How To Prevent Water From Getting In A Building

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1 ISSUE 1 Basement conversions Japanese Knotweed Weep holes in rendered cavity walls Level thresholds Canopy Flashings & Weathering Details Lightning protection systems

2 To promote high standards of construction we believe it is important to share the technical expertise we have developed through our surveying, product assessments and claims investigations, we are therefore pleased to bring you the first of our technical newsletters. This newsletter features only a few of the technical articles and resources available from our online technical library. We also have the following materials available free of charge from our website: The last 12 months have seen a dramatic turnaround for the construction industry, in particular the housing sector and reassuringly, many economists predict continued growth over the next 3 years. With these improvements directly reflected in LABC Warranty registrations we welcome this progress, however we are aware that the industry is not without its challenges. As the focus moves to increasing capacity, it is perhaps inevitable that access to materials and skilled labour will become the key constraints to sustained growth. With the cost of traditional materials at a premium, we have seen an increase in the demand and use of alternative construction methods. To ensure we continue to meet demand and adapt to these new techniques we have been working with our partners at LABC to review and approve new products and systems through LABC Registered Details. Whilst many of these products offer benefits, inexperience with the design and installation of these products has led to some issues on site. Technical articles Technical manual Foundation depth calculator If you can t find the information you are looking for, or have a technical query then please contact us at technical.services@labcwarranty.co.uk or tweet and my team will do their best to help. The next few years are an exciting time for our industry and we look forward to working with you. Regards, Richard Smith richard smith Head of Technical Services Our Foundation Depth calculator enables users to easily determine the exact foundation depth required even when there are multiple trees on-site. The calculator can be accessed from our website Our technical manual, which is endorsed by RIBA and CIAT is available to view and download free of charge from our website. The manual is divided into easy to read chapters each including a functional requirement and guidance on how to meet this requirement. Visit for your free copy of our technical manual. keep up to date with the latest news... follow us on or find us on LINKEDIN

3 The need for a credible basement waterproofing specialist Converting damp basements and building parts of new dwellings below ground has become more popular with self-builders and developers. More living space can be created within the limits of the building footprint without the need to build too high. However, if these are not designed or installed properly this can lead to an increased risk of water ingress. It is therefore essential that the risk is managed accordingly by engaging the appropriate specialists. When? LABC Warranty requires the services of a waterproofing specialist to be engaged for the construction of basements, floors and other structures that are constructed partially or entirely below ground where the passage of moisture into the building must be prevented. A typical example of a construction partially below ground would be where any floor on a sloping site becomes below ground level on 1 or more elevations. Why? BS8102:2009 (Protection of below ground structures against water from the ground) states that: A waterproofing specialist should be included as part of the design team so that an integrated waterproofing solution is created. The Technical Manual Section (Substructure Design responsibility) States that: The basement design should be completed by a suitably qualified Waterproofing Design Specialist. The waterproofing specialist must take responsibility for the design liability of the waterproofing and have appropriate professional indemnity cover which covers their business activities. They must also have an understanding of hydrology and soil mechanics and hold a relevant professional qualification (i.e. Certificated Surveyor in Structural Waterproofing (CSSW) or similar. Who? A credible waterproofing specialist would be someone who has gained the qualification: Certificated Surveyor in Structural Waterproofing (CSSW) or equivalent. Where? Individuals who have attained the above qualification, hold the required Professional Indemnity Insurance and have met the requirements of the Property Care Association (PCA) can be found on the property care website

