In this section we have answered some of the most frequently asked questions associated with pitched roofs and the Danelaw product range.
If there are any questions that you feel are unanswered we are always happy to help, you can contact us here.
Product prices can vary for several reasons, but generally you get what you pay for. More expensive products are usually manufactured and tested/certified to higher quality standards and can be expected to be easier to use and perform better.
In roofing, the term ‘dry fix’ generally refers to the installation of roof components without the use of mortar either as a fixing agent or filler, and more especially where mortar would have traditionally been used.
Depending upon the material used, some products such as valley troughs and flashings manufactured from GRP carry a service life guarantee of thirty years, with an expectation that they will continue to perform well in excess of this period.
By their very nature, dry fix products can often be relatively quick and simple to replace at the end of their useable life.
The increasing extremes and unpredictability of UK weather in recent years has required changes in various Standards and requirements that reflect this. This has included the requirement for increased mechanical fixing of all products including roof tiles, and mechanical fixing where mortar might previously have been adequate.
Accordingly, a wide range of products to meet this requirement have been introduced into the market with an equally wide range of quality and performance. This new Standard is BS 8612:2018 ‘Dry fixed ridge, hip, and verge systems for slating and tiling. Specification’. First published in early 2018, it sets out to create minimum performance and durability standards for dry fix products used on ridges, hips and verges for slate and tile roofs.
Lead has been in use in roofing for hundreds of years and due to its workability, it is versatile and can be very durable when used in the right quality and thickness, however the health hazards were not recognised until late in the 19th century.
Lead sheet and flashing has been awarded BRE Green Guide ratings of A and A+ when manufactured to British Standard BS EN12588, but this is based on its ease of long-life expectation, recyclability and due to a low melting point and high value, an equally high recycling rate. The high value also makes it a target for thieves.
In roofing applications, rainwater run-off is contaminated by the lead and therefore is unsuitable for many rainwater harvesting & recovery systems.
Patination oil can be used to delay the effect of oxidation that creates the white appearance and unsightly staining that affects roof tiles, slates and brickwork, but is also toxic and flammable.
It should be remembered that lead is toxic and banned in some countries. When using lead, operatives need protection from inhalation of lead dust and fumes, and absorption through the skin. Control of Lead at Work Regulations 2002 Approved Code of Practice and guidance (HSE L132) provides much more information and requires that where an alternative is available, it should be used.
There are 18 species of bats found in the UK all with different characteristics and habitation requirements, and there are many ecologists willing to offer varying opinions on what is or is not bat friendly. We would always recommend seeking advice from the Bat Conservation Trust, however the Trust now no longer endorses specific products for use without lengthy ecological studies.
The modern generation of lightweight high performance spun-bonded roofing underlays do however pose a risk to some bat species where it is possible that their claws will become entangled in the fibres and therefore should not be used in bat habitation spaces.
No. This is something that we have considered, however all universal designs are a compromise and usually considered quite unsightly when installed.
We do offer a wide range of discreet flush fitting tile ventilators to suit most applications.
Yes, a hole that corresponds with the rear spigot or aperture of any vent should be cut in the sarking board when the vent is being used to deliver ventilating air into the roof void.
The underlay should be cut and dressed around the opening to divert any rainwater or condensate around the opening in the roof.
Generally, the airflow is restricted by the length, size and straightness of the ducting being used, and the adaptor that connects the pipework.
We can only quote the pressure resistance created by the baffles and louvres in vent design. The extractor fan should be selected to suit the variables found in each different application, and as advised by the extractor fan manufacturer.
The Danelaw HD 10/10 plain tile ventilator is designed to carry small cuts of the same tile that is being used on the roof, and therefore is not visible on the completed roof except for the small black ventilation slot that must remain exposed.
This depends on the individual product. All of our slate and tile roof vents are designed to suit the minimum pitch of the slates or tiles that they are intended to be used with.
No good quality roof vents leak when installed correctly. If a slate or tile vent is suspected of leaking, the circumstances should be considered.
