70 INSULATION
Insulating flat roofs in accordance with new British Standard and fire regulation revisions
considerations for insulating flat roofs. Ensure your project requirements are being met by following Bauder’s guidance on achieving minimum U-values, thermal performance of inverted roofs and fire safety
T
BS 6229:2018 The 2018 update of British Standard 6229 – flat roofs with continuously supported flexible waterproof coverings, brings in significant changes that affect the design of flat roofs and the installation of a waterproofing system and associated insulation. The document comprises updated practices that directly impact the design of roofs on new buildings and those to be refurbished.
Minimal U-Values and Control of Condensation Under the revised British Standard, the minimal U-value levels permitted at any point on a roof, must be 0.35W/m²K (clause 4.7.2). ‘At any point’ includes the minimum thickness of tapered roof areas and gutter to maintain the thermal performance of a heated building. This is a new design consideration under the standard’s revision. In such roofs, the risk of surface condensation is removed if continuity of insulation, including at upstands and roof penetrations exists. This uplift in the standard looks to eradicate the practice of thinly insulated gutter soles and excessively low points in tapered schemes. For reference: 0.35W/m²K is achieved
using approximately 60mm BauderPIR FA-TE or 100mm of BauderROCK.
Thermal Performance of an Inverted Roof When designing an inverted roof construction, the principal thermal insulation layer is located above the roof structure and waterproofing, resulting in the waterproofing, structural deck and support structure being
he recent review of the flat roof design British Standard and Approved Document on Fire feature new design
at a temperature close to that of the interior of the building. In order to prevent water from passing around the insulation, through the joints, and reaching the waterproofing layer, where it would have a cooling effect on the building, the correct installation of a Water Flow Reducing Layer (WFRL) is required. However, the construction tolerances and installation of the WFRL can result in a less than desirable reduction of water flow and as such the corrective action is much reduced. The advice Note in clause 4.6.2.2 – Inverted Roofs to counter this reduction suggests increasing the design thickness of the thermal insulation of an inverted roof where a Water Flow Reducing Layer (WFRL) is being relied upon by “not less than 10 per cent”. Bauder provides in project specifications both the design thickness for the target U-value plus the advisory minimum 10 per cent increase in thickness for the specifier to choose if they wish to follow the advice. To ensure comparable tendering Bauder recommends that you should clearly state if you are following the advice in BS 6229:2018 Clause 4.6.2.2
Update to Fire Safety Approved Document B On the 30th
(EPS), Extruded Polystyrene (XPS) and Polyisocyanurate (PIR) and are excluded from ‘Specified Attachments’ – fixed balconies, but they are perfectly acceptable in a flat roof build-up where the whole build up achieves BROOF(t4). There are currently a number of ‘grey
areas’ in the legislation that further complicate this. While there are several non-combustible insulants that can be used on balconies or vertical flashings, the waterproofing membrane used will typically be Class ‘E’. The MHCLG need to be more specific on their requirement for flat roofs. Non-combustible insulants, such as cellular
glass along with mineral wool, are clearly desirable materials to include in a flat roof specification because of fire performance, and it is important to consider and balance the factors for inclusion within a roof system. In general, non-combustible insulants are not as thermally efficient as PIR insulation and therefore extra thicknesses, increased weight and reduced compressive strength can be a limitation in some applications. PIR has the advantage of being highly efficient, which reduces the height and weight of a roof covering build-up whilst also offering good compressive strength meaning greater versatility on a project. Within a Bauder warm roof waterproofing
August 2019 the new edition of
'Fire Safety-Approved Document B' (ADB) came into force and with-it considerations that affect insulation within flat roofing design. For a full understanding of the testing procedures, classifications and further guidance, please visit
bauder.co.uk/fire- protection-statement.
Specifying roof insulation based on fire performance Individual construction products are covered within BS EN 13501-1 for which insulation as a separate component will be encompassed and allocated a Class according to their reaction to fire test results with letter classifications from ‘A1’ through to ‘F’. On the whole, materials manufactured from plastics will achieve an ‘E’ rating, which will include the insulants Expanded Polystyrene
system (excluding ‘Specified Attachments’) the insulation, be it mineral wool, cellular glass or PIR, is not directly exposed and is therefore protected through the performance of the cap sheet and its system classification of BROOF(t4); thus these insulants in-situ all conform to Building Regulations for external fire on roofs in the same way – not one achieving a higher rating than the other.
0845 271 8800
www.bauder.co.uk
WWW.ARCHITECTSDATAFILE.CO.UK
ADF NOVEMBER 2019
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100
