Can You Put a New Roof Over an Old Flat Roof in the UK

Skyline Swindon Roofing

Renovating or replacing a flat roof in the UK raises questions about the feasibility and practicality of installing a new roof over an existing one. Home and business owners alike may wonder about the potential benefits, challenges, and legal considerations of such a project. In this article, we explore whether it’s possible to put a new roof over an old flat roof in the UK, examining the factors involved and providing insights for informed decision-making. Consulting with a roofing company experienced in flat roof installations can offer valuable guidance and expertise throughout the process, ensuring the best possible outcome for your property.

Assessing the Current Flat Roof

The condition and integrity of your existing flat roof should first be thoroughly assessed before installing a new roof over the top. Identifying any signs of wear and damage early on can help determine if a roof overlay is feasible or if a full roof tear-off and replacement is necessary instead.

Some key things to inspect for include:


  • Carefully check for any water leaks, moisture, or damp patches on the ceiling inside your property. This indicates that water is already penetrating your existing roof.
  • Leaks must be fully fixed and repaired prior to installing a new roof overlay. The source of the leak also needs to be identified and addressed.
  • Multiple leaks or continued seepage even after repairs may signify it’s time for a full roof replacement if issues persist.


  • Look for any areas on your flat roof that appear to be sagging, dipping, or sloping unevenly.
  • This can denote that the roof deck and infrastructure is weakening or warping. Sagging roofs have compromised structural integrity.
  • Attempting to add the weight of another roof layer on top can cause further damage if the existing roof is already sagging or uneven.

Ponding Water

  • Flat roofs should enable water runoff without large pools or puddles accumulating in sections.
  • Ponding water adds substantial weight and strain to roofs over time, accelerating deterioration.
  • If ponding water cannot be mitigated prior to overlaying with a new roof covering, it usually indicates a full roof replacement is the better option.

Determining the Current Roof’s Material

  • Identifying what your current flat roof on your property is made from is crucial when assessing if it can support another roof build-up added on top.
  • Common flat roof materials seen in the UK include:
    • Felt roofing
    • Asphalt
    • EPDM rubber
    • PVC single ply membranes
  • A structural engineer can best evaluate if adding roof layers exceeds maximum load capacity for the existing roof’s composition and infrastructure.

Roofing Options for Flat Roofs

There are a range of options when selecting materials for flat roof installations and overlays in 2023. Some key pros, cons, costs, and considerations for common choices include:

Traditional Roofing Materials


  • Felt or bitumen is the original material used for flat roofs traditionally made using rag felt embedded with bitumen. It remains a fairly affordable option.
  • Pros: tested material with long track record, inexpensive
  • Cons: Prone to degradation, cracking, blisters, joints opening up
  • Usually requires replacing every 10-25 years. Multiple layers can be installed if structurally sound.


  • Asphalt is a related roofing material made from an asphalt rolling membrane or hot asphalt applied in layers with reinforcing plies in-between.
  • Pros: time tested water resistant material, relatively low cost
  • Cons: deterioration from UV exposure leading to cracking and leaks over time. Prone to damage if walked on when hot.
  • Asphalt roofs typically last around 15-30 years before needing replacement. Check manufacturer guidelines on overlay limits.


  • EPDM rubber roofs remain a popular choice on commercial flat roofs but are also used residentially. Seamless sheet membrane applied using adhesive and sealant.
  • Pros: Exceptional durability and weatherproofing. Seamless nature avoids leaks. Long 50 year lifespan.
  • Cons: Professional installation is critical. More expensive upfront than other standard flat roof choices.
  • Multiple EPDM layers can be overlaid if needed and the roof structure allows the weight.

Emerging Roofing Materials

As technology progresses, some property owners are moving towards newer eco-friendly flat roof materials:

Green Roofs

  • Green roofs have a waterproof EPDM or PVC membrane base layer topped with drainage mats, growing medium, and vegetation.
  • Pros: Excellent insulation, stormwater management, promotes biodiversity, nice aesthetic
  • Cons: Much heavier loads, higher installation costs, maintenance requirements
  • Check if roof can structurally support the heavier load before overlaying an existing roof with a green roof.

PVC Membranes

  • PVC single-ply flat roof membranes are durable, lightweight and simple to install over existing flat roof builds.
  • Pros: Cost effective, various colors available, durable sheets resist weathering.
  • Cons: Avoid cheaper low quality PVC which can become brittle and crack over time.
  • High grade PVC roofing overlays are a great solution if your roof framing allows for the extra weight.

When selecting materials, always consult with roofing specialists to ensure the product chosen will be compatible with your existing flat roof in terms of weight, structure, insulation needs and local regulations. Getting professional guidance is key.

Installing a New Roof Over an Old Flat Roof

If your flat roof is deemed structurally sound to withstand an additional layer, here is an overview of the basic overlay installation process:

Cleaning and Preparing the Existing Roof

  • Thoroughly clean, dry and inspect the existing roof and repair any holes, leaks or faults.
  • Cut back and prepare blistered areas, seals and upstands. Remove debris, moss and vegetation.
  • Prime the existing roof surface so the new membrane bonds securely.

