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Thatching Advisory Services
Thatching Advisory Services

The Complete Thatch Guide

Thatching handbook for owners, thatchers and architects

A thatched roof, laid in the traditional way, will last up to 50 years. Although largely maintenance free it is always advisable to review it annually. As well as the insulation and aesthetic benefits, a thatched property retains its value better than conventional buildings. The popularity of thatch is reflected in the increasing number of new builds.

Today 3 different materials are widely used:

Long straw

Combed wheat reed

Water reed

The type of reed used will determine the style of finish. Your thatcher will advise accordingly. In essence, Long Straw retains a `shaggy` look whilst Combed reed is widely used in the south and west of England. Water reed, traditionally costs more but is regarded as a superior product.

Our comprehensive thatch guide provides valuable information on every aspect of thatching.

The Complete Thatch Guide

Thatching handbook for owners, thatchers, and architects

Contents

General Maintenance
Buying a Thatched Property
Chimneys, Flues & Fires
Materials
General Information
Roof Construction Detail
Thatch New Build & Extensions
Fire Retardants & Barriers
Thatch Fire Protection Systems
Questions & Answers

General Maintenance

It is wise to take steps to guard against the problems that winter can cause. Insurance can protect you against many things but it is not a maintenance contract.

Check that roofs and chimneys are sound and that drain gratings are clear so that water can run away. Pipes and tanks should be insulated, but leave the space beneath your water tank free so that warm air can reach it.

Central heating systems should be regularly checked by an expert. Electrical wiring should be tested every five years many fires have been started by faulty electrical systems.

Always, if you are employing the services of an electrician, plumber, Thatcher or any building contractor make sure they have their own Public Liability Policy which should cover any damage caused by possible negligence your own insurance policy will not cover you so it is important to ask.

If you have an open fire, make sure your chimney is swept regularly and at least twice a year. Having your chimney lined is a sensible precaution and a requirement of many insurance companies.

If you are leaving your home unoccupied for a few days or more, consideration should be given to draining the hot and cold water system. If you have any doubts contact a local plumber.

Buying a Thatched Property

All too often prospective owners of thatched houses are persuaded by family and friends that owning a thatched property is expensive and requires constant attention. THIS IS NOT THE CASE.

Thatching Advisory Services are able to offer a range of services that will indicate, before you exchange contracts, the immediate costs, future planning and of course the benefits of owning a property that is part of our National Heritage.

SURVEY OF THE THATCH ONLY - Carried out by thatch surveyors employed by Thatching Advisory Services which will confirm exactly in writing the condition of the thatch, what precautions can be taken to extend the life expectancy of the roof and indicate the current price of the works to be undertaken.

NO MATTER AT WHAT STAGE YOU ARE IN THE PURCHASE OF A THATCHED PROPERTY TAS IS ABLE TO OFFER YOU INDEPENDENT ADVICE.

Chimneys, Flues & Fires

There are 60,000 thatched properties in the UK, of which 50-80 suffer a serious fire each year, most of which are completely destroyed. The cost to the Fire Brigade is £1.3million per annum.

Thatch fire insurance losses totals £18million per annum, 90% of the homes struck by thatch fire have a combination of a wood burning stove either a flexible chimney liner or no liner at all.

If you are in any doubt with regard to the condition or suitability of your chimney, flue or fire, please contact a HETAS registered installation and maintenance engineer.

Five tips to help prevent chimney fires

Please take note, the Fire & Rescue Service recommends the following advice:

Chimneys should be lined and swept properly by a professional
The chimney should be swept if you haven`t used it for some time
Extinguish your fire before going to bed or leaving the house
Never use flammable liquids, burn paper or rubbish or overload with fuel
Always burn well seasoned or kiln dried wood

Chimneys

The chimney, including the pot, should terminate at least 1.8m above the height of the ridge. Due to the risk of condensation forming as hot gases cool, the chimney pots should be limited to a maximum height of 600mm.

Due to many of thatched buildings being listed a `common sense` approach has to be taken into account when making this decision, this is because some of the restrictions by Local Authorities may not permit alterations of chimneys to such a large extent. In these cases please take the advice of a specialist engineer that has experience with Thatched properties. The most well known approval body for heating engineers is HETAS.

Advice from the Fire & Rescue Service

Without proper maintenance, any flue from a fire or stove can cause a dangerous build up of carbon monoxide gas. A carbon monoxide detector will help protect you from this risk. Make sure you are not at risk from carbon monoxide poisoning by having appliances installed and serviced by a competent engineer. Never block air bricks, vents or flues.

