Footing design for home

By: Peter Huber
Posted By: BHIS
Source:http://bit.ly/1Ww1RM1

What is probably as important as consistent compaction is the design of the footings and the actual digging and pouring is equally as important. Firstly footings should be designed according to the nature of the soil. For example you would not design the same size footing when building in clay soils as you would if you were to build on sandy well drained soil.

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It has always been our advise to firstly sample and categorise the soil, if you are to build on clay or loamy soil, especially where drainage is poor. This will then determine the type of footing design for the home and will minimize any settling or cracking that would normally occur.

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Well we now have got, consistent compaction and a footing, designed specifically for the soil and a slab to match. The next step is to examine the perimeter masonry walls to see if and what type of settling cracks have occurred if any.

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The settling cracks that are visible on the brick work or internal walls are a signature or blue print as to what has occurred under the slab.

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The walls are a reflection or and indication as to the stability of the foundation. Below are some diagrams showing the different type of cracks that can occur and why.

What to inspect when buying a home?

By: Peter Huber
Posted By: BHIS
Source: http://bit.ly/1VHVbtP

It goes like this, before you buy something, and a friend had described it to you in detail ”warts and all”, it would have helped in shaping your ideas in the purchase of that something.

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Well the same goes for when buying a car or a house. These are major purchases for most people and for some it is the single most important investment in their live. This being the case then, would it then not make sense that before buying, some one thoroughly checks out your proposed purchase before a final commitment is made on paper in the form of an offer to purchase. Preferably a mate in the building industry or a professional inspection institution can be called upon to give an unbiased opinion based on the structural nature of the building.

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The things that a buyer should be aware of is that firstly the foundation, walls and roof construction are sound, as theses components constitute the shell and anything else is purely cosmetic.

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Firstly the foundations:- If they are Limestone, then one would have to appreciate that they are large chunks of rock, shaped and placed into a hand dug trench and mortared into position, there was never any compaction carried out to the soil below the first laid limestone, hence the ground could move and settle as the weight of the walls was placed upon the Limestone. Large homes were built upon the limestone foundations and later the settling took place and was and still is evidenced in settling cracks noted on wall.

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These days we build the foundations a different way, mostly it is a concrete perimeter beam and a floating slab is resting on top of these footings. This latter method is built on soil that has been compacted to a uniform compaction. If this compaction is not uniform then uneven settling can be the major source of settling cracks, as the foundation settles under the weight of the walls and roof. The importance of uniform compaction is so vital that theoretically, if the compaction was uniform then no settling would occur.

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The importance of keeping the perimeter foundation at a constant moisture level is equally as important since a constant change in concentrated moisture levels content will cause the soils supporting the perimeter footing beam to move. This movement is transferred to the walls and settling cracks appear over windows and doors as these are the most vulnerable areas. So it is important that the down pipes are connected to soakwells which are at least 1.8 meters away from any footing.

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Next week we will continue with this, so that by the end, you will have a comprehensive check list.

why concrete tiles for roof?

By: Peter Huber
Posted By:BHIS
Source:http://bit.ly/1rtHhzd

Ok lets continue where we left of in the last article, on the fact and fiction about roof tiles.

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If you are worried about the usage of concrete tiles when collecting rain water, well there is nothing to worry about as we are assured that the surface of the concrete tile is a suitable surface from which to gather water for drinking, and best results are achieved when an appropriate collection system is fitted.

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If you are building near the coast you also need not worry, as the prolonged exposure of concrete tiles have a proven record of resistance to corrosive atmospheres.
Similarly in tropical conditions the added weight of a concrete roof helps to counteract wind uplift during storms making it less susceptible to damage than some other roofing materials.
Normally concrete tiles require very  little if any maintenance due to their exceptional durability, if some is required then only the affected tile will need to be replaced.

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Cleaning of the tiles is also not  a necessity but Lichen and moss can be removed by high pressure jet water sprays or by the application of a specific chemical formula sold for this purpose of removing the lichen and moss. In fact the formula for the magic potion is this:-  200 grams of copper sulphate, to 4.5 litres of water The average roof will need ten times this amount, the solution is broomed onto the offending areas and eradication will take place over the following couple of months and it should be left to work on its own as the moss and lichen will gradually disappear. On porous tiles the solution has a residual affect as it remains and inhibits any future or early re-growths.

