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but it’s R value (resistance to heat transfer) is poor compared to others like phenolic foam as is the K value (conductivity). confused as to how that makes for better heat management in summer?
https://www.buyinsulationonline.co.uk/blog/the-ultimate-guide-to-insulation-values
Mr_Smyth-
Conventional insulation like phenolic is good at keeping heat in - which obviously you want during the winter - but less good at keeping heat out because its heat storage capacity is poor. Wood fibre insulation buffers heat, which is good when temperatures cycle on a daily basis with an afternoon/evening peak, because overheating is both delayed and reduced, and the stored heat can escape outwards during the evening/overnight.
The poor heat storage capacity of conventional insulation is one factor in why you end up with so many new builds that cost nothing to heat but are unbearable in summer.
Bear in mind that while K-value does represent thermal conductivity , U-value represents heat transfer overall as it considers K-value, the thickness of the insulation and other factors.
Not all wood fibre insulation is the same and the Steicoflex 036 we're planning to use has a U-value of 0.36 as the name suggests. You've got to consider the overall buildup of where you're putting the insulation too - e.g. our external wall buildup for the brick walls will contain 140mm of Steicoflex and give an overall U-value of 0.223.
This is all a bit academic though to be honest! There's no way I'd be using foam EWI on an Edwardian house as it's not breathable, plus the type of insulation will have very little impact on overall overheating factors. As per the paper I linked to above, reducing solar gain via shutters/solar control glass will be key.
Fox
Although we're going to fill/cover our house in insulation overheating is a way bigger concern for me than keeping it warm in winter. As badly insulated as it is at the moment, we only set our heating to 18 when we run it so we've not actually been spending that much on gas at all really.
This was a factor in going for wood fibre insulation: it's got high heat storage capacity and better heat protection than conventional insulation, so should buffer summer heat better.