Vapour barrier in loft?

[Hugh1983]

Untitled

• Hugh1983
• 28 Aug 2011
• 2

Hi, please consider the structure of my roof as shown in the picture (ignoring the strip of incorrectly fitted loft roll)

I am going to insulate the low wall parts with loft roll held in place and 12.5mm plasterboard screwed to the rafter. There is a void behind for ventilation.

I will be leaving a ventilation gap in the sloped roof and insulating between the rafters with sheet insulation such as kingspan and then screwing 12.5mm plasterboard to the rafters. Vent slates are being installed in the roof.

In the ceiling section I will be laying 100mm loft roll between rafters, crossed with 170mm loft roll. 9.5mm plasterboard screwed to the rafters.

MY QUESTION:

Once I have put the insulation in place to the wall/sloped roof and ceiling areas... should I staple a vapour barrier to the rafters before screwing in the plasterboard?

The main beam will not be boxed in so I will be plasterboarding up the sloped roof to the beam and then plasterboarding from the other side of the beam accross the ceiling. Will this create a problem with the vapour barrier? Will it be efficient? Is it worth doing?

Thank you in advance

 

[mointainwalker]

You should have a vapour barrier which can be either a thin poly sheet or foil-backed plasterboard with taped joints although this variant might be difficult where it meets the beam as the vb needs to be continuous to completely enclose the insulation.

It is worth doing.

 

[diycooper]

I would just get foil back plasterboard. Little dearer but worth it.

 

[JamesNorton01]

I'd always go for a separate VCL then batten to suit plasterboard sizes, tape and seal the VCL to the beam hidden by batten/board zone.

Alternately rigid foam to the underside of rafters foamed between rafters and joints foil taped.

J