Is it a good idea or not such a good idea – well let’s look at the possibilities. It will most definitely help stop heat from leaving the enclosed space through the gyprock wall however it actually is defeating the purpose of having a cavity at all.
MAYBE IF YOUR HOUSE IS ON A SLAB YOU WILL GET SOME BENEFIT
However this comes at a cost if you have no roof ventilation and your cavity is filled with rockwook, glass fibre or cellulose, these are packed in so tightly that there is no air gap – when air is trapped in a hollow area it is one of the best insulators of them all.
What is the cost: - You no longer have the trapped air as an insulator and you will more than likely end up with a condensation problem due to the insulation filling the cavity.
GOOGLE: Condensation Problems Caused By Cavity Wall Insulation
IF YOU ARE THINKING OF RETROFITTING CAVITY WALL INSULATION IN AN EXISTING HOUSE WITH A SUB FLOOR MAYBE YOU SHOULD THINK AGAIN
For hundreds of years we have been building homes with a cavity air gap, this cavity is there for a specific purpose to allow air to pass up between each layer of brick in a solid brick home or for a brick veneer home with a timber frame and an outside layer of brick.
THE IDEA IS TO ALLOW THE AIR FROM THE SUB FLOOR TO RISE UP THE CAVITY AND INTO THE ROOFSPACE AND EXHAUSTS FROM THE ROOF VENTILATION
So the moist air rises up from the sub floor between the cavity into the roofspace and out of the ventilation in the roofspace – keeping the whole home dry. The value of this phenomenon is the moist air from the sub floor rises due to convection and relieves the possibility of moisture in the sub floor and walls evacuating through the roof ventilation – result no sub floor dampness – no inside wall dampness – no condensation.
THEN ALONG COMES AN INSULATION COMPANY THAT FILLS THE CAVITY WITH INSULATION FIBRE AND BLOCKS THE AIR FROM THE SUB FLOOR
What type of problems do you think this will cause – this will cause more unwanted problems – sub floor dampness (rising damp) – the possibility of fungi causing timber rot or mould – health issues – condensation. Then moving up the wall the possibilities of penetrating dampness and unfilled air pockets leaving cold spots on the inside walls which attract condensation. Moisture in the insulation cavity filled walls can cause corrosion of the metal ties that tie the brick work to the timber frame.
MOVING UP INTO THE ROOFSPACE IF YOU DO NOT HAVE ROOF VENTILATION
Cavity wall insulation will further exacerbate roof condensation problems in the roofspace, I would seriously contemplate rethinking your idea of having any type of cavity wall insulation that does not leave a decent air gap in your wall cavities – keep your money in your pocket – do not buy any more problems. If you really want to make a difference in your home comfort invest in a really good roof ventilation system Universal Tile Ventilators have the best – most effective roof ventilation systems for home comfort and health available, check our site out.