Loft insulation advice

29 Aug 2015
Reaction score
United Kingdom

I am planning to top up the existing loft insulation. Joists are 100mm high and about 330mm apart. Current insulation is old, between 50mm and 80mm deep (yes, I know).

I'm not keen on removing the existing insulation unless I really have to. So options seem to be:

a) Lay 100mm loft roll in line with the existing insulation, then another 170mm roll at right angles. But first new layer would stand well above the joist tops, and would require a lot of cutting as none of the rolls seem to be perforated at 330mm.

b) Lay 100mm loft roll at right angles to existing insulation, on top of the joists, leaving a gap between top of existing insulation and bottom of first new layer. Then lay another 170mm roll at right angles to that, i.e. in line with existing insulation. Sounds like a lot less work as no cutting required, but of course would leave a gap.

Neither option seems that great, any advice appreciated.
Sponsored Links
Option B.

The insulation will settle and the 'floor' will look al wavy, but meh.

The gaps are below the main insulation so will have little or no practical effect, as long as these gaps are not continuous all along to the eaves which will allow airflow under the insulation.

So around the eaves pack the gaps with cut strips under the insulation (leaving gaps above the insulation for roof ventilation).
Sponsored Links

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local