Important Information: For all updates and Celotex announcements since June 2017, please see the links below...  See more

Declared lambda values - Read more >

5000 Class 0 testing - Read more >

Rainscreen cladding & RS5000 - Read more >

FAQ

Here is a page dedicated to questions frequently asked by our customers.

U-value Calculator
Start your U-value calculation >
Use the calculator

Filter by category or search for what you need to know


Can Celotex be exposed to the ground?

We advise that when used in ground floors, Celotex must always be above the damp proof membrane (DPM ).


Can Celotex be used as a cavity fire barrier?

No, where cavity fire barriers are required by national building regulations, they should be installed in line with the manufacturer's instructions.


Can Celotex be used below the damp proof course in a masonry cavity wall detail?

Celotex CW4000 can be used below the damp proof course (dpc) in a masonry cavity wall detail. When the product is used in situations where it bridges the dpc in walls, dampness from the ground will not pass through to the inner leaf provided the wall is detailed in accordance with the requirements and provisions of the national Building Regulations. The insulation boards should be supported clear of the ground on the first row of wall ties and a clear cavity should be maintained between the insulation and the outer leaf. Please refer to BBA certificate 16/ 5343 for more information.

Can I insulate between and over my flat roof joists?

Installing thermal insulation between and over flat roof joists is not an accepted method of construction.

Thermal insulation in a flat roof may be placed:

a) above the roof deck but beneath the waterproof covering, maintaining the temperature of the deck close to that of the internal occupied space – creating a “warm roof”

b) beneath the roof deck, leaving the deck colder than the internal occupied space – creating a “cold roof”.  There should be a cross-ventilated void, not less than 50mm between the deck and the insulation.

These guidelines are taken from BS 5250: 2011+A1: 2016 “Code of practice for control of condensation in buildings”


Can I recess electric cables into Celotex?

No. We would not recommend electrical cables to be channelled / cut into Celotex products, as that would reduce the thermal performance of the Celotex product. As with other insulation products, it may be necessary in some cases to de-rate electrical cables buried in insulation. In BS 7671 : 2018, it is recommended that where wiring is completely surrounded by insulation it may need to be de-rated to as low as half its free air current carrying capacity. Guidance should be sought from a qualified electrician.

Source: BBA application certificate 16/5352 PS2 section 11.


Can I recess my downlighters into Celotex?

The use of downlighters in an insulated ceiling requires careful consideration.

Best practice would be to use timber battens under the joists to create a service void between the vapour control layer and the plasterboard. Downlighters can then be installed within this clear void – this will ensure the integrity of both the insulation and vapour control layers above are not compromised.

If downlighters are installed into an insulated ceiling (without the use of battens) then you should seek expert advice from a down light manufacturer in order to select a product specifically designed for this condition.


Does Celotex have a BS EN ISO 14001:2015 certificate?


Does Celotex have a BS EN ISO 9001:2015 certificate?


How is polyisocyanurate foam board made?

It is made by a lamination process, formed between aluminium foil facings that are glued together in a continuous laminator, where the 'adhesive' is a mixture of MDI and polyol. An added blowing agent causes this adhesive to expand into foam that hardens and is cut into manageable board sizes.

 


Is Celotex board packaging environmentally friendly?

We only offer shrink-wrap packaging on products requiring protection from rain while stored on site. Most boards feature banded cardboard packaging, which is easily recycled, and is biodegradable, minimising pollution from careless disposal.

Please see our sustainability statement for more details


Is Celotex suitable below a raft slab?

No. Celotex product is not designed to be used beneath a raft foundation.


Is Celotex suitable for inverted roofs?

No. Celotex is not suitable for use in inverted roofs (protected membranes) as it must remain dry at all times.

Refer to our Applications page for more information on roofing.


Is Celotex suitable to use underneath floor tiles?

No. Celotex is not suitable directly below floor tiles. A screed is required to spread the load and prevent movement between the tiles.


What are the Target U-Values for England, Wales and Scotland?

Target U-values for floors, walls and roofs can vary depending upon the nature of the project. Key factors that affect compliance are whether the building is domestic or non domestic and whether the project relates to a new or existing building. In addition, different performance targets now apply in England, Scotland and Wales. The requirements of the building regulations are laid out in the following documents: England: Approved Document L. Wales: Approved Document L (Wales). Scotland: Scottish Technical Handbook - Section 6.  Further guidance on elemental U-values can also be found in the Celotex Handy Guide

Contact the Celotex Technical Centre


What can I do if I have excessive glazing?

You are allowed 25% of the floor area as glazing plus any windows covered by the proposal if applicable.

If your glazing levels exceed 25%, contact an energy assessor for an overglazing calculation. 


What do I need for a SAP calculation?

