covering Kingspan in loft question

[mungo21]

Looking for some help with my loft, new to diy....

ill try an explain as best I can..

insulating the rafters in my loft they are 100mm deep, so putting 50mm kingspan in gap.. roof is felt backed.

The loft is being used as an office but not officially to regs just a temp solution for a year or so ... thus needs to be warm for me..

Tthe part im stuck on is covering the the kingspan. looking at the roof, I really would not feel comfortable with putting plasterboard up , there is a single wood beam going across the wide of the loft on both sides of the roof, held in place at the wall with a rusting metal spike sticking out of the brick work, supported with 2 struts coming down to the floor of the loft. the hose was build in 1890.
I was going to cover the kingspan with U-FOIL DOUBLE ALUMINIUM BUBBLE INSULATION .

However I have read that can not put this straight onto a surface and need to leave a gap of appro 1".

SO any help as to what I should use would be great.. also should I tape the kingspan where it is in contact with the rafters.

I hope I was clear in my explanation ...

Thanking all the help in advanced....

 

[tony1851]

Why are you worrying about putting plasterboard up? Is it the weight? If so, you're probably worrying needlessly.

You do need a gap for the foil stuff otherwise it defeats the object, but that doesn't matter because it's useless anyway.

Just tack some polythene sheet over your k'span, and then plasterboard - it won't collapse.

 

[mungo21]

Why are you worrying about putting plasterboard up? Is it the weight? If so, you're probably worrying needlessly.

You do need a gap for the foil stuff otherwise it defeats the object, but that doesn't matter because it's useless anyway.

Just tack some polythene sheet over your k'span, and then plasterboard - it won't collapse.

Cheers for the reply Tony..
yes its the weight of the plaster board. really dont think it could take the weight of plasterboard, plus I dont have an life insurance ... javascript:emoticon('') cheers for the head up on a vapour barrier.. forgot to ask about that ..

what i might do is cross line over the kins span with a thiner layer of kingspan 25mm that should do the trick ..

 

[geraldthehamster]

what i might do is cross line over the kins span with a thiner layer of kingspan 25mm that should do the trick ..

I was just going to suggest that. Used foiled Kingspan and tape the joints and you'll have a vapour barrier as well.

Regards
Richard

 

[PaulJR]

A few years ago we sorted our loft for storage. We put kingspan between rafters and then lined it with the foil bubble wrap stuff. I agree that it doesn't do anything for the insulation, but it is a good vapour barrier/wind shield, and very reflective so the loft is bright and stuff is easy to find. It was actually cheaper to hammer tack the foil in place rather than buy enough of the foil tape to seal it all up.
A bonus is that you can see the foil move slightly in the wind so I know the rafters etc. are well ventilated.

 

[geraldthehamster]

A few years ago we sorted our loft for storage. We put kingspan between rafters and then lined it with the foil bubble wrap stuff. I agree that it doesn't do anything for the insulation, but it is a good vapour barrier/wind shield, and very reflective so the loft is bright and stuff is easy to find. It was actually cheaper to hammer tack the foil in place rather than buy enough of the foil tape to seal it all up.
A bonus is that you can see the foil move slightly in the wind so I know the rafters etc. are well ventilated.

Surely if the foil is moving in the wind, the rafters are not effectively insulated? You shouldn't be getting cold air coming down between the rafters; that is what the Kingspan is for.

Cheers
Richard

 

[PaulJR]

Richard.

In an ideal world it would be a perfect seal. The rafters date back to 1950 when the house was built and they are all bowed, curved and warped to some degree or another. I did seal the biggest of the gaps with expanding foam and taped up as much as possible, but it isn't 100% airtight. So if it's really windy the foil moves a bit, and the foil completes the seal. The foil moves both sides, so I know that the rafters are ventilated against condensation.

The House is insulated by about 300mm of various types of insulation under the loft floor, this is just comfort/frost insulation for the stuff stored and the boiler etc. that live in the loft.