On our projects we set out to make huge heat loss improvements at wall and roof levels and ground floor improvements in 7 of our 9 homes.  Addressing the insulation issue as part of any up-grade will, without doubt, give the best benefit in terms of the savings to be made not just in terms of heat loss but also in on-going energy costs.

All building materials are assessed for their heat loss potential and this is referred to as their lambda or U Value.  When looking at this U Value, the lower the number, the better, e.g. a wall with a U Value of 1.5 loses 10 times more heat than one with a U value of 0.15.  Insulation products have much better U Values than other building products and are used specifically for reducing heat loss from the building.  In Ireland the current standard for new buildings is to try to achieve a U Value of between 0.15 and 0.2, depending on the location of the insulation.

External Wall Insulation

As walls have the largest surface area and therefore, the greatest heat loss potential, we will begin there.  Our aim for all of our home up-grades was to reduce the U Value from over 1.5W/M2/K to below 0.23W/M2/K and in doing so, completely eliminate any wall related thermal bridges.  We chose to use wall insulation, externally applied (external wall insulation) on all of our homes and the great advantages of this approach include, no restriction on the insulation thickness, no reduction in room sizes, no thermal bridges and no internal inconvenience to the home occupants during the works.  We typically fitted external insulation with a thickness of between 120mm and 150mm and in all cases made sure it was extended to intersect with all roof insulation, windows and doors.  Because the homes were already built, it was impossible to link floor and wall insulation so instead we always carried our wall insulation all the way down to and below outside ground level, thereby greatly reducing the thermal bridge at this point.  In the final wall heat loss calculations we achieved U Values of between 0.15W/M2/K and 0.22W/M2/K, with no thermal bridges at roofs, windows, doors and minimal bridges at ground floor level.

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Roof and Attic Insulation

When fitting insulation at roof level there are two different approaches depending on whether the attic space is used as a room or not.  When the attic is not used as a room the insulation is placed at ceiling level and the up-grade is very straight forward.  If the attic space is partially or fully used as a room then the approach is much more detailed and has to be addressed carefully.  In 5 of the nine houses on our project the insulation was at ceiling level (this is called a cold attic space) and for these we typically used 300mm to 350mm of soft fill insulation placed between and over the ceiling joists.  As part of the up-grade some of our mechanical services were placed in this attic space and we provided rigid insulated walkways to these services and to the water tanks to allow access for maintenance purposes.  The attic entrance hatch, the water pipework and the water storage tank were all insulated to prevent freezing in winter.  In cold attic spaces the other really important issue to address is, where the roof underfelt is a bitumen product, it must never be allowed to come in contact with any insulation and the cold attic space must be permanently vented from eaves to eaves to allow any roofspace condensation build-up to dissipate.

When part, or all of the attic is used as a habitable or warm space, then some or all of the insulation must be placed at rafter level and this presents more difficulty in achieving not only good U Values but also good room height.  The difficulty is again the bitumen underfelt which must be continuously ventilated and this means ensuring there is a gap or void of at least 50mm between this underfelt and any insulation.  In addition this void must be permanently ventilated from roof eaves to ridge to allow condensation to dissipate.  To offset these difficulties, we used rigid insulation with a much better U Value at rafter level and this had the dual effect of guaranteeing a consistent 50mm void and good U Values with reduced insulation thickness, this is because rigid insulation generally has a much better U Value than soft insulation.  In all of our roofs we achieved less than 0.15W/M2/K and in some cases we achieved as low as 0.13W/M2/K, this is in line with current regulations for new construction.

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Floor Insulation

In 7 of the 9 homes we were also able to insulate at ground floor level as the original floors were traditional raised and ventilated timber floors.  This type of floor is normally finished with tongue and groove softwood floorboards, with joists and a ventilated void below.  This type of floor was ideal for our up-grade plans as it meant we could not only insulate the floor but also use it to house an underfloor heating system (more later).  This void is normally between 300mm and 400mm deep and we used this space to fit a suitable loadbearing rigid insulation, the underfloor piping network and a concrete heating screed to dissipate the heat into the rooms above.  For underfloor heating to work effectively it is important to achieve really good floor U Values (usually less than 0.2W/M2/K), in all cases we achieved U Values less than 0.15W/M2/K.


If you are considering an energy up-grade of your home or business premises, why not call FloElen Construction on 087 7542450 and we will be delighted to call out to discuss your plans.  Our expert team provides a full service beginning with a free energy consultation, a full planning service and a team of very experienced construction professionals dedicated to completing your project to the highest standards.  We are an SEAI/NSAI registered contractor for all grant schemes and we guarantee a very a competitive quotation for your works.

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