Landlords, letting agents, and tenants

Lanlords are legally responsible for:

Maintaining solid fuel heating systems, chimneys and appliances (Office of Fair Trading 2005) Providing literature for the relevant appliance

Tenants are responsible for:

Using a solid fuel heating system and using only appropriate fuels for the fire/appliance Informing the landlord/agent as and when defects arise with the fire & appliance

Materials

There are three commonly used thatching materials:

Water Reed
Long  Straw
Combed Wheat Reed 
Others include Flax, Heather, Broom, Sods, Marram Grass etc

Water Reed (Phragmites Australis) is the most durable thatching material.

Long Straw is a winter wheat straw that has not been combed (its name refers to a style of thatching rather than a material achieved by any singular process although generally for the last 90 years long straw thatching has used the processed straw from the threshing drum). It has the shortest life expectancy of the three commonly used materials.

Combed Wheat Reed is winter wheat straw which has had the leaf removed and is laid in a similar way to water reed. With modern farming methods tall strong straw has become less readily available.

Life expectancies

Water reed, which is the most durable thatch, can last up to 50 years. Maintenance will include re-ridging every 10 to 15 years.

Combed wheat reed can have a life expectancy of 25 to 35 years. Long straw will last from 15 to 25 years. Both these materials will require re-ridging at 10 to 15 year intervals.

These life expectancy figures can drop noticeably the further west the thatched property is situated. This appears to be due to climatic conditions.  The warm, high humidity, clean air conditions experienced in the West Country are ideal for the microbes that begin the decomposition process.

Diagram 1: The pitch of the roof will relate directly to the pitch of the thatch and equally the thickness of the thatch will influence the pitch of the thatch. Thus, an l8" (457mm) coat of thatch will lie at a much slacker pitch than a l2" (300mm) coat and therefore a thicker coat will wear more quickly. The thinner the thatch, the steeper the pitch, however there must be adequate thickness of thatch over the fixings, thus a 4" (100mm) coat of thatch is steeper than a l2" (300mm) coat, but because the exposed stem length is longer (and therefore wears more quickly) and because there will be very little thatch over the fixings the thatch will not last as long as a l2" (300mm) coat.

An optimum thickness for maximum longevity would be between 9" (228mm) and l5" (381mm) for water reed and 9" (228mm) and l2" (300mm) for combed wheat reed and long straw. Therefore, the point to remember is that there are an almost infinite number of specifications depending on pitch of roof and length of the thatching material.

Thatch Pitch Roof

General Information

Water Reed Specification for New Build Thatch

Thatching is generally recognised as a craft and as such it is almost impossible to give a single specification for a re-thatch. However in the field of new build thatching the majority of work is undertaken using water reed and therefore a specification is possible.

The Water Reed should be laid to a thickness of approximately 12" (300mm) The ridge most commonly used is a block cut, patterned and saddled type ridge Supply and fix, ¾ inch (19mm), 22 gauge galvanised wire mesh to the ridge only Chimney flashings are usually lead although cement flashings are perfectly acceptable.

Fixings (For All Types of Roof)

Hazel or steel runners can be applied and secured by steel thatching nails, fixing wires, twine or spars. The method will depend on the roof in question and the material used, however water reed on a new roof is usually fixed with thatching nails or stainless steel wires attached to rust-proof screws.

Roof Pitch

It is advisable to set the pitch at about 50 degrees. This is not due to the weight of the material which is in fact not over heavy, but rather to facilitate efficient drainage. Dormer roofs and eaves window-roofs should be at least at a 45 degree pitch, if possible.

Insulation of a Thatched Roof

Thatch is inherently a good thermal insulator with a Thermal Resistance value of 3.333 and 4.286m²K/W for reed and straw respectively. It is worth noting that generally thatch is considered a `warm roof construction` and consequently does not require the ventilation of a tiled roof.

U Values

The U value of a roof refers to its thermal conductivity, i.e. how quickly heat is lost from it, and is measured in watts per m² per Kelvin. Typically the U value for a roof construction with 300mm - 350mm of water reed would be in the region of 0.22W/(m²K). This is based on a fire barrier being fitted and a non-vented space behind  the thatch.

The current building regulations state that the U value required from a new roof should be 0.2W/(m²K). Therefore there has to be some sort of insulation even under a thatched roof.

The calculations for U value are relatively complicated and therefore should be left to the architects. However it is definitely worth telling any interested parties that Thatchbatts and either Thatch Firewall or Thatch Fireboard underneath the thatch will give a U value in the region of 0.16W/(m²K).

Weight of Thatch

When calculating for a roof construction a weight of 34 kg/rn² should be assumed.

Roof Construction Detail

Smaller Span Roofs

Small Span Thatch Roof
Medium Span Thatch Roof

For a 16`6" (5.03m) span roof with a clear span a simple form of truss is required as indicated in diagram 3. The trusses should be set at between six to eight feet apart. Rafters, ties, collars and diagonals should be 4" x 2" (100 x 50mm). The diagonal members should be notched so that the purlins will be held at rght angles to the rafter.

