loft insulation / ebay

[Jacko74]

Hello all,

Have just spoken to my architect. He informed me that in my loft, the insulation (kingspan/celotex..) will need to be 120mm between the rafters with a further 40mm underneath.

Just found the following on ebay
http://cgi.ebay.co.uk/Job-Lot-Off-C...ryZ63894QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

For the amount you get it looks like a bargain.
But, if I had these off-cuts between my rafters Would I have to (foil) tape every single joint before putting the 40mm boards underneath?
Or can they just be butted up to each other without the need for foil?
Held together by foam maybe?

Thanks in advance..

 

[mointainwalker]

Presumably your roof is going to be inspected by a BCO for compliance ?

If that's the case, his/her view is the only one that counts but since there will be gaps between the cut edges, it clearly would not meet the same insulation value as a solid, uncut board.

 

[Jacko74]

You presume correct. (If I wasn't going to go through BC, I wouldn't be going through the cost of an architect)

Excuse my ignorance, but.......... purely theoretically...

I have to put insulation between the rafters.
The sheets are only 8ft long, the runs are longer.
So when I butt a piece up next to it, if I've read correctly.
I then foil tape the joint (is this correct so far?)

Is there a major difference between this, and butting a few smaller pieces together?
If they are tightly fitted / taped, I dont see how.

 

[mointainwalker]

"...If they are tightly fitted / taped, I dont see how. "

You are of course correct. If they are all cut square and tightly butted and taped there should be next to no difference, although you will have lost the T+G seal on most of the joins.

I don't think loose fit would be acceptable and foaming might also be "iffy" but if you want to try that, ask the BCO beforehand.

 

[geraldthehamster]

Hello all,

Have just spoken to my architect. He informed me that in my loft, the insulation (kingspan/celotex..) will need to be 120mm between the rafters with a further 40mm underneath.

Just found the following on ebay
http://cgi.ebay.co.uk/Job-Lot-Off-C...ryZ63894QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

For the amount you get it looks like a bargain.
But, if I had these off-cuts between my rafters Would I have to (foil) tape every single joint before putting the 40mm boards underneath?
Or can they just be butted up to each other without the need for foil?
Held together by foam maybe?

Thanks in advance..

This would work, but you'd be creating a lot of work in persuading the offcuts to stay in place. Foam would fix them, but you could spend on foam what you saved on Kingspan. I suppose as long as you could wedge them in place until your 40mm went underneath.

The important thing from a vapour barrier point of view is that the 40mm you put underneath would need to be foil-backed, and properly taped. My BCO didn't query my use of gaffer tape rather than the special tape you can buy. Then again my BCO only saw it after the 25mm over that I needed was fixed, and was happy to take my word that I hadn't left a void underneath (I hadn't).

Another approach is do what I did and order seconds of full sheets, from Secondsandco (with whom I have no connection), or similar.

Cheers
Richard