Insulating and Boarding the loft... Planning, no progress

We have a fair amount of ceiling insulation, although a bit more would certainly help as our house does cool off quite quickly. Unfortunately there is currently no insulation between the rafters, it's just beams, the membrane sheet thing, followed by tiles. Insulating and boarding up the loft is definitely a job we can do ourselves, and since we are using it as our office, it'll make things quite a bit cosier for us. It'll also encourage me to get an electrician to come round and drop a 16A wire down to the distribution panel, which is conveniently located, but dropping wires can be a huge hassle. Currently there is an extension lead going up into the loft hatch.

Wickes sells polystyrene boards which are 402x610x60mm, in packs of three for £8.50. Ignoring the depth for a moment, each pack will cover 0.74m². Each side of the loft is 330x220cm, but we need to deduct the area occupied by the beams. There are nine beams on either side, each 5.5cm wide. This comes to a little over 49cm. So, the effective area on each side which we would like to cover is 281cm. This means each side is 9.3m². Let's add 10% and double it for the other side. Roughly 20.5m². This means we will need 28 packs of insulation board. Ouch, that's £237, but between two people, not too bad. At the moment, my main concern is depth. Is 1.5cm enough of an air gap after the plastic sheet?

Since it is the loft, I am not quite so bothered about it being plastered. Timber cladding might be the way to go, working out at £7.60/m². Hm, but then we also have the sides of the eves, which makes me wonder if we should look into plastering.

Tags: house