It is possible for rainwater and condensation to run down the roofing underlay and drip though the opening cut into the underlay. This will usually be apparent on the outside of the vent, or on the underlay. To prevent this, the underlay should be cut and dressed around the opening to divert any rainwater or condensation around the opening in the roof.
If water is draining through a ceiling extractor fan, it is most likely that it is condensation forming in the ducting and draining back to the fan. To minimise this, the ducting should be as short as possible and lagged with insulation where it passes through a cold roof space. If this is not possible, or the problem persists and a condensation trap has not been fitted above the extractor fan, then this should be done.
In very extreme conditions, such as experienced during the ‘Beast from the East’ in 2018, extremely low temperatures combined with fine dry powdery show can create a situation where small amounts may enter through the ventilator. It is not possible to produce a ventilator cost effectively that will allow the free flow of ventilating air and not the very fine snowflakes.
In these situations, in-line or flush fitting ventilators often perform better due to an internal rainwater trap rather than those that rely on a covering hood or cowl.
Ventilation openings can be provided at the eaves over a fascia, through a soffit or at a brick corbel, at low or high level through the roof surface using slate or tile ventilators, or high level using a mechanically fixed dry ridge system.
The actual requirements will depend on the pitch of the roof and the span of the roof.
Warm roofs generally do not require ventilation as there should be an Air & Vapour Control Layer (AVCL) or vapour barrier on the warm side of the insulation to prevent the passage of warm moisture laden air to the colder uninsulated parts of the roof.
Where the insulation follows the line of the rafters, often referred to as a ‘hybrid’ roof, this may or may not require ventilation depending upon the design detail and the roof covering type.
This will depend on the opening area equivalent. At the eaves, it will be either 10,000mm² per metre or 25,000mm² per metre of eaves and 5,000mm² at the ridge or on both sides of the ridge depending upon the situation.
The calculation is: area opening requirement (mm²/m) x length of eaves (or ridge) in metres.
vent airflow area opening (mm²)
We would not recommend this as it is likely that high levels of moisture in the form of vapour would flow under the tiles in the courses above and condense on the underside of the tiles, battens and wall facing material.
Technically yes, however because it is not usually possible to access, dismantle and clean a roof ventilation terminal of any build-up of grease etc, we would not recommend it.
The use of these roofing underlays/membranes and requirements for ventilation depend on other factors, often outside the control of the roofer, so these must be considered.
If the roof covering is not sufficiently ‘air open’, then ventilation openings will need to be provided anyway. It might be argued that air permeable membranes are more effective in allowing the dissipation of moisture, but their use needs to be considered in the tile fixing specification as there will be increased wind loading on the tiles.
If there is any doubt about the permeability of the ceiling construction or air openness of the outer roof covering, then ventilation openings should be provided.
The membranes are not designed for long term UV stability as this is not required in service. The Danelaw range have a generous three-month exposure limit.
Yes, in all situations the horizontal laps should either be restrained by a batten located on the lap, or the two layers should be effectively taped together.
The use of a retraining batten on the underlay laps means the use of an extra batten, or the lap length increasing to coincide with a planned batten position reducing the coverage rate of the underlay.
Using a taped lap system, none of this is necessary and the wind load and zone performance is often improved. Separate lap tap tapes can be more difficult and time consuming to use. They have to be applied carefully to the underlay that must be clean, dry and free from all dust and debris. For this reason, roof underlays with an integral lap tape are recommended for speed, ease of use and reliability.
An airtight, moisture vapour permeable membranes in conjunction with ventilation openings is a method recognised in British Standards and one of proven reliability. Unventilated roofs, including air permeable membrane only use are outside the scope of the Standards and each case needs to be designed for the application. This might change with the publication of a revised BS 5250 later this year.
Yes, clause 7.2.15 allows the use of high level or ridge ventilation only where a vapour permeable or Low Resistance underlay is used in conjunction with an outer roof covering that is classified as ‘air open’. This is usually limited to single lap interlocking tiles.