The size of purlin is dictated by the distance between trusses and will vary from 5" x 2" (130 x 50mm) to 7" x 2" (180 x 50mm). Binders will vary from 5" x 2" (130 x 50mm) to 6" x 2" (150 x 50mm). All ceiling joists should be spiked to the binder to prevent sagging. Binders can be omitted if there is a convenient structural wall at or near the centre of the span. Up to an 11`0" (3.35m) span the construction can be of a simple collar type with the collar set in the bottom third of the roof. 4" x 2" (100 x 50mm) ceiling joists can act as collars if conveniently positioned.

All rafters must be bird-mouthed over the wall plates. 4" x 2" (100 x 50mm) rafters are normally spaced at 400mm centres, to ensure an adequate and secure fixing for the thatch. It is not recommended to exceed this distance.

Large Span Thatch Roof

Valley

A 7" x 1½" (180 x 38mm) layer board is placed over the rafters of the main roof. The jack-rafters are attached to this and the ridge can be set between the twin rafter members of the truss. See diagram 5.

Thatch Roof Rafters

Medium Span Roofs

The truss illustrated in diagram 4 is suitable for a 24`0" (7.3m) span. Ridge collars and diagonals and bottom ties should be 4" x 2" (100 x 50mm), hangers are 3" x 1" (76 x 25mm). With a span of this size the ceiling joists require support in three positions if the joists are to be kept at 4" x 2" (100 x 50mm). This truss provides for three binders which can be omitted whenever a convenient structural support is available.

Valley

With large and equal spans, a conventional 7" x 1¼" (180 x 32mm) valley rafter should be used. Jack-rafters should then coincide as far as possible. Where rafter spacing`s of the two roofs are different, a layer board should be employed.

Ridge

Assuming that the rafters are 4"x 2" (100 x 50mm) at a pitch of 50º a ridge board of 9" x 1¼" (229 x 32mm) should be provided. The top batten should be 2" (50mm) from the ridge and the up stand of the ridge board should also be 2" (50mm). Thereafter, battens should be spaced at 9" (228mm) centers.

Detail at Eaves

For construction see diagrams 6, 7 & 8.

Thatch Roof Constructions Thatch Roof Eaves

Close Boarded Raking Eave is constructed with a 15" (380mm) fascia held by 2" x 1½" (50 x 38mm) bearers and hangers. The hangers are spiked to the rafters, see diagram 6.

Vertical Fascia & Close Boarded Soffit. The fascia board should be 1¼" x 12" (32 x 300mm) and grooved to take ¾" (19mm) tongued and grooved boarded soffit. The soffit bearers should be 2" x 1½" (50 x 38mm) as per diagram 7 and are fixed to 2 x 1½" (50 x 38mm) plates which are plugged to the wall.

Open Eaves Type. See diagram 8. This roof is finished with a 3" x 3" (76 x 76mm) tilting fillet. The overhang is in filled with eaves boards and battens and then rendered underneath to prevent vermin getting into the thatch. Unlike diagrams 6 & 7 the top of the cavity is in filled with expanded metal and mortar.

Thatch Roof Open Eaves

Eaves Windows

These are often necessary due to the steep pitch of the roof and the deep over hang of the eaves. The windows can be held in a brick spandrel above the normal wall plate. The wall plate is continued through the spandrel to provide support for the untrimmed rafters. These are further secured by 3" x 1½" (76 x 38mm) spacers.

The top of the wall cavity is closed with expanded metal and cement and capped with a 3" x 2" (76 x 50mm) wall plate. The ceiling joists above the eaves window can be extended beyond the rafters to offer an extra securing point or the 3" x 2" (76 x 50mm) rafters forming the roof over the window opening. These rafters have been laid in a staggered formation to provide a curved seating for the thatch. The eaves treatment illustrated (diagram 9) joins onto a standard eaves type at the bottom of the spandrel.

Thatch Roof Eaves Windows

Verges

See diagrams 10 & 11. In both cases illustrated the barge - board should up stand the batten by 1½" (38mm). The top of the cavity may be closed by slates bedded in mortar with the batten passing over this.

N.B. Built -in purlins should not project beyond the wall into the verge. Also the last rafter is set approximately 1" from the inside edge of the brickwork.

Thatch Roof Eaves Verges Thatch Roof Eaves Rafters

Velux Windows

See diagrams 12, 13 & 14 Velux window is installed on top of the thatch by  constructing a box, the height of which above the rafters is determined by the thickness of thatch (a new single thickness of combed wheat reed or water reed is usually 12" (300mm).

At the rear of the box, sloping lay boards overlain with lead can be placed to facilitate the run-off of water onto the side and front flashings which are on the surface of the thatch.

