Remedies: matching new to existing

With any renovation of a 1970s house, there will be areas where original construction needs to be replaced or new construction must merge with existing.


With any renovation work, there will be areas where original construction may need to be replaced or new construction must merge with existing.

Materials and fittings used in 1970s houses may no longer be 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

Current framing sizes are slightly smaller than the gauged framing used during the 1970s. For example, original framing would have been gauged metric ex 100 x 50 mm which had a finished size of 94 x 47 while current framing has a finished, dry size of 90 x 45 mm.

If necessary, the differences in timber size can be addressed by:

  • packing new framing to increase thickness
  • adjusting packing to give an even line
  • aligning a change at an internal wall location so the change in wall thickness is masked - this may mean removing some sound existing framing
  • for small areas, removing the existing wall back to a junction, then installing new framing
  • machining timber to match existing.

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Cladding

Where existing claddings are damaged or the building is being extended, a decision must be made whether to retain and merge or replace the claddings. The availability of matching materials and the extent of the remaining cladding will affect the decision-making process.

Damaged weatherboards - for example, split, bowed and cupped boards - compromise the weathertightness of the building and must be replaced. When matching weatherboards, first check the dimensions of the board used as it may be available ex stock. If not, options 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 (and fitting corner boxes to mask the difference)
  • masking the change with a coverboard to make the difference in size less obvious.

For claddings which were not commonly used or only available for a limited time, such as vertical plastic, it is unlikely that new or second hand material can be sourced. A change in cladding over part or all of the building may be required.

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Roofing

Metal roofing was generally longrun, which eliminated the end lap corrosion of shortrun roofing. New metric corrugate material can generally be side-lapped to existing imperial longrun to make a join, for example where the building has been extended. However, it may not be possible for other profiles to be side-lapped due to subtle changes in the rolling of the sheet edge.

Where the roof is still in sound condition and only one or two sheets need to be replaced, it may be possible to use new material. Second-hand galvanised steel material may be an option if available; otherwise the roofing may need to be replaced.

New zinc/aluminium alloy roofing should not be used in direct contact with the original galvanised steel roofing, nor installed where it can drain water onto it.

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Interior finishing

Standard interior timber moulding profiles such as skirtings and architraves have not changed much since the 1970s and a match may be found. Today, plasterboard is subtly different - current material is 10 or 13 mm thick while the material used in the 1970s was 9.5 and 12.5 mm thick. However, this should be able to be masked during stopping.

Other options for interior finishes, where a match is not readily available, 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 be repaired in-situ by filling and painting. This means the natural timber appearance is lost, but this is not a problem if a paint finish is required.

Boric treatment for timber provides protection against borer attack, but where untreated native timbers and untreated pine have been used there is a possibility of borer damage, particularly where the timber is damp. However, even boric treated and H3.2 treated timber will rot if it gets wet and has stayed wet.