No, a breathable or more correctly a vapour permeable or Low Resistance underlay generally allows the amount of ventilation to be reduced, but this does depend on other factors, particularly the air-openness of the outer roof covering.
Breathable roofing underlays, more correctly referred to as a vapour permeable or Low Resistance (LR) underlay, is designed for use under slate and tile roofs and can reduce the requirement for roof ventilation in order to prevent interstitial condensation and consequential damage and decay. Depending on the strength and weight of the underlay, there may be limitations on where it can be used in different wind zones. The product data and packaging should identify these limitations.
An underlay is required under slates and tiles on boarded roofs, whether the sarking boards are in sheet or plank form to carry any moisture from condensation or wind driven rain down to the eaves to drain safely away. Vapour permeable underlays are now just as cost effective as non-permeable or High Resistance (HR) types.
In sheet forms of sarking, the vapour permeability is not considered as the roof cannot ‘breathe’ through the boards. In planked applications, providing that there are sufficient and regular gaps between the planks, then the permeability of the underlay is still useful. Leaving these gaps is generally not recommended where slates or tiles are being nailed directly to the sarking boards because of missing the board or splitting the board edge with the nail.
The use of this type underlay allows the level of ventilation provided to be reduced, not omitted. The continuous 10mm equivalent opening at the eaves in conventional cold roof construction can be reduced to a continuous 7mm equivalent opening for a normal ceiling, or down to a 3mm continuous opening equivalent for a well-sealed or ‘continuous’ ceiling. This is not work usually carried out by the roofing contractor.
Yes. The underlays are not designed to resist UV or water saturation over long periods as damage can occur. It is advisable to use an underlay support tray or a strip of BS 747 type 5U bituminous underlay at the eaves.
It is now recognised that the use of a good quality lead replacement product is no less reliable, and both quicker and more cost effective.
Lead has traditionally always been used as a versatile flashing product to form a saddle detail. This is still an option, but with the increasing concerns over health, environment and theft, there are now many lead-free flashing options available – some better than others and some good products but with limitations.
Fast Flash from Hambleside Danelaw is one of the best options here. It is an easy to use, high quality product with fully adhesive properties market leading stretch ability.
The requirement for all unsealed laps in roofing is generally 150mm when measured vertically, and this rule is applied to all Danelaw strip flashing products such as slate and tile valley troughs, Bonding Gutters, Conti-soakers etc.
For a roof pitch below 22.5°, the overlap should generally be 350mm. This can be significantly reduced using a sealant in the lap, but because of the additional time, cost and unknown reliability of this method, it is rarely used.
No, unless the recommended minimum overlap cannot be achieved (see previous answer).
Yes. The design, function and operation of valley trough remains the same. The height of the central upstand should be at least as high as the highest point of the lapping slates or tiles, but for aesthetic reasons, the profile should be chosen to best suit the external roof covering.
No – these additional components are not required with the Danelaw design.
We always recommend that the valley trough is installed with the central upstand pinched together. This minimises the visible opening which can easily be filled with a good quality external grade grey sealant such as ‘Leadmate’.
Generally, valleys are not recommended below a 17.5° rafter pitch, and rarely used in rafter pitches above 60°. GRP valley troughs can accommodate this range, subject to roof area, valley length and pitch differential considerations.
The Danelaw design of dry fix valley trough can accommodate a greater pitch differential and can be used for larger roof areas and longer valley lengths. For further guidance on applications falling outside our standard published criteria, please contact out Technical Department.
Conventional ‘open cut’ tile or mortarless valley troughs are limited to 15°. The Danelaw dry fix valley trough can be used with a roof pitch differential of up to 20°.
Many years ago when these products became popular, the issues with lead were less understood and the wide range of flexible lead replacement products that we now have were not available. While still permissible, it is now considered to be slower and more costly to use lead, so it is rapidly falling out of favour.
In all cases and with all inclined roof valleys, valley troughs and valley lining materials, including membranes should be supported by valley boards or sark boards.
