How to Hit 0.15 U-value on Flat Roofs
The following page by Multifoils Direct will display alternate ways to hit the common U-value of 0.15.

We appreciate hitting U-value targets for building control can be difficult. There are many restraints and difficulties to combat, such as rising costs and labour installation time.

U-values Explained

U-value is a measure of heat loss and the rate of heat transfer through a structure. A U-value is calculated by an addition of all the R-values (thermal resistances) that makes up the structure. For example, in a standard flat roof, you would find timber joists & a rubber roof. All the R-values in the structure can impact the U-value in a positive or negative way.

The better thermally the structure is, the lower the U-value.

Building Regulations for U-values in 2023

Approved Document Part L has been updated in relation to U-values, heat gain and heat loss. The new target U-values came into play June 2022. More information on Part L can be found at the following link on the UK government website – See Data Source.

New for 2023 – U-value requirements for existing dwellings
Application	Current U-value
Roof (Flat Roofs & Pitched Roofs)	0.15
Wall	0.18
Floor	0.18

What does this mean for my project?

In a nutshell, the lower the target U-value, the more insulation required for your project.

Recommended Products for Flat Roofs

Multifoils Direct are the leading distributor of SuperQuilt Insulation. SuperQuilt is a 19 layer multifoil, including true aluminium outer layers, PE foams and recycled wadding. SuperQuilt equates to approx 75mm of installed PIR Insulation, whilst saving cost, space & installation time. You will find recommended details with just SuperQuilt, alongside details with SuperQuilt & additional insulation.

SuperQuilt For Flat Roofs

• SuperQuilt – Product Link – Click Here!
• 19 layer multi-layered foil blanket
• 40mm thick, compresses to 7mm
• BDA Agremont Certified
• Built-in Vapour Control Layer
• Made in the UK
• Made of 83% Recycled Materials

Systems to achieve 0.15 U-value

Below are a variety of methods recommended by Multifoils Direct to achieve a 0.15 on flat roof projects. You will find the 9 solutions will vary dependent on if you are insulating above the joists, over the joists, or a combination of both. There options also differ dependent on the joist depth. You will find additional comments below each image.

 

• Option A – 3 Layers SuperQuilt, Standard Plasterboard – Insulating Above & Below Joists
  See our How-To Video for this detail here!

 

• Option B – 2 Layers SuperQuilt, 50mm PIR Insulation, Standard Plasterboard – Insulating Above & Below Joists

 

• Option C – 2 Layers SuperQuilt, 100mm Knauf Earthwool (Mineral Wool), Standard Plasterboard – Insulating Above & Below Joists

 

• Option D – 1 Layer SuperQuilt, 90mm PIR Insulaiton (Continuous), Standard Plasterboard – Insulating Above Joists Only

 

• Option E – 1 Layers SuperQuilt, 125m PIR Insulation, Standard Plasterboard – Insulating Below Joists Only

 

• Option F – 2 Layers SuperQuilt, 57.5mm Insulated Plasterboard – Insulating Below Joists Only

 

• Option G – 1 Layer SuperQuilt, 150mm Mineral Wool 0.032 (High performance Wool), Standard Plasterboard – Insulating Below Joists Only

 

• Option H – 2 Layer SuperQuilt, 150mm Isover Mineral Wool 0.044, Standard Plasterboard – Insulating Below Joists Only

 

• Option I – 2 Layer SuperQuilt, 50mm PIR Insulation, Standard Plasterboard – Insulating Below Joists Only

 

• Option J – 2 Layer SuperQuilt, 100mm Mineral Wool 0.032 (High performance Wool), Standard Plasterboard – Insulating Below Joists Only

 

• Option K – 2 Layers SuperQuilt, 50mm PIR Insulaiton (Continuous), Standard Plasterboard – Insulating Above Joists Only

Require a certificate for building control?

If you’re going through building control, it is likely they will want to see a document displaying the achieved U-value. These can be downloaded from our Online U-Value Calculator. Once the calculator is completed, our system will email the bespoke calculation in PDF form. This can be sent over, or printed off for your building control officer.

Not found the correct calculation? If so, please use our Request a U-value! Mention the above option (e.g. Option E of F) and we can provide a bespoke U-value calculation. Please advise m2 quantity and we will also supply a quote at our lowest trade prices.
Please request a bespoke U-value calculation by following the link – Click Here!

Delivery Schedule

Multifoil’s Direct offer YBS SuperQuilt with next-working day delivery!

You can purchase these as loose rolls, or save cost with our Trade Pallet Deals!

See below links to order both online with next-working day delivery;

SuperQuilt Loose Rolls – Click Here!
SuperQuilt Trade Pallet – Click Here!

Disclaimer

All build-ups and suggestions are provided in good faith. We recommend having these details double checked by building control before proecceding. The U-value table is a guide, and your desired target U-value is to be advised from your building inspector. Please check the calculations for correct air-gaps and battens, battens may be required to be installed perpendicular to how they are supplied in the image. 2D images are not to scale, and for illustrational purposes only. Multifoils-Direct cannot be held responsible for any losses financially or physically from advice provided on this webpage