Glass-fibre roof insulation perpendicular to joists

My elderly parents had their roof insulated recently under some govt grant or other; I haven't seen the result but apparently the installers have laid a thick layer of Rockwool-type stuff at right angles to the joists.

I recall as a teenager when I lived there myself, back in the 70s, laying the original 3" insulation between the joists - bugger of a job as it's an old house with lath and plaster ceilings, the spacing of the joists is very variable, and the joists themselves are in poor shape, very irregular in cross-section and many certainly wouldn't take a man's weight if you were to step across them without using crawling boards.

So now, I gather from Mum (and can picture), the whole roof space is just a homogenous sea of glassfibre; its impossible to tell where any of the joists are, let alone the decent ones you can stand on. I'm sure this scenario happens a lot, and probably doesn't matter too much provided the roof space doesn't need to be accessed; but the main problem with my parent's house is that there's a somewhat bizarre arrangement with the chimney whereby the flue from the solid-fuel fire it has a horizontal run of some 5 feet (IIRC) within the roof space. This means there's a flue box up there (ie, a cast iron door in the side of the flue) which the chimney sweep needs to access to clean the chimney. Mum is convinced (with some justification IMO) that next time the guy comes to clean the chimney , he's going to wind up falling through on to the spare room bed...

Is there any obvious solution to this? Must be a reasonably common problem. Short of lifting all the new Rockwool, all I can think of is to just lay new, long, crawling boards between the loft hatch and the flue box (quite a long way) and assume that there will be adequate support along the way and at the ends...

David

Reply to
Lobster
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Warmfront I should imagine and the normal, not far removed from cowboy, installation by the sounds of it.

Well you only need to lift the sections between the hatch and the flue box. How thick is the new insulation? Buy some 2 by whatever the thickness is timber and some at least 18mm chipboard. Decide on a suitable width for the access way say 18" and cut the 2 by whatever into those lenghts. Locate the joists along the route and diagonal screw these bits to the top of the joists, replace the insulation and screw the chipboard panels cut to length as required onto the top. Screws in preference to nails so as not to knock the lath and plaster ceiling off or crack it... I'd construct a larger working area at the flue box.

Reply to
Dave Liquorice

Similar to the clowns that wanted to do my late mother's bungalow under similar grant scheme. This was boarded and the space between the boards and ceilings was already effectively full (OK, maybe 4 inches in a 5 inch space). They wanted me to take up the boards. They were going to lay along the existing joists and then I'd have to re-board. Couldn't convince the oik that this would not in fact improve the insulation significantly. He'd been on a course, so he knew all about it.

Reply to
newshound

The top of the insulation needs to be ventilated, so you either need to make sure any boarding is raised a couple of inches above the top with air flow from the sides, or lay slats (2 or 3 boards with 1" gaps between them). If you don't do this, the underside of the boards will become permanently wet, that being the first cold surface which air leaking through the lath and plaster will encounter with no ventilation, and it will eventually cause rot.

The other thing you could do is remove 12" strip of the new insulation, and put the boards on the joists. That won't make much difference to the effectiveness of the insulation overall. (Same comments about ventilation apply.)

Reply to
Andrew Gabriel

Good point and one that I had completely missed. Our ceilings are foil backed plasterboard so it wouldn't be a problem here but worth bearing in mind with "porous" ceilings.

Reply to
Dave Liquorice

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