Valley boards may be inset or continuous over the rafter. The width of the board should be sufficient for the valley being used and a minimum of 12mm thick plywood (or 19mm softwood) and supported on bearers of 50mm x 25mm or similar fixed to the rafter sides and set at a depth to finish the valley board flush with the top of the rafters.
Continuous overlaid valley boards may be used and should be a minimum of 6mm thick plywood butt jointed only over supporting rafters. On rafter spacings above 400mm, it is recommended that support noggins of 75mm x 50mm minimum are securely fixed under the outer edge of the valley board between the rafters.
The fascia or barge board may be trimmed to allow the valley trough to pass through without flattening the profile. Alternatively, a lead or lead replacement soaker may be used if required.
It is normally recommended that a small gap of 40 to 50mm is left when using our Conti-Soakers to facilitate cleaning where there is a risk of the accumulation of leaves or moss and lichen, unless used in combination with a step and cover flashing or our individual soakers.
This is a judgement that should be made based on the application. In high wind & rain exposure conditions, particularly with low roof pitches, then this would be recommended. This would also apply to any roof where there is a large, multi-storey abutment wall next to the roof that could create a high level of water run-off.
Apart from the material cost, using a preformed product significantly speeds up installation time and avoids the use of lead where the water may be required for recycling and re-use.
The individual soakers that fit over the top of the tiles are not designed to prevent water from passing below. They cause the rainwater draining below the product to drain out onto the course below.
Both the traditional Danelaw mortared type and the Dry Fix Bonding Gutter® design work to the minimum recommended pitch of the slates or tiles being used with them.
This depends on the situation. If the external roof covering is at the same height on either side of the Dry Fix Bonding Gutter®, then the central upstand should be cut down at an angle to allow the ridge tile to pass over the joint in the roof.
If the external roof covering is higher on one side of the Dry Fix Bonding Gutter®, e.g. tiles on one side, slates on the other or flat tiles on one side and profiled tiles on the other, then the ridge tile cannot be carried over the joint in the roof. In this case the central upstand should be mitre cut on both sides of the roof so that the ridge tiles can butt against it.
In both situations, a saddle should be formed over the joint. This is most easily achieved using a good quality flexible, fully adhesive flashing product such as Fast Flash.
Unsealed overlaps such as this should lap by a minimum of 150mm when measured vertically. This converts to 350mm at this low pitch.
The design of the product when fitted on top of the tile or slate battens will cause this effect. It acts in the same way as a swept verge and encourages the water to run away from the roof joint.
Whether using slates, plain tiles or interlocking tiles, the first course at eaves should be the full tile or larger slate cut.
If this is not desirable at low pitches, then Dry Fix Bonding Gutter® may be installed with the side flange ribs at the same height or lower than the top surface of the roof battens, providing that it is adequately supported.
No, this is not necessary. Where the roof is in the same plane either side of the roof joint, the wind loading is not increased in the same way that it is at the eaves, verge, valleys and ridge.
The slates or tiles should be bedded on either a roof mix mortar or a low shrink, high quality external grade sealant taking care not to use excessive amounts that will spread out and block the side water channels. This is the first line of defence against rainwater and can assist in securing smaller cuts of slate or tile.
The side water channels are designed as a secondary line of defence should water enter the roof covering at this point.
Like all products, ‘there are a range of quality and function available to purchase’. The quality, function, durability and usability of the components can all vary, and some kits may not be truly universal or been fully tested to the recently introduced British Standard for dry fixed ridge, hip and verge products.
Many costs of producing these kits and getting them to market can be similar, therefore small increases in cost can deliver a much better product.
The centre strip is a polypropylene fabric perforated to meet BS 5250 ventilation requirements with a corrugated aluminium edge strip to suit all profile tile requirements. This also contains a wider and thicker butyl adhesive strip than is offered with many other systems.
This is generally not a limitation of the kit, unless deeply profiled tiles are being used at very steep roof pitches.