Installing Insulation if Necessary

  • Upgrading thermal insulation is advised when overlaying existing flat roofs in the UK to meet modern energy efficiency standards.
  • Insulation levels needed depends on your roof size/shape, intended use, and local regulations.
  • Various insulation solutions suit flat roof overlays from rigid boards to mineral wool. Get professional input on optimal solutions.

Applying the New Roofing Material

  • Once existing roof is prepped and insulated as required, the new roof membrane can be professionally laid.
  • Ensure suitable membranes are chosen for overlay suitability and meet weight restrictions.
  • Fully seal joints, perimeters, protrusions and edges using quality sealing products suitable for flat roofs to avoid leak risks.

Compatibility Considerations

It’s critical that the existing roof is compatible with any overlay installation in terms of:

Weight Implications

  • Adding another layer on top increases dead weight loading on your roof that the frame and structure must be able to safely withstand.
  • As a general rule of thumb, most modern flat roofs in the UK have sufficient capacity to support one new overlay addition if the roof is in reasonable condition.
  • For older roofs or those showing deterioration, get the maximum weight load capacity professionally assessed to determine overlay feasibility.

Structural Integrity Assessment

  • A structural assessment helps identify if the roof deck and infrastructure needs any reinforcement work before another roof layer can be installed on top safely.
  • A structural engineer will check the roof meets wind uplift requirements and the frame can cope with any increased loading without risk of collapse or failure down the line.
  • Seek professional engineering evaluations of roof integrity if doubt exists on structural stability or load thresholds.

Regulations and Permits

Building Regulations for Roof Replacements

There are a number of regulatory requirements surrounding roof replacements in the UK that must be met:

UK Standards

All roofing work in the UK must comply with standards outlined in the Building Regulations document for England & Wales. Key regulations cover:

  • Structural safety
  • Fire resistance
  • Energy efficiency requirements
  • Electrical and lightning protection

Local Regulations

In addition to national Building Regulations, local authorities often have certain codes or planning permissions required for roof replacements that must be checked. Common local regulations cover:

  • Aesthetics – for conservation areas
  • Tree protection
  • Ecological considerations
  • Noise restrictions
  • Hours/days when roofing work is permitted

Permits and Permissions

Obtaining Approvals

  • Building control approval must be obtained for most structural roof work. This involves submitting an application with your upgrade plans so the council can ensure compliance.
  • Planning permission may be needed in certain areas, such as conservation sites or listed buildings. Always verify with your local authority what permissions are mandatory.

Compliance with Building Codes

  • Any contractor carrying out a roof overlay or replacement must work in accordance within all applicable UK building codes and regulations during installation.
  • This covers codes related to materials used, fire safety, insulation, fall protection, waste disposal, energy efficiency and more. Be sure whichever roofer you hire follows approved codes.

Cost Considerations

Overlaying a flat roof invariably costs less than undertaking a full roof tear-off and replacement. Prices are influenced by:

Factors Influencing the Cost

Roof Size

The larger the flat roof area getting overlaid, the higher the overall project costs.

Material Choice

Upgrading to modern PVC and EPDM membranes typically costs more than basic felt or asphalt overlays but provide better durability and lifespans.

Labor Expenses

Most of the project budget goes towards specialized roofer labor and installation work rather than material supplies.

Budgeting Tips

To keep expenses in check, two money-saving tips are:

Obtain Multiple Quotes

Get overlay quotes from several reputable local roofing companies before committing. Comparing prices allows you to find the best value.

Explore Financing Options

If cash-strapped, see what finance facilities they offer on roof upgrades and replacement. Make sure affordable payment plans are available from whoever you select.

Frequently Asked Questions

Can a new roof be installed over any old flat roof?

It depends on the condition. If the existing surface is excessively uneven, leaks persistently or structure is compromised, a overlay may not be feasible. An inspection helps determine if a roof overlay is suitable.

How long does the process typically take?

A straightforward flat roof overlay on a medium home may only take 1-2 days total for a professional team to fully install. Larger or complex roofs with insulation upgrades may require an additional 1-2 days.

What are the common problems with overlaying a new roof?

Overloading the roof structure beyond safe weight limits, inadequate preparation and cleaning before applying overlay, compromised sealing leading to leaks, condensation buildup in trapped moisture, and inadequate insulation or ventilation are among risks requiring mitigation.

Are there any environmental benefits to choosing specific materials?

Cool roof coatings, green roofs with vegetation and PVC membranes made from recycled plastic offer eco-friendly credentials. Get professional guidance on the most sustainable roofing solutions for overlays.

Do I need to evacuate during the roof overlay process?

On most standard residential flat roof installations, families typically don’t need temporary displacement during the 1-2 days required as it is confined to the roof itself. Check with your roofer on any safety or disturbance considerations that could necessitate temporary alternative accommodation whilst work is carried out.

Can I perform a roof overlay as a DIY project?

Roof overlays on occupied residences are complex installations best left to accredited professional roofers for safety, quality, insurance and peace of mind. They follow codes and practices most homeowners cannot replicate.

How long does the new roof last compared to a traditional replacement?

Correctly installed quality roof overlays can provide up to 20 years of reliable performance. But full tear-off replacements may last 5-10 years longer than overlay solutions before requiring work again. Get professional guidance on ideal lifecycles for your roof type and needs.

Thanks for reading our post, feel free to check out our other services: