Insulation vital for warm homes

Awell-designed new home or renovation has an envelope of insulating materials in its ceilings, floor and walls that keep it warm during winter and cool during summer.

A home that keeps in the heat has: plenty of insulation thermal mass good double-glazing with insulated frames

a good level of airtightness.

Good insulation is the key to a warm and comfortable house that doesn’t cost a fortune to heat. And the best time to do it is when you are building so you can access all areas as you go.

For a really well-insulated new home: Make room for your insulation. For timber- or steel-framed houses, use 150 millimetre or even 200mm framing in external walls and reduce the number of framing members to what is structurally necessary – this makes more room for insulation.

Exceed the minimum Building Code insulation requirements.

For better warmth and comfort, it is worth putting in more than the minimum insulation levels, especially if you are in a colder part of the country.

Insulate cavities before they become inaccessible. Some cavities become inaccessible by the time normal insulation installation happens, so it is important to insulate them beforehand.

Areas such as external and internal wall junctions, window lintels and blocking of double studs are usually only accessible from the outside and should be insulated just before the wall underlay is installed.

If you have steel frames, a layer of insulation is needed between them and outer cladding to prevent thermal bridging. The NASH House Insulation Guide provides guidance.

Make sure the hollow steel profiles get completely filled with insulation. This is a common insulation installation fault in steel framed construction.

If your house has an attached garage, insulate the internal walls and ceiling between the garage and the rest of the house.

If you have a skillion roof, choose 240mm or 290mm rafters that provide enough room for good, high R-value insulation while still allowing for a 25mm gap between the insulation and the flexible roof underlay. If you have a concrete-slab floor, make sure it is well insulated.

Insulating both underneath the floor, around the footings and around the perimeter reduces heat loss.

Avoid recessed downlights. They require holes to be cut in your insulation for fire safety reasons, which creates heat loss. They can also cause draughts. Minimise plumbing and electrics in external wall cavities – they can make it impossible to install insulation properly in affected cavities, and can affect the building’s airtightness. Try to locate such services in internal walls instead. Plan your construction workflow well so that once the insulation is installed it won’t get disturbed by other trades.

Get it installed properly. Insulation doesn’t perform well unless it is installed properly.

Have your insulation installed according to the New Zealand Standard 4246:2006.

Double glazing is now standard in new homes as it is the easiest way to meet the current Building Code insulation requirements. It still lets in as much sunlight as single-glazed windows or skylights, but double glazing is much better at retaining heat.

Some double-glazing is better than others. For best performance, look for the following things.

Frames that are thermally broken, or made from an insulating material such as PVC or wood.

These will perform better thermally than windows with standard aluminium frames. It can reduce window heat loss by about 20 per cent (thermally broken aluminium frames) to 40 per cent (PVC or wooden frames), compared to double-glazing in standard aluminium frames.

Low-emissivity (low-e) glass. This allows light and heat in, but reflects escaping heat back to the inside.

Low-e glass cuts window heat loss by about 20 per cent to 30 per cent, compared to double-glazing without low-e Multiple layers of good seals to keep draughts, moisture and noise out.

The joint between the glazing unit and the frame also needs to be well-sealed. Spacers made of plastic or stainless steel to separate the glass panes (instead of aluminium) to reduce heat loss and condensation at the glass edge.

An inert gas filling (such as argon) between the glass layers. This acts as a better insulator than air, reducing window heat loss by about three per cent to nine per cent, compared to doubleglazing with air filling.

Close-fitting thermal curtains will reduce heat loss through double-glazed windows even further.

When choosing skylights it is critical to pick ones with good thermal performance characteristics to avoid high heat losses on cold winter nights and overheating in summer. Apart from the features listed above, it is highly recommended to select one with a low solar heat gain coefficient and to install effective shading devices to block out the sun on hot summer days and to improve insulation on cold winter nights.

Skylights that open can be effective for summer cooling through ventilation. If your skylight is installed through a roof space make sure the lightshaft is well insulated.

Even well-insulated houses can be hard to heat if draughts constantly replace hot air with cold air.

Good building airtightness, coupled with controllable ventilation (like openable windows, vents or mechanical ventilation systems), lets you manage air replacement and avoid unnecessary heat loss. For good airtightness: Plan for airtightness during the design stage. This means all design details can allow for proper, continuous sealing without gaps.

Design simply. Fewer construction joints means less potential for air leakage. Minimise external wall penetrations.

Holes for electrical and plumbing services can reduce airtightness – aim to have them through internal walls instead.

Make sure it’s well sealed. That means the joinery and the wall, floor and ceiling construction should all be properly sealed.

This can be done with airtightness membranes, which have recently become available in New Zealand at some hardware stores.

The store or the manufacturer should be able to advise you on the best solution for your circumstances.

Use airlocks at external entrances to your home, which are a buffer between inside and outside your home.

Entry ways, laundries and attached garages can all function as airlocks.