4 We can be thankful to the Victorians for many things importing Japanese Knotweed is not one of these. Fallopia Japonica or Japanese Knotweed was first introduced to Britain by the Victorians as an ornamental plant. Since then the plant has become the UK s most aggressive, destructive and intrusive plant. Why is Japanese Knotweed such a menace? The plant is extremely fast growing; in fact it can grow 75mm a day reaching heights of 3m tall. Whilst this growth can be a nuisance it is below the surface that Knotweed causes problems, its rhizomes (root system) can extend up to 3m deep and 7m out from the parent plant. These extensive roots can grow through and cause damage to paved and tarmac surfaces and also cause damage to drainage. Whilst not known for growing through concrete, it can grow through cracks and gaps in and around concrete finishes/ floors both internally and externally of a property. It has even been found to grow within external wall cavities and within sub-floor voids. These destructive qualities are intensified by the fact the plant can stay dormant for twenty years and be spread easily by rhizomes and cut stems or crowns. In addition if not properly treated there is an extremely high likelihood of regrowth. So how do you deal with Japanese Knotweed? In response to the problems presented by Japanese Knotweed the Environment Agency produced a Code of Practice in 2006 which has since been amended in Since the publication of the superseded 2006 code, various soil screening and sieving methods have become a popular method for rhizome removal. Where conditions are appropriate for this method, screening can provide an effective means of rhizome removal. Screened soil must still be regarded as potentially containing viable Knotweed rhizome and must not be reused off-site or sold for re-use. If soil is taken off-site, it should be disposed of at an approved landfill as Japanese Knotweed is classed as a controlled waste. There are various control methods available from companies specialising in Japanese Knotweed management on development sites and some offer insurance backed guarantees for its eradication. Therefore, careful consideration should be given to products and methods that claim to quickly eradicate Japanese knotweed and the guidance for treatment of Knotweed recommended in the Environment Agency s code of practice should be followed. There is no cover under the contamination cover of the LABC Warranty policy for Japanese Knotweed as it is not a notifiable contaminant. Managing Japanese Knotweed is the responsibility of the owner/occupier of a site. The owner/occupier of the site has a legal obligation not to allow it to spread.

5 To summarise: If Japanese Knotweed is found on the site, the Developer should ensure: The area is cordoned off where the Knotweed is situated in order to prevent machinery/foot traffic from accidentally spreading the material across the site. The builder/developer should seek specialist guidance, referring to the Environment Agency s code of practice for dealing with Japanese Knotweed on development sites. The Environment Agencies guide to Managing Japanese Knotweed on Development sites (Amended July 2013). For a copy of the Knotweed Code of Practice please visit the Environment Agency website: Managing Japanese knotweed on development sites. That a copy of the Japanese Knotweed Management plan should be obtained and followed. If herbicide treatment is to be carried out it is essential the contractor is a competent and qualified person and must have appropriate National Proficiency Test Council (NPTC) certification. That a copy of any insurance backed treatment offered is obtained.

6 Are Weep Holes Necessary to Drain Cavity Trays from Rendered Cavity Walls? Render on Traditional Masonry Construction Modern polymeric and traditional sand and cement renders are still very popular finishes to external envelopes of new individual dwellings and apartments. This is often in the form of rendered sections of a dwelling, or the entire external envelope being completely rendered. Rendered finishes have the advantage of allowing more cost effective block work, or alternative material, to be used for the external leaf of a traditional masonry constructed house. Or as the cladding element for timber frame construction either on the masonry external leaf or on a lathing system fixed directly to a structural timber frame. Render may also be specified due to planning conditions which stipulate the use of render finishes in the context of matching existing surrounding structures or providing a contrast to face brickwork on a large development. BS 5262 indicates that the resistance to rain penetration for cavity external walls can be enhanced by the addition of render to the external leaf even though cementitious and polymeric render are porous to a greater or lesser degree depending on the specification. The render will absorb some water falling directly on it and retain this until conditions change when the water will dissipate by natural evaporation. However, in exposed areas in times of persistent wind driven rain, some water may penetrate the rendered finish to the substrate. The denser the render, the more water it will retain and the greater hindrance to evaporation of the water that may have penetrated or condensed within the background wall structure. BS 5262 also indicates that the rougher the surface of the render the more effective it is at breaking up the flow of water down the surface and avoid concentrations of water at any one point. It is worth noting that, although the manufacturers of Polymeric render generally claim that their products are a significant improvement with resisting water penetration compared to traditional sand cement render, they do not claim that their products are completely waterproof and will resist all penetration from windblown rain. Completely impervious render may actually be a hindrance to the external leaf s ability to dissipate moisture from interstitial condensation generated from inside the structure. This is why polymeric render manufacturers inevitably claim that their product will allow the substrate to breathe effectively. The combination of full fill insulation and rendering can also inhibit the drying out of any moisture that enters the outer leaf of masonry. This can potentially increase the risk of frost action and sulphate attack on the jointing and rendering mortars. Therefore, it is not recommended for full fill insulation to be used on a rendered external masonry leaf. The durability and effectiveness of rendering is affected by a combination rain, frost, sun and wind. These factors are closely linked to the degree of exposure both locally and within the broader exposure zone category. These factors should always be taken into account when designing and specifying render. Table 10 of BS will be of assistance in assessing suitable render mixes and the number of render coats for the specific areas. Even though the risk of water penetration is reduced when the external leaf of a cavity external wall has been rendered, both BS 5262 and BS 5628 accept that a degree of penetration may occur and do not relax the recommendation to install cavity trays with stop ends over openings and lower level abutments where the external wall becomes the internal wall. However, due to the decreased risk of water penetration the British Standards states that: Weep holes need not be provided if walls have a rendered external finish. It is assumed that this relaxation is based on the opinion that the small amount of water that may penetrate the outer leaf and collect in the cavity tray will dissipate by natural ventilation and not penetrate the inner leaf due to the up stand on the cavity tray.