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When using copper sulphate solutions be careful that metalwork such as guttering is protected to prevent corrosive  action. Gutters should be filled with water by blocking the downpipes as any solution running into the gutter will be extremely diluted and not affect the metal gutter.
By comparison concrete tiles are very affordable and generally cost less than metal or clay covering, on most profiles the fit is neat and even, but the coating that is applied to the tiles is still subject to weathering and will eventually wear off and needs re-painting.

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So myths like, Lichen and Moss will eat into your tiles and weathering of the original surface coating makes old tiles porous, is all a lot of old wife’s tales and scare tactics, invented by itinerant traders.

Every so often we would like to publish questions with answers that our readers may have on renovating or building, so please share your comments.

Tips for choosing roof tile for your home

 

By: Peter Huber
Posted By:BHIS
Source:http://bit.ly/1VoHkbJ

The other day I spoke to a gentleman who asked me, to confirm to him that he needs to replace his concrete tiles on his house with clay tiles, I questioned his rationale and a mountain of misleading  statements flowed from his mouth, perhaps the most memorable was that “as concrete tiles become older they start to leak and there is nothing short of replacing them with clay tiles”

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I must say I have heard many such rumour floating around, all of which I am hopefully about to dispelled. I decided to see if the concrete tile manufacturers have become aware of these rumours and what if any, their official response was?

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After talking to several people connected to the concrete tile industry, a brochure was mailed to us prophetically titled “THE FACTS ON CONCRETE TILES”

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I will summarise and add some of our own comments to the questions and topics covered in this brochure.
“ARE CONCRETE TILES DURABLE?”
The modern manufacturing process makes the tiles exceptionally durable, they are manufactured to Australian standards and the physical properties of concrete will remain unchanged well in the excess of fifty or more years, irrespective of climatic conditions.

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Concrete actually becomes stronger with time and remember concrete is the preferred  material for major structures such as bridges and high rise towers because of its inherent qualities of strength and longevity, additionally it out last other roof cover materials as it does not rust or corrode.
“DO CONCRETE TILES ABSORB WATER AND THEREFORE DOUBLE IN WEIGHT?”  No this is incorrect and a myth. The Australian standards AS1757-1989 actually specifies a maximum water absorption of only 10% per total immersion in water for 24 hrs. In practice the absorption of water by capillary action during periods of heavy rain would increase the weight of the tile by around 5%. Contrary to claims of some roofing companies, this weight increase is unlikely to cause structural roof or stump failure.

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“DOES WEATHERING OF THE ORIGINAL TILE COATING MAKE TILES POROUS?” Not true.  The colour coating is purely decorative and is not designed as a water proofing film. As in most water proof purpose made concrete, water proofing is achieved by using carefully selected, formulated, batched and graded materials which are then compacted during manufacture. This then produces a concrete product of high density and strength which naturally keeps out water.

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“ARE CONCRETE TILES FIRE RESISTANT” yes they are totally incombustible and fully fire resistant according to ASTM (USA)E108-88 tests, there is no comparable test available in Australia.
“WHAT ABOUT THERMAL AND SOUND INSULATION” Tiles  take longer to heat up and tiled roofs usually have a larger volume roof spaces which “breathe” so houses with tiles roofs  stay cooler longer, but once the heat build up accumulates for long periods, it also works in reverse that it takes longer to cool down.

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Due to the greater mass of concrete tiles they do provide a better sound insulating quality than metal roofing, they help to reduce to noise intrusion in particular caused by rain and hail.

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We will continue to discuss the myths and facts of roof tiles

Source:http://bit.ly/1VoHkbJ

Overcoming damp problems in your house | Professional Home Inspections Perth

By:Peter Huber
posted by: bhis.com
Source: http://bhis.com.au/2013/02/overcoming-damp-problems/

From time to time the CSIRO is asked to suggest remedies for dampness caused by rain penetrating solid masonry walls, below are some of their invaluable findings and suggestions which are worth passing on.
Single-leaf construction cannot be expected to be water-tight, especially if it is subjected to wind-driven rain. If the wall thickness is increased it should be more resistant to rain penetration, but poor workmanship in the form of unfilled joints and un-tooled face joints can result in walls that are prone to dampness despite their thickness and apparent solidity.

