Draft Specification

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Since every specification must be tailored to suit a particular project, the following specification gives the rudiments for obtaining a good finish, but has built in, choices that must be made. If you are unfamiliar with Collyweston roofing, or have any doubts as to what is required, it is advisable to seek the services of a qualified Chartered Surveyor, Architect, or other Building Professional. A good roof will last several lifetimes, so it is worth the investment!

 

GENERAL REQUIREMENTS

All roofing work shall comply with the Code of Practice B.S.5534: Slating and Tiling, subject to any qualifications given hereunder.

MATERIALS

Any materials referred to by name, may be replaced by equivalent alternatives, provided that evidence of such, is presented to the Contract Administrator, prior to materials being purchased and brought onto site.

Underlay: Breathable underslating felt

Nails: Use nails of adequate length and gauge to provide secure fixing as follows:-

    1. Copper to B.S.1202 Part 2 for fixing slates to battens / stainless steel to B.S. 1202 for fixing battens, sized to give secure fixing without splitting the batten.

Battens:. Battens shall be tanalised softwood as follows:

    1. Free from decay or insect attack
    2. Free from any splits shakes
    3. With wane permissible on one arris only
    4. With knots or knot holes less than one third width of any sound surface
    5. With a max. of 22% moisture content at time of fixing.

Lath: Shall be riven oak / chestnut

Mortar: Lime mortar shall be used (1:3, lime putty:sharp sand, between May and September, and 1:3 NHL2:sharp sand, when a slight risk of frost) and coloured if required only by the use of  sand’s natural colouring, by blending as required.

Plumbers Metalwork: All plumbers metalwork shall comply with the Code of Practice CP 143 Part II sheet roof and wall coverings, subject to any qualifications given hereunder.

Milled Sheet Lead: To be to B.S.1778 and used as follows, except where otherwise specified.

    1. Code 4 for all soakers, flashings and general weatherings.
    2. Code 5 for roof and wallcoverings and associated details.
    3. Tacks shall be cut from the lead being fixed, min 40mm wide.

Solder: Shall be to B.S.219 Grade D or J.

Nails for fixing lead: Shall be copper to B.S.1202, Part 2, Table 2, large round headed.

Conservation Roof Vents: Shall be by Lapvent.

WORKMANSHIP

Stripping off existing roof coverings: Strip off designated roof slopes of all roof coverings, felt, battens, flashings, aprons, soakers, valley gutters, hip and ridge cappings, etc.

Protection: Provide all necessary protection, tarpaulins, dustsheets and the like for the duration of the work, ensuring that. Any damage to property, occupiers belongings, goods, chattels, etc shall be made good at the Contractor’s expense and he shall be responsible for maintaining the buildings in watertight condition at no additional expense to the Contract sum. Polythene sheet shall be laid horizontally within the roof space prior to commencement of the works, to enable all falling debris to be removed more easily.

Cleaning: Upon completion of the works, the roof spaces affected shall be cleared of all fallen debris, as a result of the roof works, i.e. battens, broken slates and mortar, etc..

 Defective Roof Timbers: Shall be brought to the attention of the Contract Administrator / Client for action by others.

Any defects to the stonework or brickwork shall be sympathetically repaired using reclaimed materials to match existing. The mortar shall be 1:3 lime mortar, as before, with a suitable brushed / rubbed finish.

Detailing: All existing roof details shall be recorded prior to commencement of works (a comprehensive set of photographs may be the best method), and these shall be reproduced in the new work, unless agreed otherwise by the Contract Administrator / Client. This shall include the following:

 

Underlay shall be fixed as follows:

    1. Lay parallel to eaves commencing at eaves and with slight drape between rafters.
    2. Lap 150mm at sides and ends with end laps centred over rafters.
    3. Tack / nail sufficiently to make secure until battens are fixed.
    4. Lay over any tilting fillets and extend into gutters. Prevent any sagging which could trap water.
    5. Do not extend over fire breaks or party walls
    6. Lay a strip over the ridge to overlap general underlay by 150mm min.
    7. Lay 600mm wide (min) strip at verge below general underlay and to lap by 150mm min.
    8. Lay 600mm (min) strip at hips over general underlay and extend fully to eaves line.
    9. Extend underlay up wall at top abutment to suit cover flashing.

Battens / Laths: Shall be securely fixed with copper / stainless steel nails to every rafter as follows:

    1. At centres to give the correct lap.
    2. In long lengths (min length to be supported by at least 3 rafters with both ends supported.
    3. With ends cut square and centred over rafters and nailed without splitting.
    4. Packed where necessary to maintain level.
    5. Provide additional battens / laths and tilting fillets etc. at eaves, ridges and other perimeter features.
    6. Provide additional battens / laths if necessary to prevent windlift of horizontal laps in the underlay.
    7. Nail penetration into rafters shall be 50 mm, min.

Slates shall be laid as follows:

    1. Slates shall be laid in diminishing courses to suit the roof situation, fixed with a single copper nail / oak peg at the head of each slate.
    2. Maintain a minimum side and end lap of 3" (75mm), at any point. Head /tail lap shall be a minimum of 2" for slates less than 7" in length, and 3” for larger sizes of slate.
    3. Where underslating felt is used, spot bed slates on a lime mortar bed, with the edges of the slate and the centre of the slate filled fully and the remainder left open to allow air flow beneath the slate. Shales shall be used to support the middle part of the slate, or where a large gap exists beneath the slate and the bottom edges struck back so as "to allow a fly to be able to shelter from the rain".. Mortar shall not be taken over the top edge of the slate.
    4. Where no underslating felt is to be used, the slates shall be solidly bedded in lime mortar and the bottom edges pointed and struck back . (This is to form a drip and give definition to the slate courses)
    5. When there is a risk of heavy frost, or a prolonged period of frost, working with mortar shall cease, with previously laid work protected by insulation covered with tarpaulins.

 

Ridge or Hip Tiles:

    1. Shall be to match existing, or in new or reclaimed "white" clay hogs-back wherever possible.

 Hips:

    1. Shall be close mitred with code 3 lead soakers / code 4 lead roll / formed using clay hogs-back hip tiles

Verges:

    1. Shall be formed using the main roofing slates, rendered below using lime mortar, and "pecked" using a trowel tip to match existing. (Note: Two or more thin coats will shrink less than one thick coat.)

Abutments:

    1. Shall be formed using code 4 lead soakers, coated with 2 coats of bitumastic paint, covered using a lime mortar flaunching / lead apron.

Valleys:

    1. Shall be laced / swept / secret / open to match existing

Dormers:

    1. Shall be vertically hung Collyweston slates fixed as the main roof / given 2 coats of 1:3 lime render, on stainless steel expanded metal backing / riven oak or chestnut laths, fixed to the cheeks using non-ferrous fixings. The surface shall be given a wood float finish / and "pecked" using the tip of a trowel to match existing.

Rainwater Goods:

    1. New guttering shall be cast iron or cast aluminium.
    2. Existing guttering shall be cleaned out and repaired after works are completed to the roof area.

 Roof Ventilators:

    1. Shall be fitted in accordance with the manufacturer's instructions.

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