Karl Wootton
Senior Technical Consultant/Director

Some of you more distinguished members of the waterproofing community may say,
“but we’ve always had them. We called them inverted roofs.”

Yes, you could say that, but there is a distinct difference in the form they take and the thermal Insulation value they ultimately provide.

Warm roof construction in both Europe and America have been in use for quite some years and are generally accepted as the norm in low slope roofing. Here in Australia, we are only just catching up.

Warm roof construction takes the form of installing a vapor barrier and hard rigid thermal Insulation board to the top of the roof structural decking. Over the principal Thermal Insulation, the roof membrane is then applied. The finish can be left exposed or over laid with hard and soft landscaping, pavers on pedestals etc. This form of Thermal Insulation is one of the most efficient forms of thermally Insulating a roof structure. One of the first benefits is that thermal heat transfer in summer or the Dew Point in winter (the point at which moisture reaches 100% RH) is kept at the Insulation / Membrane external interface. Neither heat nor condensation is allowed to affect the roof cavity.

If we prevent thermal heat transfer or condensation from affecting the roof cavity then your air conditioning must therefore run more cost effectively. This is because the roof ceiling cavity temperature will more closely match the interior temperature of the rooms below it.

What we typically use in Australia is “cold” roof construction. Whereby we insulate the ceiling cavity with a mineral wool type insulation. There are some draw backs to this form of Insulation, one of which is that at certain times in the year the due point can be reached within the ceiling cavity. I have seen this from time to time where the roof membrane has been blamed but in fact the conditions were such that condensation formed in the space between the top of the mineral wool and the underside of the roof substrate, this is known as Interstitial condensation. There are other issues such as heat build up within the ceiling cavity during summer and the subsequent transfer of some of the heat to the internal spaces. Both of the issues described above have a negative impact on Air conditioning performance for the spaces below.

Ok you ask, but what about an Inverted roof?

The typical construction for an Inverted (or sometimes referred to as an I.R.M.A roof) roof consists of a roof substrate, typically concrete, to which a membrane finish is installed.

Then a rigid insulation board, typically DOW corning extruded polystyrene, is installed with a screed layer or stone ballast then installed overall to keep the whole
system in place to prevent wind uplift or floatation issues. A reasonable system for its time but from a performance and maintenance view does have some draw backs. From an Insulation point of view, it is not all that efficient as water from any rain event will percolate down to the interface between membrane and underside of Insulation, how does this affect long term thermal performance. If any maintenance or repairs need to be undertaken it becomes problematic from a logistical point of view. It is generally a “heavy” system compared to a warm roof construction.

Warm Roofs in the Remedial construction market?

In this sphere of the building and construction market we are seeing a move towards improving overall building performance when the time comes to refurbish a low slope roof.

It makes sense to review what is possible so that the full benefit of any refurb can be realized. There are many ways to carry out this process. However, if you talk to the right people a plan can be prepared to meet the expectations of all involved. Planning for these types of projects is critical to ensuring the smooth running of any project undertaken.

Did you know that you can also correct the slope of a roof with Insulation!

In this case we use what is known as tapered insulation, a lightweight solution without the need for heavy screeds and the like, perfect for older buildings where weight may be an issue. The insulation provides both thermal performance and fall on the roof, again as above there are some critical steps needed to make sure this works but talk to us and let’s see what is possible.