Thatch Roof Velux Thatch Roof Velux Sides Thatc Roof Velux top

Dormer Windows

See diagram 15. The construction of the dormer roof is similar to that of the eaves roof except in our examples 3" x 2" (76 x 50mm) ceiling joists have been incorporated to make a flat ceiling above the window aperture. At the foot of the dormer window the rafters are trimmed with an 8" x 2" (203 x 50mm) up stand. The bottom of the sill should be a minimum of 1` 6" (457mm) from the structural roof level. As with verge details a fascia is required with an up stand of 1½" (38mm).

It is important that the pitch should be at least 45º and on no account less than 40º.

Thatch Roof Dormer

Chimney Flashing

See diagram 16. The tilting fillet should be 2` 6" (762mm) from the chimney (as shown) and a minimum of 12" (300mm) above the bed of the gutter. This fillet should be 2" x 3" (50 x 76mm) and the gutter bed and up stand should be 1" tongued and grooved boarding. The substructure consists of 3" x 2" (76 x 50mm) bearers, struts and plates. The rafters below and above the chimney should be trimmed into either 4" x 2" (100 x 50mm) or 4" x 3" (100 x 76mm) trimmers dependant upon load exerted on these trimmers.

Thatch roof Chimney Flashing

N.B. Care should be taken that the gutter discharges above the level of the thatch and that the pargetting to the lower portion of the chimney is not lower than the thatch.

Dorset Model

Technical guide to planning requirements for thatched properties.

Thatch is enjoying a resurgence. Architects, builders and owners increasingly acknowledge the advantage of thatch insulation and aesthetic qualities. Recognising this increasing popularity the eight building control authorities throughout the county of Dorset reviewed current building controls for a thatched roof.

The Dorset Technical Committee carried out extensive research with the Fire authorities and all the Thatching services. The Dorset Technical Committee produced a Design Guide for thatchers and architects known as the Dorset Model. The Department of the Environment are reviewing it. Architects, builders and owners now have a definitive guide to explain the controls.

The result of these controls will:

Either protect the main structure of the building if a fire occurs
Or provide better protection for the roof members if a fire occurs
Require an acceptance to treat the thatch as sacrificial in a fire

Companies specialising in thatch roof insurance welcome the "Dorset Model" and recognise that it will reduce the premiums paid.

Please click the link to view the latest Dorset Model Document:
dorsetforyou.com/dorsetmodel

Fire Retardants & Barriers

Thatching Advisory Services has played a prominent role in promoting and applying fire prevention techniques which can be used in isolation or as part of a complete system.

TAS Thatchsayf

Thatchsayf is a water-based solution containing fire retardant and intumescent chemicals for the protection of thatched roofing. When applied correctly, Thatchsayf penetrates the stems of the thatch by up to 75mm, forming a thin protective film on the surface of the thatch stems.

On exposure to sparks from chimneys, bonfires or barbeques, Thatchsayf will foam (intumesce) and form a carbonised char, which binds the thatch stems together, cutting off the supply of oxygen to the fire, delaying the spread of flame and lowering the radiated heat output.

Thatchsayf is a spray on fire retardant that is applied to the exterior of the thatched roof. Thatchsayf is environmentally acceptable and prevents bacterial and fungal growth. Once applied, the roof will not need treating for five years.

What are the benefits of Thatchsayf?

  • Can reduce insurance premiums
  • Fire penetration delayed for over 30 minutes
  • Can be applied to new or existing thatched roofs
  • Contains preservatives
  • Retards bacterial and fungal growth inc. moss
  • Application by approved Thatchers/Contractors
  • Application is fully certified
  • Environmentally safe

Thatchsayf Testing

Thatchsayf is tested to BS476: Part 3: 2004 and achieved the designation of EXT.S.BA.

Application

The application of Thatchsayf is undertaken by TAS trained and approved contractors using a high pressure spraying system. This ensures that the correct pressure and coverage is applied to the thatch.

The homeowner or builder will be issued with a Certificate of Completion by TAS. This certificate can then be issued to Architects, Building Control Officers, Insurance Companies etc. as proof that the thatch has been correctly treated with Thatchsayf. Certification is valid for 5 years before re-application is required.

Thatchbatts®

Beware! Thatch is one of only a few roofing materials that is combustible. Therefore,Thatchbatts® are the ideal product because they are non-combustible and will reduce the heat transfer around the roof timbers in the event of a fire!

Thatchbatts® are non-combustible, semi-rigid, high quality resin bonded mineral rock wool slabs. The Thatchbatts® have been manufactured to a width of 400mm, to allow them to be installed between the roof joists. They also have a high density for increased fire protection on the underside of thatched roofs.

Thatchbatts® can be also used to improve thermal and acoustic values. When Thatchbatts® are used in conjunction with other components in the roof system, they can help to achieve U-Values in the region of 0.16 to 0.14.

