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NBS Specifications

Standard Details

General Design Considerations


SikaSpec is the fast efficient way to create specifications for roofs and many other applications, providing two easy to use online ways to create specifications; SikaSpec Basic and SikaSpec Pro. Once registered users can create, store, duplicate, modify and e-mail specifications to single or multiple recipients.

SikaSpec Basic
We do most of the work for you. Simply choose the roof construction, the method of attachment and the guarantee term and get a basic specification covering the deck, vcl, insulation and waterproofing membrane complete with preliminary items.

Sika Spec Pro
Through 8 simple steps Sika Spec Pro enables you to specify each element of the roof construction through a step by step process. At each step a range of options will appear guiding you through the selection process. Where the roofing components are not supplied by Sika-Trocal there is the option to specify a generic solution or select a preferred 'equal or approved' supplier. Sika Spec Pro even allows you to specify up to 3 different roof areas on the same building.

Visit SikaSpec - Online Specification Tool

NBS Specifications

Where an NBS Specification is required we recommend the initial completion in SikaSpec Pro, as the majority of the information we require to create an NBS Specification will be contained within this.

Standard Details

Please visit the Downloads section of the website to download standard details in pdf and dwg format.

Building Regulations

The 2006 revisions to the Building Regulations Approved Document L for England & Wales introduced the requirement to notify Building Control of any intended refurbishment work to a thermal element (Roof, Wall or Floor) of a certain size and to present the Building Control Body (BCB) with proposals for the upgrade of its thermal performance, to a required minimum standard.

The 2010 revision of Approved Document L requires a further flat 25% reduction in energy use, over the 2006 regulations for dwellings and an aggregate 25% reduction for buildings other than dwellings, based on a notional building type.

The requirements of the Scottish Building Standards Association (SBSA) Technical Handbook, Section 6 are very similar.

With 99% of the annual built environment consisting of existing buildings, significant carbon emission reductions can only be achieved by upgrading existing building stock (Saving around 150 million tonnes of CO², according to EU figures), the benefit to the building owner/operator will be a reduction in the energy costs associated with heating and cooling.

Can you avoid the extra expense?

Building Regulations Approved Document L (ADL) Part L2B: Conservation of fuel and power (Existing Buildings other than Dwellings) England and Wales requires minimum U-values to be achieved. The regulations state that when refurbishing a flat roof, a check on the insulation within that roof must be made to ensure that it meets the requirements of Approved Document L 2010.

The Exceptions

There are some exemptions, unheated buildings, some listed / heritage buildings or where the payback period (total cost of upgrading versus savings made) exceeds 15 years to achieve. Ultimately the BCB is required to make a judgement on what will be required, Sika Trocal therefore advises that Building Control is consulted early in the planning process of the project, as the potential financial consequences for non compliance could be significant.

These requirements are that:

  • A roof that already has insulation installed must achieve a U-value of 0.35 W/m²K
  • A roof with a U- value of less than 0.35 W/m²K must be improved to achieve a U-value of 0.18 W/m²K
  • A new build property / extension roof must achieve a minimum U-value of 0.25 W/m²K
  • A roof repair or overlay that accounts for more than 50% of the individual roof element or 25% of the entire building must comply with the new requirements

When an extension is built consequential improvements to the existing building are required and should be not less than 10% of the cost of the extension.

Pressure Testing for Air Leakage

Part L requires that uncontrolled air leakage in all new buildings is reduced to an acceptable level and that the results of air permeability tests (carried out by registered competent companies) are taken into account when calculating the energy performance of a building.

The design air permeability used in the TER (Target Emission Rate) calculations is 10m3/h-m2 @ 50Pa pressure. However, it will probably be necessary to design for better performance than this to achieve a satisfactory BER (Building Emission Rate). Some designers may therefore use higher standards of air tightness to achieve a BER better than the TER.

Roofing contractors should be aware of this, as to achieve higher levels of air tightness during construction will demand a higher standard of workmanship, which will be tested at completion and if the test fails may require expensive remedial work and re-testing for which the roofing contractor may be liable. For example eaves details are a common path for air leakage.