7 Render and Timber Frame Situations It could be argued that in a timber frame situation the condensation from the water that may collect in the tray will have a detrimental effect of the inner timber structure. This could possibly be alleviated by the provision of additional ventilation in the form of weep holes to the external rendered leaf. The TRADA Timber Frame Construction manual calls for cavity trays, stop ends and weep holes in every situation and does not relax the need for weep hole installation in rendered block external cladding. TRADA prefer to use the term full open perpends as they do not accept the smaller preformed pencil type weep hole as meeting the ventilation requirements for timber frames. The TRADA requirement for open perpendicular joints (perps) with rendered finishes, indicates that the requirement was as much for enhancing ventilation to dissipate moisture and prevent condensation, as it was for discharging water that may have penetrated the render and collected in the cavity tray. Conclusion In situations where the external leaf of a traditional cavity external wall is rendered using both traditional and modern polyrender it is important to ensure that the render has been designed in light of the exposure of the immediate locality and the national table of exposure zones. For example: three coats of sand and cement are required in very severe exposure zones. The recommendation is for cavity trays and stop ends to be installed. However, weep holes can be omitted providing there is no un-rendered face brickwork above the rendered panels including single courses of decorative header or soldier courses above the window head. The addition of weep holes should not be considered acceptable in order to compensate for a poor or incorrect render specification for the local and national exposure zones. In Timber Frame situations where the external cladding is rendered block work/brickwork using both traditional sand/cement and polyrender, then a cavity tray with stop ends and weep holes (open perp joints) are required. The open perp joints should not be the preformed pencil type components but must be the full depth of the perps and installed at a minimum of 900 centres or at least 2 per opening. This conclusion is based on the recommendations of the Technical Department and the Timber Frame Construction manual of The Timber Research and Development Association (TRADA). Action Required: Where correctly designed and specified render is used on the external leaf of traditional masonry cavity walls then cavity trays with stop end are required. Weep holes can be omitted. Where the external masonry cladding is rendered for Timber Frame construction then cavity trays with stop ends and full perp weep holes are required.

8 The objective of access requirements in building regulations, is to ensure that the threshold of an entrance to a dwelling should allow reasonable access for wheelchairs users and ambulant people to and from the building. This guide provides advice to LABC Warranty clients on the main risks associated with level thresholds which include water entering the building and thermal bridging. Statutory Requirements In England and Wales, the statutory requirements are set out in the Building Regulations 2010 Part M. Requirement M1 states that Reasonable provision shall be made for people to a) gain access to; and b) use the building and its facilities. Approved Document M sets out provisions that satisfy the above requirement: Clause 6.19 states that Where the approach to the entrance consists of a level or ramped approach, an accessible threshold at the entrance should be provided. In addition to the above, the threshold design must also satisfy the provisions of, or be compatible with, other aspects of the Building Regulations, particularly in respect of: minimising the risk of water ingress or damp entering the building (Part C) the provision of adequate sub-floor ventilation (Part C) requirements for the provision of soil/gas membranes thermal insulation requirements to ensure there is no thermal bridging the provision of durable solutions, taking account of workmanship requirements

