Doubling up insulation board? Good or bad idea

[mushymat]

Long story short,,…we have a loft conversion (came with the house when we brought it) with loft space that runs along the side, these are small spaces but I have access. There are 3 sections, more like crawl spaces but each about 12ft long.

In these crawl spaces we have a single layer of insulation board on the backside of the wall. Not too sure about it’s thickness but… A friend has some insulation board going cheap (lots of off cuts), and with some Facebook market place shopping I’m sure I could get enough to double up the layers in these crawl spaces.

Anyway, no idea if this is a good idea, it seems like it might be but I’m no heating/insulation expert.

Can anyone tell me if it’s a sound idea or if I’m being an idiot?

 

[Deleted member 174758]

It is common to double-up plasterboard for fire proofing and sound/thermal insulation, also cement fibre board for the same reason. The main thing is to make sure that joints in boards are not directly above each other and that there are no gaps in the insulation

 

[thomp1983]

Doubling up celotex or the like is perfectly fine just make sure you foil tape all the joints, the majority of my extension roof is made up of 2 different thicknesses as it was alot cheaper at the time, it's just time consuming cutting and fitting 2 lots of board compared to one but for me the saving was well worth it

 

[ShowerWoe]

This may not apply to you;

In a general sense, humidity will condense on the coldest spots. When the weather gets very cold, where there is plenty of insulation, it will stay warm, but where there is insulation missing the cold spots my act like a magnet to damp air condensing on those points with potential for mould.