Home Energy Efficiency and Sustainability Assessors
Accredited with NatHERS, Scorecard, RET and VEU
Thermal Bridging, gaps and leaks
Thermal Bridging, gaps and leaks
The importance of insulation was recognized long time ago but only recently the significance of correct installation has become a concern. During our inspections we've found many houses with missing or misplaced insulation, incorrect coverage or, where clearance was required around recessed lights (downlights) more than required amount of insulation was removed - in some cases half or even whole batts missing.
All these imperfections in insulation coverage result in heat "leaks" in and out of the house - depending on the season.
A more technical collective name for these leaks is thermal bridging. In this article we will concentrate on most common and most significant issues and suggest the correct way to install in new, or fix in existing buildings.
So what is thermal bridging? It is the movement of heat across an object that is more conductive than the materials around it. Simply put, this more conductive material acts like a bridge allowing heat to pass between interior and exterior of the house. Thermal bridging can be avoided either by correct installation or by adding thermal breaks to slow down the transfer through thermal bridge. Here are some common examples of thermal bridging.
Metal building materials easily conduct heat and need to be fitted with thermal breaks (min R=0.2) in the example on the left steel stud frame is covered with insulating tape. For the external side insulated cladding can also be used like insulated vinyl cladding.
Missing insulation also forms a thermal bridge as the uninsulated section conducts heat much better than when insulation is in place. Relatively easy to fix by replacing the insulation.
Clearance around recessed lights is required for safety reasons. Same case as missing insulation above, except in practice the clearance can be a lot more than required, creating large thermal bridges. The solution is to use IC4 rated LED lights which can be entirely covered with insulation. IC4 rated lights are clearly marked so do not cover your lights with insulation unless you can see the IC4 symbol.
Thermal bridging from incorrectly installed insulation. To avoid thermal bridging on wall to ceiling and wall to floor joints the floor or ceiling insulation must extend over and under wall frames. The circled areas on the picture show that the corners are quite cold despite the fact that they are at the ceiling level where the room temperature is the highest. Apart from leaking heat there is also higher risk of condensation. Relatively easy to fix by repositioning all insulation to extend over the top plate of the wall frame.
Like ceiling above, thermal bridging in wall corners is also due to missing insulation between adjoining walls. However this thermal bridge is not easy to fix as the access to it is only from the outside and it requires removing external cladding. So its best to make sure the insulation is placed in these corners at the time the house is being built and before the external cladding is installed. This isn't always convenient or easy to remember as the insulation in walls is usually installed after external cladding. The problem with corner gap is that the corner studs must be spaced that way in order to provide backing for fastening plaster sheets and the second wall covers that gap from the inside so after frames are put together the only way to access and seal the gap is form outside. Another way is to have 3 full height studs in each corner instead two studs separated by a nogging or a spacer.
Another type of thermal bridging can be seen on ceilings or larger wall areas. The lines of different color mark the timber structure behind plaster. Timber does not conduct heat very well but its not as good as insulation. In fact, timber conductivity places it just outside insulation range and it shows in "colder" color - yellow on red and green on yellow. We can also see the opposite effect around the fan in upper left corner of the picture. In there, timber color shows warmer than surrounding plaster which means there is no insulation behind plaster in that section. Thermal bridging from timber is not as bad as from steel framing and its usually ignored. We included it here as another example.
Thermal bridging often occurs around openings. As the house is built, wall frames openings for windows and doors are made slightly bigger to allow fine adjustment which is done with packers or spacers. This leaves small gaps between door/window reveal and the frame which are very hard to insulate and therefore often ignored. But the heat gets through them no matter how small they are so one way to prevent thermal bridging is to spray expanding foam into the gaps.
In multi-storey buildings the area between floors which contains floor trusses is often uninsulated to the outside. It is a significant size, approximately 300mm band around the house so should be insulated or it will result in effect similar to wall-to-floor or wall-to-ceiling joints above. If not done at the time of building, retrofitting is difficult and can be very expensive, best done when external cladding has to be removed for renovation or replacement.
Some other leaks are can be from uninsulated holes for water and waste pipes, cracks in plaster, gaps around skirting boards and between floorboards, how water pipes or pressure valves, ceiling and wall vents, manhole etc, etc. To find them you need to inspect the house, prepare the list and fix them, most can be done as part of one or two weekend DIY projects. Or, for a small fee, we can do the inspection, prepare a report (Super-Seal) and even fix them if you prefer.