IMPORTANT: On 1 September 2017, Celotex took the precautionary measure to temporarily suspend the supply of Celotex FR5000, Celotex CG5000, Celotex CF5000 and Celotex SL5000 while we investigate the results of recent tests (Parts 6 and 7 of British Standard 476). Materials relating to these products are for information only.
What is a cavity wall?
The cavity wall as the name suggests consists of two masonry walls with separated by a clear cavity. By design the wall resists wind driven rain soaked up by the outer leaf migrating onto the inner surfaces. The width of the cavity has gradually got wider as the years have gone by and in the 1970’s insulation was introduced into the cavity with it becoming compulsory in Building Regulations during the 1990’s.
As part of ‘Factors shaping and driving insulation choice for masonry cavity walls’ I explained how the following impact insulation choice.
- Compliance to Part L1A 2013 and FEES as part of SAP.
- Approved Document C part 2.
- Full BBA Certification
FEES are a real challenge to Housebuilders and Architects. It demands a more robust, thermally efficient building envelope in order to comply with SAP. One factor of compliance means lower U-values through the walls as well as better thermal bridging values around junctions and openings. They are challenged to find, the most economic build recipe that optimises improved technical build performance to comply with FEES and SAP, yet give commercial value.
Building Regulation compliance for wall construction
Celotex CF5000 is a high performance rigid foam full-fill solution for masonry cavity walls. The Celotex CF5000 product datasheet will confirm its physical properties but essentially it is a 97mm board to fit a 100mm cavity space. The three millimetres allows for mortar squeeze which means CF5000 is in contact with both the inner and outer masonry leaves. This qualifies it as a full fill solution.
Celotex CF5000 makes use of the whole cavity space. This optimises the thermal performance through the wall and such it can achieve lower U-values without having to widen the cavity. The Celotex Technical Centre will confirm 97mm of Celotex CF5000 in a 100mm cavity wall using either an aircrete or lightweight concrete internal blockwork will give 0.18W/m²K U value which is exactly the target as outlined in Part L1A notional dwelling.
BBA Certification and Resistance to Wind Driven Rain
A refresher from my last blog reads how Approved Document C Part 2 sets out design considerations on how to keep a building dry. It has a section on walls and the requirement of cavity wall insulation having third party certification commonly known in this country as a BBA certificate.
Why does cavity wall insulation need a BBA certificate? – As the insulation fully fills the cavity, it must be able to resist wind driven rain crossing the cavity making the inside walls wet. The BBA have a test regime for this product function which is necessary for certification called a wet wall test
Celotex CF5000 was installed into the wet wall rig. The test ran for three weeks and during this time the outside masonry leaf was exposed to up to 5 litres of water a minute sprayed at wind speeds equal to 60 mph.
Celotex CF5000 board edges are rebated and fit together in a jigsaw fashion. This effectively stopped water penetrating from the outside leaf onto the inside walls as tested, witnessed and validated by the BBA.
Celotex CF5000 is BBA certified under certificate number 94/3080 as a full-fill solution in a masonry cavity wall and able to resist wind driven rain contacting the inside walls.
Thermal Bridging Models
Going back to the subject of improving the fabric performance to comply with FEES, heat loss through junctions is increasingly more important. The fabric of a new building is made up of the walls, roofs and floors and the point at which they meet is commonly known as a ‘junction of element’. A junction represents any weak point in the continuity of insulation and is therefore an obvious path of heat loss.
Thermal Bridging Models provide some guidance to Housebuilders and Architects on how to insulate the many differing types of junctions within a building. They also provide energy assessors the heat loss values (psi values) for each junction required by SAP. (There are a list of standard values available known as Accredited Construction Details (ACD’s) available on the Government’s website. They offer a ‘best practice approach’ on how to design out heat loss.)
Celotex CF5000 has its own set of bespoke thermal bridging models with psi values that are better performing than ACD’s. When these are specified in conjunction with CF5000 as part of a package it simplifies compliance to SAP. The Celotex Technical Centre (CTC) can run U-value calculations through the wall which give 0.18W/m²K but when the SAP assessor uses the bespoke psi values rather than standard ACD’s it can help eliminate the need for alternative measures to comply.
Celotex CF5000 coupled with the bespoke thermal bridging models are a key specifying tool which are influential in the decision making of which high performing full fill solution to specify. I think it’s true to say CF5000 coupled with its own thermal bridging models offer a full fill solution that provides SAP assessors the opportunity to optimise the build performance, simplifying compliance to SAP.
Where can I buy Celotex full fill insulation?
You can purchase Celotex CF5000 from our distribution and merchant partners which are available UK wide. To find your nearest stockist click here.
For more information on this product, click through.