loft insulation

  rickf 15:37 20 Feb 2013

Hi, Can I simply just lay new insulation over the old ones? This would make them job quicker and less having to inhale dust from the dirty, almost blackened old layer.

  john bunyan 16:00 20 Feb 2013

That is what the "free" installer did with me. I wanted to keep some storage space so arranged to screw some additional height to the rafters ad installed some loft boards above the extra insulation.

  Diemmess 16:11 20 Feb 2013

Yes layer can be laid on layer if mineral wool.

A very real danger applies if the build-up exceeds the depth of the ceiling joists. If a surplus of mineral wool is above the joist height over a large area and covered by boards, it can and will push the ceiling down!

  rickf 16:15 20 Feb 2013

Thanks guys. Much appreciated info.

  spuds 16:19 20 Feb 2013

Perhaps worth thinking about?.

I believe the government subsidy scheme is due to end this month or very shortly. If you or someone else in the home 'fits the criteria', then you can get this done for free.

Be warned though about the approved company you might select, some are very fussy about anything in the attic, which may hinder their speed and bonus!.

  fourm member 16:39 20 Feb 2013


'some are very fussy about anything in the attic'

I read something the other day about the No 10 'nudge unit'. It was realised that people weren't taking up the insulation schemes because they didn't want the bother of clearing out the loft. So the 'nudge' was to get the insulation companies to offer a 'clear out and get rid' service at a reasonable cost. That increased the uptake considerably.

  oresome 22:02 20 Feb 2013

On a practical note, new insulation should be laid at right angles to the existing insulation to avoid any matching gaps where the roll widths meet.

This poses a problem in that a new roll, due to it's diameter, cannot be unrolled under the lower part of the A trusses and if rolled out first in a place nearer the apex, will not then slide over the top of existing insulation to get it into it's final position.

I eventually gave up on the cross laying technique and followed the same line as the original. The rolls were cut down to match the width between the trusses and layed tightly together avoiding any gaps. The process was then much easier.

A solution to the cross laying problem would have been to lay a film of polythene first for the insulation to slide on, but I didn't have any sufficiently sized.

Don't under-estimate the effort involved. It's hot dirty work, made worse by wearing a mask and goggles and the rolls are heavy and ours were a tight fit through the loft hatch, having first man-handled them through the house and upstairs from the garage where they were stored after delivery.

  Forum Editor 23:43 20 Feb 2013

"This poses a problem in that a new roll, due to it's diameter, cannot be unrolled under the lower part of the A trusses"

It's worth pointing out that insulation should never be fitted so tightly that it completely blocks the natural air flow into the loft space via the eaves.

It's essential that there is air movement in a loft, as a complete lack of movement, coupled with moisture that might seep in via a cracked tile or leaking valley can ultimately lead to dry rot in the roof timbers. Dry rot (contrary to what you might think) needs two things to thrive - a steady supply of moisture and still air. Without those two ingredients it can't establish and spread.

  Graham* 23:48 20 Feb 2013

'pointing pit' -)

  Forum Editor 23:53 20 Feb 2013


Thank you eagle eyes - typo now corrected.

  oresome 12:03 21 Feb 2013

When we purchased the house we live in some thirty years ago, it was only 12 months old. On inspecting the loft, I was surprised to find black mould developing on the roof timbers.

The reason for this was a lack of ventilation, the moisture content in a new house and a central heating system that vented to an expansion tank in the loft.

The builders were called back and they replaced one of the ridge tiles with a ventilation type and cut a hole in the roofing felt. This cured the problem, the mould disappearing within a few months and no further problems in the following thirty years.

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