To encourage the removal of water from the roof surface falls need to be formed to direct it towards the gutters or rainwater outlets. BS 6229:2003 Code of Practice for Flat roofs with continuously supported coverings recommends that no part of the finished roof should have a fall of less than 1:80. The guidance given is that to ensure the finished fall requirements are met then design falls need to be greater in order to allow for deflections caused by dead and live loads and for tolerances in construction. Space in the absence of any accurate information or calculations about the level of those deflections and tolerances etc, the design fall should be double that of the minimum required, 1:40.

Where two planes of a roof meet in a mitre, the fall along the junction is less than that of the two planes; this should be taken into account when deciding the design falls.

Tilting the supporting structure, laying screed to falls or the use of tapered insulation can create the necessary falls. With long runs of roof, care should be taken to ensure that the build-up of thickness does not compromise details at abutments with walls or make the actual construction of the various layers difficult.

Sika-Trocal membranes are not adversely affected by a reasonable amount of retained water, ponding is not a material related issue. Occasionally areas of standing water can occur on the roof surface due to errors in construction. Ponding water on a roof when associated with fallen leaves can sometimes lead to the development of certain bacteria that can cause some staining of the membrane. On exposed membranes this stain is purple and ballasted ones, brown. Whilst unsightly, the stain does not affect the Sika-Trocal materials.

It should be noted that some insurance based design guides and some clients will actually require falls to be constructed at greater angles than the minimum’s specified in BS 6229:2003 Code of Practice for Flat roofs with continuously supported coverings.


Sika-Trocal roofing systems are suitable for a variety of visual roof designs, including barrel vaulted, curved, double curved and domed. When designing roofs where aesthetics will be an important part of the finish, we recommend early involvement of your local Area Technical Manager. Through our experience we can assist with consideration of installation layout that can complement the design.

For example, Sika-Trocal SE decorative profiles that can be welded onto the membrane after installation to create the appearance of a raised seam. Butt joints in external Sika-Trocal Metal can be positioning to compliment the design and the layout and positioned of the sheets, can also have a dramatic effect.

Internally, it should be noted that when using a mechanically fastened system with a metal and timber deck, the mechanical fasteners securing the roof insulation and membrane will penetrate the deck and protrude from the underside by at least 15mm. This is necessary for the correct functioning and performance of the fasteners and, under no circumstances should the fasteners be shortened or cropped after installation, as it could lead to failure of the fixing system.

In these applications the use of a single fastener and disc to attach the Sika-Trocal membrane, provides a positive advantage compared to other mechanically fastened systems that utilise separate fasteners for insulation and membrane attachment.

In the case of metal decking, all of the membrane restraint fasteners will be located in the crown of the profile which is recessed when viewed from below and helps to make them less obvious. With metal decking account should also be taken of the ‘lap stitching’, which is a row of screws installed along each side lap and is at the lowest point and hence most visible, of the deck. On most projects these protruding fasteners do not cause any concern, but in the event of a painted finish to the soffit or heights being low, consideration should be given to the level of visual intrusion of the fasteners.

It might be worth considering a false ceiling or some other method of making them less visible. In some cases and in suitable locations, it might be worth considering a build-up of adhered insulation and membrane, in order to omit the fasteners, although it should be noted that the lap stitching of the deck would still be present.

Fire Performance

The ‘fire performance’ of a roof construction is determined using either BS476-3 or test 4 method as described in CEN TS 1187 and classified according to BS EN 13501-5.

When tested in accordance with the above, the most commonly specified combinations of deck, insulation and mechanically fixed exposed Sika-Trocal membrane will normally achieve an FAA or FAB rating. Cold deck timber roof constructions with mechanically fixed exposed Sika-Trocal membrane will normally achieve an FAB rating WITH BS476 or a Broof (test 4) classification according to BSEN 13501-5. Ballasted gravel/paved membranes are generally deemed to achieve an FAA rating.

The Building Regulations define the acceptable areas of use for roofs with various fire ratings by means of type of building, size and distance from the site boundary. Ratings AA, AB and AC have unrestricted use.


