TECHNICAL
Q&A Weatherboarding
It is, perhaps, Britainʼsmost underrated buildingmaterial – a simple solutionworthy of better understanding, as Douglas Kent, the SPABʼs Technical Secretary, explains
What is weatherboarding? Weatherboarding comprises lengths of board used for cladding buildings. In Britain, it is found onmany building types but is associated especially with barns, smaller houses, church towers andmills in south-east and eastern England.Oak was commonly used inmedieval times, elmin the 17th century and, later, softwood. Early boards were typically riven (split) instead of sawn, fixed vertically and formed infill panels between structural timbers. The boards could be held within grooves in the timber structure or pegged on to rails.
Why is old weatherboarding worth keeping? Weatherboarding ismore than a cheap, temporary cladding, andmakes a considerable contribution to the character of historic buildings. Theminor distortion of boards in response to gentlemovements in the underlying building structure and the patina acquired by their surfaces, often reflecting the irregular build-up of different coatings, impart visual qualities that cannot be replicated readily.Old weatherboarding should, therefore, be retained wherever possible.
What problems might arise with weatherboarding? Boards can deteriorate due to beetle infestation or fungal attack as a result of dampness (arising, for example, fromleaking gutters). Theymay also split along the lines of inherent weaknesses or become displaced (for instance, when nails corrode), allowing rainwater to penetrate behind and cause damage.
What might repairs to weatherboarding entail? Defective weatherboardsmight be repaired by splicing in seasonedmatching new timber (joints should coincide with studs) or inserting timber plugs.Whole boards may otherwise need replacing. To repair a split, apply glue and attach a block to the board below to act as a clamp against the lower edge while this sets. Splits or holes can be temporarily covered with thin sheetmetal. Tap loose boards back into position and re-fix thembeforemore serious deterioration occurs.
Can weatherboarding be stripped and re-used Where possible, it is best to avoid disturbing old boarding, which, because of embrittlement,may be easily damaged. However, in some instances its removal may be justified (for example, to introduce insulation behind).
Left, weatherboarding at ancient Harmondsworth Barn. Above, old weatherboards in detail If so, the careful removal and re-use of existing boards is preferable to their
replacement. Boards should be carefully numbered and a sketchmade of their arrangement to assist with reinstatement. Nails can be cut between the boards with a chisel or saw.
If necessary, how might I replace weatherboarding? Where replacement is unavoidable, new weatherboards should usuallymatch the timber type,method of cutting, size and thickness of the existing ones (taking care not to copy inappropriatemodern work). Ensure that boards are also of the same profile – often “feather edged”, ie wedge-shaped, rather than “shiplap” – and that any faces to be painted come planed. Follow, too, existing details around openings. Softwood will generally require pressure treating. Itmay be appropriate to use concealed lead soakers below vertical joints or an underlay for improved weather protection.
What fixings are suitable for weatherboarding? Rosehead and similar nails with raised heads resembling those commonly used historically for weatherboarding are still obtainable, often now in galvanised steel.Other galvanised or stainless steel nails can also be employed, including those of the lost head type popular for painted weatherboarding fromthe mid-19th century. With a feather-edged board, one nail is usually driven through a pre-drilled
hole about 25mmabove its bottomedge at each stud. Screw-fixing is advisable near fragile internal plasterwork.
What are the appropriate surface finishes, if any, for weatherboarding? Early hardwood did not require a protective finish, but the practice of tarring boards developed by themid-18th century with increased use of less durable softwood. Toxicity concernsmean tar is only available today froma few specialists.Opaque stains provide amore widely available but less authentic alternative. Lead paint was commonly used with planed softwood on houses and mills. Its use is now restricted but linseed paints promise good durability. Boards should be pre-painted before fixing, including vulnerable end grain that has been exposed by trimming.
The SPAB runs a technical advice line for technical enquiries, 9.30am-12.30pm, Mon-Fri, on 020 7456 0916. This number is sometimes subject to change.
Cornerstone, Vol 32, No 2 2011 63
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