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Is thermal insulation performing?

BRANZ has been investigating how well thermal insulation is being installed and using a thermal camera to assess the impact of any folds,

gaps and tucks on performance.

BY IAN COX-SMITH, BRANZ BUILDING PHYSICIST

A RECENT BUILDING RESEARCH Levy-funded BRANZ project has looked at insula-tion during council prelining inspections of new houses under construction in the Wellington region. Particular attention was given to areas where the quality of the insula-tion installation was not optimal.

In some cases, follow-up visits were made after the walls and ceilings were lined and a thermal camera was used to assess what impact the defects have on the thermal image and the possible impact on thermal performance.

Relating anomalies in the thermal images back to faults in the insulation seen at the prelining stage helps understand the capa-bilities of the thermal camera as a tool for assessing the quality of installation.

New design tool to be developedThe study has provided data that will be used to develop a design tool to make more realistic estimates of the likely thermal performance of the walls, floors and ceilings of houses.

Both steel and timber framing had the same range of installation quality and common issues.GapsThe most common issues are gaps between:

● insulation and framing ● insulation segments.

For wall insulation, the gaps are typically less than 5 mm in width, and the small thermal impact is mostly undetectable in the thermal images. Often, the thermal signature is swamped by the thermal bridging from framing. Gaps are more common where three or more pieces of insulation are used to insulate a frame bay.

Gaps in ceiling insulation are of more concern – they are typically wider than in wall insulation, and there is a greater chance of significant convective heat loss effects occurring. Thermal imaging surveys over the next 6 months will focus on this issue.DownlightsFitting of insulation around recessed down-lights is inconsistent – some have excessively large gaps in the insulation, and others

Behind the walls FEATURESECTIONFEATURESECTION

Results will help update NZS 4246The results will also feed back into the proposed review of NZS 4246:2006 Energy efficiency – Installing insulation in residen-tial buildings. This standard includes the requirement that compressible fibrous insulation products are cut to size and friction fitted between the framing in such a way that there are no gaps, tucks or folds.

NZS 4246 also requires that insulation is neatly fitted around plumbing, electrical wiring and electrical fittings and that care is taken when fitting insulation around recessed downlights. This is to ensure the clearances in light-fitting installation instruc-tions are maintained for safety reasons, while keeping any uninsulated area of ceiling to a minimum.

Some common issuesIn the houses inspected, the installation standard requirements were met for at least two-thirds of the insulated area, and in one or two houses, probably 95% of the insulation was installed perfectly.

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Behind the wallsFEATURESECTION

have no gap or a gap only around one side. It is common to see large anomalies by downlights in the thermal images.Cables and plumbingThe second most common issue is gaps around cabling, plumbing and electrical flush boxes. With walls, the typical fault is insulation tucked behind the services creating a gap between the face of the insulation and the wall lining – and potentially a chimney for heat to escape.

For ceiling insulation, the gaps are often caused by the insulation being lifted by cables draped over and under framing.TucksOnly two houses had a significant amount of insulation tucked at the edges. Folds in the insulation are typically associated with large tucks.

Figure 1 shows very poor installation. Strong sunlight on the cladding highlights the thermal impact of the tucks and folds. The thermal image was taken before the lining was installed.

Figure 1: This very poor installation has insulation tucked at the edges. Figure 2: Insulation installed well into wall and around downlights.

Figure 3: Insulation installed with a small gap indicated. Thermal images pre-lining (left) and post-lining.

Wind washEvidence in the thermal images for wind wash undermining thermal performance was only seen in a few cases, typically at the ceiling to wall junction associated with the ceiling insulation and not the wall insulation.

Optimal conditions for thermal camera imagingThere are a few important considerations when using an infrared camera to assess insulation:

● The temperature difference between the inside and outside of the house needs to be greater than 5°C and preferably at least 10°C.

● Winter is the best time for an infrared survey, but summer can also be practical. Useful results are harder to get in spring and autumn. Solar gains can be both a help and a hindrance.

● Steady – at least an hour – and uniform air temperatures are best, but dynamic conditions can sometimes be used to advantage.

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● A follow-up visit under different environmental conditions can help separate the various factors that can influence a thermal image, such as moisture and wind.

● When the conditions are right, a thermal image with sharply defined edges to the thermal signature from framing is a good indicator that the insulation has been well fitted against the framing (see Figure 2). However, when these edges are not sharp, it may be because the temperature conditions were not suitable or the insulation has relatively low thermal resistance.

● Gaps associated with wall insulation are usually too small for the thermal influence to be readily detectable in a thermal image.

Figure 3 shows a stairwell with a ceiling space above and a garage on the opposite side of the wall. In the first image, there is a small gap in the insulation marked.

On the middle thermal image, solar heat gain in the garage roof space highlights the defect. Air leakage through the corner framing, a fold and a gap between pieces of insulation is also highlighted near the bottom of the image.

The third image shows the same area post-lining. The thermal image shows heat leakage through the corner framing and through the small gap in the corner of the segment of insulation. Other defects are no longer detectable. In the right-hand thermal image, the surface of framing is colder than the surface of the insulation whereas in the left-hand thermal image, the situation is reversed. Apart from the small defect, the thermal image demonstrates that the insulation has been well installed.

Well fitted glasswool needn’t slump with ageThe refurbishment of a test house on the BRANZ campus provided an opportunity to check the durability of wall insulation after 20 years of use.

The building has been subjected to fires, racking from hydraulic rams and being moved 100 m to its current location. In its new location, it was racked again.

Only one area of insulation slumping was found.Two insulation segments that stumped a significant amount were

only just touching the framing around their edges, whereas the other two segments, which only slumped about 5 mm, had a slight friction fit.

Interestingly, the insulation stayed in place – at least temporarily – when stretched back up to fill the frame cavity.