Benefits

  • Zero spread of flame
  • Easy to cut and install
  • Water Repellent
  • Thermal & acoustic insulation
  • Lightweight
  • Reduces Heat Transfer
  • Improves insulation U-Values

Specification

  • Length 1200mm
  • Width 400mm
  • Depth 50mm
  • Weight: 3.5kg/m²
  • High Density
  • Excellent Thermal Conductivity

Testing

Thatchbatts® have been tested by the Loss Prevention Council in conjunction with other products in our range as part of a system.

Application

Since the release of Thatchbatt® we have seen most architects selecting a minimum of 100mm of Thatchbatts® to achieve increased fire protection and thermal values. 

Thatchbatts® are designed to be friction fitted between rafters set at 400mm centres. Although the slabs, in most cases, are self supporting, we still recommend that consideration be given to following one of the wired fixing systems as detailed on the installation instruction document below.

When multiple layers of Thatchbatts® are being used, we recommend that the joints are staggered to give a more comprehensive solution.

Thatchbatts® - Installation Instructions

Supply

Although Thatchbatts® offer increased fire protection, where permitting they should be used in conjunction with either Thatch Firewall or Thatch Fireboard to create a comprehensive fire barrier system.

Supply

Thatchbatts® are available exclusively through Thatching Advisory Services, please contact us on 08455 20 40 60

Thatch Firewall Barrier

Thatch Firewall Barrier is a flexible fibre glass woven fabric, coated on both faces with a temperature resistant inorganic aluminised polymer system.

Thatch Firewall Barrier is more commonly used on an existing thatched roof when the timbers are not able to take the rigid Fireboard System. Firewall is classified as Water Vapour and Air Permeable, this coupled with its good tensile strength makes it an ideal fire barrier for thatched roofs.

To create a comprehensive fire barrier and to achieve BS476: Part 3: 2004 and CEN/TS 1187: 2012, test 4, it should be used with a minimum 50mm thick Thatchbatt® and our wired fixing system.

Thatch Firewall has a 120 minute fire resistance rating for integrity to BS476 Part 22.

Benefits

  • Easy Application
  • Water Resistant
  • Breathable
  • Water Vapour Permeable
  • Strong and Durable
  • Flexible

Specification

  • Roll Length: 50m
  • Roll Width: 1m
  • Roll Weight: 26kg
  • Area Weight: 450g/m²
  • Thickness: 0.40mm
  • Thermal Resistance: 0.0033 m²K/W

Testing

In addition to the 120 minute fire resistance, Thatch Firewall Membrane has been tested to:

  • BS476: Part 6: 1989+A1: 2009 Fire Propagation
  • BS476: Part 7: 1997 Surface Spread of Flame
  • Class 0 Summary Report
  • *BS476: Part 3: 2004 - Classification and method for external fire exposure to roofs
  • *CEN/TS 1187:2012, test 4 - Test method for external fire exposure to roofs
  • EN 13501- 5:2005 - Classification report for external fire exposure to roofs
  • Water Vapour Permeability Test (In accordance with BS7209: 1990)
  • Air Determination Test
  • WIRA Shower Test (In accordance with BS5066)
  • *These test reports are based on a combined test using a minimum 50mm Thatchbatt.

    Application

    Thatch Firewall Barrier is laid horizontally across roof timbers that are normally set at approximately 400mm centres, with a minimum 75mm overlap required on all joints. The Thatch Firewall membrane can either be stapled or nailed to the rafters and then battens are fitted over the top with 300mm centres, with the first batten 125mm from the arris rail.

    If required, TAS Fire Silicone can be applied between the membranes at the point that they join. For best results; apply a 5mm diameter bead of silicone using a wave effect pattern within the 75mm overlap point. Although the TAS Fire Silicone will have some instant grip, it will require 24 hours to fully cure. For best results, please ensure that the surface is clean and dry and not exposed to frost during the curing process.

    Systems

    To achieve both integrity and insulation, Thatch Firewall needs to be used in conjunction with Thatchbatts® to create a more comprehensive thatch fire barrier and increase thermal insulation values. As already mentioned you will also need to follow our Firewall System to meet the requirements of BS476: Part 3: 2004 & CEN/TS 1187:2012, test 4. Please see Thatch Fire Membrane System for more details.

    Supply

    Thatch Firewall is available exclusively through Thatching Advisory Services.

    To prevent damage, each roll is individually packaged in a strong cardboard carton and one set of installation instructions are supplied with each order.

    For individual rolls we would send out via a courier and for multiple rolls these will be euro strapped onto a pallet and sent out via our pallet distribution provider.

    PU28 Fire Membrane

    PU28 Fire Barrier is a medium weight fibre glass fabric membrane with a specially formulated aluminum pigmented and fire retardant polymer on both sides. The material is halogen free and has an improved resistance to hydrolysis.

