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Attic insulation options

H.E. Pennypacker · 2015-05-03 13:50:39

The fibreglass insulation in my attic was fitted across the joists rather than between them. I started to remove it yesterday and am planning to fit new insulation properly and floor some of the attic once an electrician has put in some lights and sockets. The insulation on the east facing side of the house was wet to the…

03-05-2015 1:50pm

#1

H.E. Pennypacker

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Join Date: November 2013

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The fibreglass insulation in my attic was fitted across the joists rather than between them. I started to remove it yesterday and am planning to fit new insulation properly and floor some of the attic once an electrician has put in some lights and sockets. The insulation on the east facing side of the house was wet to the touch underneath but the joists that it sat on seemed dry. The insulation wasn't packed against the eaves and the attic usually feels very well ventilated - breezy in fact. The insulation hasn't collapsed, is dry on top and has been fitted about ten years ago. The house is a bungalow, built in the late '50s/early '60s and the ceiling plasterboard isn't foil backed. The bathroom is on that side of the house so that could be one source of moisture. Its possible that the airflow under the insulation is causing condensation in damper weather. The kitchen is in an extension with its own attic (newer build, foil backed plasterboard & no moisture issues there). We don't dry clothes in the house.

I haven't decided on what to insulate with - the pink fibreglass that I'm taking out is really nasty, dusty and irritating. I've used Knauff Earthwool in the extension attic and while its better to work with, its still a bit of an irritant. Hemp and wool are two other materials that I'm considering.

I have three questions:

Firstly, given that a fair amount of moisture may be rising from the house, would we be better off with more breathable/moisture buffering insulation such as hemp or wool?

Secondly, the joists range in height from 110mm to 120mm, width varies from 305mm to 330mm. Earthwool, hemp and wool batts seem to be available only in 100mm, 150mm and greater thicknesses. If I put 100mm insulation between the joists and run another roll of 200mm across the joists there'll be a 10mm. I'd imagine that something like Earthwool would sag into that gap but stiffer batts might not. Will that 10mm gap be an issue?

Thirdly, given the odd sizes of my joists would blown cellulose be a good option if additional supports for flooring were put in beforehand? (there's quite a breeze through the eaves)

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