Most 1970s houses are likely to be fairly sound, though some design and structural issues may need consideration as part of any renovation.
Most houses built during the 1970s are likely to be weathertight and structurally sound. For most houses of this era, large eaves gave good weather protection, windows were airtight, and subfloors had good ventilation.
In some cases, there was a lack of understanding of new building materials and methods, which may lead to problems with durability or moisture.
But, for most houses, renovations will focus on upgrading comfort and energy efficiency, adding space, improving layout and orientation, improving indoor/outdoor flow, upgrading services, and replacing outdated fixtures and finishes.
Before undertaking any renovation or remedial work, the condition of the existing building should be carefully reviewed. There are a number of aspects of the building that should be considered, evaluated and (possibly) addressed as part of any renovation project. These are explained below.
The original design and layout, and/or subsequent unsympathetic or poorly carried out alterations, may need to be addressed to rectify issues such as:
- arrangement of rooms and incorporation of new materials to increase benefit from passive solar gain
- requirements for additional space such as adding a separate living area, additional or larger bedrooms, or extra bathrooms or toilets
- improvement of internal layout and movement through the building
- a lack of or poorly organised indoor/outdoor flow
- insufficient services such as power outlets, light fittings, extract ventilation.
Any new construction work must comply with the Building Code and may involve consideration of compliance with current district plan constraints for side yards and site coverage.
Specific engineering design may be needed where existing loadbearing walls are removed/modified, the basement is excavated, the building lifted or another floor is added.
Where the building is added to or altered, wall and subfloor bracing requirements may have to be recalculated, particularly for the ground floor when another floor level is added.
1970s houses may need strengthening as part of any renovation. Check to see if loadbearing walls have been removed, if bracing is adequate, and or if there is other evidence of structural problems such as floors slumping. Read more.
Houses built during the 1970s generally have few weathertightness issues. However, weathertightness is sometimes an issue if cladding is damaged or deteriorates, or around windows - especially when no flashing has been used.
With renovation, attention will be needed to ventilation to ensure that internal moisture does not become a problem. Read more.
Matching new to existing
With any 1970s house renovation, there will be areas - such as framing sizes, claddings, and roof profiles - where original features need to be replaced or new construction must merge with existing. Read more.
Few houses built in the early 1970s were insulated, and where insulation was installed it is unlikely to meet modern requirements. Insulation may be required as part of any renovation project, and in any case will provide benefits for occupants. Read more.
Copper pipes will probably not need replacement but plastic pipes may - have them checked. Read more.
- plumbing - are there any signs of leaks? Are fittings easy to operate? Is there adequate water pressure?
Low pressure hot water systems may need to be upgraded to mains pressure. Pipes may need replacement to cope with the higher pressure. Read more.
While wiring is likely to remain in good condition, many 1970s houses will not have enough power and light outlets. Read more.
Foundations and subfloors
Most foundations will be in good condition, though some may lack adequate earthquake bracing. Check for unevenness, moisture and other signs of damage or deterioration. Read more.
Original floors may remain in good condition, but should be checked for borer, rot, moisture damage or other signs of deterioration. Read more.
Original roofs may need maintenance or replacement. Consider the condition of the cladding, whether there are signs of water entry, and whether drainage is adequate. Read more.
Also consider whether roof insulation is adequate.
Claddings may still be in good condition, but some claddings may need repair or replacement. Checking for signs of water entry, damage, or places where cladding has been up against the ground. Read more.
Also consider whether wall insulation is adequate.
Internal walls and ceilings
Problems may include walls that are unsuitable for paint finish, and linings that have cracked due to building movement. Read more.
Original windows are unlikely to be double-glazed and may not be airtight. Original frames may be in poor condition. Read more.
Metal elements such as roofing, fixings and flashings may have corroded and need replacement. Corrosion can affect structural performance. Read more.
Borer, rot and mould
- Borer damage in 1970s houses is more likely to occur where rimu sapwood or untreated radiata pine has become damp in service. Borer risk is higher in untreated radiate pine framing, interior trims and flush panel internal door frames, and joinery carcases. H1 treatment (now called H1.1) provided protection against borer.
- Mould is not generally a significant problem in 1970s houses, but may be found where there has been a leak from the outside or plumbing, or there are high internal moisture levels. During demolition or renovation work, mould may also be found within walls, under the floor, or behind linings during demolition and renovation work.
- Rot may be found in 1970s houses where timber has been exposed to moisture for extended periods - for example, in joints in weatherboards and exterior trim, skirting boards in wet areas, timber and MDF window reveals, and timber claddings that are too close to the ground. The boric treatment of radiata pine framing gave some resistance to rot where timber was occasionally wetted.
See Borer, rot and mould for details of how to identify and respond to these problems.
Health risks: asbestos
Asbestos-cement was in use in houses as wall and roof claddings (Figure 1), soffit linings, bitumen roof cladding, as a backing to flooring and in textured ceiling finishes until the 1980s. To determine whether fibre-cement sheets are asbestos-based, a general rule of thumb is that sheets that are pre-1988, or have a corrugated profile or a dimpled back surface, are likely to contain asbestos fibres.
Asbestos becomes a health hazard when old materials containing it are being removed or break down, allowing the fine particles to become airborne and breathed in.
See Asbestos for information about safety requirements for removal of asbestos.
Health risks: lead
Lead was used in house construction in external and internal paintwork, flashings, valley gutters, nail heads and waste pipes.
Oil-based paints containing red lead were commonly used until the mid-1960s when the health hazard of lead became more fully understood. The use of white lead in paint was finally banned in 1979 but some special-purpose paints still contain red lead. It is not possible to identify lead-based paint from its appearance, but if a building is over 35 years old, assume that it has been painted with lead-based paint.
See lead for information on dealing with lead contaminants.
Health risks: treated timber
Timber treatments protect timber from insect or fungal attack, but the chemicals used to preserve timber are also hazardous to people, so care must be taken when working with treated timbers.
During the 1970s, boric treatment was used to protect against insect attack (particularly borer) for interior use and for exterior painted timber (trims, fascias, weatherboards. CCA (copper chromium arsenic) treatment was not used extensively in 1970s houses but may be found in exterior uses such as decks, piles, fencing and poles.
Fire safety was not generally a consideration in the design and construction of 1970s houses. Although plasterboard linings reduced the risk of internal fire spread, furniture, furnishings and dry timber present a significant fire load, so fire safety should be incorporated in any renovation work. Read more.