    PU28 Fire Barrier has a 75 minute fire resistance rating for integrity and conforms to BS476 Part 6 and 7: Fire protection surface spread of flame.

    Benefits

    • Easy Application
    • Water Resistant
    • Breathable
    • Strong and Durable
    • Flexible

    Dimensions

    Supplied in 40m X 1.27m Rolls, which covers approximately 50m² including, overlap (75mm).

    Testing

    PU28 Fire Barrier has a 75 minute fire resistance rating for integrity and conforms to BS476 Part 6 and 7: Fire protection surface spread of flame.

    Application

    PU28 Fire Membrane is laid horizontally across the rafters with a 75mm overlap on all joints. PU28 Fire Membrane can either be stapled or nailed to the rafters and then battens are fitted over the top with 300mm centre`s, with the first batten 125mm from the arris rail. PU28 Fire Membrane can also be used for other applications such as partition walls, suspended ceilings and loft space firebreaks.

    If required, TAS Fire Silicone can be applied between the membranes at the point that they join. For best results; apply a 5mm diameter bead of silicone using a wave effect pattern within the 75mm overlap point. Although the TAS Fire Silicone will have some instant grip, it will require 24 hours to fully cure. For best results, please ensure that the surface is clean and dry and not exposed to frost during the curing process.

    Systems

    To achieve both integrity and insulation, needs to be used in conjunction with Thatchbatts® to create a more comprehensive thatch fire barrier and increase thermal insulation values. Please see Thatch Fire Membrane System for more details.

    Supply

    PU28 Fire Membrane is available through Thatching Advisory Services, please contact us on 08455 20 40 60

    TAS100 Thatch Fireboard

    TAS100 Thatch Fireboard is an environmentally friendly composite board offering a fire barrier in accordance with BS476 Part 3: 2004.

    TAS100 Thatch Fireboard out performs cement based boards and regular gypsum plasterboard, due to its superior environmental credentials and performance characteristics.

    Benefits

    • Zero Spread of flame
    • Easy to install
    • Water Resistant
    • Impact Resistant
    • Water Vapour Permeable
    • Termite, mould and insect proof
    • Can be cut, drilled, nailed & screwed with no splitting
    • Each board is supplied with a smooth & rough side

    Dimensions

    Standard board size is 1200x2400x8mm

    Testing

    TAS100 Thatch Fireboard is tested to BS476 Part 3: 2004. This test was completed by the BRE, Watford.

    Also tested to demonstrate Water Vapour Permeability.

    Application

    TAS100 Thatch Fireboard is positioned on top of the rafters and fixed down with either nails or screws. We would then recommend that all joints are sealed with a intumescent joint sealant, battens are then fitted over the top with 300mm centres, with the first batten 125mm from the arris rail.

    Systems

    TAS100 Thatch Fireboard can be used as a stand alone fire barrier in accordance with BS476 Part 3, however we also recommend that TAS100 Thatch Fireboard be used in conjunction with Thatchbatts® to create a more comprehensive fire barrier, meet the criteria of the Dorset Model and increase thermal insulation values. Please see Thatch Fireboard System for more details.

    Supply

    TAS100 Thatch Fireboard is available exclusively through Thatching Advisory Services, please contact us on 08455 20 40 60.

    Thatch Fireboard System

    The Thatch Fireboard System is designed to meet the performance criteria of `The Dorset Model`. The combination of TAS100 Fireboards for Integrity and Thatchbatts® for Insulation makes this system an ideal fire protection solution, with the added benefit of providing the required thermal insulation values.

    The system consists of:

    • Thatchbatt® Wired Fixing System 
    • Thatchbatt® Slabs
    • TAS100 Thatch Fireboard
    • Intumescent Joint Sealer

    System overview:

    The TAS100 Thatch Fireboards will offer a fire barrier in accordance with BS476 Part 3: 2004. The Intumescent Joint Sealer is used to give the roof integrity for both fire and water resistance.

    The Thatchbatts® are designed to be friction fitted between roof timbers that are set at 400mm centres. Thatchbatts® are non-combustible, semi-rigid, high quality resin bonded mineral rock slabs. These are therefore ideally suited for use within the construction of a thatched roof because they offer zero spread of flame and good thermal transfer properties.

    The minimum requirement is for 50mm Thatchbatts®, however, consideration should be given to the following two points in relation to the thickness and possible full fill:

    • If the Thatchbatts® are installed at the same depth as the roof timbers, then the fire resistance is increased in terms of reducing the charring to the roof timbers. Therefore, this will help protect the roof structure from either a fire on the outside or on the inside.
    • An increase in Thatchbatts® thickness will also result in increased thermal values.

