Loft conversion advice

[BigBigHit]

Hi there.


I am in the process of converting my loft into 2 bedrooms, study and on-suite.

I have had three pitched roof dormers build and i'm carrying out the insulation and plasterboard work myself by following the plans.

The original pitched roof (120 year old) is unfelted with slates. I have been able to force 120mm kingspan in the comb spaces leaving a 50mm air gap. In some areas I want to kingspan the full length of the comb right down to the wallplates as I will be using it for storage space. rather than room space. I wasn't sure if this was a good idea then I noticed that I don't have any ventilation ayway. The pitched timbers are laided into pockets in the sandstone so I don't have any eave or soffits etc for ventilation.

My question is - Do I need any? and can I insulate right down to the wallplates?

I have done a bit of research and I think I have converted a cold roof to a warm roof. Do I need ventilation If I don't have any felt? There are spaces in the sarking and the slates where I can see directly outside and can feel the wind. I'm not sure where the wind would go If I blocked right down to the wallplates on both sides.

Whilst I am on - Can I use normal plasterboard for drywalling my en-suite or should I use Moisture resistant plasterboard?

And another thing - Should I put visqueeen behind the plasterboard in the en-suite or will the foil backing of the kingspan do that job?

Regards

 

[freddiemercurystwin]

Yes insulate down to the wall plates. If you have no felt then you do not need any other vents. Just a gap between the underside of the tiles and the insulation.

You have not converted your roof to a warm roof. A warm roof is defined as having the insulation outside whilst the structure remains inside all warm and toasty.

You should use MR plasterboard in the ensuite, any tiled walls that are likely to get wet should be Aquapanel rather than plasterboard. Use either a foil backed board, foil backed insulation or a separate vapour barrier the choice is yours but non need for more than one.

 

[BigBigHit]

Thanks Freddy you have put my mind at rest.

I haven't really got a layout for the ensuite yet so will need to work out where I am going to tile. That's next on the list. The ensuite in in on of the dormers and the room is fully boxed in using foil backed Kingspan boards. Will this be enough for a vapour barrier? There will be tiny gaps where the Kinspan is squeezed into the studs. And onviously the studs don't have a vapour barrier. I have some left over visqueen and I was thinking about stapling that onto the studs on the ceilng and walls. Is this overkill? Will the foil backed Kingspan be enough?

 

[freddiemercurystwin]

Won't do any harm or alternatively use some foil tape which you should be using at any junctions or joins anyway.

 

[BigBigHit]

Freddy.

I have only started using the foil tape! This was after having done half of it already.

Althugh I made sure the Kingspan was as tight as it could possibly be. I actually had to persuade it in place with a block and hammer. Any small gaps I had I used expanding foam and then trimmed off. I read about the foil tape afterwards!

Hopefully it will be Ok as it is.

 

[freddiemercurystwin]

I expect it will be fine although bear in mind when in the depths of winter your studwork will have shrunk a little and your insulation may not be as tight.

 

[BigBigHit]

Freddy - Just whilst you are on.


With regards to the floor of the loft.


The joists are around 6" deep. I planned to just fill with Rockwool right all over the floor and into the eaves. Then floor with chipbaord. Also flooring into the eaves for my strage space.

However, half my ceilings below are still lath and plaster. Half have been replaced with plasterboard.

I know a little knowledge is dangerous but I read somewhere that it is not a good idead to lay rockwool onto lath and it should be suspended with chicken wire. Something to do with fire regs. Do you know if this is the case?

If I lay on chicken wire and leave a gap I will not be able to use so much insulation.

What is best practice.

Before we converted the Rockwool was just lying on the lath.

 

[freddiemercurystwin]

That's something you'll need to discuss with your BCO tbh, some BCO's insist on proper plasterboard.