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Gaps in insulation
If 10% of the ceiling is bare due to insulation being tossed aside or being incomplete, the heat loss can double.
I have rarely gone into a roof space (even a new one) and found the insulation properly distributed. Since I have bought a thermal imager, I have not found a ceiling without an insulation fault of some sort.
The most common issue is ceiling batts tossed aside by a tradesman and not replaced. (Although there are many good tradies, there are too many electricians, air conditioning installers and plumbers who don’t make a habit of checking that the insulation has been returned to the correct place after they have finished their work). If you are employing someone who will be working in the roof space, let them know that any insulation that needs to be removed, needs to be replaced properly (for example trimmed around a fan)
Some of the worst examples of failure to replace insulation occur with down lights. If you have down lights you might have a dozen in the room and if a ceiling batt is tossed aside at each light, you would have 12 displaced ceiling batts, which may well more than double the heat loss or gain through the ceiling.
Often this can be readily improved if this is in an attic roof space. Do bear in mind that depending on the type of downlight you may need to give a gap, which depending on the light and insulation may need to be up to 100mm clear around the light. Check the make and model of the downlight to determine the clearance required.
Although I prefer surface or pendant lights to downlights, some of them, particularly the newer LED downlights can be safely covered with insulation, however check the manufacturer's instructions.
Another common issue is ceiling fans. they need a clearance around them to avoid jamming the blades, but often a whole batt is tossed aside. Ideally the ceiling fan should be a ducted fan and discharged above the roof. If the ceiling space is well vented, e.g. an un-sarked tile roof, depending on your climate you may get away with it discharging into the roof until you replace it. However, it is preferable to install a DraftStoppa so that you can safely insulate to the DraftStoppa and also so that when the fan is not working you don't get air leakage and lose the heat or cool in your house.
When improving the insulation, gaps in the insulation, for example around framing timbers or at edges, should be filled with offcuts.
Insulation that has been wetted or compressed doesn’t perform as well as it should and should be replaced.
Manhole covers are often uninsulated. Gluing insulation using a construction adhesive (Liquid Nails) to the top of the cover, will reduce heat loss to the roof.
Another issue with insulation is often the extent is insufficient. Ideally the insulation should extend over the top of the walls.
If you intend doing the insulation yourself there are a number of considerations:
If you are planning on increasing the insulation thickness, I suggest you consider creating a plan to ensure you achieve an optimum insulation level and consider what options you should do when. See Energy Audits.