INSULATION


When it comes to insulating performance, the key metric is the U-value


wall is at slowing heat transfer. Building Regulations in England, Scotland and ales set improvedmaximum U-values which your builder should typically either meet or improve on for your loft conversion. These values may vary depending on whether you are retaining the existing tiles (renovating) or replacing them. n some cases, it may be possible to relax these values where meeting them is technically impractical. The thickness of insulation needed to meet these values will depend on the thermal conductivity of the material being installed. Again, the lower this value is, the more effective the insulation is at stopping heat from passing through. This can allow a thinner layer of insulation to be installed than would be possible with a worse performing product. This could help unlock extra headroom if your insulation is being fi tted between and below rafters. Phenolic boards are some of the thinnest commonly used insulation solutions for pitched roofs with a thermal conductivity as low as 0.0  mK. Phenolic insulated plasterboard products are also available which combine insulation, drylining and vapour control in a single layer for below rafter


applications. t is important to check the thermal conductivity of the product being installed matches the designs for your home as there are a number of insulation products which look similar but can have very different thermal conductivities. Your contractor should also consider how the construction will handle condensation risk. n homes, warm moist air will rise into the loft. f this is not effectively released it can condense on cool surfaces such as sarking boards and timbers in your roof, leading to potential damp problems.


n a ventilated construction, this moist


air is removed by maintaining a 50mm clear cavity between the insulation and the sarkingtiles. This cavity should be fi tted to allow air to fl ow through the eaves and out through the ridge, carrying moist air away. t is important to check that this 50mm cavity is included in your contractor’s plans, where relevant. Alternatively, contractors can use a


breathable sarking material which allows water vapour to pass through and out of your roof. This avoids the need for an air gap meaning a greater thickness of insulation can be fi tted between your rafters, allowing the target


U-value to be achieved with a thinner thickness of below rafter insulation – maximising headroom. Whatever approach is taken, your contractor should take care to eliminate any gaps in the insulation layer during installation. For phenolic boards, this should include carefully measuring and cutting the boards to fi t the exact space between rafters, fi lling any small gaps with expanding foam and using fl exible insulation to fi ll any unwanted gaps at the eaves. Careful installation can prevent potential issues in the future and some manufacturers can provide specifi c best practice guidance to support this.


BETTER RESULTS


Getting the insulation right in your loft conversion needs to be a key consideration and not an afterthought. With good planning, the right insulation solutions and careful installation, it should be possible to create a loft which can be kept comfortable at an affordable cost across the year and has plenty of headroom.


Matthew Evans is director of technical & regulatory affairs at Kingspan Insulation GB


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