When we are talking bad building practices regarding roof ventilation the major problem is builders are reluctant to use roof ventilators. This is a major bad building practice. The builders seem to be uninterested in providing ventilation in the build and if they are actually forced to they will provide a whirlybird which will be totally useless for the ventilation of the roofspace.
WHICH TAKES US TO THE SECOND MAJOR PROBLEM OF BAD BUILDING PRACTICE
When providing a roof covering for a home using corrugated iron or colorbond not allowing for sisalation foil (sarking) or a 50mil blanket with aluminium foil fixed under the metal roofing. The problem:- depending on where you live not having a vapour barrier under the metal roof sheeting can cause a huge problem of condensation, with this problem it could be raining in your roof.
THE THIRD PROBLEM OF BAD BUILDING PRACTICE
If the chosen vapour barrier is sisalation aluminium foil (sarking) this should be given at least a 30mil slump between rafters. If the foil is laid tightly across the rafters it will come in close contact with the roofing sheet and this will cause the same problem as if you did not have a vapour barrier at all. You will experience a major condensation problem - this is a bad building practice (naughty builder).
SO WHAT DO YOU DO
1 – If you use a foil blanket under the roof sheeting you must have roof ventilation you cannot literally seal a roof up you need to have air movement otherwise you will still have the condensation problems. So a good foil blanket 50mil minimum and an excellent roof ventilation system you will not go wrong.
2 – If you use the aluminium foil sarking you must give a minimum 30mil slump between rafters, this allows an air gap to counteract condensation that is the principle action of the foil. When the foil is slumped any condensation that could be formed above the foil (which would be minimal) will run down the foil into the gutter. Again you need a good effective roof ventilation system and you cannot go wrong.
Using either of these ways for a vapour barrier without effective roof ventilation will result in condensation. The builder needs to make sure the roofer has done the job properly and also supply and install an effective roof ventilation system otherwise you will have problems.
SO IN CONCLUSION YOU NEED TO:
(This will save you money).
Make sure in your contract with the builder that the foil will be fixed to the BCA (Building Code of Australia) and that an effective roof ventilation system has been figured into the cost. This way you will not have the problems that other people do with condensation and SBS (Sick Building Syndrome) in their new homes. (Read our BLOG – Warning Read Before You Design Your Next Housing Project.)
FOR AN EFFECTIVE ROOF VENTILATION SYSTEM: UNIVERSAL TILE VENTILATORS
PREPARE TO BE AMAZED
ANYTHING ELSE IS A COMPROMISE
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