Avoiding common energy mistakes in a new build

By Richard Keech (May 2018)

In the course of assessing many homes for energy efficiency, I’ve seen that even new homes exhibit problems in the basic build.  Here are a few ideas of things that are often overlooked. This list doesn’t include the many and varied mistakes that can be made in the basic design (floorplan, materials, orientation, shading etc).


When you specify the details of the build that you want, here are some things to consider.

1. Skylights. Skylights may be needed because daylight penetration into living space may be poor in places. However, skylights penetrate the thermal envelope and reduce thermal performance. One way to have your cake and eat it too is to use something like a Kimberly Illume solar skylight that uses PV/LED and doesn’t have a skylight shaft at all. These also give you more flexibility about where and how the light is delivered compared with regular skylights.

2. Downlights. If you use downlights then ensure that you choose a type that is safe and legal to cover with insulation because the normal way of doing skylights involves much greater compromise of the insulation than is commonly supposed.  See here for more info on why getting downlights right is so important.

3. Exhaust Fans. Make sure in-ceiling exhaust fans have back-draught protection. For kitchens, an alternative is to use a recirculating exhaust fan which doesn’t vent outside, and traps fat and odours in a filter.

4. Alfresco area. I don’t like the all-to-common alfresco areas (topic for a separate discussion). If you do have one then make sure to fit insulation properly to the ceiling above this outdoor space. This is because on a hot day, without insulation, the ceiling will reach temperatures much higher than ambient, and radiate considerable energy downwards making the space much less comfortable;

5. Garage. Often insulation isn’t fitted over/around a garage. You should fit some even if it’s not as thick as the main ceiling. This applies to the ceiling and the all walls adjoining the garage.

Don’t oversize

Avoid the temptation to oversize the house.  This will save you money, which can be better used making the place more comfortable and efficient.  Keeping the design smaller also tends to improve the options for passive solar because it’s less likely to be squeezed right up to the fence.

Efficiency thinking

Apply good passive-solar efficiency thinking to your design.  See here for more info.  With these things in mind, set a target star rating.  I suggest a minimum of 7.5 stars on the NatHERS scale.

Don’t over glaze

It’s common to see homes with windows that are too big.  This works against efficiency.  The star rating system helps avoid the worst problems in this regard, because often big windows will penalise the design.  Even so, it’s not uncommon to see windows on new builds which are too big.

See Jenny Edwards’ excellent tips about glazing here and here.

No gas

Using gas as a fuel in buildings is problematic for a lot of reasons.  And the good news is that efficient gas-free new homes are much cheaper to run.