Flat Roof Insulation in City Of Westminster (4)

Need flat roof insulation in City Of Westminster?

Whether you’re retrofitting insulation on an existing flat roof or insulating a new build, enter your postcode to find checked insulation installers near you.

All our tradespeople are checked and reviewed, helping you to hire with confidence.

What is flat roof insulation & why it matters

Flat roof insulation is a barrier added to a flat or slightly sloped roof to reduce heat loss, eliminate condensation, and improve energy efficiency.

It can help lower energy bills, reduce damp issues, and maintain more stable internal temperatures.

There are different types of insulation systems for a flat roof:

• Cold (inverted) deck: Insulation is installed beneath the roof covering (often used when adding to existing roofs where height is constrained)
• Warm deck: Insulation is placed on top of the roof structure, under the waterproof membrane
• Inverted roof systems: Insulation on top of the waterproof surface with a protective ballast

Flat roof insulation materials

Some materials commonly used for flat roof insulation include:

• PIR boards
• EPS/XPS foam boards
• Mineral wool
• Spray foam

Each has strengths in U-value, moisture resistance, compressive strength, and cost.

How thick should flat roof insulation be?

• Many flat roofs require insulation of around 120–150mm of PIR/EPS to meet modern regulations or to get good thermal performance
• Material performance (U-value) is just as important — thicker isn’t always better if the material doesn’t perform
• For renovations, flat roofs must have a U-value of 0.16–0.18 W/m²K; for new builds, it’s 0.18 W/m²K or lower

How much does flat roof insulation cost?

The cost of insulating a flat roof will vary depending on several factors, including:

• The size of the roof area
• The material chosen (rigid board, spray foam, mineral wool etc.)
• Roof condition and whether waterproof membranes or ventilation modifications are needed
• Access (how easy it is to reach, height, labour complexity etc.)
• Whether existing insulation needs to be removed or repaired

As a guide, expect to pay between £10–£37 per m² for flat roof insulation, with sheet insulation (PIR) costing around £35 per m² (materials only).

Flat roof insulation regulations and building requirements in the UK

Current building regulations require certain U-values for insulation to comply with thermal performance standards.

Flat roofs must also respect insulation thickness and structural load limits so that the roof covering and structure are safe and durable.

In addition, ventilation and vapour barriers are often needed to prevent moisture and condensation issues.

• U-value: For renovations, flat roofs must have a U-value of 0.16–0.18 W/m²K; for new builds, it’s 0.18 W/m²K or lower
• Thickness: For flat roofs, rigid foam boards should be between 120–150mm to meet UK regulations

A checked flat roof insulation installer in your area will ensure compliance with UK building regulations.

How is flat roof insulation installed?

Planning for flat roof insulation installation? Here’s what you can expect:

• Survey and assessment: Check roof condition, any existing insulation, and structural integrity
• Preparation: Remove damaged layers, ensure the waterproofing membrane is intact, or check if it needs renewal
• Lay insulation: Either boards (PIR/EPS/XPS), or other material, depending on system type (warm deck/ cold deck)
• Add protection: Waterproofing, covering, ballast (if an inverted system)
• Finish and seal: Ensure all edges, penetrations (vents, skylights) are sealed to prevent leaks

For a job done right, search for flat roof insulation installers in City Of Westminster with Checkatrade.

How long does it take to install flat roof insulation?

• Small roof sections (e.g., a dormer or rear extension) typically won’t take longer than a day
• Larger flat roofs with multiple layers or complex access may take 1–2 days

If additional work is needed, for example, the removal of old insulation or the repair of the structure or membrane, this adds time.

Tips for hiring flat roof insulation installers in your area

When searching for flat roof insulation companies near you, follow these steps to help ensure the right choice of hire:

• Check an installer’s experience with flat roofs, especially warm deck vs cold deck systems
• View past projects/photos to see the waterproofing and insulation quality
• Confirm what materials are used and their certifications (e.g. thickness, U-value)
• Ask for a detailed quote to include: materials, labour, membrane work, finish, warranty
• Check reviews, insurance, and whether the warranty covers both insulation and waterproofing

For tradespeople committed to quality and a job done right, search for flat roof insulation installers in City Of Westminster with Checkatrade.