9 Accessible or level thresholds consist of three principal elements: 1. The external landing and its drainage Objective: The external landing should be sufficiently large and level for ambulant disabled people and wheelchair users to be able to approach and if necessary turn to face the door. It should be designed to avoid standing water and limit the amount of surface water reaching the threshold. The size of the landing should follow the guidance in Approved documents M. External landings on a ramped approach should be laid to fall between 1:40 and 1:60 to provide surface water drainage, falling away from the doorway in a single direction. There should be no cross falls. A drainage channel should be provided between the landing and threshold where surface water is likely to be blown towards the threshold. The channel should discharge to a drainage system or permeable field drain. In extreme conditions, further drainage should be provided at the junction of the ramp and the landing, in order to avoid ponding and to keep storm water well away from the threshold. The drainage channel can be constructed either as a site formed slot above a discharge channel, or by a proprietary drainage channel. In either case the drainage slots should be no more than 18mm wide to maximise drainage and to reduce the risk of wheelchair wheels and walking sticks becoming trapped. In addition to specific guidance for the threshold design, consideration should be given to additional measures which would facilitate access to the building, e.g. A porch roof will provide considerable protection to ambulant disabled and wheel chair users whilst they locate keys, codes etc., at the same time as helping to reduce the risk of direct water entry. Additional field drainage to adjoining land may be required on low lying or steeply sloped sites, to prevent the drainage channels from flooding.

10 2. The threshold sill and its intersection with the external landing 3. The intersection between the door threshold and the internal floor finish Objective: The threshold profile should allow access for ambulant disabled people and wheelchair users while minimising the risk of surface water entering the dwelling. Objective: The transition between the lower threshold unit and the internal floor level should accommodate accessible transfer for ambulant disabled people and wheelchair users, while permitting occupants the choice of varying the type and thickness of floor coverings. The internal floor adjacent to the threshold should be level or gradually sloped by means of an internal transition unit in order to make it easier to get indoors. The threshold sill to external landing interface requires a difficult compromise to be made between achieving an almost level threshold whilst maintaining sufficient weatherproofing to reduce the risk of moisture ingress. Where a drainage channel is located in front of the threshold sill, it is preferable for the surface of the landing / drainage channel to be level with the door sill. However, where this is impractical due to exposure to wind driven rain, then the landing can be up to 10mm below the level of the threshold sill. In this case, the leading edge of the threshold sill should be rounded or chamfered to assist the transition for wheelchair users. Threshold sills should have between a maximum slope of 15 degrees and a minimum slope of 7 degrees to discourage water ingress and to facilitate water run-off. The upper leading edge of the door threshold unit should be no higher than 15mm; if it is more than 15mm, the exposed edge should be rounded or chamfered. Due to the risk of moisture ingress and the subsequent deterioration of timber components, a drained and ventilated void should be created directly in front of any timber sills or associated components. In order to substantially reduce the thermal bridging risk at the threshold level, the floor insulation should be taken around concrete slabs and timber floors and is continuous with any wall insulation. To achieve this, insulate the edge of the slab; set door frame back so that it laps with the edge insulation; use an insulated door. In addition to the level threshold, there should be sufficient space provision. The width of an entrance should be at least 800mm, but ideally it should be 900mm. There is no requirement for a graded platform or internal transition unit where the expected finished floor level is designed to be less than 15mm below the level of the door threshold unit. This clearance should be reduced to 10mm where the floor covering specified is an uncompressed soft pile carpet. Where a graded transition is specified this should have a maximum slope of 15 degrees and have a slip resistant surface. There should be sufficient space within the internal lobby area to allow full turning for wheelchair users and unobstructed entry for other disabled users. Further guidance: Level thresholds are solely for their intended purpose. The principals adopted here should not be used to justify the positioning of external ground levels flush with internal ground floors. To comply with the Warranty Technical Manual and Part C of the UK Building Regulations; damp proof courses must be positioned at least 150mm above external ground level. The sole plates of timber framed houses must be at least 150mm above external ground level and be served by a drained and ventilated cavity. It is also recommended that raised Cavity trays or damp proof courses should be installed in external cavity walls in the vicinity of ramps. References: Accessible Thresholds in New Housing. Guidance for House builders and Designers. Produced by the DETR and published by The Stationery Office. BRE Good Building Guide 47: Level External Thresholds: Reducing moisture penetration and thermal bridging. Building Regulations Approved Documents M. Technical Manual Section : Example construction details for level thresholds to dwellings.

