Underfloor insulation options – timber construction

There are many options to consider for underfloor insulation to the underside of timber-framed floors, for both existing and new homes.

Not all underfloors are equal! Items to consider include:

  • Is the perimeter of the underfloor “open” or “closed”?  Meaning, is the cladding or lining all the way to the ground significantly reducing wind flow, or is the underfloor fully or partially exposed meaning wind flow?
  • Is there moisture on the ground during winter, or following rainfall?
  • Is condensation forming on the underside of the timber flooring/joists?
  • What is the building code requirements?
  • Is this a rental or other house needing to meet minimum prescribed standards?
  • How does the underfloor perform in relation to the rest of your building construction?

One of our trained assessors will need to visit for existing homes. For new construction, send us your consented plans.  The options we present will be based on what the structure and conditions allow, as well as the level of comfort you want.

Just meeting the minimum

The RTA (rental standard minimums) and the current EECA Warmer Kiwi Homes underfloor requirements only just meet the minimum requirements based on the current NZ building code.  That means the R-Value for the insulation is typically R1.5.  The types of products we offer in this range are white low-density R1.5 polyester fibre products.

Better than the minimum

For “open” perimeter underfloors we recommend using higher-performing underfloor insulation to reduce the effect of wind flow.  Where wind can freely flow over the surface of low-density fibrous insulation, the effectiveness of the insulation is reduced dramatically.  BRANZ research found that;

  • Data for the low-density glasswool reveals a 9% decrease in R-value for a 1 m/s increase in average wind speed.
  • The value for two low-density polyester products was similarly 12% for every 1 m/s increase.

BRANZ Build 153 April 2016

To avoid this, we recommend using either higher density insulation or more often an insulation system that has a “wind-wash barrier”.  This is generally at R1.8 or higher, has a durable facing for both fixing the insulation in place, as well as providing a wind wash to minimise the effects of uncontrolled wind flow.  This can be installed easily into existing houses, and also in new construction.  The finished product has a black face/lining visible.

Doing the best – and meeting the new NZBC H1 requirements!

The updated H1 requirements of the NZ building code see underfloor insulation/thermal performance almost double.   If you want to do the right thing – once – and really make your new or existing home perform, and meet the standard, then we will offer solutions for you using higher density insulation options, from R2.6 to R4.1.  Many customers are already “SupaCharging” their underfloors.  This is what we recommend for all new homes and existing homes from now on.

What about moisture?

Removing moisture buildup, either from condensation or ground moisture, is a good thing.

For moisture in the ground, we will recommend a ground moisture barrier – find out more HERE

Condensation forms as a result of poor airflow/ventilation and also from moisture present from the ground.  So increasing natural airflow is important.  Leaking pipes are also important to repair, and to ensure water is not running under your house following rain.

Call us so we can start the process to improve the performance of your building – old or new.