Roof insulation can be installed before or after plaster. Often the insulation installers will find it easier to install before plaster. The roof insulation batts are simply pushed up into place between the ceiling joists with long sticks. The roof batts are precut to ensure a snug fit between the ceiling joists assuming that the joists are spaced at the industry standard; 450mm or 600mm. If the spacing is excessive or uneven it can make it difficult for the installers to insert the roof insulation from underneath and the decision may be made to preload the roof with unopened bags of insulation and install them from above.
Calculating the amount of insulation needed
The number of bags required is easily calculated by dividing the number of square metres in the roof space by the number of square metres of insulation in the bags and then deducting 10 percent to allow for the timber framing itself. R2.5 batts are on the thinner end of the scale and less rigid, making them more difficult to install from underneath, even if the joist spacing is optimal. This may also provide a reason to opt for installing the insulation after plaster, from within the roof cavity. Installing roof insulation in the cavity of a new home is usually a much more pleasant experience compared to older homes. Unlike old houses, new buildings haven’t had time to accumulate the layers of dirt and dust that an old roof will inevitably accumulate over a number of decades.
The retrofit installation process
While it is fully possible for someone to install the insulation on their own, installers will often choose to work a fellow team member. Working as a team of two has several benefits. Apart from the social element of doing a tough job together with a mate, working as a team of two can use less than half the time the installer would need on their own. Benefits are especially felt when loading bags through the manhole which can be quite tedious and time consuming to do alone.
Installing insulation from within the roof cavity
Roof cavities are typically very hot, so installers usually prefer to start early, before the temperature inside the roof cavity becomes too high to work in safely. Installers often bring a couple of extra bags of insulation with them “just in case”. Up in the ceiling space the installer will split one bag open at a time and, using their installer sticks, (this might be as simple as a broom handle with a nail fixed to the end), will get to work deftly fitting the insulation batts between the ceiling joists. Once the roof insulation installation is complete installers can be expected to clean up any leftover scraps before fitting the final piece of insulation over the manhole cover. Roof insulation is by far the most cost-effective way towards keeping your electricity bills down and maintaining a pleasant indoor temperature all year round.
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