Often people seek a quick and easy “brush-on” treatment, preferably to be applied from the inside, but we consider the latter to be unrealistic and a false economy. External treatment aimed at preventing the masonry from becoming damp in the first place is a more sound approach. Some possibilities are described:

 

SILICONE TREATMENT

Silicone formulations brushed or sprayed onto porous surfaces make them water repellent, so that water then runs down treated walls instead of being absorbed. There is a risk in this, however, because fissures wider than hairline crack are not bridged by these materials. The increased amount of water running down the wall during a shower can result in more water penetrating the wall, via such fissures, than before the treatment. With this in mind walls should be examined carefully, and repaired if necessary, before silicone is applied. Silicones deteriorate in sunlight and periodic reapplication is required if the wall is to remain water repellent.

 
CEMENT-BASED PAINT

This is a useful treatment. Two coats should be applied on the wall after the necessary preparation. A minimum preparation would be to repair gaps and defects in the mortar joints, but in practice “bagging” of the whole wall is advisable. A mixture of 1:4 cement: plasterer’s sand is suggested for this, the wall being “wetted down” before starting.

 
ORGANIC PAINTS

If organic paints are to be used “bagging” is an essential preparation. As long as the paint film is intact the system will be effective, but once cracking starts water will be trapped behind the paint. This water will take a long time to evaporate and, under adverse conditions, the wall can become progressively damper. In any case the life of the paint system there-after is likely to be short.


RENDERING

This treatment is virtually permanent and should be effective in all but the most severe conditions. For resistance to rain penetration a rough-textured and porous rendering is normally more effective than a dense and impermeable plain finish. Suitable cement: l lime: sand mixes are given in the British Standard Code of Practice CP 221, “External rendered finishes”, available from the Standards Association of Australia.

The discussions and hint given above will suit most homes that have damp problems, in fact silicone treatment seems to be the most popular, especially in the case where the external walls are face bricks.

If you have any further questions please call our office.

We want you the reader to write to us on, any Building matters, and questions or if you seek advice, we will gladly answer any topic that you wish us to discuss, so please send your letters to “B. & H. I. S.” C/O. 17 Battye Road, Kardinya, W.A. 6163 or fax/ph (09) 331-3031

Best Wall Coverings practices | Pre Purchase Building Inspections Perth

                                 
By:Peter Huber
Posted By:bhis.com
Source: http://bit.ly/1iIkPO6

Vinyl wall coverings (vinyl laminated to paper or fabric) have become very popular over the last few years, largely because they are more easily cleaned than the uncoated open-textured types. Yet it is just this impervious, otherwise-desirable surface that sometimes creates a mould problem.

Pre Purchase Building Inspections Perth   

In one home examined by the Division of CSIRO, red and purple stains were found to be showing through from behind a light coloured vinyl wall covering within two weeks of application. The stains, which originated in the paste layer, were identified as a type of mould. The key factor in this rapid mould growth was the fact that paste had been sandwiched between a painted wall and a sub-substantial vinyl membrane.

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On one hand, the impervious vinyl layer prevented evaporation of moisture from the paste layer while on the other hand, the painted background drastically reduced absorption of water into the wall. Thus, the paste was kept moist long enough for mould growth to start. Had an adhesive offering less nourishment to moulds been used, mould growth would have been unlikely. Similarly, had the wall covering been a plain paper or one of the “spongeable” wallpapers (papers with a very thin plastic film on the surface), or one of the “breathable” vinyls, mould growth would again have been unlikely since such coverings “breathe”, enabling the paste to dry by evaporation.

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When hanging wall coverings of solid vinyl sheet laminated to paper, it is a wise precaution to apply a fungicidal wash such as two percent sodium hypochlorite solution to the wall before sizing it with a dilute solution of a cellulose adhesive with fungicide added. For best results manufacturers suggest applying lining paper to the wall before finally hanging the wall covering, using the heavy-duty cellulose adhesive for both operations. In the case of mould staining described above the vinyl wall overing had been hung, without a preliminary fungicidal ash, using a starch paste (instead of a cellulose adhesive) with fungicide added. Obviously this was not enough protection.

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When the weather is very cold and damp the cellulose adhesive may take a long time to set, so an acrylic-reinforced latex adhesive might be advisable under such conditions, to avoid lifting of the seams. Alternatively, he cellulose adhesive could be used and, if the seams do lift, they could be bonded to the wall with the latex. When hanging wall coverings of vinyl sheet laminated to fabric, only the specially formulated adhesives recommended by the manufacturers should be used.

