Installing VCL for loft conversion & ventilating using l

[jonifife]

O.k. so have begun converting loft and have had builders in to put the joists in and installl some velux- for the next phase will be insulating and dry lining ourselves.

A few words of wisdom would be appreciated on the following:

As is good practice now days will be installing a VCL on the warm side of the insullation which is fine for the sloped part of the roof and down the stub walls- the problem is where it becomes horizontal and sealing it at the eaves level to the external wall.

Also the builders I had in advise it will be difficult to get over fascia vent or pack it out to get a vent gap at the eaves without sending the eave tile out of kilter with the gutter etc.

I have seen some products on the web for venting between the lap of the roofing felt . Sounds good in theory and having put my hand in the gap they would go can feel a good flow of air - any one had experience of using these and if they do what they say on the tin.

Also what is max thickness of insulation below rafters that can in practice be fixed through- I would rather board out 120mm of kinspan type under rafters rather than chopping bits up to go between the rafter. but 120mm plus battens plus plaster board sounds a lot to fix through so perhaps no options here.

Thanks

 

[freddiemercurystwin]

As is good practice now days will be installing a VCL on the warm side of the insulation which is fine for the sloped part of the roof and down the stub walls- the problem is where it becomes horizontal and sealing it at the eaves level to the external wall. Frankly I wouldn't worry about it. Millions of lofts have insulation at ceiling level and do not have a VCL between the plasterboard and the insulation and have no damp issues. Good ventilation of the void and gap above the insulation will ensure any moisture that does get through will be extracted. If you're really that bothered though install a VCL beneath the horizontal Rockwool insulation above the existing ceiling and this can be joined to the VCL behind the plasterboard in the dwarf wall as best as you can. At the eaves where the existing ceiling meets the external wall just lap it up to the wall plate.

Also the builders I had in advise it will be difficult to get over fascia vent or pack it out to get a vent gap at the eaves without sending the eave tile out of kilter with the gutter etc. So does the eaves not possess an existing form of ventilation? Normally this can be utilised There may be alternatives, soffit vents etc.

I have seen some products on the web for venting between the lap of the roofing felt . Sounds good in theory and having put my hand in the gap they would go can feel a good flow of air - any one had experience of using these and if they do what they say on the tin. Never seen the product you describe/not sure I follow tbh.

Also what is max thickness of insulation below rafters that can in practice be fixed through- I would rather board out 120mm of kingspan type under rafters rather than chopping bits up to go between the rafter. but 120mm plus battens plus plaster board sounds a lot to fix through so perhaps no options here. Ludicrously long screws aside, a problem you are likely to encounter is how to actually keep the insulation and plasterboard in position whilst you fix it all to the rafters. There will also be an impact on the headroom although if you have a large loft not so important. I'd start sharpening your bread knife.

 

[jonifife]

Building control are keen on the VCL- having said that they have just turned up today- week later than they should of, good job I was in!

They agreed it was problematic on the horizontal as it would have to go up and down between rafters and difficult to seal to eaves so they agreed it could be left out here. It is in the dead space behind the stub wall at eaves so as long as well vented should be o.k.

No real existing vent at the fascia - it feels naturally drafty up there and no existing condensation problems. The fascia is upto the wall with no soffit- http://www.lapvent.co.uk/ is the type of product I was thinking of- just wondering if anyone had experience of it- building con said they will probably accept it as it has a BAA cert but waiting for confirmation.

Bread knife at the ready javascript:emoticon('') I will put 50mm between leaving res cavity above and 70mm under rafter held in place with battens screwed through then fix plasterboard to the battens- gives a void for running cables etc.

Cheers

J