    Although the Thatchbatts® have been designed to be semi-rigid, the wired fixing system is required to ensure that the top of surface of the slabs are level with the top edge of the roof rafters.

    Application

    1. Thatchbatts® are friction fitted between the rafters set at 400mm centres; they are then supported by the wired fixing system as detailed on the installation instruction document below.

      When using multiple layers of Thatchbatts® are being used, we recommend that the joints are staggered to give a more comprehensive solution.

      Thatchbatts® - Installation Instructions

    2. TAS100 Thatch Fireboards are positioned on top of the roof rafters with the smooth side facing upwards and fixed down with either nails or screws.

      When fixing the boards, the first row is normally laid out horizontally along the eaves and then working towards the ridge, each subsequent row of fireboard is laid in a way so the joints are staggered.

      All joints need to be sealed with a bead of intumescent joint sealant. Battens are then fitted horizontally over the top at 300mm centres, with the first batten 125mm from the arris rail.

    All the framing and substances used must comply with relevant building regulation and standards.

    The components within the Thatch Fireboard System contribute to a part of the overall roof construction. Therefore please consult with your Architect with regard to the performance of the complete roof structure, to include requirements for other components such as vapour barriers etc.

    Additional information for both Thatch Fireboard and Thatchbatts® is available from the main menu of our website.

    Thatch Fire Membrane System

    The Thatch Fire Membrane System is designed to meet the criteria as recommended by Building Control for both spread of flame and penetration, with the added benefit of providing the required thermal insulation values.

    Please note that this system does not meet the criteria of `The Dorset Model` for new build projects and extensions where the property is 12m or less from the boundary. If your project meets these criteria, please look at our Thatch Fire Board System.

    The system consists of:

    • Thatchbatt® Wired Fixing System
    • Thatchbatt® Slabs
    • Thatch Firewall Membrane

    System overview:

    This system will offer a fire barrier in accordance with BS476: Part 3: 2004 & CEN/TS 1187:2012, test 4.

    The Thatch Firewall Membrane system offers a flexible, water resistant and breathable solution for those projects that are not able to accommodate the rigid Thatch Fireboard System.

    The Thatchbatts® are designed to be friction fitted between roof timbers that are set at 400mm centres. Thatchbatts® are non-combustible, semi-rigid, high quality resin bonded mineral rock slabs. These are therefore ideally suited for use within the construction of a thatched roof because they offer zero spread of flame and good thermal transfer properties.

    The minimum requirement is for 50mm Thatchbatts®, however, consideration should be given to the following two points in relation to the thickness and possible full fill:

    • If the Thatchbatts® are installed at the same depth as the roof timbers, then the fire resistance is increased in terms of reducing the charring to the roof timbers. Therefore, this will help protect the roof structure from either a fire on the outside or on the inside.
    • An increase in Thatchbatts® thickness will also result in increased thermal values.

    Although the Thatchbatts® have been designed to be semi-rigid, the wired fixing system is required to ensure that the top surface of the slabs are level with the top edge of the roof rafters.

    Due to the flexibility of this system it is favoured for many existing properties.

    Application

    1. Thatchbatts® are friction fitted between the rafters set at 400mm centres; they are then supported by the wired fixing system as detailed on the installation instruction document below.

      When using multiple layers of Thatchbatts® are being used, we recommend that the joints are staggered to give a more comprehensive solution.

      Thatchbatts® - Installation Instructions

    2. Thatch Firewall Membrane is then fitted directly on top of the roof rafters. The membrane is fitted horizontally with a minimum overlap of 75mm at each point the membrane joins.

      The membrane can either be stapled or nailed to the roof rafters to hold it in place on a temporary basis until the battens are fitted.

      25mm x 50mm battens are then fitted horizontally over the top of the Thatch Firewall Membrane at 300mm centres, with the first batten 125mm from the arris rail. Please note: if the Thatcher is going to use crooks, the size of the battens may need to be increased.

    3. If required, TAS Fire Silicone can be applied between the membranes at the point they join. For best results; apply a 5mm diameter bead of silicone using a wave effect pattern within the 75mm overlap point. Although the TAS Fire Silicone will have some instant grip, it will require 24 hours to fully cure. For best results, please ensure that the surface is clean and dry and not exposed to frost during the curing process.

    The components within the Thatch Fire Membrane System contribute to a part of the overall roof construction. Therefore please consult with your Architect with regard to the performance of the complete roof structure, to include requirements for other components such as vapour barriers etc.

    Additional information for both Thatch Firewall Membrane and Thatchbatts® is available from the main menu of our website.

    Questions and Answers

    1. Should I fit a spark arrestor?

    No. The fitting of spark arrestors is not recommended because the mesh has a tendency to become blocked by soot and tar. In this condition they are likely to increase the risk of chimney fires.

