Since April 2006 it has been a requirement of the homeowner when removing or adding a layer to an external wall that the need for insulation must be incorporated into the renovation work.

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Part L1B of the Regulations governs floors, roofs and external walls and sets out the standards that are to be reached in terms of insulation and reduced heat loss . In layman’s terms if you have solid walls or an uninsulated cavity wall you cannot simply re-render or pebbleadash an exterior wall without submitting a Building Notice to the  Building Control Dep’t of your local  Council.

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At first glance it seems that the rules do not apply if you are altering less than 25% of the property’s walls and many people believe this to be the case. In fact the Regulations state that you are only exempted if less than 25% of any single wall is being altered and not 25% of the total wall area across the whole house.

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A further misunderstanding is that the insulation must hit a U value of 0.35 to meet the rules. In fact this figure is only a target figure and a lower insulation level is perfectly acceptable if it is technically, functionally and economically impossible to hit the 0.35 target.

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In most retro fit cases to hit 0.35 U value will mean bringing the wall out by around 3 to 4 inches in depth and thereby having implications for roof line overhang, cill depths, soil pipe and boiler flue clearance etc . As a result of the technical and financial challenges faced in hitting the target the vast majority of external wall insulations to existing properties are of a ” best achievable”  insulation standard and perfectly acceptable to Building Control.

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