Thatch roof & materials specification

It is strongly suggested that any estimate should have a specification so that you can compare with others. See  Specimen Estimate for the very bare basics.

The following may appear daunting but it is be worth reading so that you understand your estimate and the complexity of thatching better. This is only an opinion of a reasonably comprehensive specification and guideline; unfortunately no nationally recognised one exists yet within the thatching industry.

 

Quality of materials  

Long straw

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The variety shall be recognised as suitable, or recommended as suitable if a new variety. It will normally be a hollow stemmed, winter grown wheat, although other materials are recognised.

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It shall have an average cut length of at least 760 mm (30 inches)

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Whichever method of threshing is employed, it shall leave the straw stem as little bruised and broken as possible, removing cavings and all other rubbish.

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The straw should be strong, supple and able to resist, or even defy efforts to break it by twisting a handful continuously.

Combed wheat reed

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The quality of straw required is the same as that recommended for long straw.

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Providing the length of the straw does not fall below 685 mm (27 inches) it is still suitable for combing, although the ideal length is 915 mm (36 inches)

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The straw shall be suitable, if, on passing through the reed comber, comes out undamaged, with grain and leaves removed and with all the stems laid in one direction.

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No straw should travel through the drum.

Water reed

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  Short reed should be between 914 mm (3ft) and 1220 mm (4 ft)

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Medium reed should be between 1220 mm (4ft) and 1676 mm (5ft 6 inches)

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Long reed should be above 1676 mm (5ft 6 inches) with the majority of the reed around 1830 mm (6ft).

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The reed strength should not be confused with hardness when the reed may also be brittle. The reed should have a fibrous quality and should not break easily.

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Reed should be grown in unpolluted area’s to avoid risk of disease to operatives and degradation of the material.

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The bundle should not contain more than 5% non reed plants.

Sedge

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The quality required of sedge is that the material shall be a leaf flattened at the butt of not less than 13mm ( ½  inch)

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It shall have an average cut length of at least 1m (39½ inches)

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The sedge should not be brittle. It should be strong, supple and able to resist or even defy efforts to break it by twisting a handful continuously after dampening.

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The bundle should not contain more than 5% non sedge plants.

 Ground work – material storage and preparation

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 Stacks on site should be covered to protect against adverse weather and raised from the ground to prevent rising damp and stacked to prevent displacement and risk of injury.

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Materials/components stored level to prevent distortion, damage and crushing.

 All units 

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Material within the unit cleaned of damaged or foreign materials.

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Unit tied firmly to avoid twisting and ensuring all material is well held.

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Unit size; girth and length graded and shaped appropriate to required use.

 Long straw

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 Material is damped to be workable and loosely arranged to allow free drawing into units.

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Units be of consistent density, length and without weakness throughout, all straws within should be parallel.

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·Units have no twists throughout, and are able to be handled without parting.

Combed wheat reed

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·Units should be cleaned of any damaged material, butted and then trimmed to clean exposed ends.

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The units should be lightly damped and allowed to steep prior to use. This damping practice is not so essential when hooking on new work.

Water reed

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Units should be cleaned of any damaged or foreign material and butted to level out the cut ends.

 Sedge

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 Units for ridge skirts and wrap over should be prepared as for long straw.

Evaluate condition of roof structure

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Assessing working surfaces in accordance with requirements from bare roof frame (new or recently stripped

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Main frame is complete, in good order and capable of accepting fixings.

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Internal roof inspection carried out to determine if roof details are correct and existing timbers sound enough to carry the weight and tensions of new thatch

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Roof architectural details are sound and generally the pitches are 45-60 deg

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Battens are of adequate strength and number.

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Tilting fillets are correct according to type of material to be used.

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Barge boards are sound and large enough to constrain the thatch, or act as tilting fillets.

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Any abutments which may cause problems or need additional work have been identified.

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Identify any existing thatch that should be removed and any low or high areas are rectified.

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Any gables or eaves that need to be stripped out or replaced are identified.

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The condition of exposed brickwork under old thatch is satisfactory.

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·Further preparation or remedial work that is necessary is identified and recorded.

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·Any historical items that may be discovered are notified to the relevant persons.

Checking for potential hazards (both inside and outside of roof)

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Any exposed defective cables are identified and recorded.

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Any potential fire hazards are identified and recorded, particularly defective masonry to chimneys.

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Any pest infestation or damage is identified and recorded.

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Any plumbing works faults are identified and recorded.

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Any defective timbers are identified and recorded.

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Any safety hazards compromising scaffolding and ladders are identified and recorded.

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Loft hatches to inspect interior and allow fire crews access are adequate to all bays.

Preparation of roof prior to casing

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All old wire to be removed

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All defective or superfluous thatch removed in those parts to be replaced, chimney areas to be stripped to allow examination of the stack.

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The restoration of the base coat has been carried out where it was necessary to part strip down to roof frame.

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High and low parts filled in or out respectively and adequate to create a sound and level work surface.

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The base coat is the requisite thickness, density and is secured by relevant fixings, as and where needed.

Preparation of materials for fixing

Coppice materials 

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Preparing spars/brotches and liggers/rods from coppice materials.

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Spars/brotches for coating will not buckle on being used, be twistable and be clear of snags throughout length.

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Be thin enough not to leave holes in exterior use, not too long for task in hand and be sharply pointed

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Liggers/rods will be straight, of even thickness, clean and of good appearance trimmed at each end for flush lap jointing.

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Thick enough not to bow between spars, thin enough to allow overfixing of spar twists.

 Thatching nails, screws and other fixings 

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The type of fixing shall be appropriate to the material and substrate.

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The length of fixings will be adequate to hold the materials without damaging the substrate.