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Normally, coverings are not hung on absorbent surfaces. Manufacturers recommend that bare surfaces be painted with a flat oil paint, and it has been assumed in the above that this has been done.

For now till next week when we will discuss

“RAIN PENETRATION OF SOLID MASONARY WALLS”
your “Handy Jock”.

Any questions that our readers may have would be gladly welcomed and endeavoured to be answered as seen fit.


Source: http://bit.ly/1iIkPO6

How to stop condensation? | Professional Building Inspections WA

By:bhis

Posted By:Peter Huber

Source: www.bit.ly/1NzosBy

Continued from the post > CondensationIssues

How to stop condensation?

Condensation is basically simple. It involves preventing moist air from coming into contact with cold surfaces (ie. surfaces at temperatures below the dew point of air). In practice this can be achieved by:

§  Removing moisture laden air (by ventilation) and/or

§  Raising the temperature of any cold interior surface to a level above the room air dew point (by heating).

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The best way to remove moist air is to use exhaust fans as its source. An electric fan should be installed in the ceilings of the bathrooms and switched on when using showers or baths. To enable the fan to work more effectively, leave a door or window slightly open while the fan is running.

A ceiling vent is recommended over every sink, basin or trough in the house.

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More water vapour is normally generated in laundries tan in any other room. Clothes driers should be ducted to the outside air.

A hood fitted with an exhaust fan is recommended over hot plates and stoves as follows:

§  The exhaust fan should be at least 200 mm in diameter.

§  The distance between the hotplate and hood should be 600 mm, this distance may be increased to 750 mm if absolutely necessary.

§  The width and depth of the hood should be preferably the same as the hot plate or stove.

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If it is not practical to install a hood, an exhaust fan may be located in the ceiling over the stove and used while cooking.

In rooms where exhaust fans are impracticable (eg. bedrooms) adequate ventilation can be obtained by opening windows.

Remember it is better to ventilate continuously by having all windows slightly open than by opening one window wide for a short time.

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Heating

In addition to good ventilation, heating can also help to reduce condensation on walls and ceilings. Condensation on window panes and metal window frames, however, is not significantly reduced by heating. This is because glass and metal are good conductors of heat. Any heat which reaches these surfaces does not warm them appreciably as the heat quickly is lost to the outside air.

In very cold climates (and in Australia this can be takes to mean in areas above the snow line), it may be necessary to provide double glazing to raise the temperature of the inner pane.

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It is better to provide some continuous background heating rather than short burst of heating. Continuous heating allows wall and ceiling surfaces to warm up and stay warm, which greatly reduces the risk of condensation. On cold days try to keep inside air temperatures at least 5oC higher than outside air temperatures.

Insulation

The risk of condensation is considerably reduce in any room if walls and ceiling are insulated, because it allows these surfaces to reach a higher temperature. For an existing house it may not be practical to insulate walls, but ceilings can usually be easily insulated. Apart from reducing the risk of condensation and mould growth, insulation will substantially reduce heating costs.

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Technical information by Courtesy of CSIRO.

Your “Handy Jock”.

Any questions that our readers may have would be gladly welcomed and endeavoured to be answered as seen fit.

Source: www.bit.ly/1NzosBy

Inspect Home before Selling | Professional Building Inspections Perth

By:bhis
Posted By:Peter Huber
Source: www.bit.ly/1NzosBy
Before You Sell Your Home, Have it Inspected!

So you’re considering selling your home and now you want to be sure that there will be no unpleasant surprises to upset the settlement process. Well, we’re here to help make sure of that! Building and Home Inspection Service currently has five offices spread around the wider Perth metropolitan area, all of which draw on a wealth of experience to ensure that your home is thoroughly inspected with the most up-to-date equipment and reports digitally collated for your future reference.

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Common Problems with Building Integrity

1) Termite Infestation and Damage

This is one problem you never want to let get out of hand. Termites just love untreated pine and will turn structural timbers to dust in months if left unchecked. We will endeavor to find their trails, any timber that has been affected from ceiling supports to floor joists, and record all the sites photographically and in your written report.

