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Raising and Renovating
In Queensland, people are raising and renovating the older weatherboard homes with stunning results. This is a great concept, as most of these homes are framed in termite resistant hardwoods, and while initially they can look a bit sad, the structural bones of these homes are usually (not always) OK. There are a few simple tips that can make the process a bit more durable. Some of the advice falls outside the scope of termites, but hopefully you'll find it all worthwhile.
The first part is a pre-purchase or pre-raising inspection to confirm the structural bones are OK, and some guidance as to what timbers will require replacement, or be useable. Remember that in the course of renovating, some damage within walls etc not previously visible for inspection may become apparent, but generally with these style of homes, there are not too many hidden surprises.
Next is the raising on steel posts. I'd encourage you to spend the money on "hot dipped" galvanised posts. They cost a little more, and a bit more lead time is required between ordering them and delivery (planning), but I've seen too many posts fail from rusting (corrosion), in some cases despite some of the lighter galvanised finishes. "Hot Dipped" galvanising appears to be the way to go for durability.
Before the concrete slab is poured underneath, the termite protection is installed. I prefer Granitgard or Termimesh stainless steel mesh as the termite protection method. Granitgard is a graded stone barrier, too heavy for termites to shift, and packing too tightly for termites to fit between. It has full Australian Building Codes Board (ABCB) accreditation, and has been referenced in the appropriate Australian Standards since 1995. It is installed to the slab penetrations (steel posts and plumbing etc) prior to the concrete pour to leave a standard concrete finish, and is regarded a true "life of building" product. If the external soil heights are at least 75mm below the top of the concrete slab or bottom of any waterproofing flashing, then the exposed slab edge can be regarded as part of the termite barrier, and we would expect that the Granitgard charges would be well less than $600.00 with most homes. If concrete block retaining walls are used as part of the walling, then some additional termite protection may be required.
The concrete slab is an important part of the termite barrier, and requires some attention. Domestic concrete slabs are covered by Australian Standard 2870. Concrete has a specific water/cement ratio. The cheapest concrete and most commonly supplied is 80 slump which is a stiff mix that needs some effort to work it into shape. Most concretors like to work with it at 100 to 120 slump. Most concrete truck drivers seem to wet the mix up further on site without being asked. NOT GOOD. This can upset the water/cement ratio, and according to a 10 page Concrete Information document from the Cement and Concrete Association of Australia, can provide a 30% reduction in the strength of the concrete. To view this document, visit this Page. The concrete companies may have recently started to deliver their standard concrete at a higher slump, which has to be a good thing.
Compaction or vibration of the concrete slab is another issue commonly overlooked. It has been said that most domestic concretors wouldn't know what a concrete vibrator was if it fell on top of them. Thankfully that situation is changing, with vibrators being seen used on most (not all) sites now. AS 2870 says "concrete shall be handled, placed and compacted so as to - in part (d), completely fill the formwork to the intended level, expel entrapped air, and closely surround all reinforcement, tendons, ducts, anchorages and embedments". To my way of thinking, the term "shall" is the important one. It doesn't say should, might or could be. It says SHALL. According to the same Cement and Concrete Association document, the drop in concrete strength by not compacting can be 20 to 25%.
In order to get a smooth edge, some concretors use sheet metal boxing. There is another way to get a smooth, presentable slab edge. I've seen a 300mm strip of "visqueen" or moisture barrier plastic used as a curtain on the inside of the boxing. A quick poke with a vibrator near the edge, and the concrete against the plastic is left as smooth as a baby's backside. Quite a presentable edge without the cost of specialist boxing.
Once the slab is laid, you can start to build in underneath. I'd encourage you to look toward termite resistant framing. This can be hardwood, cypress pine, T2 (blue) treated pine for south east Queensland, or steel. Whilst the walls under a renovation of this nature are rarely load bearing (the structurals are the steel posts, and the role of the framing under is to support the wall sheeting), by maintaining termite resistant framing it means the integrity of the home is rarely threatened by the time termites are discovered. (If the concrete slab cracks excessively (rare with a properly designed and poured concrete slab) for instance, termites can still enter the home.) I prefer to see any window reveals or door jambs in a termite resistant materials (treated pine etc). If termites damage a window reveal to the point it needs to be replaced, commonly the window needs to be removed and reinstated to replace the reveal. With door jambs, if their termite damaged, the door can fall off. Much better to do these in termite resistant materials. A further assistance can be the use of "finger jointed pine" (termite susceptible) trim timbers to skirtings and architraves etc. (Don't paint behind them before installing!). The termite susceptible trims provide an inbuilt early warning system, in that they're relatively inexpensive, and easy to replace if termites ever occur.
The end result is a home with termite resistant framing throughout, on durable steel posts, with "life of building" termite protection. Heaven forbid if termites were to be able to enter the home through a failing slab, or another unusual entry point, then they're going to be discovered in trims that are relatively inexpensive and easy to replace. From our point of view, that's got to be good!!
The ongoing termite management of such a home is regular annual inspection.
For more information, please don't hesitate to contact us at any time. © Mark Porter 2009
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