Remedies: matching new to existing

With any renovation of a 1940s-60s house, there will be areas where original construction needs to be replaced or new construction must merge with existing.

Many of the materials and fittings used in the construction of 1940s-1960s houses may no longer be readily available. While timber profiles can be run to match existing, the options for sourcing other materials and fittings are generally limited to sourcing second-hand materials or finding replicas.

Framing

The dimensions of new framing timber differ to old framing. Original timbers are usually rough sawn and will vary in size including sometimes being slightly larger than the nominal size. For example, a 4 x 2” (100 x 50 mm) timber could actually be 4¼ x 2 ⅛” (108 mm x 55.25 mm). Current nominal 100 x 50 mm framing is 94 x 47 mm green gauged and 90 x 45 mm dried.

The differences in timber size can be dealt with by:

  • packing new framing to increase thickness
  • adjusting packing to give an even line
  • aligning a change with an internal wall location so the change in wall thickness is masked
  • removing the existing wall back to a junction for small areas, then install new framing
  • having new oversized framing run – this will incur a set-up cost at the supplier
  • using new rough sawn timber adjacent to older gauged timber.

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Cladding

Where existing claddings are damaged, a decision must be made whether to retain or replace the cladding and to what extent. Damaged weatherboards such as split, bowed and cupped boards may compromise the weathertightness of the building and will need to be replaced.

The decision as to whether or not to replace boards must take account of the availability of matching materials to make the repair, and of the risk of further damage to boards during removal.

The original timber species used for the weatherboards and finishing timbers may not be available or only available in limited amounts, although this is not a problem for painted weatherboards as the timber is concealed by the paint coating.

One difficulty when continuing a line of weatherboard cladding with a different species is that the two species will move differently in response to changes in the relative humidity different species and where the difference in moisture movement is great the effect may be noticeable.

Modern standard timber cladding profiles are metric, not imperial, so an exact match may not be possible. Other options for matching weatherboards include:

  • having matching weatherboards made as a special run
  • obtaining an exact match replacement from a demolition yard
  • increasing the lap so that bottom edges line up for bevel-backed boards
  • making the change from old to new timber at an external corner (where other corners in the weatherboard are not mitred)
  • masking the change with a coverboard to make the difference in size less obvious.

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Roofing

Steel

The metric corrugated roofing profile is different to the imperial size roofing that may still be in sound condition. Where one or two sheets need to be replaced, new material can be used, but for larger areas of replacement, the profile difference cannot be accommodated.

Second-hand material may be available; if not, the roof will generally need to be replaced. The use of new long run roofing eliminates the need for end laps which have a greater risk of deterioration. Note that new zinc/aluminium alloy roofing should not be used in direct contact with or above the original galvanised steel roofing.

Tile

Current concrete and clay roof tiles may be manufactured to a different size. If this is the case, it may be possible to source a small number of matching tiles, but where a significant number of tiles need replacing, new tiles are likely to be required.

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Interior finishing

Standard interior timber moulding profiles such as skirtings and architraves that are now available are in metric, not imperial, which makes an exact profile match where they abut difficult. Also sheet lining materials may not exactly match the original even though the composition is similar.

Other options for matching interior finishes include:

  • removing all existing trim in the room and replacing it (use the removed material to make good or repair in other rooms)
  • having new profiles run to match the existing
  • sourcing second-hand material.

In some cases, damage may able to be repaired in situ by the judicious use of specialist fillers, or by filling and painting, which means the natural timber appearance is lost but the profile is retained.