2) Foundation Settling

A common problem with suspended houses – those on stumps – but also on concrete slab foundations are cracks that appear as a house settles, or as the ground dries out or becomes wetter over years. Cosmetic or structural repairs are called for, but in terms of selling your home, so long as the issue is catalogued, no-one can complain they didn’t know what they were buying.

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The movement of buildings can also result in problems with main lines in and out of the structure. While electricity and gas are not usually a problem, due to the malleability of the materials used, even modern day PVC pipes are susceptible to fracture. This can result in leakage from waste pipes wherever the connection becomes stressed – even in the wall cavity of your home.

3) Construction Short-cuts

We don’t want to seem overly critical, but even the width of mortar joins between bricks must meet a minimum standard – too much mortar compromises the structural integrity of the wall. Elsewhere, poorly secured flooring can result in buckling of verandah floors, or the use of untreated or uncured, water-sensitive wood close to down-pipes can result in much the same thing.

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All these and many, many more criteria are examined and checked with a Building Inspection reports Perth – there is one for your budget and building, no matter where in Perth you are located. Call one of our offices today! or else go to:www.bhis.com.au/contact-us/

Source:www.bit.ly/1NzosBy

What causes condensation in houses? | Building Inspection specialists Perth

By:peter
Posted By:bhis.com
Source:www.bhis.com.au/2012/10/condensation-issues/

CONDENSATION IN HOUSES:-
What Causes condensation?

THE AIR AROUND US ALWAYS Contains A CERTAIN AMOUNT OF WATER VAPOUR BUT THE AMOUNT THAT CAN BE PRESENT AT ANY TIME DEPENDS ON THE TEMPERATURE OF THE AIR.
Building Inspection specialists Perth:
When moist air is cooled below its “dew” point that is (cooled to temperature at which it cannot contain all the water originally present) and if the cooling is caused by contact with a colder surface, then the surplus water appears as droplets on that surface, we call this condensation.

In real every day analogy it translate like this:- we hardly notice the air around us on an average day, then night time approaches, the temperature drops, and things become cold as the temperature drops, so does the air, if this dropping in temperature continues then the water vapour that occurs naturally in the air turns into water and if cold enough into ice.

Air in a house can become moister because the occupants and some appliances produce water vapor. Typical quantities of water vapor produced in a home are:-

    Adults breathing 0.1 liters/hr
    Hot Bath 1.5 liters/hr
    Washing Machine 3.0 liters/hr
    Clothes Drier 5.0 liters/hr
    Hot Shower 10.0 liters/hr

Water vapor is also generated in large quantities by gas stoves/hot plates and kerosene heaters so much so that a lot of water may be stored in the air each day as water vapour.

Building Inspection specialists Perth:
On cold days much of this water will condense (if the ventilation rate is low) on cold window panes and even on walls. Little wonder then when some house holders complain of mold, decay and damp carpets.

Steam coming from service areas such as kitchens laundries and bathrooms travel to other rooms in the house, even if these rooms are a considerable distance away. The worst condensation problems generally occur in unheated rooms facing south which receive little heat from the sun. The movement of the water vapour within the air (using the air as a travel medium) travelling from service areas to other rooms such as bedrooms is due to the difference in water vapour pressure.

Condensation in new homes

Severe condensation problems often occur in new homes as construction moisture is stored in the bricks floor etc. in addition to the moisture generated by the occupants. It will take about six to 12 months for the water to evaporate. Some of this moisture will be lost to the outside air by natural ventilation and much will find its way into other rooms in the house.

Building Inspection specialists Perth:
If moist air from the rooms is exhausted into the roof space, sever condensation may occur within the roof space causing costly damage to ceilings, roof members and insulation materials.

    Poorly vented pitched tiled roofs with aluminium foil sarking directly beneath the tiles. To reduce the risk of condensation, ventilation should be provided in the eaves and gable ends.
    Flat metal deck or cathedral roofs. On no account should moist air be exhausted into these roof spaces. It should be carried by flues passing right through the roof space (or external walls) to the outside air. Sever condensation could also occur if such roof spaces were connected via wall cavities to a moist sub-floor space.

Technical information by courtesy of CSIRO.
For now till next week when we will discuss
“HOW TO STOP CONDENSATION IN HOUSES”
your “Handy Jock”.