Because there is no mortar packing to compensate, it is important with all dry fix ridge and hip applications that the ridge or hip tile is chosen for compatibility with the roof pitch and the external roof covering slate or tile. The edge of the ridge or hip tile should sit on the corrugated metal strip.
The system is designed to be used at the minimum pitch that is recommended for the slates and tiles that are being used. In low pitch applications, it may be necessary to build the ridge battens or ridge tree higher to accept the stainless steel screw supplied with the kit.
Yes, in some situations it can however it is dependent on the ability to be able to securely fix the ridge tile. The supporting timber below the ridge tile may need to be increased in height to allow this fixing and an extra piece of flashing material may be required, subject to detail, at the bottom of the vertical side of the tile.
Yes, the jointing gasket is uniquely designed to facilitate this. It requires drilling the capping section of the ridge tile to receive the main fixing screw and snipping off the side of the ‘T’ tabs on the side of the gasket. A detail showing this is available upon request.
Yes, however it will be necessary to trim the jointing gasket length to suit the baby ridge and the roll will require a ‘tuck’ under the tile to reduce the effective and visible width of the Rollflex strip.
The stainless steel ridge batten straps supplied with the kit are the simplest and most convenient way of securing multiple battens at the ridge on trussed rafter roofs, and may also be used on traditionally cut roofs that incorporate ridge boards or ridge trees. These straps are used in the load testing required under the BS 8612 dry fix Standard for ridge fixing to demonstrate compliance.
Straps are generally not required on the hips, however the hip battens and any hip packer battens must be screwed to the roof structure and not nailed.
We also have a range of fixing kits available depending on the application – download the datasheet here
The adjoining profiles are simply overlapped by 100 mm or so, with the upper section inside the lower one. This prevents any water draining out of the joint allowing it to be carried down to the eaves.
Where there is a sprocket or change of angle in the verge, the end of lower section is cut to be perpendicular to the angle of the upper section allowing the upper section to fit inside without distortion. Click for more information on the DV7.
A batten end clip is the term given to a device that is fitted on to the batten ends at the verge to allow nailing or screwing into the end grain of the tile or slate battens.
Screws are sometimes recommended without a batten end clip but can be unreliable over long periods or if the batten ends are wet when the screw is inserted.
This will depend on the application. If it is desirable or necessary to ensure long term secure fastening, then batten end clips should be used as end grain fixing is not reliable or recommended.
Yes, they have all been tested for suitability and compliance. If the dry verge system is to be used or classified as a fixing, then the Danelaw batten end clips (HD IDV/BC) should be used, and they should be of the type and design tested to demonstrate wind zone compliance with the verge system being used under BS 8612.
Hambleside Danelaw have not tested other manufacturers batten end clips with any of the Danelaw dry verge systems, therefore compliance to BS 8612 cannot be claimed where these are used. Not all products available on the market meet the minimum product specifications for these either.
It is the most universal product on the market for single lap interlocking tiles, but may be limited in application depending upon the required batten gauge and is not suitable for some clay products with an interlocking headlap arrangement where the tiles are installed to a fixed gauge.
The batten range is from 260mm to 355mm.
No, this dry verge system is designed to suit single lap interlocking tiles that simulate the appearance of double lap plain tiles.
Currently there are no dry verge systems specifically designed for double lap tile installation.
For more information on the HD IPTDV, click here.
Yes, all our interlocking verge systems have design features specifically to prevent this and discharge water away from the wall complying with the test described in BS 8612. They should be installed with a small gap between the verge units and wall or barge boards.
At each course, only a little bit of water will pass into the verge unit where it will drain away rather than into the next lower unit. The same thing happens where the first unit is engaged with the starter unit which, by its very nature, extends beyond the line of the building or fascia board.
The design of Fast Flash delivers a product with greater stretch-ability that similar products for better dressing and detailing and is manufactured in such a way that the two faces of the product cannot separate.
The fully adhesive backing improves and simplifies some of the more complex applications while reducing the waste from off-cuts.
There is a patent covering the manufacturing process of Fast Flash that delivers superior performance to similar materials.