Consideration should be given as to whether the roof needs to have any acoustic properties.

There are a variety of methods of controlling acoustic performance/sound transmission at roof level, that can be included within a Sika-Trocal roof construction, including;

  • The use of mineral fibre roof insulation
  • The addition of heavily filled sound deadening polymeric layers of membrane at deck level.
  • The provision of acoustically attenuated suspended ceilings below the deck.
  • The use of ballasted roof finishes and/or use of heavyweight concrete decks.
  • Combinations of one or more of the above.

Acoustics is an extremely complicated and specialist subject and expert advice should be sought for all applications. It is also advisable to liaise with all parties concerned within the construction process to ascertain that any proposed ‘acoustic solution’ is actually buildable and that suitable materials have been selected.

Roof Upstands

BS 6229:2003 'Flat roofs with continuously supported coverings Code of practice' and BS 8217:2005 'Reinforced bitumen membranes for roofing Code of practice', state that all weatherproofing upstands occurring around the roof area; including doorways, openings, rooflights, smoke vents, plinths etc must have a minimum height of 150mm, measured from the finished surface of the roof, if unwanted water entry into the building is to be avoided.

On exposed membrane roofs the upstand height is measured directly from the membrane surface. Where gutters’ are located alongside an upstand, the finished roof level is measured from the adjacent main area of roof, not the sole of the gutter. In ballasted/green roofs the upstand height is defined as being measured from the upper surface of the finished roof covering i.e stone ballast.

The implications of the requirements of minimum 150mm upstands should be considered at design stage, especially when designing balconies, as it might be necessary to allow for a cranked floor slab at the external walls, so when the insulation, membrane and surfacing of the balcony are installed, it does not compromise the upstand height.

In cases where disabled or wheelchair access is required, this is best achieved by constructing ramps, preferably with a porous or perforated surface, which not only allows rainwater to drain through, but provides a surface with grip.


BS EN 12056 – 3:2003 Gravity drainage systems inside buildings, Roof drainage, layout and calculation, and the Building Regulations Approved document Part H, provide guidance on calculating the amount of precipitation to allow for and the number of outlets and downpipes required to remove the water from the roof.

To assist the drainage engineer with these calculations Sika-Trocal provides rainwater outlet capacities for each of its drainage products (with leafguards) in accordance with BS EN 1253-2:2003 Gullies for buildings Test methods. If using alternative outlets this data should be clarified with the manufacturer and passed to the services engineer calculating the drainage requirements.

When using Sika-Trocal roofing membranes it is not generally necessary to create box gutters where two roof planes meet, nor when a single plane meets an abutment, which provides a significant benefit as box gutters are slow to construct and difficult to incorporate into current building construction without accidentally creating a cold bridge.

Where roofs are drained internally, i.e. when there is a parapet all the way around the roof perimeter, they should incorporate some sort of over flow provision to at least give warning and relief in the event of the normal outlets becoming blocked.

Ponding Water

Normal good practice is to remove rainwater from the main roof surface as rapidly as possible, avoiding ponding which is often unacceptable to building owners. Ponding can also cause a number of undesirable aspects including;

  • Encourages dirt/moss build-up, which can become dangerously slippery
  • Impact on the condensation risk performance; water is an extremely effective vapour control layer
  • Water can freeze in winter and present a safety hazard
  • Standing water forms a reservoir that can allow a greater amount of water to enter the roof than would have been the case in the event of any accidental damage.
  • Standing water in sufficient quantities can also provide suitable breeding areas for insects such as midges.
  • Too much retained water on a roof could lead to deflection of the roof structure, and in some extreme cases, collapse of the roof itself.

Correct falls and drainage provision are therefore recommended.

Roof Decks

Suitable deck’s for use beneath Sika-Trocal roofing systems include profiled metal sheet, plywood, oriented strand board (OSB), timber, woodwool cement slab, insitu, pre-cast and lightweight aerated concrete.

Pre-stressed concrete, in-situ or pre-cast, without a structural topping is not suitable for mechanically fastened applications but can be used with ballasted or adhered systems.