11 Unless the canopies have a third party product approval that indicates that only a silicone sealant is required, then for warranty purposes: Should flashings and cavity trays be provided to canopy roofs? Chapter of the Technical Manual offers guidance on expected weathering details to roof abutments. Site Formed Canopies Where a site formed canopy is constructed to provide some level of weather protection above a non-enclosed external door; e.g. a front entrance door canopy, a suitable lead or lead alternative flashing is to be provided at the abutment of canopy roof and the external wall. This is to ensure that the construction materials are protected from moisture and avoid premature deterioration due to wetting. A lead or alternative lead type cover flashing is required. As with site formed canopies, the flashing is not required to link to a cavity tray, however a cavity tray is still expected over the external doorway. Site Formed & Prefabricated Canopies over Habitable Accommodation Where either of the above is to be provided over habitable accommodation; e.g. a walk in bay construction or enclosed porches and conservatories: A flashing is to be provided which must be linked to a cavity tray at all times in accordance with the Technical Manual. The flashing in this situation is not required to link to a cavity tray; however a cavity tray is still expected to be installed over the external door opening. Prefabricated (GRP) Canopies Where a prefabricated (GRP) canopy is to be used above a non-enclosed external door, some manufacturers indicate that the canopy only needs to be sealed back to the external wall with silicon sealant to reduce rainwater ingress getting behind the unit. However, the structural fixings that secure the canopy to the wall may be exposed and certain elements of the construction may be exposed against the wall face and vulnerable to moisture within the brickwork, stonework / recessed joints. Throughout the year we host a number of technical seminars. At these seminars we provide updates on Building Regulations, new products and how to avoid common building defects. For details of our next event near you please check our website or follow us on For all sites registered with LABC Warranty we can provide a comprehensive range of free marketing materials. To request any materials visit our website or marketing@labcwarranty.co.uk Want to find out our latest updates? Follow us on or find us on LinkedIn.

12 A Lightning Protection System (LPS) is designed to protect a structure or building and contents from damage caused by the intensely high voltage currents of a lightning strike. The highly conductive lightning rods of an LPS are normally made of copper or aluminium creating a low resistance path to ground, drawing any high voltage currents away from the structure of the building before any serious damage or harm can be done. But what is expected of the Developer / Designer when installing an LPS? Chapter 7 Subsection of the LABC Warranty Technical Manual highlights factors to be considered if there is a proposal to incorporate an LPS in relation to installation of continuous membrane roofing systems. Where a LPS is installed in these circumstances, the Developer / Designer will be expected, to ensure that the installation adheres to the following requirements: Design in compliance with BS EN 62305* A Risk Assessment, based on BS EN undertaken by a qualified LPS engineer who is part of the building design project team. This is to ensure that a correctly specified system is installed about the continuous membrane roofing system. Evidence of the above should be sought by the Risk Management Surveyor when collecting details of the roof covering specifications. The guidance is included so that consideration to the effective water tightness, durability and structural (if appropriate) performance of the water proof roof membrane is assessed and that where a Lightning Protection installation is proposed; the membrane installation is not compromised. Are Lightning Protection Systems (LPS) covered under the Warranty? The performance of LPS is not governed by the technical manual, however a valid warranty claim could exist if an incorrectly installed LPS directly leads to failure of the continuous membrane roofing system. * BS EN Protection against lightning (This supersedes the requirements of BS 6651 which was withdrawn in August 2008 as part of the EU harmonisation of National Standards). T: E: info@labcwarranty.co.uk 2 Shore Lines Building, Shore Road, Birkenhead, Wirral, CH41 1AU LABC Warranty, is a brand of MD Insurance Services Ltd. MD Insurance Services is authorised and regulated by the Financial Conduct Authority.