Boarding floor and rafters - air circulation advice

[stevejnotjobs]

Hi there

We've moved in to a house with clay tiles fixed on via mortar and - naturally enough, I guess - no felting. This means that the loft has got super-dusty over the years.

We're going to board the loft floor, and because of the dust, the plan is also to board the rafters, as a way of controlling the dust. We'll also add in some insulation between the rafter boards and the tiles/mortar to help with the house's heat retention, but I could do with a spot of advice about the following:

1) Is there much of a risk of messing with the airflow in the roof by adding rafter boards and getting damp/mould etc up there?

2) The house is about 100 years old and the loft floor joists aren't super-deep. I'd guestimate around 4-5in (100mmish), but I need to check. Is there any reason NOT to pack in a good 200-300mm of insulation there? Does it need to be left unpacked to insulate better (more air, etc etc)? I ask because I'm not sure how much to buy. The loft's around 9m by 9m.

Cheers
Steve

 

[freddiemercurystwin]

Do not board the underside of the rafters this wil drastically reduce the airflow through the loft. //www.diynot.com/forums/viewtopic.php?p=1412543#1412543 Tack it to the underside of the rafters. Or use a breathable membrane eg http://www.ebay.co.uk/itm/POWERLON-ULTRAPERM-LITE-BREATHABLE-MEMBRANE-1m-x-50m-/260705666094

 

[mointainwalker]

Fibre-wool uses trapped air to insulate, so compressing it diminishes its insulating properties.

 

[stevejnotjobs]

Thanks for the pointers, folks.

We're building up the rafters so that when I board across them, very little of the 200mm of insulation will be compressed, because I know that the air in the insulation is mostly what makes it work (just didn't think it through enough).

I'm definitely not going down the plasterboard route either -- I'll be seeking out some breathable membrane, I reckon.

Looking forward to getting it all finished!

Cheers
Steve