Where pre-cast reinforced concrete units and composite constructions incorporating hollow tiles, pre-cast beams and planks etc are installed, a levelling screed will be essential due to the tolerances and curvature of these items.

Timber based particleboards (chipboard) and boards of compressed straw are not suitable decks for any purpose. If these types of deck are found in a roof refurbishment situation, the only recommendation is total removal.

When constructing warm roofs it is important to avoid incorporating any timber-based products into the build-up above the insulation, in order to prevent them from being adversely affected by condensation. Plywood topped insulation boards and timber based reinforcement to walkways should not be used, for example.

Rough Surfaces

Where in-situ concrete and cementitious screeds are concerned, the finish should generally be the equivalent of a power or wood float. Particular attention also needs to be paid to achieving a level surface at the correct falls; any deficiencies here will only be mirrored in the final surface of the roof. Additionally where pre-cast reinforced concrete units and composite constructions incorporating hollow tiles, pre-cast beams and planks etc are installed, a levelling screed will be essential due to the tolerances and curvature of these items.

Sika-Trocal membranes should not come into direct contact with rough or abrasive surfaces, either above or below the membranes. To prevent contact, a protective layer of Sika-Trocal Type P 300 g/m2 polyester fleece or Sika-Trocal Type A 300g/m2 polypropylene fleece, can usually be installed or in some circumstances the more robust type SBv PVC faced polyester fleece layer can be used.

Typically the surfaces that would require the use of the Type T polyester fleece are: - in-situ concrete: cementitious screeds: aerated concrete panels: brickwork: masonry: plywood and oriented strand boards: timber boarding: wood wool slabs: metal sheets: existing mineralised bitumen felts and asphalt.

Ballasted roofs of all types must always have a protective layer installed on top of the SGmA membrane prior to laying the ballast.

Compatibility of Components

In order to ensure the maximum working life for Sika-Trocal membranes it is necessary to separate them from contact with incompatible materials, and to protect them from rough surfaces.

Most materials manufactured from hydrocarbons are likely to create an adverse reaction if placed in direct contact with either the upper surface or underside of Sika-Trocal membranes. Typically this list includes such products as;

  •  Bitumen (felt, liquids and repair treatments)
  •  asphalt
  •  liquid bitumen
  •  bitumen based roof treatments
  •  liquid applied roofing materials
  •  fibre glass
  •  Unfaced polyurethane
  •  paints of any type
  •  solvents, cooking oils and fats
  •  other single ply membranes
  •  rubber based materials
  • certain mastic sealants

None of the listed products should ever be applied directly to the membranes themselves, however it is possible in the case of roof refurbishment projects to overlay bituminous based products by first installing a separating layer, usually either Sika-Trocal Type A fleece (in the case of Bitumen products use Type T), SBv or a suitable insulation board.

Mechanical Services

In order to avoid problems arising on site, the location of plant on the roof needs to be agreed early in the overall program. This should include the location and means of all the service runs and subsequent roof penetrations.

Roof Mounted Equipment
Where there is a requirement to position items directly onto the surface of an exposed Sika-Trocal membrane, such as free standing handrail systems with rubberised pads, cable and trunking supports or lightweight items of mechanical plant etc, suitable measures must be taken to protect the membrane.

In these situations a patch of Sika-Trocal SBv separation layer, welded to the waterproofing membrane surface, will be required.

In the cases where small items of plant are fixed to a paving slab prior to being positioned the same requirement exists.

There are a number of simple principles that need to be observed to help prevent the service installation becoming a problem.

All penetrations rising vertically through the roof surface, need to be encased in Sika-Trocal Laminated Metal with a permanent cravat fixed to the penetrating item to weatherproof the gap between the two. Alternatively an upstand sleeve of rigid PVC can be installed prior to the cravat.

All services running horizontally along the roof surface that need to then pass through the roof itself, must swan neck upwards first and then pass under a cowl before being turned down through a sleeve. All services running horizontally across the roof that need to enter the building through a wall must rise up before entering the wall and also be shielded with a cowl. These requirements are to provide weathertight entry points and to prevent water running along the underside of the services and entering the building (see Sika-Trocal CAD details).

