Components of the Building Project

We mentioned in the June 2012 Newsletter that we proposed to look at different components of the building project which can help to improve the thermal performance of your home. The first component we would like to discuss is the Sub-floor design and some potential insulation ideas.  We will address the Roof/Ceiling and Walls (including glazing) in the next edition.

With the Sub-floor, your design and product selections will be guided in large part by your site conditions and the steepness of the land.

On steep building sites or those sites with reactive soils, some sort of pier design may be required.  

If piers are needed and are over 1.5m in depth, screw piers may be a viable option. Screw piers can be taken into consideration during the structural engineering stage as the engineer will design the piers to the desired depth to provide the resistance necessary to handle the load of the project and its planned use. Basically, screw piers are a steel tube which have a cork-screw-threaded-end which is held by the excavator and screwed into the ground to the desired depth and resistance. Portion of the screw pier is left protruding out of the ground to affix to the footings and slab thus forming the pier and beam design which fairly standard building practice.

If the piers are less than 1.5m in depth, a standard drilled and concrete filled pier is the more viable option.

In both instances, your designer or engineer may incorporate bearer and joist construction. This type of construction is well suited to steeper sites as it will help with ease of construction and generally, is a more cost effective option.

Once your piers and flooring structure are in place, there are a few types of insulation alternatives that you may wish consider.

The area under timber flooring is the main area of heat loss in the cooler climates. Ideally, insulation products should be fitted between floor joists prior to laying any flooring. However, they can also be installed at a later date if there is clear access under your floor framing. This insulation can be referred to as sub floor or under floor insulation and is very cost effective.

When you are shopping around, it is important to note that these products may be partially or fully exposed to natural elements. Therefore, it is imperative that the necessary homework is done to ensure the right products are chosen for your location. 

For more level sites, a slab on ground may have been designed. In this case, there are still some decisions to be made (in conjunction with your engineer) about how to optimise the thermal efficiency of your home.

The following covers the three main types of slabs and how they can be incorporated into your design to improve your home’s thermal efficiency.

1. Standard reinforced slab on compacted fill – usually with 50mm sand topping and vapour barrier (builders’ plastic).

2. Waffle pod with reinforced slab – 1100mm x 1100mm x necessary depth foam pods which are used instead of compacted fill. Position and reinforcement of the waffle pods are stipulated by the engineer to ensure consistent strength across and throughout slab. The positioning of the waffle pods will need to be braced to ensure there is no movement during the pouring of the concrete. Foam pods (waffles) are a good thermal performer in colder climates, as the waffle pods provide a barrier between the slab and the natural earth thus limiting temperature change to the slab.

3. Cupolex with reinforced slab – Structural dome concrete floor system made from 100% recycled battery casings.  They have been designed to lock together to form a dome and pier system. The locking mechanism facilitates the speed of onsite installation by owner builders or concreters and gives confidence in the correct placement of the domes.

The dome design gives you a hollow section under the slab providing better thermal performance in the warmer climates.  The void under the slab slows the transfer of the external heat to the internal environment. During cooler months, the void under the slab can be heated by drawing the warmer air from your ceiling space and channelling the warmer air throughout the Cupolex domes thereby providing cost effective under slab heating.

Your designer will be able to guide you on how to best utilise your site conditions to optimise the thermal performance of your sub-floor or under-floor insulation. Whatever options are selected, it is important that they work in concert with the other thermal construction elements (eg roof/ceilings and walls etc) which we will discuss in the next Newsletter.

In the meantime, the team at DirectBuild would be happy to discuss the design options for your particular site.

Brendon Wilkie

Director
DirectBuild Australia Pty Ltd

Telephone (02) 9713 7428