    2. How long does a thatched roof last?

    The life of thatch will depend on a number of factors which include the pitch and design of the roof, type and quality of material used, geographical location, and degree of skill exercised by the thatcher. In ideal circumstances thatched roofs have been recorded to last in excess of 100 years but under normal conditions the following life expectancies can be used as a guide:

    Water Reed 30-50 years
    Combed Wheat Reed 20-30 years
    Longstraw 15-25 years

    3. How long does a ridge last?

    Depending upon the style of construction and type of material that is used, ridges can normally be expected to last for 10-15 years.

    4. How do I identify what material is on my roof?

    Not easy to define but the following generalisations may give a clue:

    Water Reed
    Even dense coat showing butt ends of material only
    Likely to be angular in overall appearance with eaves dressed into place, ends of material at right angles to the stem
    Likely to have a `block` ridge
    Likely to have wire netting on the ridge only

    Wheat Reed
    Even dense coat showing butt ends of material only
    Likely to be softer and more rounded in appearance with eaves cut into shape leaving an angled quill like end to the straws
    Likely to be totally covered with wire netting

    Longstraw
    Less dense and more `shaggy` appearance to coat, may show a mix of butts and ears
    Soft contours to the roof, especially windows
    Should have a continuous line of hazel rod running on the surface at eaves and gables
    These are called `liggers` they may appear as two lines with cross-sparring between them

    NB: Be cautious, thatching materials are not easy to identify and there are many traps for the unwary.

    5. Does my roof have a fire barrier?

    If you can access your roof void safely, look between the rafters at the underside of the thatch. If you can see the thatch you do not have a fire barrier. If you can see a sheet or board material you may have a fire barrier.

    Try to establish whether this material is a bituminous or other type of sarking felt which does not constitute a fire barrier or it may be a fibre cement boarding or shiny flexible material which does provide a fire barrier.

    6. What fire retardants are available?

    Please review the Fire Retardant Section of this document

    7. What does it cost to re-thatch a roof?

    Approximately £100-£125 + VAT per m² of roof area including overhanging of eaves and gables. (Excluding scaffolding)

    8. How thick is thatch?

    A single coat or thickness of thatch is normally between 300mm and 350mm. This thickness will reduce through the life of the roof as the result of natural erosion.

    9. Why do some roofs have wire netting?

    Wire netting is fitted to thatch to prevent or reduce damage from birds or other vermin. Ridges are netted in most cases, as are roofs of Longstraw and Combed Wheat Reed. It is common practice to leave Water Reed without netting because it is more resistant to vermin damage.

    10. How does thatch stay on the roof?

    Thatch is either fixed directly to the roof timbers with steel `crooks` or screw fixings, or it is fixed to an underlying coat with hazel `spars` which are twisted to form a staple which is driven through the new thatch into the old beneath.

    11. How long does it take to thatch a roof?

    Dependant upon the size of roof and number of thatcher`s. A family sized four bedroom, detached house would probably take a team of three men about one month.

    12. Does strong wind affect a thatch roof?

    Under normal conditions a thatched roof, which is in good condition, is surprisingly resistant to high winds. The gale of the late 1980`s proved this to be the case.

    13. How do I choose a thatcher?

    Select a Thatcher via the `Find a Thatcher` section on the TAS website
    Select a member of the National Society of Master Thatchers.
    Select a member of one of the county associations
    Ask for references or to see examples of work

    14. How do thatcher`s price a job?

    By means of accurate measurements which is cross referenced with appropriate specifications and market rates prevailing in the area.

    NB: Measurements should always allow for the thickness at eaves, gables and ridge.

    15. Is there an added fire risk to thatch?

    According to statistics, the incidence of fire in thatched properties is no higher than any other type of roofing materials, but it is likely to cause greater damage. This may reflect the caution which is exercised by thatched property owners.

    16. Does my insurance premium come down if I have a fire retardant or a fire barrier fitted?

    Some insurers will offer a discount in these circumstances.

    17. Can I install a velux window?

    Velux windows are relatively easy to install in a new roof i.e. prior to thatching. They are less easy to retro-fit in an existing roof but it is usually possible.

    18. What pitch should my roof be?

    It is advisable to set the pitch at about 50º, dormer windows and eave windows should be at least at a 45º pitch, 45º is normally accepted as the minimum pitch at which thatch will perform effectively.

    19. What is the Dorset Model?

    The Dorset Model is a set of guidelines to advise you of certain requirements if you are considering extending or constructing a thatched roof building less than 12m from your boundary.

    Technical Services

    Further information, help and advice on these products and their application is available from Thatching Advisory Services.

    Tel: 08455 20 40 60

    Email: info@tas-uk.co.uk

    Website: http://www.thatchingadvisoryservices.co.uk/

Thatching Advisory Services
Thatching Advisory Services
Thatching Advisory Services
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