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U-value calculator

U-value Calculations

Recticel Insulation supports the accurate calculation of U-values for the construction industry. Calculations are issued under the Competent Person scheme administered by the BBA (British Board of Agrément) and TIMSA (Thermal Insulation Manufacturers and Suppliers Association).

All U-values are calculated by the Combined Method, in accordance with the conventions detailed in BRE 443 (2006), BS EN ISO 6946:2007, and other standards laid out by the BBA in their Scheme guidance.

Calculations are provided free of charge to demonstrate the performance of Recticel products and compliance with Building Regulations. To accord with the BBA / TIMSA scheme, calculation requests can be made in writing to our technical services team

E-mail: technicalservices@recticel.com

Fax: 01782 590497

Accuracy of calculations is improved by the amount of information available. To aid the submission of requests, particularly if you are unsure of what information we might need, a checklist of information for common calculation types is available below.

Click to use on online u-value calculator

Condensation Risk Analysis

Every Recticel U-value calculation is supplied with a Condensation Risk Analysis, and additional guidance is offered when required. Advice on condensation risk is given in accordance with BS 5250:2011 and BS EN ISO 13788:2002.

We recognise that on-site constraints mean it is not always possible to construct buildings in an ideal manner, and we endeavour to provide an honest appraisal of a proposed build-up relative to best practice guidance.


U-value Calculation Request Checklist

When applying for a calculation, please supply as much of the following information as possible:


Contact Information

Contact name / Company name / Address & postcode / Telephone number / E-mail address

Project reference & postcode


Environmental Conditions (as defined in BS 5250:2011)

Please specify which of the following your project falls under:

-        Class 1: Storage areas

-        Class 2: Offices, shops

-        Class 3: Dwellings with low occupancy

-        Class 4: High occupancy dwellings, sports halls, kitchens, canteens, buildings heated by unflued gas heaters

-        Class 5: Special buildings, e.g. laundry, brewery, swimming pool


Construction Details

-        Target U-value for all calculations requested.

-        A breakdown of all construction elements for which a calculation is required.


The following additional information will improve the accuracy of calculations, and should be provided if known:



All types of ground floor construction:

-        floor area (m2) and floor perimeter (m)

-        thickness of edge/perimeter insulation to screed or slab

Timber floors (ground or intermediate): size of joists and centres

Block and beam floors (ground or intermediate): thermal conductivity of infill block



Masonry wall constructions:

-        type of cavity wall tie

-        blockwork: thermal conductivity (l value, W/mK); or block manufacturer and make

Timber frame wall constructions: size of timber studs and centres

Internal dry lining: confirm dot and dab or mechanical fixing of insulation to wall.


Flat roofs

Warm roof:

-        type of vapour control layer (VCL)

-        method of fixing insulation (bonded build up, or type of mechanical fixings)

Cold roof (ventilated airspace above insulation): size of timber joists and centres


Pitched roofs

All types of pitched roof construction: size of rafters and centres