A SAP ( Standard Assessment Procedure) calculation, is a stable state thermal model of the dwelling. To make this model accurate the exact dimensions, passive heat losses and gains, and any thing that affects the ventilation, space and water heating of the property. This includes, U-values, PSI values, and detailed information on all mechanical and electrical services running the dwelling. Contact the Energy Assessments for more information.


What is a Predicted Energy Assessment?

The Predicted Energy Assessment (PEA). Is a preliminary Energy Performance Certificate for the dwelling as designed. After the dwelling is built, the as built EPC is created. Contact the Energy Assessments for more information.


What is a VCL?

A vapour control layer (VCL) is a layer within the construction that has a high resistance to the passage of water vapour. A polythene membrane would be a classic example. The job of the VCL is to prevent water vapour migrating into the insulated construction where it could lead to interstitial condensation.

Source: BS 5250


What is a warm roof?

A warm roof is where the main construction elements of the roof are kept at or near internal temperatures. A warm pitched roof is where the thermal insulation is installed at the rafter line - between, beneath or above the sloping roof structure or a combination of these. A warm flat roof is where the thermal insulation is installed above the roof deck but beneath the waterproof covering, maintaining the temperature of the deck close to that of the internal occupied space. These definitions are taken from BS 5250: 2011+A1: 2016 “Code of practice for control of condensation in buildings”


What is an Energy Performance Certificate?

Energy Performance Certificates (EPCs) are now required, by law, on all homes. EPCs became mandatory in October 2008 on all buildings, whenever they are built, sold or rented out.

An EPC is a measure of the energy efficiency of a building as well as the environmental impact as measured by CO2 emissions. The EPC provides 'A' to 'G' ratings for the building, with 'A' being the most energy efficient and 'G' being the least efficient. Buildings built from 2006 typically achieve a much higher rating due to modern standards of insulation.

An EPC will provide a Recommendation Report that offers advice and suggestions on how to further improve energy efficiency. This will ultimately have a positive impact on reducing CO2 emissions, and running costs for the home.

Contact the Energy Assessments for more information.


What is cold roof?

A cold roof is where the main construction elements of the roof are maintained at a similar temperature to the external surfaces.

A cold pitched roof is where the thermal insulation is installed at the horizontal ceiling, leaving an unheated loft or attic.

A cold flat roof has the thermal insulation installed beneath the roof deck, leaving the deck colder than the internal occupied space.  There should have a cross-ventilated void, not less than 50mm between the deck and the insulation.

These definitions are taken from BS 5250: 2011+A1: 2016 “Code of practice for control of condensation in buildings”


What is Part L?

Approved Document L provides guidance on complying with the building regulations in respect of Conservation of Fuel and Power covering Engalnd and Wales. For more information on building regulations, click here.


What is the Company's sustainability policy?

It is the policy of Celotex Limited that the Company will at all times pursue strategies within its operations, product development and commercial activities to assess and minimise negative impacts on the environment whilst adhering to the principles of sustainable development, and to expect similar environmental standards from its suppliers and contractors.

For our Sustainability Statement or to view our BRE Environmental Profiles, please refer to the Sustainability page.


What is the specific heat capacity of PIR insulation?

The specific heat capacity cp states how much heat energy is required to increase the temperature of 1kg mass of a material by 1K. Specific heat capacity cp is measured in J/(kg·K).

More heat energy is required to raise the temperature by 1K of a material with a greater heat capacity. And inversely, less energy is required to produce a 1K increase in temperature in materials with lower heat capacities.

Calculated values of specific heat capacity cp of various materials
Material Specific heat capacity cp = J/(kg·K)

  • Rigid polyurethane foam (PUR/PIR) 1800
  • Wood-fibre insulation boards 1000
  • Mineral wool 840
  • Wood and wood-based materials 1600 - 1700
  • Plasterboard 1000
  • Aluminium 880
  • Other metals 380 – 460
  • Air (ρ=1.25 kg/m³) 1008
  • Water 4190

Where can I buy Celotex?

Celotex is very well known throughout the construction industry and is supported by a nationwide network of leading distributors and builders merchants.

Visit our Stockists page to find your nearest stockists.


Why is there a polythene membrane between the Celotex and screed?

A polythene membrane on top of insulation below a screed or concrete oversight performs three tasks: it acts as a vapour control layer (VCL); it prevents migration of the screed / concrete which can force the boards apart leaving cold spots in the floor; and it prevents a reaction between the wet screed / concrete and the foil facer where small volumes of gases given off can weaken the screed/concrete. Flooring BBA certificate can be found here.

We’d like to make finding the answers to your questions as simple as possible, and want to help you use our website with ease.

Take a look at our collection of questions. If your query cannot be answered on this page, please contact the Celotex Technical Centre on 01473 820850

Can't find what you're looking for? Contact us with your query Calculator Icon