Loft insulation beneath chipboard - do I need to leave a gap?

[volks]

Having some work done in the loft and the plumber took up the chipboard the previous owner fitted. Beneath the chipboard is some old fashioned yellow fiberglass loft insulation and some vermiculite (already seen elsewhere in the loft and tested clear for asbestos)

There's a fair gap between the existing insulation and the top of the joist where the chipboard rests. Can I add another layer of top up insulation before putting the boards back down, or do I need to leave a gap between the chipboard above?

It's a chalet bungalow with dormers so the loft floor is the downstairs ceiling - I've got the pitched roof just above which I'm adding Celetex to, but just wanted to add extra insulation to the floor so the downstairs room keeps more heat in there - the celetex is to just keep any escaping heat from completely exiting the property.

Thanks in advance!

 

[blup]

That's what I did and have not had problems. As you say you are keeping the heat in the house, but any water vapour that does go through will end up condensing under the roof which you will have ventilated. Hot air rises

Blup

 

[harrythefurrysquid]

Are you sure you want to celotex the pitched roof? Do you need the roof space to be warm?

Putting down another 200mm layer of insulation over the existing (with or without the chipboard) is very easy and cheap, and I would think it'd be easier to ventilate the pitched roof if it's not covered in celotex.

 

[foxhole]

Celotex under roof is expensive waste of money unless you intend to use the loft as a room.

 

[volks]

Celotex under roof is expensive waste of money unless you intend to use the loft as a room.

Well, it's a former conversion and it's fairly cold so it's helping keep some heat in upstairs. Maybe a waste to some degree but it's better than before, having felt and tiles just the other side of a plaster board partition.

 

[volks]

Are you sure you want to celotex the pitched roof? Do you need the roof space to be warm?

Putting down another 200mm layer of insulation over the existing (with or without the chipboard) is very easy and cheap, and I would think it'd be easier to ventilate the pitched roof if it's not covered in celotex.

Originally made it warm as the loft space has water pipes that froze in cold weather. So added celotex to try and prevent the pipes freezing again in cold weather.

 

[harrythefurrysquid]

Main thing to consider then is that the better you insulate the floor, the colder the loft will be.

Might be OK if you're just adding a small amount, but worth thinking about other options - pipe lagging, etc.

 

[volks]

Main thing to consider then is that the better you insulate the floor, the colder the loft will be.

Might be OK if you're just adding a small amount, but worth thinking about other options - pipe lagging, etc.

Thanks for the help! It's ideally just for storage so will insulate the floor to keep downstairs warmer and add some thin celotex to keep in any latent heat for the pipes. Will also put the pipes below the insulation, not above.