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A Guide to Insulation Products for Loft Conversions


Loft Conversions are one of the favourite ways to extend a property - enabling families to stay in the property they are already living in for longer by expanding mostly on bedrooms and bathrooms and leisure / hobby rooms.

Most families like where they live and want to stay there - but just run out of bedroom accommodation as their family grows, and growing up into the roof space enables them to stay in their familiar area, and still attend local schools and clubs or work places, whilst the considerale costs of moving can be invested in the existing home and potentially give a good return instead of being wasted on moving expenses, stamp duty, estate agents fees and more.

There are several factors to consider when looking at insulating your loft rooms - there will be a minimum thickness of insulation required to meet the Building Regulations or Building Standards and this is in many cases a minimum thickness of 270mm of Fibreglass Loft Roll, or could also be a total of 140mm of thickness of PIR type insulation such as Celotex, Ecotherm or Kingspan.

Because of the thickness of Fibreglass required it is often not practical to use such a product for a conversion where you are trying to create space, and more common would be PIR insulation or Multifoils such as Actis Tri-Iso Super 10+ or perhaps a Superfoil or Thinsulex product instead. in the case of using a multifoil, you must remember that to work effectively they need to have a clear air gap of at least 25mm either side of the insulation and this can often create more thickness in the construction than you may be looking for. It is also common for PIR and multifoils to be combined to give the overall required U value through the roof construction to meet regulations - talk to your local Building Inspector for more advice.

It is especially important when insulating roofs to ensure that there is a clear air gap between the back of the insulation and the felt or breathable membrane under your tiles or slates. You will need to allow 50mm minimum air gap for roofing felt situations, and 25mm minimum air gap for breathable membrane situations. You may also need to allow space to run ducting for MVHR or for other services within your void spaces and that ducting running in those voids may also need to be insulated.

Insulated plasterboard is another product which can make things easier and quicker when carrying out your conversion - they are either Polystyrene bonded to Plasterboard (Thermaline Basic or Thermaline Plus) or PIR insulation such as Celotex or Ecotherm bonded to Plasterboard. For further increased performance you could also upgrade to Phenolic Insulated Plasterboard (Kingspan Kooltherm K118) which could help to ensure that you preserve as much of your finished room dimensions as possible. Insulated Plasterboard can be mechanically fixed using our range of Insulation Fixings, or bonded to the wall using Drywall Adhesive and traditional dot and dab methods (although you will still need to mechanically fix with a smaller amount of fixings until the Drywall Adhesive has set). Insulated plasterboard is also useful for thermally isolating and insulating the junction between the inside face of the joists and the plasterboard.

For advice on use of loft space and more specifically for a look at dormers vs roof windows vs balcony windows in loft conversions, please see our seperate blog due soon!

For more advice on insulation options for your loft conversion, or to discuss velux window options or MVHR / Heat Recovery Ventilation Systems, please call the office on 01793-791010 or use our contact form here.

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