Building Inspection specialists Perth:
Any questions that our readers may have would be gladly welcomed and endeavored to be answered as seen fit

Do you What causes condensation in houses? Condensation problems often occur in new homes as construction moisture is stored in the bricks floor etc. in addition to the moisture generated by the occupants. So Call 08 9331 3031 for Home Inspections reports Perth  and Building Inspection reports Perth for complete home solution.

Source:www.bhis.com.au/2012/10/condensation-issues/

Building Inspections reports Perth | Improving Sub-Floor Ventilation

bhis.com.au

By: Peter Huber
Posted By: bhis.com.au
Source: bhis.com.au/2012/10/improving-sub-floor-ventilation/


Improving Sub-Floor Ventilation

We will look at improving sub-floor ventilation which if not done correctly can be a cause of decay to timber components.

The other day we were asked to inspect an older style home in Nedlands it was a grand old mansion with timber flooring through out, massive ceilings space and it was oozing with old world charm. Generally the home was in good shape some of the roof timber were showings signs of sag and ageing but one room in particular was extremely cold, and it almost reminded me of the spooky stories one reads about cold rooms in haunted homes, but no such luck.
It turned out, after removing the inspection (male/female) opening in between the floor joists, it was obvious why the room was so cold.

Building Inspections reports Perth:

For starters the distance between the ground and the floor was very close, the home was on a sloped block, and sub-floor ventilation was minimal. I will insert some data facts as supplied by CSIRO to us, on how to improve the subfloor ventilation with some interesting and commonsense applications, but you may well ask what has a sloping block to do with it, well when water via rain is deposited around the perimeter of a house if the home sits on a flat block of land the water will seep into the ground vertically down, if the block is sloped the water that may pond in areas can and will flow down the hill and seep into the ground as it progresses down the incline of the land and hence we get damp and moisture under areas that would mot normally get damp on a level block.

Now the CSIRO Division receives an steady stream of requests for advise on prevention and correction of decay in flooring and in the majority of cases the problem is one of inadequate subfloor ventilation, that is for a free flow of air under all parts of suspended timber floors.

In older buildings the problem can be complicated by an ineffective dam-proof course, by leakages from water supplies or wastes or by the discharge of storm water into the sub-floor cavity, further more in older buildings the provisions for under-floor ventilation is often inadequate.

Building Inspections reports Perth:

We shall take a case in point, where in a double brick dwelling circa(1920) most of the timber flooring had to be renewed. During the repairs the size and numbers of openings in the brickwork below floor level was increased because, with a few exceptions, the only provisions originally provided for ventilation was the openings in the brick work beneath the doorways. Before the new flooring was laid, extra openings were provided within one(1) to two(2) meters of every corner of every room and midway along any wall over five(5) meters long. Each of the new openings occupied the space of at least two bricks.

In addition because of the low sub-floor clearance and the difficulty of providing good cross ventilation, plastic sheeting was spread out over the ground and under all new flooring so as to reduce the area from which soil moisture could evaporate into the sub-floor cavity. Mortar droppings and other debris were removed from the inside of all external ventilator openings and finally the ventilators themselves were replaced.

Replacement of the ventilators was an essential part of the repairs. Surprisingly the smaller of the original terracotta vents provided for rather more free airway than the double brick size, even though the latter had one more opening. However in practice, nether allowed for much air exchange between the subfloor space and the outside because the openings had been blocked by spiders and assorted debris. The pressed metal vents that were used to replace the original terra-cotta air bricks allow for about ten(10) times as much air flow through each opening. This together with the other measures taken should ensure that conditions conducive to decay do not develop again under that floor.

Adequate subfloor ventilation is also an essential requirement which is often overlooked when remedying the problem of excessive dampness in walls, by effectively ventilating all subfloor cavities, moisture that evaporates from the soil or the foundation is removed and the sub-floor humidity is prevented from rising. However achieving an airflow across or along the sub-floor space can be difficult in some houses, especially in terraces where there can be problems in providing vents at both ends of the house.

Building Inspections reports Perth:

In case like that the Division often recommends the utilisation of disused fireplaces as a means of venting. If decorative facing is placed over the front of a fireplace openings cut through the hearth to the sub-floor space and a cowling or chimney pot placed on top of the chimney then a n up-draught will be created when the wind blows over the roof and air will be drawn from under the floor.

Any questions that our readers may have would be gladly welcomed and endeavoured to be answered as seen fit.

Source: bhis.com.au/2012/10/improving-sub-floor-ventilation/