membrane-only replacement or overlay methods are only viable when the roof substrate has been thoroughly inspected and deemed structurally sound and compliant. If so, either of the following methods will effectively waterproof your roof structure without the cost of reconstruction:

Membrane overlay

Membrane overlay is when the existing waterproofing layer remains in place and a new membrane system is installed over the top.

If the existing membrane is still doing its job: ie: sheds water, doesn’t pond and is not leaking — but is tired and past the building code’s minimum durability period of 15 years, then a specific membrane can simply be laid over the top without the expense and labour of removing the old material.

This option is cost-effective in more ways than one:

  1. Minimises churn — the temporary displacement and relocation of people is hugely disruptive, inconvenient, costly — and sometimes very difficult eg: hospitals and elderly care.
  2. Minimises cost — not just with churn, but the materials and labour costs associated with complete destruction and rebuilding of the roof; let alone the disposal cost and environmental impact of filling the local landfill up with construction waste.

If the existing membrane is beginning to detach from the substrate, an overlay would not be appropriate. Bonding to something that’s not anchored properly to the substrate would ensure it fails to meet building code — particularly the overall objectives of building code clauses B2 and E2.

This is where membrane replacement would be the appropriate solution.

Membrane replacement

Membrane replacement is the process of completely removing the old membrane and replacing it with a comparable material onto the existing substrate (again, needing to be deemed structurally sound).

This method doesn’t require building consent as you’re simply replacing the material with a like-for-like system.

Despite the inconvenience and cost of having to remove the existing material, this solution still allows for the structure of the roof to remain in place. No rebuilding is required.

Re-roofing examples:

  • An existing bitumen roof that is completely well bonded to the substrate, can either be overlaid with Viking Enviroclad FBS (fleece-backed system) or Viking Torch-On.
  • An old butyl membrane roof that been assessed and deemed as well bonded to the substrate can be overlaid with Viking Enviroclad, adhering over the top using standard adhesive.
  • A warm roof can be installed on-top of any structurally sound, compliant substrate, including metal roofing in which PIR “fingers” are installed into the steel tray troughs, topped with a complete layer of PIR board on top of which the membrane is installed. Where appropriate, tapered board can be used to create more slope.

NB: It’s not for Viking to decide whether one should adopt just a membrane replacement or overlay, or re-construct the entire assembly. Viking’s hands-on technical team can use their experience to advise what’s possible. Through on-site inspections, and a good understanding of the building code, sensible, accurate decisions can be made. However, at the end of the day, council has the final say. Additionally, it’s up to the building owner to decide whether to apply for a consent or not. If in doubt, we recommend they contact their local council and Viking Roofspec will always be available to assist with technical input where required.

This article isn’t an encouragement to cut corners to save pennies. It’s about demonstrating what’s possible whilst complying with the building code and remaining responsible guardians of our planet.

Too many existing roofs are unnecessarily destroyed and dumped.

With a little contemplation before decision making, we can do our part to prevent this where possible.

If you’d like to discuss re-roofing options available to you, please contact Viking Roofspec: [email protected] or 0800 729 799.

View more information on Viking Roofspec, including contact details.
comments powered by Disqus
June 2024 EBOSSNOW Product News

News from Viking Roofspec

Membrane Overlay vs Complete Roof Replacement
Schedule One the Real Hero in School Membrane Roof Upgrade
Membrane Overlay Offers a Smart Solution for Minimising Roof Construction Waste
Get a free weekly digest of essential news

New and updated architectural products, design solutions, inspiration, technical advice and more when you sign up for EBOSS.