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The strength of the fixings will be sufficient to hold the materials without allowing them to bend or move substantially.

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Sways are of sufficient strength not to bow between fixing points.

Position and secure thatching materials

 Main roof

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 Coatwork is laid tight to sub-structure and the laid pitch angle formed is commensurate with the pitch angle required for main roof.

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Cover over fixings to be maximised without affecting pitch. At least: long straw 175mm (7inches) combed wheat reed150mm (6inches) water reed (130mm 5inches)

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No course marks or crossed materials, each course or layer applied to provide enough kick for the next course.

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Minimum depth of material above the batten or substrate, long straw 380 mm (15 inches) combed wheat reed 305 mm (12 inches), water reed 305 mm (12 inches) casework 255 mm (10 inches)

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Sways applied at a frequency so as to hold the top of the preceding course.

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Sways to be tightened so as to maintain kick without crushing the materials or causing them to kick up.

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Oversail finished to level and even top, excessive kick to final course removed, top course pitch maximised to roof pitch angle.

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Oversail finished to the pitch of other side, top course thick and tight enough to receive ridging spars, no voids between ridge rolls and oversail courses.

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Overall thickness maintained throughout feature.

Eaves and gables

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All units fixed securely in the horizontal and vertical plane and fixed without obvious joins or twists.

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Eave and gable units fixed to give adequate overhang along complete length of wall with consistent overhang commensurate with coat to be applied and dressed or cut to at least 90° or undercut.

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Units fixed tight to wall or sub-structure to give correct kick.

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Pitch angle of material not too flat in relation to the roof, fixed to a consistent density and tension.

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Apex units fixed firmly maintaining consistent pitch with gable, so it does not kick backwards maintaining a correct line with the main roof.

Valleys

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Material turned to align with centre line of valley with a rate of turn to give the most effective dispersal of water.

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Rate of turn is such as to maintain same density through valley consistent with the main roof.

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Material rounded to give minimum depth over centre of valley of: long straw, 406 mm (16 inches) combed wheat reed 330 mm 13 inches water reed 380 mm (15 inches) casework with long straw or combed wheat 305 mm 12 inches.

Hips

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Material turned to align with centre point of hip.

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Rate of turn is such as to maintain same density through the hip consistent with the main roof.

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Rate of turn is such as to maintain the tension through the hip, even density and maintain cover over the fixings.

Saddles

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Ridge taken back to valley junction sub-structure

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Ridge material at point of the saddle edge turned so as to carry water away from the junction.

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Ridge pitch maintained through valley junction at the pitch of the valley.

 Ridge

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 Ridgework is secure, with a pitch angle maintained throughout greater, or at least that of the main roof.

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Rolls of consistent size and density fixed securely and not deviate from apex.

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Knuckle or butt courses fixed in pitch to main coat pitch or greater.

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Skirts laid to consistent thickness and are additional to the main roof, skirts laid to optimum thickness of 75 mm (3 inches) for a cut block finish.

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Skirts laid to consistent density, well fixed and are fixed high enough to ensure adequate cover over fixing.

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Wrapover is fitted to firm and consistent density, of required pitch, effective thickness, and fitted level and pointed on the apex (minimum 75 mm 3 inches depth to the final roll.

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Butt up ridge is (minimum 75 mm 3 inches depth to the final roll, additional to the main roof, firmly jointed at apex and fitted according to prevailing weather.

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Block ridge pattern, the cut should be firm, even and consistent with rod work, does not affect coatwork and is at 90° or greater to the ridge surface.

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Flush ridge as wrapover with the lower edge merged seamlessly into the coatwork.

Ligger work 

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Spars not easily withdrawn and not easily depressed, sufficient number of fixings to hold externally each 150mm (6inches) length of material with a minimum of three liggers per side.

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Correct pattern placement determined with liggers parallel to ridge top line, liggers parallel to cut line.

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Spars are inserted at an angle so as to avoid the ingress of water, ligger work sufficient to hold ridge stable and tight.

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Decorative rod work is consistent and not excessive to the point that it impedes water shedding.

Forming joins between thatch and other structural materials

 Box gutter 

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Flashing is adequately fixed with sufficient upstand, flashing is: seated to fitted boards, carried into the roof horizontally to above the first sway and vertically at least 230mm (9inches)

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Of adequate size to permit cleaning, dressed to cover side flashings.

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Introduced into the coursework at the sides with upstand to avoid water penetration, dressed to ensure discharge of water.

Applying thatch around vent pipes 

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Lead, slate or composite alternative is fitted over and around pipe; apron to front is fitted over the thatch filled flush to under apron surface.

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Apron to the rear introduced into coat at course pitch angle and taken back above the fixing.

Fitting stepped/side flashing

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Adequately fixed with sufficient upstand, sufficient cover over thatch and abutment, sufficiently overlapped with front apron, is sufficiently underlapped at apex.

 Mortar fillets

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Mortar mix allows effective, continuous adhesion; fillet has sufficient surface area to masonry to allow effective continuous adhesion, thatch and masonry abutment sufficiently covered.

Applying appropriate finish for gables, eaves, main roof and ridges

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Cut or dress eaves and gables to shape and correct line, trimmed and or plucked to tidy finish with no cut marks and correct and consistent angle achieved.

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 Coatwork sheared/clipped/dressed/raked to an even finish, with no cut or course marks.

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Surface of ridge superfluous material trimmed above and between liggers/patterns.

Applying protective netting to the thatched roof

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Correct netting selected for the material to be protected, netting to finish flush to the roof shape, fixed securely throughout.

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All joints must be secure, bird proof, of the correct type, without excessive overlap, correct tautness and tension achieved and look tight.

Very simple sketch of thatching basics

If you are uncertain about these points see Trouble Shooting & Surveys

 

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