In all cases it is important to leave sufficient space around the penetration to enable the Sika-Trocal Licensed Contractor to install the waterproofing and seal the penetration.

Plant Location
The most practical and trouble free way to locate items of plant on to a roof is to put some stub columns through the waterproofing with a grillage of steelwork fixed to the top, so as to provide a fixing base for the plant. The grillage also leaves the membrane visible and accessible, thus avoiding the need to de-commission and lift plant should access ever be required.

This avoids all the pitfalls of trying to locate items of plant onto plinths that are notoriously difficult to waterproof successfully. Note that Sika-Trocal membranes are not suitable for task of waterproofing the upper surface of plinths.


Infrequent maintenance access on to an exposed Sika-Trocal membrane surface roof, such as for the regular biannual inspection of rainwater outlets, checking security of flashings etc, can be carried out without any special precautions. It should be noted however, that when wet, Sika-Trocal can be slippery underfoot and that appropriate footwear should be worn.

In situations when there is plant that will need frequent inspections and/or maintenance on the roof i.e. regular foot traffic, then precautionary measures are required to contain the potential effects of that traffic on the thermal insulation and waterproofing.

To provide that protection Sika-Trocal provide two options of purpose made walkway materials. On most ballasted roofs, walkways would normally be created with rows of pavers, as gravel ballast is unsuitable for foot traffic. Note that even with the provision of walkways, exposed membrane roofs are not intended or suitable either as fire escape routes or for public/leisure use.

Sika-Trocal WPB20
A standard walkway can be provided by simply welding 2.0mm thick pyramid embossed Sika-Trocal WPB20 on top of the Sika-Trocal waterproofing a layer.

Where higher resistance to foot traffic is required a mechanically fastened galvanised steel sheet can be installed under the SIka-Trocal roof waterproofing membrane. The walkway need to be planned and installed in advance of the primary waterproofing. A protection layer such as S-Felt Type A must be installed between the steel sheet and the Sika-Trocal membrane.

Note: the steel plate used as reinforcement to the walkway is not vapour permeable, its use should therefore be restricted to no more than 20% of the total roof area.

Sika-Trocal WPB40
A heavier duty walkway can be provided by simply welding 4.0mm thick pyramid embossed Sika-Trocal WPB40 on top of the Sika-Trocal waterproofing a layer.

Where higher resistance to foot traffic is required a mechanically fastened galvanised steel sheet can be installed under the Sika-Trocal roof waterproofing membrane. The walkway need to be planned and installed in advance of the primary waterproofing. A protection layer such as S-Felt Type A must be installed between the steel sheet and the Sika-Trocal membrane.

Note: the steel plate used as reinforcement to the walkway is not vapour permeable, its use should therefore be restricted to no more than 20% of the total roof area.

Lightning Protection

Lightning protection systems are designed to collect a strike and dissipate it safely to earth, with their design covered by the BS EN 62305 Series Protection against lightning. This document contains the required information to design a system appropriate for the building under consideration and its location.

Where a lightning protection system is required, early involvement of all parties is advisable as there is a degree of collaboration required between the Sika-Trocal Licensed Contractor and the specialist that will install the lightning protection system, mainly to ensure that Sika-Trocal lightning protection clip bases are installed in the correct locations.


Guarantees come in all shapes and sizes, often with the detail hidden in the small print. Sika-Trocal product guarantees cover 12, 15, 20 and 25 year durations subject to roofing system and membrane type, each with clear terms and conditions and maintenance requirements.

Sample Guarantees can be downloaded below.



Guarantee Duration


Membrane Thickness


Membrane Thickness


Membrane Thickness


12 years
15 years
20 years
25 years

Adhered12 years
15 years



12 years
15 years



Green Roof12 years
15 years



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Care and Maintenance of Sika-Trocal® Membranes

GuaranteesEnglishpdf0.10 MB

Membrane Guarantee - 12 Years

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Membrane Guarantee - 15 Years

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Membrane Guarantee - 20 Years

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Membrane Guarantee - 25 Years

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